Inventors at Work, with Chapters on Discovery

by George Iles

Two Observers of the Skies.

Edward Emerson Barnard, of the Yerkes Observatory, Williams Bay, Wisconsin, is in the first rank of living astronomers. Among his many discoveries the most remarkable is that of the fifth satellite of Jupiter at the Lick Observatory. His early work at the Vanderbilt Observatory, Nashville, gave full promise of his later achievements. One evening in November, 1883, he was observing an occultation of the well-known star Beta Capricorni by the moon. He had patiently waited for his opportunity; such an occultation is best seen when the moon is a small crescent, the star disappearing at the dark curve of the moon where its beams do not overpower the feeble stellar ray. When the moon passes between the eye and a fixed star, the disappearance of the star is instantaneous. At the distance from which we look at it the star is a point only, and as the moon has no atmosphere, the instant the edge of the lunar surface touches the line joining the eye of the observer with the star, it vanishes from sight. When the moon passed in front of Beta Capricorni Mr. Barnard noticed that instead of disappearing at once, there was a sudden partial diminution of the light of the star, then a total extinction of the remaining point. The interval between the diminution and complete extinction of the light occupied only a few tenths of a second, but it was long enough to put his keen mind upon inquiry. Mr. Barnard in an astronomical journal called attention to the phenomenon and suggested that instead of there being only one star, as formerly supposed, there were really two stars so close together that in an ordinary six-inch telescope, such as he had used, they appeared to be one. He inferred also that one of the pair must be a good deal brighter than the other, because at the beginning the change in brightness was less than at the end. This surmise was soon afterward fully verified by Mr. S. W. Burnham with the eighteen and one half inch equatorial of the Dearborn Observatory at Chicago, revealing a close and unequal double star which would have remained unresolved had he used a less powerful instrument.

This Sherburne Wesley Burnham is the most successful discoverer of double stars who has ever lived. “The extreme acuteness of vision,” says Professor John Fraser, “which enables one to prosecute such research with the highest success is a very rare gift; and the discovery of close doubles, as in his case, is its severest test. To measure a star—that is, to ascertain by means of the micrometer the distance and position angle of the companion with reference to the principal star—is one thing, and to find new and close doubles is a very different thing. Baron Dembowski, the most noted measurer of double stars, had no success as a discoverer, and confessed his inability to find new doubles. When, however, a new double had been found by another observer, and the distance and position angle of the companion approximately estimated, he could readily find and accurately measure it. When Mr. Asaph Hall, in 1877, had found the two satellites of Mars and described their positions, it was not difficult for any astronomer who had access to a large Clark telescope to find them and see all that Mr. Hall had seen. The whole difficulty was in seeing them for the first time. Besides the ability to see a difficult object, there is required an intelligence and experimental knowledge of the subject, which are as rare as the visual faculty itself. Some of the lower animals have more acute vision than human beings; but they do not know all they see, or understand relations to other facts. They have plenty of sight, but they lack insight. Mr. Burnham’s powers in both these respects is extraordinary.”

At the Cape of Good Hope Observatory remarkable observations of double stars have been recorded. Sir David Gill, the director, says:—“At the Cape Observatory, as has always been the case elsewhere, the subject of double star measurement on any great scale waited for the proper man to undertake it. There is no instance, so far as I know, of a long and valuable series of double star discovery and observation made by a mere assistant acting under orders. It is a special faculty, an inborn capacity, a delight in the exercise of exceptional acuteness of eyesight and natural dexterity, coupled with the gift of imagination as to the true meaning of what he observes, that imparts to the observer the requisite enthusiasm for double star observing. No amount of training or direction could have created the Struves, a Dawes or a Dembowski. The great double star observer is born, not made, and I believe that no extensive series of double star discovery and measurement will ever emanate from a regular observatory through successive directorates unless men are specially selected who have previously distinguished themselves in that field of work, and who were originally driven to it from sheer compulsion of inborn taste.”