POSITIVE PHOTOGRAPHY, WITH SPECIAL REFER- 

 ENCE TO ECLIPSE WORK.* 



Francis E. Nipher. 



During the last year the writer has been making an attempt 

 to adapt the process of positive photography to service in the 

 two solor eclipses which occur during the next two years. t 

 The unusual duration of the period of totality in both, makes 

 them peculiarly favorable to the use of such a process. 

 And while this will also be to some extent an advantage in 

 securing negatives, still an over exposure is then always pos- 

 sible. When such over exposure is corrected by the use of 

 a restrainer, the effect is to dissolve away the very details 

 which the long exposure was intended to secure. 



By great over exposure in the old sense of the word, and 

 development in the light instead of in the dark room, no 

 over exposure for positives is possible. The only limitation 

 then is an under exposure, which causes the positive picture 

 to fog. 



The object of the present paper is, to give the present 

 condition of the process, and to request any who may be able 

 to do so, to aid in so improving it, that the best results may 

 be secured in these eclipses. There will be no other oppor- 

 tunity so favorable in the next generation. 



Let the stop of the camera be set at No. 8 of the universal 

 system. The ratio of focal length divided by diameter is 

 then 



/=4|/n = 4 T /8"=11.3. 

 a 



* Presented by title to The Academy of Science of St. Louis, October 16, 

 1900. 



t These Transactions, Vol. 10, No. 6. — Nature, 1900. July 12, p. 246; 

 Aug. 9, p. 342; Aug. 23, p. 396. — Am. Journ. of Science, July, 1900, p. 78. 



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