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10. PHYSICS

1

Mary-Dell Matchett, Hinsdale, Illinois, decided that tele­scope making should not be an exclusively male province. Here is a report of her ambitious project, "Construction of an Eight-Inch Cassegrainian Telescope," which helped her to become one of the top forty winners in the Fifteenth Science Talent Search.

Introduction

Amateur telescope making is not merely a hobby or an interest—it's almost an obsession. There is a satisfaction in it that nothing else can quite equal. Perhaps it is the high degree of accuracy—the near-perfection-—required that gives this sense of satisfaction to even the rank novice; or per­haps it's just the remoteness of the interest from all else. Whatever the cause, there is something intriguing about mirror making. Apart from its being a science, a skill and a sport, mirror making is an art.

The Geometry of Telescoptics

If a spherical mirror is struck by light rays radiating from its center of curvature, they will be radii of the sphere and will be reflected back to focus on the center. Since a circle is actually an ellipse whose conjugate foci coincide, let one focus move away from the mirror and it becomes elliptical; rays from either focus will still converge upon the other. Again move this outer focus out all the way to infinity and our ellipse reaches its limit: the parabola. A parabolic mirror, then, will reflect rays from one of its foci, infinity (parallel rays), to the other at a finite distance from the mirror. As we increase the parabolic mirror's finite focal length, the concavity of the mirror decreases; when this second focus reaches infinity, the mirror is plane. Now if we don't know any better and move this focus beyond infinity, lo and be­hold! It has traveled all the way around the universe 1, for it now appears at a finite distance behind the mirror, while thesecond appears at a finite distance in front of the mirror. The surface of the mirror is now convex and its curve is the limit of the parabola: a hyperbola. Obviously the mirror cannot bring the rays from the finite focus in front to a real focus behind itself; it actually causes the rays to diverge as if from this focus. This is, then, not a real but a virtual focus. Conversely, the hyperbolic mirror can reflect rays from its virtual focus (i.e., converging as if upon it) to its real focus at a finite distance from itself.

1. This makes a nice story. Technically, the plane mirror has a virtual focus at infinity behind itself as well as the real one in front.

Now let's apply this to the Cassegrainian telescope (Figure II). A parabolic mirror reflects the light rays from one of its foci, infinity (the distance to a star being relatively in­finite), to the other, finite, one, F. This focal point must, however, be moved back to the eyepiece behind the primary, so these converging rays are now intercepted by a hyper­bolic secondary mirror, which reflects them from its virtual focus, F, to its real focus at F'.

The Cassegrain system obviously decreases the angle at which the converging rays meet, giving us the effect of a longer focal length without lengthening the telescope tube. (This is very convenient if you don't want to have twelve feet of telescope on your hands.) A long focal length is desirable because the magnification of a given eyepiece is directly proportional to the effective focal length of themirror system.

The Primary Mirror

"Eight Inch," my primary mirror, was almost completed before I gave a thought to making her a Cassegrain. The caption, "How to Make a Cassegrain (and why not to)" in Amateur Telescope Making was an open dare. I took it. The single adaptation necessary was the perforation of the primary. This is cut by a cylindrical metal surface rigged on a drill press.

I'll skip over the strong arm work of grinding the mirror, except to mention the principle involved. When equal glass disks are ground one upon the other, the upper hollows and the lower becomes convex. This occurs because, at the ex­tremity of the stroke where greatest pressure is brought to bear, the center of the upper disk and the edge of the lower bear the brunt of the abrasive effect.

Polishing, again, is largely strong arm work — but this time the principle is a bit more complex. In fact, there is some dis­agreement on the subject. The mirror is polished against a viscous lap of pitch. According to the theory / accept, the tiny flakelike particles of the polishing agent sink into the pitch lap, producing a surface of tiny razor edges that shear away minute layers of glass. The ultimate result is an optical surface, entirely free from pits and scratches.

Figuring the polished mirror is the hurdle that separates the men from the boys. By special polishing strokes the mirror's curve is first brought to a segment of a perfect sphere, then deepened ever so slightly to a perfect parabola-of-revolution (on about the fiftieth try). An optical test en­ables us to "see the mirror's exact figure." For Foucault's test we stand the mirror on edge and, at the center of curva­ture (displaced to the left very slightly), we place a pinpoint of light. The rays diverging from this point are radii of our sphere and are all reflected back to the center of curvature (displaced equally to the right, where we may see them). At this focal point we allow a knife edge to cut the cone of light rays. As we look along the knife edge at the mirror, if the sphere is perfect, we see the entire surface shadow out evenly and simultaneously, since all returning rays pass through the focal point and are cut off. If an area of the mirror is too deep to be a part of the sphere, its focus will be in front of the knife edge and the knife edge will cut a shadow on that area, moving in a direction opposite its own. Conversely, if the area is too shallow, the shadow will move in the same di­rection as the knife edge. The parabolic mirror gives a com­puted variation in focal lengths of zones between the center and edge of the mirror. These variations are measured with great accuracy by a micrometer adjuster on the knife edge. This test is, incidentally, so delicate that the heat generated by an onlooker's body causes the light pattern to shimmer, so that the tester cannot interpret it. When the elusive parabola is finally perfected, the Newtonian maker's troubles are over— and the Cassegrain maker has just begun to fight.

The Secondary Mirror

I decided to make the effective focal length only 3.3 times the actual focal length (38 inches), for a longer e.f.l. gives greater power but smaller field. Computations for size and placement of the secondary are shown in Figure II.

Rough and fine grinding are the same routine as before, except that this time we use the convex bottom disk. The curve of a hyperbolic mirror is so far from a sphere that it is more practical to test it during the polishing process and correct as we polish. Since the secondary is convex, Foucault's test is useless; we must make a special testing mirror and use a different test. The setup is shown in Figure IV. The testing mirror is a spherical Cassegrain whose radius equals the primary's focal length, 38 inches. If we placed a pinpoint of light at its center of curvature, we would get rays reflected back at the same angle our primary mirror produces, and we could use these to test the secondary. Since inserting the secondary would cut off the source of light, we must place our light at the other focus of the system—behind the hole in the testing mirror. Now when our pinhole light is displaced slightly to the left, we can use the knife edge displaced to the right to see whether all rays are converging upon the desired focal point, and can correct accordingly. After much exacting work and—let's face it—a bit of luck, we at long last wind up with a secondary that works in perfect conjunction with our primary.

Reflections

There is as much to learn about the why and how of a telescope as about its uses. A year ago I had never even looked through a telescope. The first I ever used was my 4V4-inch Newtonian, "T. Ela Scope." It probably cost me more to build her than it would have to buy her—but I don't care. You'll never believe it unless you have made your own telescope, but it is every bit as fascinating to make the tele­scope as to use it.

A Note of Thanks

There are times when the telescope maker feels a most irrepressible urge to drop a brick on his mirror. At such moments, the influence of fellow workers (a twisted arm) is pure salvation. Thanks, then, to the other "inmates" of the Adler Planetarium's Optical Shop for restraining me.

My greatest debt of all, however, I owe to Mr. A. V. Shatzel, Assistant Director of the Adler Planetarium—for not laughing at the little ignoramus who said she was going to make a telescope. I've learned more optics from him than from any or all the books I've ever read.

Bibliography

Ingalls, A. G. (Editor). Amateur Telescope Making, BookI.Scientific American  (Pub.)

Thompson, A. J. Making Your Own Telescope. Sky Publish­ing Corporation.

Mr. Shatzel (the aforementioned). (He's not really a book —just sort of a library.)"

2

"A Solar-heated Greenhouse" was the project that Robert Kirk Seaton of Elizabeth, New Jersey, entered in the 1958 Science Talent Search for the Westinghouse Science Scholar­ships and Awards. In the paper that helped Bob to become one of the top forty winners, he says:

". . . .The essential problem was to find a way to collect heat energy from the sun, store it and release the energy as needed to heat the plant-growing area.

The greenhouse I designed is composed of two parts: a heat-gathering and storage unit and a plant-growing chamber. The heat-collecting unit is of the flat-plate type (Figure 1). It is composed of 2 panes of glass separated by %-inch air space; this is the most efficient separation distance. Behind the glass is a large sheet of aluminum foil painted black. Glass is relatively permeable to heat of short wavelengths as is contained in the sun's radiation. However, glass is opaque to the longer wavelengths of heat such as are radiated by com­paratively cool objects. The wavelength radiated is inversely proportional to the temperature of the radiating body.

The heat of short wavelength passes through the glass and is converted to heat of long wavelength by the aluminum foil. Thus the heat is trapped behind the glass. The heat is then transferred by radiation and by convection currents from the blackened foil to the storage unit, located immediately behind the collector plate. Air is allowed to pass through the space between the glass and the foil via slots at the bottom and top of the foil. In the storage unit, the heat is picked up by 1-gallon black metal cans containing water, a method chosen because of its high specific heat, its cheapness and its heat of fusion at 0°C. These cans have a capacity of 1120 pounds of water and can be stacked loosely enough for the air to circulate around them.

Since I wished to limit the size of the greenhouse base to 4 by 3 feet and still have my plant area on top of the maximum size, it was necessary to have the plant chamber hang over the collector plate. However, this overhang was designed so that it would not shade the collector plate during January, the coldest month of the year. As spring advances and less heat needs to be stored, the overhang shades more and more of the collector plate. In the fall the situation is reversed.

With masonite construction insulated with 3-inch Fiber-glas batting, the heat loss can be calculated to be about .12 B.T.U.'s per square foot per degree difference per hour. This value takes into account the masonite and glass surface areas in the completed greenhouse. Then, using the formula Ht=AU(T-TO), where

Ht—heat transmitted per hour in B.T.U.'s

A—surface area in square feet

U—over-all transmission per hour per square foot per   1°   F.  difference

T—inside temperature

TO—outside temperature,

I calculated that 4030 B.T.U.'s will be lost, assuming a mini­mum maintained inside temperature of 40° F. and an outside temperature of 0° F. and a 14-hour night.

I wanted my collector plate to be able to collect about 3 times the heat lost during a 14-hour night. This leeway would allow for a 2-day supply of heat in case of cloudy weather. Therefore, I wanted my plate to collect about 13,090 B.T.U.'s during a clear day. I used the formula A (S-L) (m) = B.T.U.'s collected per day, where C

A—collector area in square centimeters

S—the solar constant of 1.94 calories of heat falling on each square centimeter of a surface per­pendicular to the sun's rays per minute

L—loss due to glass absorption

m—collection period in minutes

C—conversion rate of calories to B.T.U.'s to com­pute the area of the plate.

I figured on a loss of .94 calories per square centimeter due to glass absorption and reflectance. I also figured on a maxi­mum collection period of 6 hours. Solving this equation for A (the area), I arrived at 9300 square centimeters for my collector-plate area. I therefore designed my plate to be 10 square feet in area (9280 square centimeters).

The collector plate is inclined at an angle of 60° so that the sun's rays fall perpendicularly on it during the coldest weeks, affording maximum collection and penetration.

During the day, the heat is collected and stored in the cans of water. At night, when the temperature of the air around the cans becomes less than that of the water within the cans, the stored heat is radiated from the cans and warms the air around them. This warmed air, being lighter, rises to the top of the storage unit, where it can be admitted through dampers to the plant chamber.

The plant chamber is 4 feet wide and 3 feet deep. The roof slopes from the rear to the front. The height in the rear is 11 inches and in the front 4 inches.

The framework is composed of 2-by-3-inch pine and the walls are of waterproof masonite. The model is made so that it is entirely collapsible, each surface being built as a prefabricated panel. All the panels are held together by bolts.

With a few structural alterations this design could be made into a large walk-in model. Once set up and running, the heating bill would be nothing. . . ."

3

"The Behavior of Soap Bubbles and Films" was reported by Arthur T. Winfree of Stamford, Connecticut, one of the winners in the Nineteenth Science Talent Search.

"Introduction

This project began, ludicrous as it may seem, as a one-weekend effort to make a nonpopping soap bubble; and what it has thus far mushroomed into is well over a pound of abbreviated notes, graphs and equations on the chemical and physical properties of soap films.

A great deal of the research up to now has resulted not so much in concrete answers as in the development of a group of more tractable, specific questions. So this paper attempts to give a representative sampling of both experimental re­sults and the further experiments and calculations they have suggested; a descriptive or qualitative summary is to be found in the text and the 35-mm. slides, with more precise informa­tion located in the appendix.

Chemistry

If any one thing was vital to this phase of the project, it was unquestionably my notebook, in which everything seen or done in the lab was recorded. I recorded in special detail those things that seemed unusual, confusing or contradictory. Thus, any time I thought I'd explained some irregularity, I was able to look months back for observations with which to confirm or discredit the new theory.

The first several weeks in the lab were spent investigating, first, various bath soaps in aqueous solution, then, finding these most unsatisfactory, pure and mixed stearates at various concentrations and temperatures. Even these were no better than commercial solutions for film strength and stability at room temperature.

Among the multitudes of other things tried were wood rosin, oleic acid and polyvinyl alcohol (PVA); these three proved to have some particularly remarkable properties, the most important of which I list here.

1. Wood rosin, digested with 4.4% NaOH solution, forms mobile red-brown soap solution which, while  incapable of blowing bubbles,  can form small films which dry without popping! (See photos 6 and 10.)
   
2. Alkali salts of oleic  acid,  at   1-5%  concentration  in water, form soap bubbles and films of surprising color and stability (which I also learned later from C. V. Boys); NTE (nitrilo-triethanol)  oleates as 1-2%  solutions form films that last for days on end and are at most about 1000A thick! Ammonium oleate, 1/5%, is similar, but greater concentrations are quite viscous.
   
3. PVA, while reducing the stability of liquid films, makes strong, perfect dried films and bubbles possible. By using a low molecular-weight grade of PVA, saturating the solution with sucrose and working in dry air, I've been able to produce soap bubbles so strong that they can be taken in hand and squeezed until they pop! I hope to improve this solution by the addition of a nonhygroscopic liquid plasticizer and a VA-insolublizer.
   

Planned are a few syntheses, notably of abietic acid esters and double-bond addition compounds of oleic acid and the rosin  acids, to produce water-soluble  additives for special-purpose films, but only one has been performed to date.

Surface Physics

The most significant physical property of soap films is their surface tensions (about 30 to 35 dynes./cm.), which causes their surface areas to be minimized under the con­ditions imposed (with a few exceptions in which the area is only a relative minimum). Thus the film between two parallel wire rings is a catenoid, because a catenoid has the least area of all such imaginable surfaces.

Another characteristic of films is that nowhere in a stable foam (as I was delighted to see under the microscope) will a place be found where more than three films intersect in a line, or more than four lines (six films) intersect in a point. Consequently, all intersections must be at a 120° angle. I've not yet been able to show why these things must be, but I am working on it.

I've made some progress in analyzing soap-bubble systems by making the assumption that where other forces resist the minimization of surface, the total potential energy of the system (gravitational, pneumatic, etc.) is minimized. How­ever, the proof that this assumption is generally valid depends on the solution to an equation which I can't solve yet.

Maxwell proved that a cylindrical bubble will become un­stable when its circumference equals its length, but, once again, I haven't completely shown why. I've outlined a proof which includes the more general case of surfaces of revolu­tion, and it will be complete the same day the differential equation mentioned above is solved. In the meanwhile, a proof based on the minimum-energy assumption is feebly progressing.

The other major lines of work in this department have been 1) an investigation of the geometric properties of multibubble systems (see Fig. B), and 2) a mathematical study, to be con­firmed in the lab when complete, of the possibility of making a stable doughnut-shaped bubble. I think it's impossible, but a conclusive proof also depends on the problematical differ­ential equation.

General

Physics Perhaps the most striking fact about oleate films is their brilliant color, caused by interference of light waves at the film's surface. However, the question arose whether this in­terference was due to the thickness of the entire film or to a monolayer of some sort on the film's two surfaces, and I collected a good bit of experimental evidence for each hy­pothesis. The monolayer idea was finally discarded and all the data was correlated without it. This means soap films are only 1000 to 10,000A thick.

An interesting aspect of soap-bubble physics, and one which is well suited to experimentation in the home lab, is the col­lapse of a spherical bubble through a controlled orifice (see Fig. C). The graphed results agree closely with the predic­tions in slope, but the Y intercept is about four times too large; the shape of Graph B may have been influenced by the extra curvature of the long orifice tube used. Bubble weight apparently had no significant effect on collapse rate.

It has been demonstrated (e.g., by Boys) that some gases pass rapidly through a film by osmosis, yet I've never seen equations about it. So I'm getting ready to determine the three constants in my general prediction, using gas-filled acoustical lenses made of soap films. The plans and calcula­tions are almost complete.

The fifth series of tests performed consisted of stretching a flat horizontal film in the open air, while feeding it with an eye dropper. Using statistical methods on the results of about 200 single tests, I found 1) that the maximum diameter of a plane circular horizontal film, beyond which it cannot support its own weight, is close to 10 inches, and 2) that the addition of about 30% glycerol (suggested by Boys) does substantially strengthen open-air films. Other experi­ments indicate that it retards evaporation, but at the same time reduces a film's ability to produce local variations in surface tension, T.

My principal instrument for studying liquid soap bubbles (as opposed to those which, containing water-soluble gums, are stable when dry) is the bottle, shown in Slide 16. I've used it for investigating the effects of chemical proportions on film characteristics, studying film physics through color patterns and gradually increasing the life span of a bubble from twenty minutes (early October) to more than fifty hours (late November).

The next major physical experiment planned (to precede osmosis tests) concerns surfaces of revolution, using the apparatus shown in Fig. D. In one kind of test, for example, let r1 = r2; attach ring 2 to the bottom of a measured bubble below ring 1 and note how far it falls when released. Know­ing h, d, W, V, the weight of ring 2, and the bubble's original volume, one can find the surface, volume, potential energy, curvature and internal pressure of the bubble.

A further occasion for some interesting math and experi­ments is the behavior of the thin sticky threads which can be drawn from a Type E solution of 2% ammonium oleate — the surface forces tend to increase while the center of gravity of the thread seeks the lowest possible altitude.

Something I've recently begun at least to think about is the transmission of low voltage AC through soap films of various contours (tried DC—it electrolyzed the soap). By varying the contour, or causing the membrane to resonate, some surface integrals could be generated which might be of interest in analog computers.

The same goes for reflected light beams; the reflection from a catenoid film, for example, would give hyperbolic trigono­metric functions.

One further possibility for an unusual study is growing bacteria or molds in a PVA-type film; their growth would be in two-dimensional space of almost any desired shape."

4

Brett Nordgren of South Bend, Indiana, top scholarship winner in the Sixteenth Science Talent Search, helped to construct an accelerator, then built an automatic Wilson cloud chamber to go with it. His report was presented in chronological order, outlining work begun two years before. The text contained a table, eight figures and four photographs. A bibliography was appended. Here is an excerpt from his work, "An Automatic Wilson Cloud Chamber."

"My cloud chamber began as a companion project to a one-megavolt Van de Graaff accelerator, constructed two years ago by a group of science students, including myself.

I plan to record phenomena occurring in the lower energy ranges with particles from our accelerator. The cloud chamber will make the paths of these particles visible for photographic study.

In general, cloud chamber research has been concentrated in the area of very high energy particles, to the neglect of lower energies. Some low-energy phenomena of particular interest which I should like to study are electron pair produc­tion, proton capture and transmutation, and gamma-ray effects, such as the Compton effect and photoejection of elec­trons.

Even though subatomic particles are invisible, their vapor trails in the cloud chamber are visible and can be photo­graphed and studied. To form these trails in my unit, a quantity of argon gas, saturated with the vapor of a 75% ethanol and 25% water mixture, is expanded to 1.08 times the original volume in a time of the order of 0.01 second. The resulting sudden cooling effect supersaturates the argon. When a particle passes through, ionizing the argon atoms in its path, the ions formed serve as condensation nuclei for the vapor. This creates a cloud trail along the path of the particle. These tracks must be quickly photographed, since within one second they will diffuse and vanish. Argon at two atmos­pheres with the alcohol-water mixture (as recommended in Electron and Nuclear Physics—Hoag & Korff) was used in my chamber because of the greater specific ionization and the reduced expansion ratio over other combinations. The optimum expansion ratios for various combinations of gas and vapor are given in Table  1.

After the picture is taken, the chamber is restored to its original condition by recompressing the argon and allowing it to "rest" for ½to 1½ minutes to dissipate the heat of compression. During this rest time a potential of 100 to 500 volts is maintained through the chamber to remove all ions formed during this part of the cycle. This prevents them from fogging up the chamber during the sensitive time. Of course, this voltage must be removed just before expansion so that the tracks to be studied are not prevented from form­ing.

MECHANICAL BETAILS GF THE CHAMBER

Ring Window Retaining Ring Window Expansion Chamber Screen-velvet Assembly Diaphragm Compression ChSttiber Bottom Plate Figure 1

The cloud chamber proper (shown in Figure 1) con­sists of an aluminum cylinder 3 inches high and 6 inches inside diameter with ⅝-inch-thick walls. The top of the cylinder is covered by a ¼-inch-thick lucite disk, through which the pictures are taken. This window is held in place by an aluminum ring bolted to the end of the cylinder. The bot­tom of the cylinder is sealed by a ⅛ -inch-thick rubber dia­phragm separating it from a lower cylinder 1½ inches high. Compressed air is admitted to the lower chamber and then released after a suitable interval, causing the diaphragm to drop and thereby expanding the gas within the upper cylinder. To reduce the expansion time to the required 0.01 seconds or less, air in the lower chamber is released suddenly through a 3-inch-diameter port, covered by a thin aluminum valve plate. The plate is locked in place (as shown in Figure 2) until expansion is to occur. It is then released by a solenoid. Several other designs for this release mechanism were con­sidered (Figure 4), but this system was chosen because it permitted the valve plate to have the least mass of any system and the solenoid needed to exert very little force to trip the valve. Due to the force of the compressed air tending to open the valve (15 psi, exerting 121 lb.) and the low mass of the valve plate mechanism (.17 lb.), the valve opens rapidly when released and allows the air to exhaust in a very short time.

When the chamber is to be recompressed, a pneumatic cylinder of my own design (see Figure 3) raises the valve plate and seals it firmly to the port. The valve is then locked in place and the cylinder drops away. . . .

In the design and construction of the cloud chamber, I have come to several conclusions. Although a magnet is useful in deflecting the particles to measure their energy, mass and charge, in much experimentation it is unnecessary. I considered using an electrostatic field to deflect the particles but this would have to be on the order of 1000 V. per cm., causing ionization problems. In the future I should like to try using a transparent disk-shaped plastic magnet recently developed, to be placed just below the window in the cham­ber. . . .

One major modification which may be attempted in the future is the addition of counter control; that is, a particle passing through the chamber will trigger a counter tube which will, in turn, trip the chamber quickly before the ions disperse. This method is generally used to record the tracks of cosmic rays. For this system, a quicker method of actuating the valve will become necessary, possibly one in which a DC solenoid, normally energized, is de-energized by a reverse pulse from a condenser. This produces very rapid action.

Design of the chamber is completed and construction is complete with the exception of the following items: camera mount and winding equipment; addition of several mainten­ance ports for filling the chamber with gas and for the possible insertion of radioactive sources; wiring of electrical con­necting cables between the chamber and the control unit; and hookup of three solenoid air valves.

The chamber will be tested with the accelerator during Christmas vacation, when I shall have access to this machine. ..."

5

Many unusual research problems were investigated by the winners of the Nineteenth Science Talent Search. A mysterious "spook" light caught the interest of young scientist William E. Underwood of Carthage, Missouri. In his paper, "Hornet 'Spook' Light Using the Double Refraction of Light Theory," he wrote:

"Last summer, I traveled twelve miles southwest of Joplin, Missouri, to a lonely road of northeastern Oklahoma, and here I first viewed the famous Hornet "Spook" Light. Even though the light had baffled all comers, including the U. S. Corps of Engineers, it was an immediate challenge to my curiosity. I shall endeavor to summarize briefly my investiga­tion of this light phenomenon.

The  Light

The case history of the light begins with observations made by residents in 1903. It appeared on some property near the state-line road now called the Original Spook Light Area. (See Appendix, Figure 1.) The light appeared self-luminous and its course was limited to a swampy draw filled with de­caying vegetation. Because it bore the appearance of a lam­bent flame and was visible only when conditions were right, I think its origin was phosphoric, and its nature that of an ignis fatuus (will-o'-the-wisp). This display no longer exists.

In 1946 the U. S. Army Corps of Engineers performed a test on another light on a road which has come to be called the Old Spook Light Area. The results of this test have been best described by the State of Missouri Resources and Develop­ment Division, which stated, "They came away baffled." The Army test was conducted on a road approximately one mile north of the road from which the light is seen today (called the New Spook Light Area) and had no connection whatso­ever with the present Spook Light.

My investigation concerns the present light.

On my first visit with friends to view the phenomenon, we parked on a gravel road at the top of a long slope. Soon after dusk, a suffused glow appeared in the sky to the west, over a range of hills. The center of the lighted area was in a line with the axis of the road. The greenish-yellow ball appeared to descend out of the hills and rapidly advance toward us. When we moved any distance toward the light, it would dis­appear.

Its maneuvers were of two types, the first being to vary in intensity, time of appearance, distance and often to become duplex. The second and less frequent display was yet more of a coup de thedtre. The light approached the observer and seemed to envelop him. But when he turned toward the east to observe its continuance, nothing was seen.

Refraction Theory

When a ray of light passes from one substance to another of a different density, it is bent out of its course, or refracted. The law of refraction is: When light passes from a rare to a dense substance, it is bent in the direction of a line that is perpendicular to the surface of the refracting body; when light passes from a dense to a rare substance, it is bent away from a line perpendicular to the surface of the refracting body. Furthermore, while light of all wavelengths travel with the same velocity in empty space, the velocity in material substances is different for different wavelengths. This effect is known as dispersion. The ratio of the velocity of light in a vacuum to the velocity of light of a particular wavelength in any substance is called the index of refraction of the substance for light of that particular wavelength. (See Appendix.) The index of refraction of a gas increases uniformly as the density of the gas is increased.

The index of refraction is also defined as the ratio of the sine of the angle of incidence to the sine of the angle of re­fraction. (See Appendix.) The index of refraction for any two media is constant, no matter what the angle of incidence.

Problem Analysis

My first concern was the light's customary remoteness. I rendered the ocular determination of its maneuvers more perceptible through  a telescope.  A 4¼-inch objective telescope was operated, using eyepieces giving magnifications of 40x, 90x and 200x.

Photographic resolution was poor because of the vibration of the telescope mount, air disturbance and natural movement of the light. (See Appendix, Figures 4 and 5.)

By using the telescope I was able to resolve as many as eight pairs of lights, the intensity of the Spook Light depending upon the intensity of the pairs of lights and the number of lights in the field of view. Upon taking into consideration the inverted image in the eyepiece, I was able to discern pairs of red lights to the right of the yellow lights, the red lights grow­ing dimmer as the yellow lights became brighter.

Occasionally the light, as seen through the telescope, ap­peared as a flame which was green at the bottom and red at the top. I remembered that the light of sealed beam head lamps is polarized vertically. The wavelength of green light (5200A) is shorter than that of red light (6500A) and green light is refracted through a greater angle. These facts are consistent with the observations if the light is refracted.

Another important experimental fact is that equal amounts of radiant flux of different wavelengths do not produce visual sensations of equal brightness. Therefore, if a source gave off blue light as well as other light, it is likely the light would appear green, yellow or red.

Further reasoning led me to think that the cause of the light lay in the refraction of automobile head lamps from a road in direct line with the gravel road where I stood.

The fact that the light did not always appear substantiated the refraction of light theory in that if the light was bent, it would come down at different points and with various in­tensities, depending on the temperature and humidity of the atmosphere.

I put together a composite map of the area and decided that a section of Highway 66, running east and west from Com­merce to Quapaw, Oklahoma, was in a direct line with my two observation points. I also noticed that Spring River crossed the area between the gravel road and the highway.

Water gains and loses heat much slower than cement or earth. Temperature and vapor content of the air above water vary as a function of the water's temperature. The tempera­ture relationship of land to water would vary with: (1) season (water being given off by foliage in summer and water temperature varying from summer to winter),  (2)  changes from daylight to dark and (3) sudden atmospheric changes. Warm moisture-laden air is less dense than cool drier air and therefore a beam of light traveling from Highway 66 to an observation point on the gravel road would suffer two changes of direction—from dense, to less dense, to dense. This effect is called double refraction of light.

The average summer and winter temperatures for this area are 72° and 37° respectively, the night temperatures varying somewhat. By making several assumptions I have been able to calculate the indices of refraction of the different media and to approximate the refraction pattern for summer and winter.   (See Appendix, Computation 2.)

The wattage of most sealed beam head lamps is 50/40, the head lamp having two filaments for bright and dim. Each car is equipped with two of these, their individual candle power rating being approximately 50/35. The intensity of the light at the point of observation would be a function of the inverse square law and the number and distance of the pairs of lights on Highway 66.

Experiments

Assuming the lights of the Old Spook Light Area and New Spook Light Area to have a common origin in automobile head lamps, even though their source was on a different road, I proceeded to carry out an experiment somewhat like the Army Engineers Test. (See Appendix, Figure 1.) Observa­tions were made at points A and B on the map and the num­ber of cars traveling the section of the highway between Commerce and Quapaw was recorded at point C. The in­tensity of the light was directly proportional to the number of cars traveling in an easterly direction. The reddish glow of the light would vary directly with the number of automo­biles moving in a westerly direction. When there wasn't any traffic on the highway, it was possible to educe the presence of the light by flashing an automobile's head lamps at point C; the flashes were observed at point B.

Using a spectrotelescope I constructed, I found that the Spook Light had a continuous spectrum, such as an incandes­cent light has. If the light had been a luminous gas under atmospheric pressure, it would have produced a bright line spectrum. Thus the spectral pattern serves as a proof of an artificial incandescent source, such as an automobile's head lamps.

I took some infrared films of the light to see if it gave off infrared rays, but the roll of film did not develop.

Future Plans

Further study will require a modification of my photo­graphic equipment to include color slides and infrared film, as well as to improve resolution. The telescope and camera mount should be made more sturdy to avoid disturbing the image.

I plan to get photographic proof of the light's continuous spectral pattern and this will require the addition of a film carrier to the spectroscope. I may also notice absorption lines near 7600A from oxygen in the atmosphere.

A photometer calibrated in lumens and used in correlation with the telescope could be used to calculate the theoretical distance of the light.

A Recapitulation

The points upon which I base my conclusion that the Spook Light is the double refraction of automobile lights are: (1) In a telescope the lights are seen as pairs of white and red lights, (2) the actual angular width of these lights com­pares favorably with their theoretical angular width, (3) sealed beam head lamps are polarized vertically and the Spook Light is refracted light polarized vertically, (4) it was possible to control the actions of the Spook Light and (5) the physical features of the area support the theory.

Bibliography

Dull, Charles E., Metcalfe, H. Clark, and Brooks, William O.

Modern Physics. New York:  Henry Holt and Company,

1955. Hodgman, Charles D. Handbook of Chemistry and Physics,

Fortieth Edition. Cleveland: Chemical Rubber Publishing

Company, 1958. How to Use Your Telescope. Barrington: Edmund Scientific

Company,  1959. Kennom, Leslie G. State of Missouri Division of Resources

and Development. Jefferson City: State of Missouri, 1946. Sasuga, John. Photocells and Sun Batteries. El Segundo: In­ternational Rectifier Corporation,  1955.

Sears, Francis W., and Zemansky, Mark W. College Physics. Cambridge: Addison-Wesley Publishing Company,  1956."

6

"Thermoelectric Cooling" was the project presented by Frederick A. Moore, Rockville, Maryland, at the Tenth Na­tional Science Fair. Here is an abstract of his paper.

"Not a new phenomenon, thermoelectricity has been known since 1823. Seebeck discovered that electric currents are generated in a closed circuit made up of two different metals when the junction between them is heated. In 1834, Peltier, a French watchmaker, observed cooling (the absorption or generation of heat depending on the direction of the current) at the junction between two different metals.

The Seebeck effect has been used for a long time to measure temperatures with thermocouples, but thermoelec­tricity for power generation or for cooling was considered impractical until 1929. At that time, a Russian, A. F. Joffe, outlined the advantages of thermoelectric generators made of semiconductors. Active work was begun about ten years ago at the Institute for Semiconductors in the U.S.S.R., and great advances made.

The advantages of semiconductor thermoelements over metals lie in the fact that they can be made with high ther­moelectric power and high thermal resistance. Metals tend to leak heat back through the bars so fast that they are im­practical for power generation or cooling.

This experiment was undertaken to investigate the com­mercial possibilities of semiconductor thermoelectric cooling devices and power generators using c.p. or analytical grade chemicals and an inexpensive, commercially feasible process. Most of my experimental work has been done with modified bismuth telluride, and to dp so, I developed a plating process using gold, which I believe to be original. Using this process, I have obtained very good results.

With present rapid developments of thermoelectric tech­nology in the United States, several commercial devices will be marketed within the next two or three years.

Several envisioned devices using thermoelements are: 1) a portable hostess cart;  2)   a clock-controlled baby bottle refrigerator and warmer; 3) a portable combination picnic refrigerator and stove operating from the cigarette lighter of a car; 4) perpetual thermoelectric power for space satellites; 5) a ten-mile-square section of Arizona desert covered with good thermoelectric generators which would generate enough electrical power for the entire United States, have no fuel costs or radioactive waste problem and practically no main­tenance costs; and 6) a portable power generator heated by a stove or fire, which would run a TV set, electric lighting system and refrigerator, for camping or life in remote areas."

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