164 



THE INDIAN ECLIPSE, 1898. 



it. The negative is consequently thin, and it shows no more 

 of the corona than the first of the same series with but a 

 a sixteenth of the exposure. 



The Sandell triple-coated plate appears, then, to offer a 

 prospect of overcoming the second of the three difficulties in 

 the way of photographing the coronal rays to which we have 

 already referred ; and the success of this attempt to photograph 

 the partial phase, whilst it accentuates the extreme difficulty 

 of the problem of photographing the corona in full sunshine, 



THE CORONA OF 1878, JULY 20. 



As drawn by Professor Nevreomb, the inner Corona being screened off by a black disc. 



does seem to make it probable that during totality, if the sky 

 be really clear, a plate may be successfully exposed for a much 

 longer effective duration than has been attempted even on 

 the present occasion. 



Summing up, and taking //1 5 as a representative instrument, 

 and supposing that the most rapid plates available are used, 

 four different classes of exposure appear to be indicated accord- 

 ing to the four different regions of which it is desired to obtain 

 a photograph. For the prominences - second to T V second 

 may be taken as normal, and for the inner corona T V second to 



