MOST APPARATUS for automatically regulating the amount of direct sunlight that enters a room involves the operation of shutters with a servomotor controlled by a photocell. One can also obtain glass that darkens in approximate proportion to the intensity of the incident light, but this material is expensive and generally cannot be found in sheets of large size. Neither alternative appealed to Milan D. Fiske (215 Lake Hill Road, Burnt Hills, N.Y. 12027), who set out to control the sunlight in his greenhouse.

Fiske, who is a research physicist, makes a hobby of growing orchids that he collects in the jungles of Ecuador. The exotic specimens require equivalent light to thrive in Burnt Hills. Fiske hit on the scheme of approximating the correct light by letting the seasonal change in the elevation of the sun control the transmission of direct rays through a uniquely proportioned set of opaque slats at the south end of his greenhouse. He determined the geometry of the slats for the installation at Burnt Hills with the aid of a pocket calculator, but the dimensions for other locations can be worked out in a few hours with paper and pencil. The project was reported last year in Orchidata, the official publication of the Greater New York Orchid Society. I am grateful to the society for permission to adapt Fiske's description as follows.

"Most greenhouses need shade of one kind or another at some season or other. Out of the great range of such needs the one to be discussed involves only one small segment. My apparatus is a relatively simple device known as the ecliptic shade. Once put in place it can stay in place without attention season after season.

"Ever since I have had a small green house I have been plagued by the shade problem. One is forever seeking more light or less. In general the problem is too much light at midday and too little in winter. What is needed is something to diminish the noonday sun. Elegance demands that it have no moving parts.

"A promising solution of the problem might be found in the moiré principle. The trouble is that moiré shades can be expensive to make because two identical grids must be built and mounted with respect to each other within close tolerances. Until a better solution presents itself I have settled for an ecliptic shade at the south end of a greenhouse that runs north and south.

"The ecliptic shade is a set of rigid slats in parallel planes. The slats are proportioned so that their width, thickness and spacing and the angle the plane in which they lie makes with the ecliptic cause them to cast shade that blocks out high summer sun and admits nearly full sunlight in winter. The area of the device does not enter into the calculation of its other dimensions. My ecliptic shade is roughly six feet square.

"The details of the construction are largely a matter of the builder's ingenuity. I slotted one-inch by three-inch risers of white pine at the desired angle, nailed in the slats and mounted the completed shade with metal fittings that attached the risers to the greenhouse. The thing has been in place three years now and I like it just fine. If the reader has a notion to try one, the formula and the graphs that are included in the accompanying illustrations can guide the choice of dimensions.

"The quantities included in the formula are for the most part given by the lettered drawing. The formula requires simple calculations that can become tedious if they are made with paper and pencil. Moreover, most readers will not have at hand the elevation of the sun as a function of the season and the time of day. This information is included in The American Ephemeris and Nautical Almanac, published annually by the U.S. Government Printing Office. (The publication is sold by the Superintendent of Documents, Washington, D.C. 20402. Copies are also available on the shelves of many public libraries.) I am indebted for the information on the sun's elevation to C. L. Hemenway, director of the Dudley Observatory in Albany, N.Y. The illustrations also include [lower right] a set of three graphs that can remove the chore of doing the calculations if the reader lives within a few degrees of latitude 40 degrees north (or south).

"The graphs are plotted on the assumption that the slats are set at an angle (A) of 27 degrees with respect to the horizontal, have a thickness (t) of 3/8 inch and a width (W) of 1-1/4 inches and are spaced (S) at intervals of 2-1/2 inches. The first graph shows plots of the ratio of slat width to slat spacing (W/S) to depict the effect of altering this quantity.

"One must be careful about two points in the calculations. First, because the midwinter sun lies below the plane of the slats in the early morning and the late afternoon (angle E is smaller than angle A), one must be careful to use the appropriate signs in the trigonometric functions for calculating the transmission of direct sunlight (T), otherwise T will rise above unity and present the designer with the theoretical problem of keeping his greenhouse cool! Second, as the sun's angle of elevation increases, the transmission (T) decreases smoothly to zero, at which point it goes mathematically negative as E gets still larger. This result corresponds to the point at which one slat begins to shade another. Ignore negative 'transmissions.'

"A few numerical examples illustrate the procedure. Assume that the elevation of the sun E is 45 degrees and that the other dimensions are as listed above. Then . Similarly, if E is 10 degrees, then . Working with another example, if E is 60 degrees, T is .099.

"The second graph plots the transmission (T) against the local time of day for the first day of selected months of the year. The third graph shows how the transmission varies through the year at various times of day. For example, at 10:00 A.M. in Burnt Hills the transmission of this shade is 79 percent on January 1, 76 percent on March 1, 33 percent on May 1 and only 14 percent on July 1. Observe that the transmission is symmetrical with respect to noon, approximately the same at 11:00 A.M. as at 1:00 P.M, at 10:00 A.M. as at 2:00 P.M. and so on.

"If you build a shade to this prescription, the transmission of direct sunlight will be just what the graphs predict. To the direct sunlight, however, you must add scattered light from the sky that streams through the slats unimpeded, as you can demonstrate with any good venetian blind. In other words, although the sun's direct rays are completely blocked out with a shade of the specified dimensions from 11:00 A.M. to 1:00 P.M. between May 1 and August 4, a lot of light from the sky still gets through. In short, this is a sunshade, not a total-light shade. The resulting illumination is precisely the kind that is needed to prevent leaf burn in orchids without retarding leaf growth.

"A shade of the dimensions required for Burnt Hills will work pretty well in most of the continental U.S. On the other hand, readers who have a yen for computing and who own a digital slide rule can with lithe effort generate graphs for any latitude and combination of shade dimensions. If all this seems like a lot of fuss for an undramatic reward, I can only respond that I think the shade is a dandy and that I fully intend to keep on using mine."

ACCORDING to theory, big astronomical telescopes show more detail than small ones. The advantage of increased resolution with size is not always realized, however, by the amateur who installs his instrument near communities where the stars must be viewed through polluted air kept aglow by streetlights. Under such conditions a 16-inch reflector shows far less detail than a 3-inch Questar situated 30 miles from town. For this reason enthusiasts in increasing numbers are substituting modified boat trailers for the imposing backyard observatory that once identified the advanced amateur astronomer. Typical of mobile installations is the 12-inch f /8 Newtonian reflector that Scott Smith, a student at Northwestern University, specifically made two years ago to be transported by a trailer. Smith reports that by keeping an eye on local weather forecasts he can with surprising frequency choose a location within reasonable driving range where seeing will be good on almost any date. Smith (11200 60th Avenue SW, Miami, Fla. 33156) describes his rig and its use.

"In general my instrument is conventional. Its equatorial mounting is of the German type in which the upper end of the polar axis carries a bearing that supports the declination axis at a right angle. The shafts for these axes were made of three-inch cold-rolled steel. They turn in heavy bronze bushings. .

"The declination bearing was made o a four-inch pipe fitting with a three-inch side inlet. Thrust bearings to support the loads of the polar shaft and the declination shaft were made by sandwiching greased disks of Formica seven inches in diameter between matching pipe flanges. The tube of the telescope is clamped by adjustable bands of galvanized iron to a saddle carried by the declination axis and is counterbalanced by four lead weights of 25 pounds each. The weights were cast in the form of perforated lead disks that slide over the opposite end of the declination shaft, to which they are clamped by pipe strapping.

"At present I am using a commercial clock drive to track the stars. It operates on standard household current. Since I am also interested in observing planets, however, I am working on a new drive. It will include a direct-current motor of the compound type that has a variable but stable tracking response.

"Notwithstanding heavy construction, it is a sad fact that mountings of the German type are not as free of vibration as one could wish for instruments with apertures larger than eight inches. One can of course use such a large instrument for visual observing, but unless German mountings are protected from the wind they cannot be used for astrophotography that involves long exposures. This is only one of a number of things that must be taken into account when a mobile rig is planned.

"Two major considerations of design for mobile installations are weather and the sustained vibration to which the instrument is subjected when it is moved from site to site. Unlike instruments housed in observatories, a telescope mounted on a trailer is exposed to road dust, weather and the heat of direct sunlight. When the installation is stored in a backyard, it can be shielded from weather with a tarpaulin of canvas or sheet plastic. Remember, however, that coverings of this kind can have a greenhouse effect. Trapped heat can cause parts of the instrument to reach temperatures in excess of 150 degrees Fahrenheit. Therefore one cannot employ in making the telescope many popular plastics and cements that soften at such temperatures. Similarly, one must avoid materials that are subject to damage by prolonged exposure to moisture. Another problem is the possibility that certain fungi will flourish under the tarpaulin.

"With these considerations in mind I made the tube of my instrument from a cardboard form known as a Sonotube. Sonotubes are available from suppliers of heavy construction materials and normally serve as molds for pouring the concrete columns that support highway overpasses. They are manufactured with heavily waxed surfaces.

"I first stripped off the wax so that the cardboard could be soaked with thin epoxy resin of the kind used for impregnating fiberglass. Both the inside and the outside surface were heavily coated. After the resin had set, a layer of fiber and cloth was epoxied to the outside surface. Kits containing fiberglass, resin and full instructions for application are available from dealers in hardware. Tubes thus weatherproofed can be used immediately after the resin sets. One precaution should be observed. Holes drilled through the weatherproofed cardboard during subsequent construction, or any abrasion that would admit moisture to the interior of the cardboard, must be sealed with epoxy.

"All wood parts of the instrument must be similarly weatherproofed. For example, the saddle of my telescope, which couples the tube to the declination axis, was made of 3/4-inch plywood cut to the radius of the tube and fastened with screws and waterproof glue to a base of 3/4-inch plywood. The plywood end pieces cradling the tube are braced between two parallel pieces of two-by-four wood. The assembled saddle was heavily coated with fiberglass. All points Of contact between the saddle and the tube are covered with pads of indoor-outdoor carpet fastened in place with silicone cement.

"The cell that supports the mirror is also made of moistureproof plywood. It consists of a 3/4-inch disk of plywood 14-1/2 inches in diameter on which the mirror rests. The cylindrical wall of the cell consists of laminated rings of 3/4-inch plywood one inch thick that fit the mirror snugly.

"Four short strips of metal covered with pads of all-weather carpeting are screwed to the upper edge of the cylindrical wall of the cell at equal distances and extend 1/4 inch over the upper edge of the mirror to hold it in place. Three bolts with their heads recessed extend through the base of the cell at separations of 120 degrees. A stiff helical compression spring surrounds each bolt. The threaded ends pass through a 16-inch disk of plywood. Space between this disk and the cell is maintained by the springs.

"The 16-inch disk is rigidly fastened to the end of the telescope tube. A wing nut on each of the bolts can be tightened to put the helical spring under compression and thus adjust the spacing between the cell and the 16-inch disk. The wing nuts therefore adjust the alignment of the optical axis of the mirror with respect to the axis of the tube. All nuts should be of the lock type, including the wing nuts, to minimize changes in adjustment caused by the vibration of road transport.

"Boat trailers are manufactured in a broad range of designs and prices. Doubtless an amateur skilled in the mechanical arts could make one, but he would not save much money. I chose a relatively light vehicle with a wide wheelbase and pliant leaf springs that seemed capable of traveling over many different kinds of terrain. The framework is comparatively open and free of braces that would hamper the movement of an observer. It is a model 1971 Rocket Boat Trailer, one of the most inexpensive rigs that I investigated. I modified it only to the extent of shortening the tongue so that the trailer would be more responsive to small, quick corrections in steering.

"For mounting the pier of the telescope I bolted a platform of two-by-six-inch planks to the bed of the trailer. Two cross members were fastened with U clamps above the axle and a single cross member was clamped one foot in front. Fore-and-aft spacers of the same material were then bolted to the cross members to form at the center of the bed a well one foot square and six inches deep. The well supports the pier on which the polar axis of the instrument is mounted.

"The pier is a square tube made of one -inch pine that is closed at the top by a plug four inches thick. The plug consists of laminated pieces of two-by-four wood. When the trailer is level, the upper surface of the plug makes an angle of approximately 26 degrees with respect to the horizontal, which is roughly correct for the latitude (26 degrees north) of my home in Florida, for which the instrument was designed. The telescope and mounting as bolted to this plug weigh about 400 pounds.

"Lag bolts screwed into the plug and through the two-by-six boards of the well anchor the pier to the bed of the trailer. Inertial force set up by the 400-pound instrument during deceleration is counteracted in part by a 3/8-inch cable attached between the top of the pier and the back of the trailer bed. The cable can be adjusted in tension and is easily unhooked and removed for making observations, since at such times it is an obstruction.

"A minimum of two accessories must be included with a mobile rig of this kind. An eight-foot stepladder is essential for reaching the eyepiece when viewing stars near the zenith. I transport the ladder by putting it sideways on the bed of the trailer and lashing it to the pier.

"A minimum of two automobile jacks must also be carried to support the bed rigidly at the front when making observations. Otherwise the flexible leaf springs allow the instrument to jiggle. Other accessories include plastic garbage bags and elastic cords that serve as dustproof and waterproof coverings for both ends of the telescope tube and smaller plastic bags that protect the clock drive and the eyepiece.

"Still further conveniences suggest themselves. For example, thc labor of setting up the telescope at frequently visited locations can be minimized by installing a couple of stakes that are accurately aligned on true north. Some tricks for quickly aligning the polar axis will be found in Amateur Telescope Making, Book Two, edited by Albert G. Ingalls."

DON H. Anderson (538 Van Voorhis Avenue, Rochester, N.Y. 14617) has developed a kaleidoscope for projecting symmetrical patterns in color that change form in synchrony with the tempo of music. Anderson, who is director of the industrial laboratory of the Eastman Kodak Company, writes that he made the gadget for the fun of it. He describes it as follows.

"The device involves several variations of the toy that was patented- in 1817 by the Scottish physicist Sir David Brewster. Brewster mounted a pair of rectangular plane mirrors facing each other so as to make an angle similar to a partly opened book. He supported the mirrors inside an opaque tube closed at one end with a thin transparent cell that contained loosely trapped fragments of colored glass. A peephole in an opaque disk that closed the opposite end of the tube enabled the observer to view the fragments as images that were multiply reflected by the mirrors. When the mirrors were canted with respect to each other at an even submultiple of 360 degrees, the images appeared as abstract patterns of perfect symmetry. By rotating the tube the observer could cause the fragments to tumble and so could form patterns of endlessly varied detail.

"I have modified Brewster's device by adding a few components that were not available in his time. My basic kaleidoscope consists of three microscope slides, two of which were made into front-surface mirrors with aluminized coatings. They are assembled, along with the uncoated slide, to form a triangular tube of glass with the reflecting surfaces facing inward. The edges are cemented with epoxy.

"In one version of the device one end of the mirror tube is cemented into a closely fitting bottle cap of black plastic. The assembly resembles a triangular box. When small objects are dropped into the box and lighted from the side through the transparent slide, they appear as a pattern of threefold symmetry as the observer looks down into the box. Jiggling the box shifts the particles and alters the details of the pattern.

"By strongly lighting the particles, as with a 35-millimeter slide projector, and substituting for the eye an appropriately placed projection lens above the box, an enlarged image of the pattern can be focused on a screen. In other words, the device functions in part as an opaque projector. As a convenience I support a front-surface mirror at an angle of 45 degrees above the device. The mirror deflects the rays horizontally to a wall screen for comfortable viewing.

"My second modification consists of cementing the kaleidoscope through a light framework of cardboard to the paper cone of an inexpensive loudspeaker. Power from a radio or a phonograph drives the loudspeaker and jiggles colored fragments in the plastic cap of the kaleidoscope The small colored spheres known to confectioners as French's nonpareils, together with short lengths of colored plastic insulation stripped from copper wire of No. 28 gauge, make effective fragments for opaque projection.

"Alternatively the kaleidoscope mirrors can be mounted on a transparent base, such as the two-inch cover glass of a projection slide. This subassembly can in turn be mounted to the cone of the loudspeaker with a cardboard framework. Silicone cement adheres well to glass. A front-surface mirror can be mounted at an angle approaching 45 degrees between the cone of the speaker and the glass slide. A source of light that is incident on the mirror will be reflected upward through the kaleidoscope assembly. If the kaleidoscope is charged with colored bits of transparent plastic, it will function as a conventional projector.

"Another fascinating variation in design consists in polarizing the incident light with a sheet of Polaroid and charging the kaleidoscope with small crumpled wads of cellophane or another highly birefringent material. Rays from the projection lens are similarly transmitted to the screen by a second sheet of Polaroid. When the loudspeaker is energized and the polarizing sheets are approximately adjusted, the details of the projected patterns change continuously in both form and color. I find it very difficult to worry about the problems of the world as I listen to music in the evening and watch the synchronously dancing patterns on my screen."

Bibliography

AMATEUR TELESCOPE MAKING: BOOKS ONE, TWO AND THREE. Edited by Albert G. Ingalls. Scientific American, Inc., 1950,1949 and 1953.

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