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SCIENCE. 



[N. S. Vol. VIII. No. 194. 



fore, to the minuter details, if anywhere, 

 that we must look for change in the moon, 

 and these at present are much beyond the 

 reach of the photographic plate. 



The sun, from its abundance of light, 

 offered special inducements to the early 

 workers in photography. It would rather 

 appear, however, that the moon had the 

 most charm for the first photographic as- 

 tronomers. This was doubtless due to the 

 singular and wonderful wealth of detail its 

 surface continually presented, while the 

 sun, except for a few occasional spots, was 

 at best only a blank surface. When care- 

 fully and conscientiously studied, however, 

 it highly rewarded those who took up its 

 study photographically. 



The first picture of the sun seems to have 

 been made on a daguerreotype plate by 

 Fizeau and Foucault in 1845. During the 

 total eclipse of the sun on July 28, 1851, a 

 daguerreotype was secured with the Konigs- 

 burg heliometer (2.4 inches in diameter 

 and 2-feet focus) by Dr. Busch, which ap- 

 pears to have been the first photographic rep- 

 resentation of the corona. It showed a con- 

 siderable number of details quite close to the 

 moon. But in the early eclipses the photo- 

 graphic work seems to have been mainly de- 

 voted to representations of the solar promi- 

 nences, which at that time were as rarely 

 seen as the corona itself. During the eclipse 

 of 1869, however. Professor Himes secured a 

 photograph which showed the brighter 

 structure of the corona; similar pictures 

 were also obtained during the same eclipse 

 by Mr. Whipple, of Boston. The corona 

 was also slightly shown on pictures made 

 as early as 1860 by M. Serrat. None of 

 them, however, showed more than slight 

 traces of the corona, extending only for a 

 few minutes of arc from the moon's limb. 

 Nearly all the pictures seem to have been 

 taken with an enlarging lens, which was 

 doubtless used to get the prominences on a 

 larger scale. Mr. Whipple, however, in 



1869, did not use any pi-imary enlargement, 

 and this gave him a decided advantage in 

 point of exposure time. In nearly all of 

 these pictures the exposures, with the slow- 

 ness of the then-existing plates, were evi- 

 dently too short to show the corona, except 

 perhaps in the case of Whipple, who gave 

 40 seconds exposure. The other observers 

 seemed to be content with much shorter 

 exposui'es. 



The first really successful photographs of 

 the corona were obtained at the eclipse of 

 of December 22, 1870, when it was shown 

 on the plate to a distance of about half a 

 degree from the moon's limb. This picture, 

 made by Mr. Brothers at Syracuse, Sicily, 

 showed a considerable amount of rich de- 

 tail in the coronal structure ; and the same 

 can also be said of the photographs of this 

 eclipse taken by Colonel Tennant and Lord 

 Lindsay's party. These seem to have been 

 the first pictures to really show the great 

 value of photography for coronal delinea- 

 tion. The eclipse of 1871 was still more 

 successfully photographed, and an excellent 

 representation of the corona, full of beauti- 

 ful detail, was secured. 



All of these pictures were made with the 

 wet process, for the dry plate was not suc- 

 cessfully used until about 1876, and it was 

 five or six j'ears later before it became gen- 

 erally useful or at all reliable. For some 

 years previous to this, photographers had 

 been at work with varied success upon dif- 

 ferent methods of preparing and sensitizing 

 plates that could be used dry. Indeed, at 

 the eclipse of 1871, at Baikul, India, it ap- 

 pears that Mr. Cherry used a dry plate on 

 which he exposed a number of images of 

 the sun before totality for the orientation 

 of the eclipse plates. It would seem that 

 he had only two of these plates and they 

 were both intended to be used for orienta- 

 tion. The second plate, however, was 

 broken before it could be used. It is prob- 

 able they were known to be less sensitive 



