1893.] on the Recent Solar Eclipse. 143 



opportunity of solving certain questions as to the connection between 

 the character of the corona and the solar cycle. Further, it was 

 hoped that by multiplying the stations along the path of the eclipse, 

 and therefore by making observations at considerable intervals of 

 time, the photographic records might decide upon the possibility of 

 changes in the form and internal disposition of the corona — a question 

 of the greatest importance in regard to the physical nature of this 

 solar appendage. 



After careful consideration of sites, and of the various sugges- 

 tions which were made as to the nature of the work to be undertaken, 

 a committee, representing the Eoyal Society, the Royal Astronomical 

 Society, and the Solar Physics Committee of the Science and Art 

 Department, decided to send two observers to Para Curu, in the 

 province of Ceara in Brazil ; and four observers to some station in 

 Senegal, preferably Fundium, on the Salum river. Substantially the 

 same scheme of work was arranged for the two parties. Spectro- 

 scopic observations with the Prismatic Camera and a series of photo- 

 graphs with what is now known as the Duplex Coronagraph were to 

 be taken at each station. In the case of the African station, it was 

 further decided that photometric measurements of the coronal light 

 should be made by the method adopted by Captain Abney and mysblf 

 on the occasion of the West Indian eclipse of 1886. 



It will be understood that the work of both parties was entirelv 

 confined to the study of the corona. In the first place, photographic 

 records of its form, its extension and internal structure were to be 

 made according to a uniform plan at both stations. The apparatus 

 to be used consisted of a sort of double camera, in one compartment 

 of which was placed a 4-inch lens of 60 inches focus, belonging to 

 Captain Abney, which has already seen much service in eclipse 

 photography. It was employed in Egypt in 1882, in the Caroline 

 Islands in 1883, in the West Indies in 1886, and in the Salut Isles, 

 in French Guiana, where that veteran eclipse observer, Father Perry, 

 lost his life, in 1889. One special reason for using this lens was 

 that tLe continuity of the series of photographs which have been 

 obtained by it might be maintained. It gives pictures on the scale 

 of about half an inch to the moon's diameter. In the other com- 

 partment was a 4-inch Dallmeyer photo-heliograph lens mounted 

 in combination with a 2^-inch Dallmeyer negative lens of 8-inch 

 negative focus, giving with the total length of 68 inches pictures 

 on the scale of over 1J inch to the moon's diameter. This double 

 camera was fitted with special plate-carriers, enabling two plates to 

 be exposed at the same time, one to each lens, so that by one opera- 

 tion of changing and exposing, two pictures of the eclipsed sun could 

 be simultaneously obtained. The times of exposure were so arranged 

 that the longest exposed picture with the enlarging combination 

 should receive the same photographic effect as the shortest exposed 

 picture with the Abney lens. The whole arrangement was equa- 



