104 THE INDIAN ECLIPSE, 1898. 



or mirror, revolving round an axis parallel to the axis of the 

 earth, and rotating at one-half the earth's speed. This method 

 is of great importance where it is necessary to take a number 

 of photographs, and consequently to change the plates with 

 great rapidity, as the shake, to which an equatorially mounted 

 telescope would be liable, is avoided. The plate on p. 81 

 shows an instrument in Professor Naegamvala's camp used in 

 this manner in conjunction with a coelostatic mirror. 



Practically all these various forms of instruments, beside 

 several other modifications were used at one station or another 

 in the photography of the corona of 1898. The large instru- 

 ments were, of course, contributed by great public observatories ; 

 the members of the Association, having only their own small 

 private resources to draw upon, were necessarily obliged to be 

 content for the most part with apparatus of quite small dimen- 

 sions. The details of the cameras employed are as follows. 



DETAILS OF INSTRUMENTS AND EXPOSURES. 



The instrument which I took out with me was an ordinary 

 refractor of 4/1 inch aperture and 60 inches focal length. 

 This I had fitted with a small camera of my own manufacture. 

 I made two exposures ; one shortly after the beginning of 

 totality of one second, the other of two seconds. The plates 

 used were Ilford ordinary. Both photographs are fully exposed, 

 and show the polar plumes and the great streamers very 

 distinctly. 



FRED BACON. 



My camera had a portrait lens, and as used had a focal length 

 of 26 in., its full aperture of 2f in. being reduced to I~$ in. 

 Four plates were taken ; two on Ilford ordinary, backed, and 

 two on Edwards' extra rapid Isochromatic. The exposures varied 

 from one to four seconds, and the plates were developed by pyro- 

 ammonia. The photographs show only the inner corona. 



GERTRUDE BACON. 



(Communicated by Mrs. Walter Maunder.) 



My lens was a Dallmeyer rapid rectilinear, the back lens of 

 which only was used. As thus used it had an aperture of 2| in. 

 and a focal length of 32J in. The camera was home-made, 

 being nothing more than a long light-tight box fitted to carry 

 half-plate slides. Along the top of the camera was fixed a brass 

 tube parallel to the major axis of the camera, having cross hairs 

 fixed at the lens end. A few inches from the other end was 

 placed a little mirror, so that when standing over the camera a 



