September 16, 1898.] 



SCIENCE. 



351 



much caution because of their uncertainty. 

 By 1881 or 1882, however, they were be- 

 ginning to be used and gave considerable 

 promise of their ultimate value, as was 

 shown by the photographs of the comet of 

 1881, which were made by Draper and 

 Janssen. These were the first photographs 

 ever made of a comet. Efforts had been 

 made to secure pictures of Donati's comet, 

 in 1858, but without success. 



In the fall of 1882 the world was thrilled 

 hy the advent of a magnificent comet which 

 suddenly appeared near the sun in Sep- 

 tember, and for the next four or five months 

 delighted astronomers with the splendor of 

 its display. Attracted hy the great bril- 

 liancy of the comet, Dr. Gill, at the Cape 

 of Good Hope, with the aid of a local pho- 

 tographer and his photographic lens, se- 

 cured a fine series of photographs of the 

 comet with dry plates. When these pho- 

 tographs reached the northern hemisphere 

 they attracted a great deal of attention, 

 not only on account of the comet itself, but 

 also from the number of stars that were 

 impressed on the plates. At this period 

 the Henry Brothers were making a chart 

 of the stars along the ecliptic in their search 

 for asteroids. They had at this time reached 

 the region of the Milky Way, and the mar- 

 vellous wealth of stars they encountered 

 upon entering the boundaries of that vast 

 zone completely discouraged them in their 

 endeavors to carry their charts through the 

 rich region traversed by the ecliptic. While 

 hesitating as to the advisability of continu- 

 ing their work the photographs of the great 

 comet came to their notice. They were 

 struck with the great number of stars shown 

 on these pictures along with the image of 

 the comet. The idea at once occurred to 

 them that they could use this wonderful 

 process to make their charts. It was to this 

 simple incident that the active application 

 of the stellar photography of to-day is due. 

 They began at once the construction, with 



their own hands, of a suitable photographic 

 telescope of 13i inches' diameter for the 

 photography of the stars. This instrument 

 was soon fiaished, and the astronomical 

 world knows to-day what wonderful results 

 these men produced with it ; the exquisite 

 star pictures which were marvels of defini- 

 tion, the photographs of the nebulae, of 

 Saturn and Jupiter, the moon, etc., were 

 perfect revelations. 



In 1859 Tempel, at Florence, Italy, had 

 found a diffused cometary-looking nebula 

 connected with and extending south- 

 westerly from the star Merope, of the 

 Pleiades. From that time on astronomers 

 wrangled over this object, which many of 

 them believed had no existence. One of 

 the first things done by the Henry Brothers 

 was to photograph the Pleiades. These 

 pictures showed nebulous strips near Me- 

 rope, and though they did not resemble 

 any that had been drawn by the numerous 

 observers of the Merope nebula they rather 

 confirmed the existence of Tempel's object. 

 Upon these plates was shown a new nebula 

 connected with the star Maia where none 

 was previously known. It required the 

 most powerful of existing telescopes to 

 verify this visually. This was finally done, 

 however, and it then began to dawn upon 

 astronomers what great possibilities lay in 

 the photographic plate for the detection 

 and study of the nebulse. It was soon seen 

 that their light was strongly photographic ; 

 that it was really more actinic than visual. 

 A later photograph with a longer exposure 

 showed the Merope nebula just as the best 

 observers had drawn it, and at the same 

 time filled the entire group of stars with an 

 entangling system of nebulous matter which 

 seemed to bind together the different stars 

 of the group with misty wreaths and 

 streams of filmy light, nearly all of which 

 is entirely beyond the keenest vision and 

 the most powerful telescope. This was a 

 revelation. The question had often been 



