54 The Great Solar Eclipse [Jan., 



1. Photographic Eesults. 



Judging from the accounts which have come to England, there 

 appears Kttle doubt that the German expedition to Aden was the 

 most successful in this respect. Dr. Vogel, one of the most eminent 

 of the German photographers, had been selected to take charge 

 of this department. His arrangements were admirable in their 

 systematic precision. Possible cases of failure were anticipated, 

 and carefully provided against, and for some time previously all the 

 staff had been engaged in rehearsing the various operations which 

 would have to be gone through diiring the eventful 2" 55" of 

 totality ; in short, everything was so well rehearsed, and every one 

 so carefully told off to his duty, that failure from preventible causes 

 was scarcely possible. Aden had been selected as the most likely spot 

 in the zone of totaHty to be free from clouds ; the evening before 

 the eclipse was, however, very cloudy, and occasioned great anxiety, 

 and on the morning of the 18th the sun rose behind thick banks of 

 purple gray cloud ; before totality commenced the clouds separated, 

 and enabled four successful photographs to be taken. The apparatus 

 employed was a telescope having an achromatic lens six inches 

 diameter and six feet focus, specially ground by Steinheil, so as to 

 get the photographic image in focus. This afforded a solar image 

 of |ths of an inch in diameter, and was mounted equatorially and 

 moved by clockwork, adjusted so as to counteract the motion of the 

 earth, and to keep the telescope rigidly fixed on the image during 

 the ten or fifteen seconds required to receive the impression. To 

 the end of the telescope was fixed a small photogra[>hic camera, 

 provided v/ith dark slides, each of which would hold a sensitive 

 plate large enough to take two images. The following is the 

 description given by Dr. Vogel of his operations : — 



" The totahty of the eclipse at Aden was about three minutes 

 long (in India five minutes) ; nevertheless, we had chosen Aden for 

 our station because there were already photographic observers in 

 India, and because the totality appeared at Aden about an hour 

 earlier than in India. Therefore a comparison of the difi'erent 

 results would enable us to decide the question if the protuberances 

 appearing at a total eclipse of the sun were changing in the course 

 of time or not. 



" Our task was to get, within those thr(^e minutes, as many 

 views of the phenomenon as possible. For this purpose we had 

 previously exercised ourselves in the employment of the photo- 

 graphic telescope, hke artillerymen with their guns. Dr. Fritseho 

 prepared the plates in the first tent. Dr. Zenker ])ut the dark slides 

 into the telescope, Dr. Thiell exposed, and I myself developed in the 

 second tent. We ascertained that it was possible in this way to get 

 six images (three plates of two images) during three minutes. 



