Mr. De la Rue on the Total Solar Eclipse of July 18, 1860. 71 



the original sketches, which are also given in fac-simile, but to some 

 extent corrected by means of the photographs. 



That the prominences belong to the sun and not to the moon was 

 rendered evident to the observer by the progressive covering of the 

 luminous prominences on the east in the direction of the moon's 

 motion, and the gradual uncovering of fresh prominences on the west ; 

 while prominences situated in a position nearly at right angles to 

 the moon's path shifted their angular position on the moon's edge 

 several degrees during the observations. The prominence which 

 became visible before totality, which the author designates by A, 

 was found to have shifted 3° 25' on the moon's limb in an interval 

 of about 2\ minutes ; it was therefore evident that the region of the 

 moon which at the commencement of the period was in apparent 

 contact with the prominence was at some distance from it at the end ; 

 and as the prominence underwent no change during that time, the 

 theory falls to the ground which ascribes the phenomenon of the 

 luminous protuberances to some peculiar action of the moon's edge 

 on light coming originally from the sun. 



The author describes the general effect of the eclipse to the unas- 

 sisted eye. He was particularly struck with the peculiar illumination 

 of the surrounding landscape as the sun became reduced to a small 

 crescent ; the shadows of all objects were so sharp and the light so 

 brilliant that it reminded him of the illumination produced by the 

 electric light ; at the same time peculiar hues were assumed by the 

 sky and landscape, which suggested the idea that the light of the sun 

 near the periphery is not only less intense than that of the centre, 

 but that it may be different in quality. 



No attempt was made to obtain accurate observations of the corona, 

 but nevertheless a few seconds were devoted to this phenomenon. 

 Even several minutes before totality the whole contour of the moon 

 could be distinctly seen ; when totality had commenced, the moon's 

 disk appeared of a deep brown in the centre of the corona, which was 

 extremely bright near the moon's limb and appeared of a silvery 

 white, softening off with a very irregular outline and sending forth 

 some long streams. It extended generally to about from 0*7 to 0*8 

 of the moon's diameter beyond her periphery. 



The darkness during the totality was not nearly so great as might 

 have been expected from accounts of previous total eclipses. The 

 illumination was markedly distinct from that which occurs in nature 

 on any other occasion, and certainly was greater than on the brightest 

 moonlit night, although at the time the light appeared to the author 

 as less bright than what he remembered of bright moonlight. By 

 subsequent trials he was led to conclude that the light during a 

 total eclipse most resembles that degree of illumination which exists 

 in a clear sky soon after sunset, when, after having made out a first- 

 magnitude star, other stars of less brilliancy can be discerned one 

 after another by an attentive gazer. Jupiter and Venus were the 

 only objects the author had time to identify, but some neighbouring 

 observers saw also Castor. 



The most important part of the paper treats of the photographic 



