TOTAL SOLAE ECLIPSE OE JELY 18, 1860. 
409 
totality, indeed, some prominences might be visible at one station and not at another, 
in consequence of the parallactic shift of the moon with respect to the sun. 
Photographs offer great advantages over eye observations in determining changes of 
position in the prominences ; but nevertheless there are some difficulties even in photo- 
graphic measurements. 
Por example, with objects which are terminated by a softened outline, there is some 
difficulty in determining, absolutely, where the boundary ceases to exist : this was found 
to be especially the case with the luminous prominences depicted on the original nega- 
tive, and also with the prominences as shown in positive photographic copies taken from 
it by superposition on an albumenized plate. Some doubt also existed in regard to the 
centering of No. 26 photograph ; but this was found not to affect the results so much as 
the uncertainty of the precise termination of the prominences, in the photographs both 
negative and positive. 
Table VI. 
Table VI. gives the results of a series of angular measures of the luminous pro- 
minences, with reference to the moon’s centre, both on the original negatives and on 
the albumen positive copies. Columns 4, 5, 6, 7 refer to the first totality-picture; 
columns 8, 9, 10, and 11 to the second totality-picture. Columns 7 and 11 are the 
measured positions, corrected for the errors of the wires, for the epochs of the two pho- 
tographs ; column 12 the difference in the position-angle of certain prominences at the 
commencement and at the end of totahty. A mere inspection of column 12 renders 
it evident that the nearer a prominence is situated to 27° 10', in reference to the sun’s 
centre (which is the case with prominence A), the greater is its angular shift in 
reference to the moon’s centre ; and the nearer a prominence is to the line of motion 
of the moon’s centre, the less is the angular change, as, for example, the bead A'" of the 
protuberance H. 
