Solar Eclipse of July 28, 1851. 107 



trace, we gave our whole attention to the appearance of the 

 beads. 



My previous opinion on this subject was very decided. I 

 had carefully studied the annular eclipse at Edinburgh, with 

 an excellent reflector carrying a power of about 100 ; had 

 seen the well-defined angular projections of the moon cut the 

 sun's edge, and followed their disappearance to the last with- 

 out perceiving the slightest distortion of the solar limb, or 

 of any of the spots which were successively eclipsed. At 

 another time, with the same instrument, I observed an occul- 

 tation of Saturn. The end of the ring, which then shewed 

 almost as a line, was seen gradually to shorten, and, when 

 the moon's edge came up to the disc of the planet, the sharp 

 angular contour of a mountain was plainly seen and observed 

 by several of our party, while the planet retained its form 

 unchanged. For these reasons, while preparing the notice 

 of the eclipse of 1847, which was almost central here, I drew 

 the attention of our observers to the ruggedness of the lunar 

 contour as sure to produce -^the appearance of a string of 

 brilliants, about the time of each of the internal contacts. 

 In all matters of difficult observation, one's pre-formed ideas 

 go for a great deal ; for this reason I have stated mine. 



On examining the edge of the sun's image made on the 

 screen, there was found a very extensive trembling, subject 

 to sudden fluctuations, as thin hazes and fleecy clouds passed 

 before us : the depth of the undulations varied from b" to 8" 

 or 10". This undulation prevented any accurate measurement 

 of the altitude of the lunar ridges, although it left their 

 existence sufficiently apparent ; the cusps also were ren- 

 dered indistinct. Had we not been acquainted with the 

 excellent performance of the instrument, we might have 

 complained of great spherical aberration, as the large and 

 palpable undulations were accompanied by a minute under- 

 tremor which gave to the outline a permanent indistinct- 

 ness analogous to that arising from a bad adjustment of the 

 focus. 



Towards 3*^ 15"^ Greenwich time, the cusps shot out and 

 retracted considerably with a leech-like motion, and at 3*^ 33"^ 



