READERS OF SCIENTIFIC AMERICAN NEED no introduction to Stanley Meltzoff. His cover paintings have adorned many issues of this publication in the past five years. But unless you happened to meet him emerging from the surf at Shark River, N. J., with flippered feet and swimming mask you would never recognize him as a frogman, skin diver and amateur ichthyologist. This sport and amateur science is becoming popular this summer, but Meltzoff took it up in 1948.

"For as long as I can remember," he says, "our family has summered on the beach. We all learned to swim early and our big sport was body-surfing. During late spring and early fall, when the breakers run high, you swim out 200 yards or so, catch a big one and skim back on your belly like a surfboard. We always dreaded July and August because then the Atlantic settled down like a millpond and that ended the thrills. At least that was the way it was until five years ago.

"Then one day in mid-July a gadget in a sporting goods store caught my eye. It was a swimming mask, an oval of rubber molded around a disk of shatterproof glass. I bought one on impulse. That week end, as usual for the season, my companions on the beach consisted of a dozen or so bass fishermen idly casting their lines into the surf and pulling them back empty, and a group of elderly ladies who enjoyed bobbing up and down close to the lifelines. The fishermen's persistence always puzzled me. Everyone knew the beach had been fished out for years.

"I fitted the mask over my eyes and nose and waded out beyond the ladies. I kicked off and dipped below the surface. The spectacle left me stunned. It was like floating in air. The sandy bottom curved away steeply into a cold, eerie blue. But within 100 yards the water was alive with clouds of bass-big ones by the hundreds. Cautiously I drifted down among them. Instead of darting away, the bass seemed to accept me as one of their own, lazily staying just beyond reach. Some weighing up to 25 pounds were wandering in and out among the ladies.

"Something had to be done about those fish. I rushed to our cottage and came back with a bamboo pole sharpened to a point. As things turned out, the bass were quite safe. My excited thrusts simply threw me off balance and robbed the spear of its force. Finally I gave up. But why weren't the fishermen hooking anything? I dove toward their lines to find out. At that moment, I suppose, I became seriously interested in the ways of things that live in the sea. The next day I bought a pair of rubber swim fins and I have been skin diving ever since.

"A few hours under water disclosed the reason for the fishermen's plight. The bass simply recognized the tackle as a clumsy fraud and kept their distance. They quickly learned to steer clear of men-fish, too. With a spear gun powered by rubber bands, bought that first season, I took several hundred pounds of fish. A half-dozen other enthusiasts also learned spear fishing. But by the end of the summer, the bass had learned to circle casually just beyond our range. In contrast the small, unhunted species came as close as ever.

"That season I also learned of some important advances in the art of skin diving. The snorkel had appeared some years before. This is a short length of plastic tubing which enables you to breathe while doing a dead-man float. One end is fitted with a mouthpiece which is gripped between the teeth; the other has a float valve which rides on the surface and closes automatically when submerged. The swimmer breathes through his mouth under water and exhales through a rubber flap valve in the mouthpiece. A snorkel enables the most inexperienced swimmer to float for hours without lifting his face from the water. Whenever you see something interesting below, you simply hold your breath, do a jackknife flip and down you go. Ordinary swimmers can dive to 30 feet and experts go down beyond 100.

"I also learned with disappointment that our waters off New Jersey are rarely as clear, or as densely populated with striped bass, as on that first day. The sea has a climate of its own and often adverse conditions cut visibility to a foot or less, especially near harbors or the mouths of rivers heavy with silt. That is why the clear waters of California and the Mediterranean make those localities world centers of skin diving. As in many U. S. lakes, good visibility is characteristic there throughout the year."

Good underwater seeing means a lot to Meltzoff, who is first of all an artist. Although the sea anemones and their relatives which coat the floor of tropical seas in brilliant colors do not thrive off the Jersey coast, he finds an endless challenge in the more subdued and less familiar forms in northern waters. At first he was content to make short dives for a hurried examination of the bottom, but such glimpses were not very satisfying. Moreover, Meltzoff wanted to try painting under water. For this he needed a means of staying below for longer periods, but conventional diving gear was out of the question. A deep-sea diving suit with air pump, tender and accessories costs thousands of dollars and gives the diver little freedom of action. He is tethered to his pump by an air hose. His shoes weigh 40 pounds or more. To move, he must adjust his buoyancy by means of a manually operated valve controlling the pressure in his suit. A slight error may cripple him for life. Hence, except for a few daring enthusiasts such as Dr. Jerome Schweitzer, the dentist explorer and diver of New York City, not many amateurs were attracted to oceanography until a solution was found for the problem of entering the hydrosphere safely and inexpensively for extended periods. This happened in 1943, though the U. S. did not learn of it until after the war. Captain Jacques-Yves Cousteau tells the whole thrilling story in a current best-seller, The Silent World. A gunnery officer of the scuttled French Navy, Cousteau was waiting out the Italian occupation by skin diving off the Riviera. There he and two swimming companions, Frederic Dumas and Philippe Tailliez, got an idea for a self-contained compressed-air lung. He submitted it to Emile Gagnan, an expert on industrial gas equipment, and together they worked out the practical details. The result was the aqualung, a device that has revolutionized diving and enabled comparative laymen to penetrate a vast new frontier as primeval as the land surface of 20,000 years ago. When it is realized that this is the last virgin territory of the Earth, the importance of the aqualung becomes apparent.

The aqualung has three major parts: a bottle of air compressed to 150 atmospheres, which is strapped to the diver's back; a two-stage pressure-reduction mechanism or "demand regulator" which automatically supplies air on demand at pressure equal to that of the surrounding water; and a loop of flexible tubing leading out of and back into the regulator, through which tube the diver inhales and exhales by means of a special mouthpiece in its center. This differs from earlier compressed-air devices, relying on manually controlled valves and a continuous, wasteful flow of air, chiefly in its ingenious two-stage air-pressure regulator. In the first stage the air is expanded to a constant pressure of about six atmospheres, controlled by a flexible diaphragm and compressed spring arrangement In the second stage this air is admitted on demand to a larger chamber where a larger diaphragm in contact with the water equalizes the pressure to match that of the surrounding medium, no matter what the depth. Anyone who has tried to breathe through a garden hose while submerged will appreciate the necessity of having air supplied at pressure corresponding with the depth. It is impossible to expand the lungs against the weight of water at a depth of six feet, J. Fenimore Cooper and his Indians to the contrary notwithstanding.

As Cousteau explains it, when a diver inhales from the aqualung he slightly reduces the pressure on the inside of the second-stage diaphragm. This actuates a demand valve which permits air to flow from the first stage until the pressure returns to equilibrium with the water on the outside of the diaphragm. When the diver exhales, his breath passes up the second section of the tube to a rubber flap valve situated near this diaphragm, which means that it is expelled at the pressure of the intake. Since all internal and external pressures are thus in equilibrium, the diver receives little subjective indication of depth. Although the total weight of the apparatus is 50 pounds, it is so designed that it is buoyantly balanced under water. The air supply is sufficient to permit a diver to work for half an hour at a depth of 100 feet, and he can breathe effortlessly down to about 300 feet. An automatic warning device operates as the air supply nears exhaustion, giving the diver about five minutes in which to surface.

A third type of diving apparatus, invented in time for World War II, also enables the swimmer to make free dives. This is the so-called "re-breather" device in which a trickle of oxygen flows continuously into a closed system of tubes and filters that re-circulate the initial supply of air and remove the waste products of respiration. No telltale bubbles emerge from this system and hence it was extensively used for underwater demolition by the fighting frogmen. Meltzoff and his diving companion, James McCloskey of Port-au-peck, N. J., believe that with further development the re-breather system may displace the aqualung. Pound for pound, oxygen should permit longer dives than air. But under water, they admit, it is tricky stuff. Pure oxygen at a depth pressure of 50 feet becomes a poison giving rise to convulsions and other violent reactions. Present re-breather apparatus is subject to malfunction, and the very existence of a variety of designs indicates the need for more development. McCloskey always tells beginners intent on purchasing war-surplus re-breather equipment at bargain prices to remember that frogmen were classed as expendable.

In contrast, Meltzoff and McCloskey point out, not a single fatality has been traced to the malfunctioning of an aqualung despite tens of thousands of dives. "Perhaps the greatest hazard of the aqualung to inexperienced swimmers," says Meltzoff, "is the perfection with which it works. You tend to forget that it is there. You are carried away with the environment and ignore the fact that you are a fragile trespasser out of your accustomed medium. Properly ballasted, you can sit in a chair while observing life on the bottom with all the feeling of comfort and security you enjoy in your living room. Breathe deeply and your lungs lift you on an effortless glide toward the surface. Exhale, and you plane down. You fly without flapping! It is easy to forget that you are a land animal. At great depths nitrogen concentrates in your blood with all the effects of heady wine. As Cousteau has observed, in this state of transport it sometimes requires a supreme act of will to avoid pulling out your mouthpiece and offering it to a passing fish. It is well for the aqualung beginner to avoid dives below 60 feet, even though he has a lot of snorkel experience."

McCloskey, like Meltzoff, also learned to dive as a boy. His first equipment consisted of an inverted bucket fitted with a window and supplied with air via a garden hose and automobile tire pump. "The helmet still has its place in amateur diving," he says, "but compressed air is a lot safer. Moreover, you can swim wherever you want to go. While stationed in Florida during the war, for example, I became interested in barracuda. They are supposed to be man-eaters. Knowing something about the habits of fish, I didn't believe it. I have a theory that the experienced skin diver is in no more danger than any big game hunter. Wild animals tend to avoid conflict unless provoked or cornered. Florida is filled with tales of swimmers who supposedly lost their lives to barracuda. I could not discover a single individual who ever witnessed such an attack. All the tales shared one feature in common: 'A distant relative once knew a man who had heard a shrimp fisherman say . . .' Finally I went down for a free-swimming look, something you cannot do in a helmet. Within the first five minutes I spotted three barracuda idling peacefully among the bathers in Miami Beach. One warning shout of 'barracuda' would have sent them all scrambling for shore.

"This is not to say that barracuda will not attack. Once, while studying the habits of parrot fish off the Coca River I happened to glance behind me and there, not more than 15 feet away, was a huge silvery shape at just about my level. He was at least eight feet long and must have weighed 500 pounds. To my dismay, I discovered that he was taking an interest in me. He wore a nasty expression and bared his teeth. Then I realized that he was between me and the beach. Perhaps he thought he was cornered. Animals can get some strange ideas. I promptly exhaled and cautiously planed toward the bottom, 100 feet below. After a few seconds the barracuda gave his tail an uneasy flip and then tore out of there like a racing dirigible, obviously as relieved as I was.

"The worst encounters I have experienced during dives have been with those creatures which every bather in tropical waters knows about: crabs, Portuguese men-of-war, sea nettles, and other animals that pinch or sting when you ignore their rights. I must confess that I always feel uncomfortable when sharks are around. I do not know why this should be so. None has ever made a pass at me. The professionals say that sharks are unpredictable beasts, so I've decided to leave them for some graduate student on the lookout for a pregnant subject for his doctor's thesis."

Meltzoff and McCloskey make a good diving team: one is interested in recording the sights of the sea, and the other its sounds McCloskey has a background in electrical engineering and is an executive in a thriving young firm making electronic computers. Friends have suggested that he should write a book someday entitled The Noisy World as a companion to Cousteau's volume. McCloskey is interested in developing a hydrophone to be worn like a hearing aid. His tentative design incorporates a local oscillator for beating against supersonic vibrations. This would enable him to hear sounds well beyond the normal range of human hearing. He also hopes to build a magnetic tape recorder for underwater use. Fish have a mysterious way of acting in unison when exposed to a variety of stimuli. If they talk, McCloskey's proposed apparatus should enable the amateur to eavesdrop. The development of sensitive ship hydrophones during the war established the fact that fish vibrate over a broad range of frequencies, but the operator could not link the sounds with the species because he could not see under water A hydrophone-equipped skin diver would not be hampered by this limitation. Whales have been known to emit certain supersonic vibrations in a group of radarlike pulses, possibly as an aid to navigation. Some fish sounds can be heard without electronic aid. Groupers, says McCloskey, occasionally make a harsh, grating noise, and Cousteau has observed that any thrashing near the surface seems to attract the attention of sharks. Perhaps they are sensitive to subaudible vibrations. Some work is already under way on this subject at various oceanographic institutions, but any significant findings must await further cataloguing of fish sounds.

"Equipped with an underwater lung," says McCloskey, "the skin diver finds himself in a territory as virgin as that of Linnaeus-a vast expanse of the unknown, by no means limited to ichthyology. Fish naturally hold the greatest interest for our club because most of us started as spear fishermen. But show me the hunter who is not also an amateur naturalist. This year our club is cooperating with Rutgers University on a census of New Jersey's coastal fish-a project suggested by Meltzoff. Eventually, we hope to map the 'swimways' of the various species just as the bird-banders have helped to chart the flyways of game fowl and other birds. In addition we hope to learn much more about our shore life. Until the advent of the compressed-air lung, these studies were largely confined to the zone that extends between the tides. Now we can observe what happens to the sea-mats, squirts, shrimp and other small crustacea at high tide.

"And what possibilities the lung opens to the fellow who lives near a freshwater lake! There the water stratifies far more sharply than in the sea, and aquatic life zones itself accordingly. I have done very little fresh-water diving, but that little revealed no great difference in technique. In salt water I must weigh off with about seven pounds of lead attached to my belt. Fresh water diving requires only three or four pounds."

The other day we asked Meltzoff a question that had been on our mind for several weeks; what about the "bends"? "First of all," he said, "it should be understood that the compressed-air lung is not a toy. You can hurt yourself with it. Below 50 feet excess nitrogen in the blood forces you to decompress on the way up for various periods at various levels, depending on the duration of your dive. If you stay at 100 feet for an hour you must decompress at 20 feet for 16 minutes and at 10 feet for another 16 minutes. But if you are at 100 feet for only 25 minutes you can surface without decompression. Experienced skin divers do not worry about the bends. However beginners have been known to hurt themselves seriously in water only 20 feet deep by an effect which has nothing to do with the bends. As the diver begins his ascent his lungs are filled with air under pressure proportionate to the depth. During-ascent the pressure of the surrounding water drops. Unless the diver continues to breathe as he rises the difference in pressure between a depth of 20 feet and the surface can rupture his lungs. On the other hand, if he remembers to exhale while ascending he can surface from a depth of 100 feet without a lung. The first requirement for compressed-air diving is experience and this is best acquired by training with a snorkel. The aqualung is no substitute for skill in underwater swimming."

TELESCOPE-BUILDING has not been treated in this department for months, but it continues, easily at the rate of several new amateur telescopes a day. Each is individually designed by its builder around basic principles described in Amateur Telescope Making. Each therefore embodies interesting original features. A 10-inch Cassegrainian reflector built by G. M. Reavis, a linotype operator of Fresno, Calif., is no exception. His is not, however, a first telescope. Like nearly all novices, Reavis began by building a simple six-inch Newtonian which he used for several years to gain experience.

In a Cassegrainian the light rays are received by a concave mirror at the lower end of the tube, then reflected to a small convex mirror near the top, from which they are reflected again through a central hole in the primary mirror into the eyepiece. To permit a more comfortable angle of observation, Reavis added a third reflection near the eyepiece by means of a flat diagonal mirror. While the Cassegrainian, being folded into short compass by its secondary mirror, may be thought of as the equivalent in magnification of a Newtonian telescope four times as long, it is much more difficult to make and is not recommended for the beginner. Nor is the 10-inch Cassegrainian the easiest size to encompass, its volume, weight and cost being 4.6 times that of a six-inch. Reavis spent $200 and more than two years on and off, with time out to make a 3 1/2-inch refractor, in building his Cassegrainian. Its primary mirror is f/5 and its spherically convex mirror amplifies the image four times. Equipped with a giant eyepiece of 1 1/2-inch focal length, the telescope magnifies 133 times. Reavis says that "even with this much power the wide field lens takes in the full image of the moon, showing a wealth of detail, and it is truly a marvelous sight.

"Each of the two finding telescopes riding on the main telescope," he continues, "has a three-inch objective lens. I usually pick up the object on the short one, a richest-field (wide-field) refractor of 12 power, then switch to the long one which has a 23 1/2-inch focal length and magnifies 50 times, though with a narrower field. All this is unnecessarily elaborate, as such finders aren't really necessary. However, they are often used as separate telescopes served by the main mounting and they do greatly impress guests."

Reavis made his own patterns for the mounting and did most of the machine work on his lathe. He finds that the telescope is rigid enough except when a Southern Pacific freight locomotive pounds along within 1,000 feet, converting it temporarily into a seismoscope. Four one-inch bolts embedded in concrete adjustably hold a 1 1/8-inch steel plate to which the heavy-wall, six-inch steel-pipe pedestal is welded. A rugged ring welded to a rigid plate is attached to the top of this pipe with four Allen setscrews, permitting easy removal and adjustment. "Here, however, the welding stopped," Reavis writes, "and I used bolted angle iron to attach the side plates and the latitude plate, because welding would have warped everything.

"The bearings are housed in cast-iron pillow blocks. The heavy T for the polar and declination axes was cast from a pattern I made. The polar axis is a two-inch shaft with a ball thrust bearing at its lower end and a Torrington needle bearing at its upper." Roger Hayward, the illustrator, who is also an architect and amateur mechanic, commented after making the drawings for this article: "Torrington bearings are of particular interest because they take so little room. Amateurs should take more advantage of them. These are the only kind of roller bearings in which the outside of the shaft runs directly on the rollers, and thus the amateur can turn this surface for himself. The rollers are small, hardened steel rods, 1/8-inch in diameter or thereabouts."

Reavis continues: "The drive consists of a 12-watt Telechron motor giving four revolutions per minute and working through the gear train shown in the drawing. This gives sun time rather than sidereal time, but it holds the telescope on an object as long as I want to look. I had to use mitre gears because I didn't allow enough room between the two vertical side plates for the motor and gears. The motor was larger than I had expected, and I had to put it on the outside of one plate and, in order to get clearance for the 96-tooth gear, I had to cut a slot in the other side plate. There is a friction clutch on the 60-tooth gear You set the telescope on some object and it starts tracking wherever you point it." Since perfect telescopes are as uncommon as perfect people, this department often urges builders to confess their mistakes, which may thus help others to avoid them. Many have willingly pointed out imperfections, at least in the telescopes.

At first Reavis felt so kindly toward the compound telescope that he writes: "How gratified I am that I made one instead of a Newtonian of equal diameter and equivalent focal length, for I like better being at the bottom end of a short tube than standing on a ladder to look into the side of a tube which in this case. would be 16 feet long. Best of all is the ability to get high powers with nothing stronger than a 1/2-inch eyepiece." After some months of use he was only a little less enthusiastic, finding that the secondary mirror gave better definition with its outer quarter-inch zone masked, which, of course, gave less illumination. He plans to refine the secondary. He adds: "The compound type suffers in comparison with other types in that the field of view doesn't have as much contrast as with a Newtonian or a refractor." Theoretically the quality of optical workmanship needs to be increased in proportion to the square root of the number of surfaces in the optical train, and thus a two-mirror telescope should have optics 1.4 times more precise than the one-mirror variety, while a three-mirror telescope should have optics 1.7 times more precise.

By counterweighting the secondary mirror, Reavis brought "outboard" stresses inboard where they are neutralized and cannot distort the supports. It is the same principle as that explained by Russell Porter in Amateur Telescope Making, page 131, and in Amateur Telescope Making-Advanced, page 375. The sliding rod permits adjusting the secondary mirror lengthwise in the telescope to place the image approximately in the focal plane of the eyepiece. This is a convenience when design calculations have erred a little.

Reavis contributes a new method for cutting clean channels in pitch laps without having chips flying all over a room. "Pour the lap, then pencil on it the outline for the channels, cover each with Scotch tape, cut them out with a razor blade, peel off the tape and your channels are almost as neat as Porter drew them." He polished his mirror until a 150-power microscope was required to show very tiny pits near its edge. For the same purpose Fred Ferson of Biloxi, Miss., with much experience in making pitless optical surfaces of a kind that few amateurs make, uses a 10-power jeweler's loupe magnifier with the light from an unfrosted lamp bulb shining obliquely on the surface. Undiffused light from the narrow filament creates stronger shadows of the pits than light from a frosted bulb.

Walter J. Kastner, Jr., of Union, N. J., has described his method of searching for pits and studying them while grinding a mirror. "After roughing out the mirror with the coarsest size of abrasive, dry it and hold it between the eye and a lamp bulb about four feet distant, with the ground surface facing you. Observe closely the manner in which the pits disperse the light. Each pit larger than average is seen to stand out clearly. After one 'wet' with the next size of abrasive, inspect the mirror in the same manner. The light will be seen to be more evenly diffused, except where the largest pits were and are; hence they will now look worse than ever. After four or more 'wets' with the same size abrasive the surface will diffuse the light more or less evenly, but you will still see extra-large pits. You may then decide that a little more grinding will remove them but even if you try this for 5, 10 or 15 'wets' you will still see extra-large pits. The probable reason is that new pits are made each time you begin a new 'wet,' because extra-large grains dig out new pits which are not fully ground out when that 'wet' is finished. Therefore forget about them and start the third size of abrasive and repeat the observing. Keep doing this for each remaining size of grains. You will observe that even with the finest size of abrasive, there are small pits that you can never seem to remove. They can at least be reduced in size by avoiding pressure on the disk, even to lifting up on it and grinding very slowly until the sound caused by these larger grains is replaced by the smooth grinding of equal-sized grains.

"Please don't tell me," Kastner adds, "that my abrasives have been contaminated. Even after stirring the grains in water, letting them settle, and using only the top part, pits appear." Unfortunately nothing as simple as elutriation or washing will remove the "cobblestones and brickbats" with which the graded sizes are contaminated when the manufacturer produces them, and which his methods of grading do not exclude. In Amateur Telescope Making: Book Three, to be published later this year, a method will be described by which the optical worker can extract this "road ballast" from his abrasive grains and be done with the scratches and outsized pits caused by them.

Suppliers and Organizations

The Society for Amateur Scientists
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East Greenwich, RI 02818
Phone: 1-401-823-7800

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