6 EDWAKD EMERSON BARNARD— FROST lMEMoras I vo"xx\'; 



which it has been observed is that of the 18^-inch equatorial of the Dearborn Observatory at 

 Evanston, with which Prof. G. W. Hough observed it on October 15 and November 11, 1892. 

 The discovery of this satellite doubtless renewed interest in the search for others by the use of 

 photography, resulting in the discovery of three further, remote satellites at the Lick Observa- 

 tory, VI and VII by C. D. Perrine and LX by S. B. Nicholson, while VIII was discovered 

 by P. J. Melotte, at Greenwich. 



During his later years at the Lick Observatory Mr. Barnard gave much attention to careful 

 measurements of the diameters of the planets, including the four largest asteroids. He made a 

 comprehensive study of the dimensions in the Saturnian system and measured the ellipticity 

 of Uranus. He gave particular attention to the diameters and the appearance of the brighter 

 satellites of Jupiter. These extensive researches were published in a series of papers in various 

 astronomical journals, several of them appearing after he had left the Lick Observatory. 



It was not only to the study of the Milky Way that Barnard was applying photography 

 with distinguished success. He studied the comets, and took a great interest in the remarkable 

 behavior of their tails as revealed on his negatives. Swift's comet (1892 I) was the first to 

 show on Barnard's photographs the extraordinary changes which the tails of comets may 

 undergo. His subsequent photographs of many comets show that these mutations are character- 

 istic of the tails of some comets, but not of others. Cloudy weather had interfered with obser- 

 vations of this comet during March, but the photographs taken on April 4 and 5 displayed 

 extraordinary transformations in the short interval between them. The significance and value 

 of the photographic records of these capricious changes were instantly appreciated by Barnard, 

 as will be seen from the following quotation from his article written some years later and 

 appearing in the Monthly Notices of the Royal Astronomical Society, 59: 355, 1899: 



This [Swift's comet of 1892] was the first comet to show to the photographic plate the extraordinary changes 

 to which these bodies are subject. Indeed, if it had not been for the photographic plate we should have known 

 nothing of the extraordinary changes that occurred in this comet and several that have since appeared. . . . 



For the study of the phenomena of the tails of comets, the portrait lens has shown itself most admirably 

 suited. It has added an interest to the physical study of these bodies that did not exist previously; for the 

 most interesting of the phenomena shown by comets must always escape the visual observer and pass unknown, 

 without the aid of the portrait lens and the photographic plate. Unlike the planets, the comets often traverse 

 the entire solar system. They are, therefore, our only means of exploring the regions between the planetary 

 orbits. Instead of ponderous bodies like the planets, they are but flimsy creations of enormous dimensions. 

 They are thus likely to be easily subject to disturbances in their forms that would produce no perceptible effect 

 on their motions. What these influences may be we do not know; probably swarms or streams of meteors, 

 which we know do exist in space, or possibly some other cosmical matter yet unknown. Such objects might be 

 (and possibly have been) revealed to us by their effect upon the form of the comet's tail as it sweeps through 

 space. 



The comet discovered by Holmes in the autumn of the same year (1892 III) was also 

 photographed by Barnard when this round, tailless object, whose motion was almost entirely 

 in the line of sight, was situated very near the great nebula in Andromeda. The motion of the 

 comet among the stars was, in fact, so slight that Barnard, with an exposure of 75 minutes, 

 obtained, on the night of November 21, 1892, a sharp picture of the Andromeda nebula, together 

 with the comet! a circumstance which is not likely to be duplicated. Brooks's comet of the 

 next year (1893 IV) excited Barnard's interest in a high degree by its behavior, which was quite 

 exceptional in those early days of cometary photography. He speaks of his plates of October 21 

 and 22 as follows (ibid., p. 358) : 



There is an utter transformation of the comet in this picture. The tail is larger and brighter and very 

 much distorted, as if it had encountered some resistance in its sweep through space. This disturbance seems to 

 have disrupted the northeast edge of the tail. The small side tail has apparently been swept away, while the 

 more distant portion of the main tail is streaming in a very irregular manner. The entire picture is highly 

 suggestive of an encounter with some sort of resistance. Is it possible the tail passed through a stream of 

 meteors such as we know exist in space? Whatever the cause may have been, the appearance of the tail utterly 

 excludes the idea of the phenomenon being due to irregular emission of the matter from the nucleus — an explana- 

 tion quite satisfactory in the case of Swift's comet. 



In passing, this particular photograph seems to explain at least one of the ancient descriptions of a comet, 

 viz., "a torch appeared in the heavens." The comet as shown in the photograph, is sufficiently suggestive of a 

 torch streaming irregularly in the wind. 



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