AND THE Lord God said unto the serpent, Because thou hast done this [beguiled Eve] . . . I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel."

Despite this curse in Genesis some people like snakes. A well-known commercial artist once raised a young constrictor as a pet in his studio. Another acquaintance of ours rarely goes any where without carrying along a garter snake or two in his coat pocket.

Most people develop in childhood an all-or-nothing attitude toward snakes. You either like them a lot or you don't- a lot! If you belong to the exclusive little band of those who do, the chances are good that you are a herpetologist, amateur or professional, and have been one for as long as you can remember.

Herpetologists find the average person's aversion to snakes hard to understand. Snakes are not only useful and beautiful but most species are harmless. According to the excellent field guide Reptiles and Amphibians, by Herbert S. Zim and Hobart M. Smith of the University of Illinois, of 250 species and subspecies of snakes found in the U. S. only 36 produce poison that can harm man, and these are rare except in a few localities. Snake bites account for fewer than 150 deaths a year in the U. S. Snakes are clean, are easy to tame, live well in captivity, need little care and are lovely to look at.

Herpetology offers to amateurs broad opportunities for original research. Zim and Smith emphasize that the life histories of many species of snakes are still unknown. Most of the adults have been described, but data on their eggs and young are far from complete. Snakes' eating habits, hibernation, mating, diseases and patterns of hunting remain relatively unexplored.

An enthusiastic amateur herpetologist who has written much about snakes is D. F. Munro, professor of modern languages at Kansas State College. He says: "Prejudice against snakes, it seems to me, stems from the same source as most other prejudices. The attitude vanishes with a little firsthand knowledge. No one could ask for a more attractive or well-behaved companion than I had in Lulubelle, a garter snake that used to share my lot. If a snake and a human being can have rapport, Lulubelle and I had it. I used to carry her around in the sleeve of my uniform when I was in the Army (left arm, to avoid jostling her when saluting). She went everywhere wit me, just sticking her nose out far enough to watch the world go by. In the evenings when I was in charge of quarters I would put her in a cloth sack and leave it lying open on the desk. She would poke her head out and get in on the act no matter what I was doing. When I used the typewriter, it seemed as if the rhythmic movement of my fingers lulled her into a contented bedazzlement. I note the same effect on the copperhead on my desk just now. He has the freedom of the desk top as I write these lines to you.

"Experiments have shown that babies and young monkeys do not fear snakes until 'taught' to do so by their elders. If you can overcome this imposed revulsion to snakes, you could hardly find a field of study more fascinating or one in which it is easier to make worthwhile contributions."

Munro has written many articles for Herpetologica, the official organ of the Herpetologists' League. He has based them on observations of Lulubelle and various other snake pets.

"I never learned to fear snakes," h writes. "Small animals, including snakes, have always interested me. Living in Nova Scotia, a region free of venomous reptiles, I was brought up with the same regard for snakes as for other creatures in the wild. During fishing and hunting trips my father was doubtless glad to have me off exploring the meadows and hillsides for snakes and other animals because he was a most exacting and expert fisherman and gunner.

"From these trips I brought many snakes home and released them in our garden, always wondering afterward why I never saw them again. Now I realize they must have made a beeline back to the tall timber.

"The fascination of snakes dwindled after I got into baseball, language study and other activities in high school and college. But it revived during World War II military service, when, paradoxically, I had the leisure for an avocation. While on a leave in Kansas City I wandered into a bookstore one day and chanced to thumb through Snakes of the World, by Raymond L. Ditmars. The striking illustrations caught my eye, and I could hardly wait to get back to camp. The volume was absorbed in a single session.

"I had had no formal training in biology, hence the story of snakes came to me as a revelation. It had never occurred to me that so much work had been or could be done in this relatively humble region of the animal kingdom. I was particularly stimulated by the emphasis Ditmars' book placed on the gaps in our knowledge of reptilian ways.

"As spring approached, I made plans for acquiring a few snakes as pets, though the idea appeared awkward because I was still in the Army and living in barracks. Nevertheless, I built a couple of cages and pinned my hopes on an understanding War Department.

"Kansas and its environs is good snake country. I quickly picked up specimens, only to release them in favor of others more interesting. From the very beginning the snakes proved endlessly diverting. Gradually I learned to recognize each individual by variations in color, scalation, mood and pattern of behavior. For some months the snakes were little more than pets. I tended and fed them. In return they amused me.

"In the summer of 1945 I captured an exceptionally beautiful female garter snake, and she bore a litter of young immediately afterward. But with one exception all of them were stillborn. 'Why?' I wondered. I decided to give Lulubelle, as I had named her, another chance. The next spring I found her a fine young mate. By this time I was so familiar with Lulubelle's behavior that the slightest departure from normal was strikingly apparent. This helped uncover some facts about the mating behavior of garter snakes not previously recorded.

"According to the books, the male snake takes all the initiative during courtship and mating. Lulubelle proved that the female is far from passive. As soon as the pair were placed in the same cage, the male approached the female, slid along her back and wriggled. The female seemed indifferent to this advance, and the male retired to a corner. A few minutes later the female began to crawl and loop over the male and arch her tail in an obvious mating gesture. But the male now ignored the female's advances and showed considerable timidity, as if disturbed by captivity.

"I placed him in another cage and the next day brought Lulubelle another newly caught male. The pattern of behavior was repeated. When this second male failed to respond to the female, I replaced him with the first. The pair immediately approached each other. The male stroked the female with his chin and the female simultaneously arched her tail. The union was consummated at once. From the moment of mating an obvious change came over the female. Whereas for several days she had been restless and sensitive to any touch in the anal region, she now became almost sluggish, apparently content to lie in a loop without moving. Four months later she produced her young, all born alive this time.

"The same summer I found Lulubelle I also caught a newborn copperhead which likewise stimulated my interest in serious snake study. When you spend a lot of time watching snakes, small details of their behavior catch your attention The copperhead, for example, has a way of staring at you with an intensity that cannot be ignored. You find yourself staring back. After a few hours of this, I became conscious of a unique characteristic of the pit viper's eye.

"Like the eye of a cat and many other nocturnal creatures, the pupil of the pit viper takes the form of a vertical slit. But in one very remarkable respect it behaves differently from a cat's eye: instead of turning with the tilt of the snake's head, the slit stays vertical, as if the pupil were under the control of an internal gyroscope! However the snake's head moves, the pupil retains its perpendicularity like a plumb line [see Roger Hayward's drawing, right].

The only exception is that when the snake is on the verge of dozing off and its head droops the pupil may tilt forward. But if the snake is aroused by a camera flash, the pupil immediately snaps into the vertical position. The snake's eye can rotate not only in a forward and backward direction but also in the sidewise direction; in sleep the slit turns under so that part of it is hidden [drawing at lower right in Fig. 1].

"When I sent a photograph of the viper's remarkable pupil adjustment to the vertical position to Herpetologica, it was a great satisfaction to receive word from Major Chapman Grant, the publisher, that I had a 'scoop.'

"Herpetologists also welcome notes on the hatching and behavior of young snakes-an area of investigation that has not been well covered. I made a careful watch of a clutch of eggs laid by a hog-nosed snake. When laid, the 11 eggs weighed about three quarters as much a the snake did. They had a smooth, soft, rubbery feel. During incubation they were kept in covered glass jars with damp paper to prevent them from drying out. I weighed and measured each egg at intervals during the two-month period. The eggs had gained about 50 per cent in weight by the time they hatched.

"Young snakes, like birds, are equipped with an egg tooth which enables them to cut their way out of the shell. Each emerging snakelet first made a slit in the egg shell and then enlarged the opening by forcing its head through During this phase its tongue flicked in and out. The head emerged from the shell upside down-a position which has brought the egg tooth into play against the uppermost part of the shell. After about an inch of the body was exposed, I the hatching process slowed down. Occasionally the snake appeared to writhe and squirm inside the egg, as if disentangling itself or straightening out kinks. The first snakeling escaped from the shell at the end of a 55-hour struggle. The remainder of the clutch followed a similar hatching pattern, the time ranging from 40 to 60 hours. The plump, newly hatched snakes averaged seven inches in length and were perfect miniatures of the mother.

"Immediately after hatching, the snakeling began crawling in an effort to shed its skin. It was dipped in water. The body skin came off easily. The fledgling's tiny, thornlike egg tooth also seems to be shed soon after birth. This tooth is a special structure in the upper part of the mouth. An eight-power magnifying glass shows it to be forward-pointing and white. The tooth does a disappearing act that would challenge the detecting prowess of Philo Vance. I was unable to find a single egg tooth in the debris of cast skin. I kept a close scrutiny over one snakelet placed in a small bare cage by itself, and when it dislodged the scale from the end of its snout, I examined the material immediately. The egg tooth had vanished! I can only surmise that the snakelet had swallowed it."

If Munro can get your ear, he will go on for hours about his pets. "Lack of time and facilities," he says, "has reduced my stock of snakes to seven. Still among them, however, is one of the early specimens from Army days, the copperhead, now a veteran of over eight years of cage life. Lulubelle died three years ago after presenting me with several fine litters. I still miss her, of course.

"One can't help being amazed that so many otherwise rational people feel an aversion for snakes. For a busy person, or one who must be away from home occasionally, they make ideal pets. Many practical considerations make it convenient to keep snakes in situations which would prohibit other pets. The reptilian tempo of life is slow, so that a study of their ways need not be based on daily contact. More important, snakes require feeding only once a week or so, and if necessary they can be left a month or so in safety if they are provided with a dish of water.

"Cages are inexpensive and easy to build [see Fig. 2]. Only one precaution need be taken in their construction: the screening should be securely attached and its rough edges covered so the captives will not injure themselves. Cleanliness is easily maintained. Snakes abhor dirty cages. Lulubelle used to insist on being taken out in the yard for excretion. She would crawl back and forth against the wire of the cage to attract my attention, and accidents happened only when I was too stupid to understand what she was trying to tell me. On these rare occasions she would meticulously avoid the soiled area until I cleaned her cage.

"Snakes do not sing, purr or dance for you, but that does not mean they are unresponsive. Even when they just lie about like crooked sticks, they are watching you and will respond to attention in their own way. Different as they are from human beings, these silent creatures throw light upon many essentials of animal behavior."

LIVES there a person who has never wondered what lies on the other side of the moon? H. P. Wilkins, director of the lunar section of the British Astronomical Association and the foremost selenographer of our time, has sought for years to elucidate this mystery. He has prepared an advance guide map for the space explorers who in the not distant future will visit the moon and become the first human beings to see its farther side.

Because of the moon's libration we get glimpses of about 9 per cent of that half of the lunar sphere facing away from us. Each month the Man in the Moon nods a little and shakes his head a little. He nods (libration in latitude) because the moon's axis is tilted so that we can see 6-1/2 degrees over one pole and two weeks later the same distance over the other pole. He shakes his head (libration in longitude) because the moon's elliptical motion around the earth is not uniform, while its axial rotation is. This difference enables us to look about 7 degrees (more than 100 miles) around each of its sides. In addition, each day the viewing position of an observer on the earth shifts by about 8,000 miles because of the earth's rotation. This diurnal libration adds about another degree to our field of view of the moon.

Wilkin's map of the back of the moon [see Fig. 3] shows around the edges the portions we can see during the various librations. It also shows rays like those on the moon's side facing us; these lines are not theoretical, for they are projections of sections of rays that can actually be seen in the zones of libration. Wilkins extends the ~-rays to the centers, presumably large craters, from which they radiate. The shaded areas on the map are his surmises as to topographical features on the other side of the moon.

On the earth and Mars each large upland mass is balanced by a large depressed region-an ocean or plain. Wilkins therefore supposes that the depressed "sea" visible in the northern part of the moon side that faces us is balanced by a mountainous portion diametrically opposite it on the other side. This area is left white on his map. Similarly he imagines that the mountainous region in the southern portion of the side that faces us is balanced by a depressed -plain on the other side. The big shaded area on his map represents a large plain or "sea" similar to the great Mare Imbrium on the earthward face. A dark area which may be one end of this region is just visible to us; it has been named Mare Incognito. Wilkins throws in three smaller plains, also shown as shaded areas, on the probability that such depressions exist in the mountainous area on the other side as they do on the earth ward face. Four such depressions are visible in the zone of libration.

No doubt when the first space ship circumnavigates the moon a selenographer broadcasting from it will report to the great listening earth audience that the back of the moon has about the same kinds of mountains, plains, craters, pits and clefts that we can see on our side, but he will nonetheless have a large and excited audience when he comes back to earth with his slides to tell the details.

To compute the path of a projectile from a gun one must measure the projectile's greatest velocity, which occurs just after it leaves the muzzle. In the case of a rocket missile the problem is different, for a rocket continues accelerating clear up to the point where it has burned all its fuel. Near that part of the flight velocity measurements must be made at two or more points in the trajectory. For this a missile-tracing telescope is needed. Because rocket missiles have exceedingly high velocities, the telescope must work photographically. The motion-picture cameras used make 16 to 64 exposures per second with exposure times of 1/10,000 second.

When Clyde Tombaugh, optical staff physicist of the Flight Determination Laboratory at the White Sands Proving Grounds, set out to design the optics of telescope cameras for tracing missiles, he realized that the optical system must be fast. The smallness of the missile and its great height above the ground would require a scale of images that could be obtained only with a focal length of about three feet. He hoped that this focal length might also make it possible to determine absolute positions of points in the trajectory by the most precise of all methods: graphing the missile with two cameras against the background of the stars. By this method the points can be determined with an accuracy of one inch in three miles.

To obtain images of enough brilliance to be photographed in the necessary 1/10,000 second at this focal length, the focal ratio must be at least f/3. Refracting telescopes of this short focal ratio would be impracticable to make. Paraboloidal reflectors, though relatively inexpensive and easy to make, would not be satisfactory because of their excessive coma and astigmatism at this focal ratio. However, Schmidt cameras of 12-inch aperture and 16.5-inch mirrors would give the necessary speed if suitably modified.

In a normal Schmidt camera [drawing at left, Fig. 4 ] the light rays enter through a thin lens or correcting plate with its surface ground to a very shallow double curve (greatly exaggerated in the drawing). This curvature bends the incoming light rays just enough to neutralize the spherical aberration that will be caused later by the spherical mirror. The corrected rays from the mirror are then focused as a spherically convex image at a point midway between the mirror and the correcting plate. Here Tombaugh might have inserted a diagonal mirror similar in principle to the one in the Newtonian form of telescope [drawing in middle, Fig. 4], which reflects the rays to a film holder outside the telescope. Unfortunately this diagonal mirror would cut off 40 per cent of the light-even more than a film holder. The decrease in light would increase the necessary exposure time from 1/10,000 second to 1/7,000 second, causing prohibitive travel blur in the images of the missiles.

The solution of the dilemma was the off-axis form of the Schmidt camera [drawing at right, Fig. 4]. Here the mirror is tilted to reflect the rays to one side of the telescope. After they pass through a small plano-convex field-flattening lens, which brings the convex image into coincidence with the flat film of the camera, they enter the motion-picture camera. This solution is not as simple as it may seem. The correcting plate used in the normal type of Schmidt is no longer suitable. The plate must now have the curvature shown in the right-hand drawing: the curve is a section of a hypothetical Schmidt corrector of the diameter indicated by the dashed lines.

The off-axis Schmidt was proposed in this department in August, 1939, by D. O. Hendrix and William H. Christie of the Mount Wilson Observatory in a classic article on uncommon variations on the original Schmidt.

One method of making an off-axis correcting plate is to make a normal one of full hypothetical size and then cut a circle from one side [drawing at lower left, Fig. 4] with a rotating glass saw or cookie cutter This method tempted Tombaugh and his associates, the physicist William C. Braun and the mechanical engineer Clyde R. Dennon, especially because it would afford two correcting plates for the two cameras they needed. Tombaugh writes: "We were hesitant to attempt it, because the ,l4-inch correcting p]ate would have been 32 inches in diameter, and we had no means of supporting it adequately during grinding and polishing to keep it from flexing. Hence we elected to make a correcting plate off-axis by the use of a special jig [drawing at lower right, Fig. 4]. The lever arm has a long, carefully machined slot through the middle, which permits a small grinding tool bolt to be clamped anywhere along a radius from the centered king bolt. The grinding tool is designed to slide up and down freely, so that variations of force on the grinding arm by the operator cannot cause variations in pressure of the tool on the correcting plate. Various weights can be put on this bolt to regulate the rate of grinding. The grinding is done by arc strokes with small tools (one to three inches in diameter) to scoop out the various zones."

Off-axis optical surfaces have been figured by professional and amateur opticians for a number of years Most of these workers regard a mechanical jig as too inflexible; it confines the abrasion too closely to separate zones without the necessary blending effects. Norbert J. Schell of Beaver Falls, Pa., who with his co-worker T. J. Beede of Youngstown, Ohio, had made off-axis telescopes as early as 1939, said then that in figuring off-axis mirrors "no machine work or mechanical controls were used, although a mechanical control was first tried and discarded, as it was found unsatisfactory." Today Schell adds: "Everybody who gives this any thought comes up with this lever method of control. Beede and I found that there was so much more to it that the machine we tried was a nuisance We wouldn't use it as in the drawing but only to control the central position of the stroke, which would be zigzag across the zone to give blending. The optician Daniel E. McGuire has used a large lever in much this manner, but with a smaller lever to make local arcs."

The principle of this method was devised independently and used by the Ferson Optical Company in 1946. Fred B. Ferson says: "This method can be readily used by hand by a skilled optician with off-axis mirrors of f/5 to f/9, and if the departure from the axis is not too great. It involves only rubbing the longest where most needed, and grading the figure to that part of a larger parabola. The figure can be determined in collimated light with the Ronchi test at the off-axis position. It can likewise be tested at the center of curvature with the Foucault test, which will exhibit the figure of that part of a hypothetical larger mirror. True correction will give straight bands with the Ronchi test in collimated light. This is the whole story."

So far as this department knows, instructions for figuring an off-axis mirror have never been published before.

SNAKES OF THE WORLD. Raymond L. Ditmars. The Macmillan Company, 1931.

AMATEUR TELESCOPE MAKING Edited by Albert G. Ingalls. Scientific American, Inc., 1952.

AMATEUR TELESCOPE MAKING-ADVANCED. Edited by Albert G. Ingalls. Scientific American, Inc., 1952.

AMATEUR TELESCOPE MAKING-BOOK THREE. Edited by Albert G. Ingalls. Scientific American, Inc., 1953.

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