64 [April 10, 



tained from the photographic measurements, was 11 "*8, calculation 

 giving as a mean 12"*8. The relative diameter of the moon, that of 

 the sun being taken as unity, as derived from measurements of the 

 photographs, comes out 1*0511, which is precisely the theoretical 

 number ; on the other hand, they tend to show that the diameters at 

 present assumed for the sun and moon, taken conjointly, are about 

 4"'0 in excess of the truth. 



The paper is accompanied by an extensive series of calculations, 

 which it is not here necessary to describe. Those, however, relating 

 to the measurements of the positions of the luminous prominences 

 on the two totality-pictures have especial interest. These measure- 

 ments were made in two ways: 1st, the original negatives were 

 measured by the author's new micrometer ; 2nd, enlarged positive 

 copies were taken on glass, and the contours of the prominences 

 traced and etched upon the glass, which was afterwards centered on 

 a dividing engine and divided, the divisions being subsequently 

 etched. Copper duplicates were then made of the glass plates, 

 which served to print off diagrams which accompany the paper. 



Without describing minutely the measurements, it will suffice here 

 to state that the results go to prove that the luminous prominences 

 must belong to the sun and not to the moon. For example, the 

 change in the angular position of the prominence at a right angle to 

 the moon's path, and designated A in the paper, has been calculated 

 to have been 5 21' for the assumed geographical position of the 

 station ; by measurement of the two photographs it is 5 32'. The 

 motion of the moon in covering and uncovering a prominence in the 

 line of her path was calculated to have been 92"*8 ; by measurement 

 it was found to have been 93"* 7. The accordance of these numbers 

 is so extremely close, that it would be difficult to obtain more con- 

 vincing proofs that the luminous prominences belong to the sun. 



The Society adjourned over the Easter Holidays to Thursday, 

 May 1st. 



