SAMUEL JOHNSON, an opinionated man on any subject, had a theory that swallows, like frogs, spent the winter hibernating in the mud at the bottom of rivers and lakes. Unlike many of his pronouncements, this one was not delivered purely off the cuff; the irascible doctor actually conducted experiments. He captured a number of swallows and cemented bits of colored cloth to their tail feathers. He later recovered some of the marked feathers at the water's edge and triumphantly produced them as proof of his theory.

The good doctor overlooked the fact that birds molt their feathers, but his approach to the scientific problem was not entirely without merit. Bird-marking is today a large and fruitful enterprise. At the turn of the present century Danish ornithologists hit upon the scheme of tracing the travels of wild birds by banding them with a ring of light metal fastened loosely around a leg. A serial number and other information is marked on the band, and whenever a bird is recovered, the information is reported to a central clearing house. The system was soon adopted throughout the world.

In the U. S. the sponsorship of bird-banding, started by the American Bird Banding Association, was taken over in 1920 by the Federal government. The project is now a branch of the Fish and Wildlife Service, with headquarters at Patuxent Research Refuge, Laurel, Md. It is under the direction of the biologist Seth H. Low.

Nearly six million birds have been banded since the U. S. program started; some 300,000 to 400,000 are tagged each year. A total of some half a million marked birds have been recovered. There are about 2,000 cooperating bird-banders, professional and amateur.

The object of bird-banding is to collect scientific data on the migration, dispersal and age of wild birds. It helps in the study of such characteristics as homing instinct, mating habits, navigation ability, flyways and related patternsof behavior.

Since only a small fraction of marked birds are recovered, it is desirable to band large numbers of them and to station banders and observers over the widest possible area. Hence the amateurs are strongly encouraged to take up this avocation.

It is an activity that can be pursued in the bander's own back yard or can take him afield on rugged adventure. It costs very little in cash and pays richly in diversion and discovery. All bird-banders must be licensed, because the trapping of wild birds without a license is prohibited in the U. S. Any citizen 18 years of age or over may apply to the Fish and Wildlife Service for a license. The applicant must prove that he can identify the various species and sub-species of birds and must give as references the names of three people with recognized ornithological qualifications.

Upon meeting these requirements the bander is issued a Federal permit and a supply of numbered aluminum bands of assorted sizes-free of charge-together with record forms and instruction pamphlets. He must then apply for a local permit in any state where he expects to do banding. He supplies his own traps and incidental equipment. At least once a year he must report to the Bird Banding Office, giving prescribed data on each bird he has banded or retaken.

Trapping and banding a bird without injuring it is an art, and no novice should undertake it without expert guidance. Two of the foremost bird-banding experts in the U. S., according to Lorene McLellan of Philadelphia's Academy of Natural Sciences, are John A. and Mabel Gillespie of Glen Olden, Pa. Mrs. Gillespie says that the precise number of years she has been a bander is outside the scope of this article, but in evidence of her experience she proudly exhibits a photograph of a common tern which she and her husband banded in New Jersey on August 5, 1923.

The Gillespies advise that one convenient way to band birds is to do it while they are still in the nest and unable to fly, but they must be sufficiently developed to hold a band that will be large enough when they are fully grown. This method is particularly suited for banding birds that nest in colonies and for eagles, ospreys and other birds of prey. For songbirds, ground-feeders and some wildfowl, bird-banders use a different technique, resorting to guile and temptation. They bait traps of various designs with tempting food. A bird that feeds on the ground, such as the native sparrow, readily follows a trail of food into a trap. Some banding traps are constructed on the principle of the maze; some are like funnel fish-traps; some have a trigger arrangement which closes the entrance automatically when a bird enters. There are also types of traps for catching birds that do not usually run on the ground. Properly conducted, trapping does birds no harm. Traps are never left "set" when the bander is absent, so that much of the time birds run in and out, feeding freely.

"Birds live in a world full of constant danger and surprise," say the Gillespies. "The experience of being trapped, if they are deftly handled and quickly released, is less disturbing to them psychically than an encounter with a cat. Within a few minutes the experience is all but forgotten. The birds usually remember the food, however, and this memory often brings them back. Sometimes a bird walks into a trap again within five minutes after it has been released. Now and then one retraps itself so persistently that it becomes a nuisance."

Banding a bird after it has been caught may be a painful experience-to the bander, not the bird. Some tough-looking specimens, such as the blue jay, usually submit with little struggle. On the other hand, cardinals and the seemingly meek purple finches may attack with a ferocity that sends the bander away nursing a blood blister. Eagles, according to the Gillespies, belie their fearsome reputation, the parents will flutter timidly at a distance of 50 feet or more, uttering feeble, unconvincing cries, as a bander climbs to their nest and casually places numbered bands on the legs of their young. But watch out for their cousins, the ospreys! A collaborator of the Gillespies, Frederick C. Schmid, once was nearly knocked out of a tree by an osprey which left the deep trail of its talons across his face.

As each bird is tagged, the bander records the serial number, the date, the kind of bird and if possible its sex and weight, and the location where it is banded. When a banded bird is recaptured, alive or dead, its recovery is reported through the Fish and Wildlife Service to the original bander. Thus a bander gradually accumulates case histories on individuals of many species. The record files of the Gillespies contain many hundreds of cards, some of which trace migratory cycles extending over periods as long as 15 years.

Few small birds survive longer than two years in the wild state, although their maximum expectancy is believed to be 9 to 12 years in nature and 18 to 20 years when protected in captivity. Mortality is appallingly high among young birds: generally 60 to 80 per cent in the first six months. Consequently most banders prefer to invest the extra time and effort required to band adults; the chances of recovering grown birds are much better.

More than 600 species of birds have been banded in the U. S. Mallard ducks lead all the others: banders have marked about half a million of them. After the mallard duck in order come the chimney swift, common tern, pintail, herring gull, song sparrow, robin, starling and purple grackle. Amateur banders account for about two-thirds of the banding activity, the remainder being done largely by government technicians and professional ornithologists.

Even a relatively low percentage of recovery can yield significant and sometimes dramatic information about bird migrations. From recoveries of just half a dozen birds it has been learned that the arctic tern nests in the Arctic Circle and winters in the Antarctic, an annual round trip of at least 25,000 miles!

Migration takes many forms. Some species follow relatively narrow routes; others range half a continent or more. There are birds that never travel farther than between a valley and its neighboring hill. The cardinal does not migrate at all; it makes every effort to acquire a small, exclusive territory for itself, and if the climate permits, it stays there as long as the place suits it.

The Gillespies have given much study to the mating and nesting habits of backyard birds. One of their case histories concerns a pair of house wrens they banded one spring. After the wrens had raised a brood and the fledglings had left the nest, the female became interested in a second male which had been hopefully building a nest nearby, and she mated with him to produce a second family that summer. The next spring the female returned to the Gillespies' birdhouse and again started the season with a banded male they suspected to be her first mate of the preceding season, though they could not catch him. The male soon abandoned her, leaving her to raise the brood alone. Again she found a second mate and raised a second family. Late in July the Gillespies caught her first mate nesting two blocks away. He returned to one of their birdhouses the next summer, but the female did not appear again. Two or three years seems to be the average life span for a house wren.

"One year," said the Gillespies, "we tested the homing instinct of a female cowbird. A cowbird, like the European cuckoo, builds no nest and lays her eggs in the nests of other birds. She is not lacking, however, in a homing or maternal instinct. We carried our cowbird to various places some distance away from the nest several times and each time she returned promptly after we released her. Once she was released in the center of Wilmington, Del., 20 miles from home, and she was back in our trap within three hours. The late William I. Lyon of Waukegan, Ill., sent a banded cowbird to be released in Denver, Col. Twenty-five days later it was back in Waukegan. Many believe that performances of this kind are confined to homing pigeons. Actually many wild birds demonstrate a much stronger homing instinct than do the highly trained pigeons."

A by-product of bird-banding is the opportunity to collect and study parasites. Mites, flies, ticks and lice can easily be removed from the birds while they are being handled. One bander whose brother specialized in research on malaria was able to help by taking blood smears of migratory birds, thus providing information on how malaria may be spread by bird carriers.

The Gillespies have found especially thrilling the banding of ospreys, or fish hawks, which have the fierce nature usually attributed to the American eagle. They have banded 457 ospreys and have heard from 70, an unusually high percentage. Forty were reported dead within a few months of the time when they were banded as nestlings. Some were found near their birth sites several seasons later. Osprey nestlings banded in July are usually well on their way South by fall. But one osprey was found in Florida less than seven weeks after it was banded, whereas his brother was still in Pennsylvania at Thanksgiving time.

"While we welcome reports of the travels of ospreys," say the Gillespies "we regret that information generally comes only through their untimely deaths. They feed exclusively on fish and are no menace to the farmer but are often killed because they are mistaken for eagles. One of our ospreys, shot by a farmer in West Virginia, made local newspaper headlines: 'Eagle Killed by Local Hunter.'

"Our most unusual recovery was that of an osprey banded in Cape May County, N. J., on July 16, 1939. It covered 6,887 airline miles between that time and December 16, 1989, when it finally encountered a bullet in Rio de Janeiro. We feel sure that it did not fly in a beeline but probably followed coastlines and explored riverways, so its total distance must have been much greater than the airline routes.

"Our bird-banding work has been rich in unusual and varied experiences. There is nothing like the excitement of a nesting colony, where the air is full of flashing wings and wild screams, and young birds are everywhere about. Our activities have taken us to unfrequented beaches, deep woodlands and vast marshlands. We have enjoyed contacts with all sorts of people, not only in this country, but throughout the Americas and West Indies."

Anyone who finds a banded bird, dead or alive, will greatly assist the work of ornithologists by sending the band or its number to the Fish and Wildlife Service, along with a statement of the circumstances of the finding. The report should be made to the Bird Banding Office, Patuxent Research Refuge, U. S. Fish and Wildlife Service, Laurel, Md. Give your name and address, the date and the location where the bird was found. If you caught the bird alive, release it with its band; if the bird is dead, remove and flatten the band and send it in with your report. The Service will inform you of the known history of the bird, and notify the bander of the recovery. Many bird-banders make it a custom, when they get a notification from the Service, to write to the finder.

ORIGINAL but sound features mark the 12-1/2 inch reflecting telescope shown in Roger Hayward's drawings. The telescope was built by Karl Esch of Cherryvale, Kan., with the assistance of his relatives and friends. Esch discovered this department while studying engineering at Independence Junior College, became interested in telescopes and chose telescope making as a project in laboratory technique. He planned to make the typical beginner's six-inch size, and wisely set about it by cornering every person in Cherryvale, population 2,956, who might throw any light on the art. This led to the unexpected discovery of a 125-inch Pyrex mirror that had lain for 22 years in a trunk. Perhaps noting the gleam in Esch's eye, the widow of the mirror's maker practically gave it to him. Esch and his physics instructor, W. L. Gill more, found that the focal ratio of the mirror was f/8.8, and sent it away to be aluminized.

This windfall set the size of Esch's first telescope somewhat large. Fortunately he enjoyed a number of advantages. Although he was only 19, he had worked four years in a foundry run by his uncle, Hermann Esch, and had pottered about in its pattern shop. Thus he could make the patterns for several of the key parts and cast them in aluminum. His older brother, Robert Esch, a pattern designer, pattern maker and machine designer, helped him with the pattern work. A family friend, Charles Jones, whose hobby is fine work on a lathe, was also eager to help. Esch writes: "I humbly consider myself fortunate to have such resources. I have never met anyone who was not anxious to help with a practical suggestion. I am now convinced that all persons are interested in the heavens."

Though Esch had much help, he had only five months to complete his project before graduation. (The local newspaper reports that he did so as valedictorian of his class.) Actually it required the spare time of three additional month to finish the job; a total of 800 man-hour were expended by all its participants. The 15-page report that Esch turned in at Independence Junior College was entitled "Hours Spent and Problems Encountered in the Frantic Effort to Produce a Telescope."

Esch "inherited" a 120-pound 1-7/8 inch shaft with roller bearings from an old boring mill, and this became his polar axis. The declination axis is 1-7/16 inches in diameter. The eccentric counterweights for balancing the tube on both its axes were the idea of his brother Robert. Jones "spent unaccounted hours at his lathe," Esch writes "meticulously finishing all the casting for the telescope, and many hours were contributed by half a dozen others." He also gives credit to Amateur Telescope Making.

Telescope builders who do not slight the assistance of others have their reward: they are often suspected of soft-pedaling their own part. The correspondence between this department and Esch shows that his telescope was planned and built under pressure. He was preoccupied with studies in chemistry, calculus, physics and surveying; yet he was able to infect his family and parts of two communities with enthusiasm for the project.

Esch continues: "The supreme thrill came with the first look through the telescope only four days before I entered the University of Kansas as an engineering physics major in September. Never have I witnessed more spectacular sights than those of brilliant, jewel-like, blue-white, orange or red stars, or chummy doubles, or the Milky Way. I found Jupiter and watched the change of position of its satellites with fascination. I was able to show all who aided me in the project, including my instructors, neighbors, friends and friends' friends, glimpses of what is above. Even my dog Mortimer attended. To make these wonders visible to others is indeed satisfying."

The support of the diagonal mirror in Esch's telescope is interesting. It is a single 3/l6-inch radius rod held by a set-screw. Esch says that the support is stable and easy to adjust. Approximate collimation of the telescope required only an hour and a half, a fussy job that can last a lifetime, or shorten one's life. The washer at the top of the half-inch axial rod prevents the accidental dropping of the diagonal on the mirror.

The eyepieces of Esch's telescope are mounted on a rotating turret head. This arrangement is becoming more fashionable because it provides easy access to the eyepieces, but unless it is carefully made the eyepieces will not be properly collimated. And unless the turret head rotates smoothly and easily, and continues so throughout the life of the telescope, its use will be much like wrestling with a bear. The Esch turret head is a 14-pound aluminum casting 14-5/8 inches in diameter revolving on three equally spaced ball-bearing rollers. Each roller is on an excentrically mounted stub shaft, as shown in the upper right-hand corner of the drawing below. This feature, the design of Robert Esch, makes it possible to assemble or disassemble the turret. A lock-screw permits the observer to fix the turret in the most comfortable position. The internal ribs of the turret casting prevent it from warping out of round and binding against the rollers.

After alterations in the pattern for the turret casting, the same pattern was used to cast the mirror cell. The mirror rests on the inner rim of an aluminum plate. If a camera is affixed to the eyepiece end of the telescope, three one-pound lead counterweights may be screwed on the projecting ends of the cell-adjusting screws to balance it.

The 8-1/2 foot tube of the telescope is made of 16-gauge cold-rolled steel welded and painted black inside. The total weight of the telescope is about 350 pounds. It rests on a concrete pier "which must weigh all of 40 tons," said Esch just after mixing and pouring the makings. The roll-off housing of the telescope measures by 12 feet, in its design Esch was helped by his father, W. D. Esch.

Esch's last words might well be the motto of the telescope maker, who, unlike the burnt child, scarcely ever shuns the fire. Says Esch: "I think I can build a better one." Months after describing his first effort, he wrote that he had been watching the making of a new 27-inch reflecting telescope at the University of Kansas, where he has been studying astronomy as well as physics. He invited his father and brother to study it. "When they went home," Esch writes, "my brother's boss, Ivan Marrow, became so excited that he gave the time and lumber to make a pattern for a larger tube saddle and his foundry for casting it. New axes three inches in diameter are being substituted for the old, with ball bearings from truck axles. The telescope is to be equipped with setting circles and a drive. I am also grinding a 10-inch mirror to round out my apprenticeship."

IN THIS department last October F. A. Luck told how to make a simple apparatus for collimating a binocular. Unaware of this article, a professional scientific instrument maker undertook to collimate a friend's binocular by the "look, blink, look" method and wrote: "After looking at my target I became so dizzy and goggle-eyed that I walked straight against the side of the house." The Luck article was sent to him. His reply: "I made the Luck rig. Without it I would never have got the binocular collimated. It worked wonderfully well."

MANY telescope users regularly obtain the annual 80-page Observer's Handbook published by the Royal Astronomical Society of Canada, 3 Willcocks St., Toronto, Ont., at 40 cents. It contains data on the planets and the sky for each month, lists of brightest stars, clusters and nebulae, with finding coordinates and many other data useful to observers. The Handbook of the British Astronomical Association, published at 303 Bath Road, Hounslow West, Middlesex, England, at five shillings (about 70 cents), contains similar but not identical data.

RECENTLY the proposal was made that the many amateur astronomical disciples of Russell W. Porter combine to erect a memorial at his grave at Glenmere near Port Clyde, Me., where he lived for a number of years and began making telescopes. Unfortunately for this proposal, Porter made it abundantly clear while living that he wished his ashes to lie in an unmarked grave.

The Society for Amateur Scientists (SAS) is a nonprofit research and educational organization dedicated to helping people enrich their lives by following their passion to take part in scientific adventures of all kinds.