Royal Institution. 



turned to the July sun : and thus the eclipse which occurred, if total 

 in 1833, would, if central, be total (not annular) in 1842 ; and so on 

 for four periods of nine years. 



The Lecturer then called attention to the great diiference in the 

 directions of the shadow-paths across Europe, for the eclipses of 1842 

 and 1851 (the former being from W.S.W. to E.N.E. nearly, the 

 latter from N.W. to S.E. nearly). This arose in part from the 

 circumstance that (as above explained) the former of these eclipses 

 occurred when the node or end of the intersection-line of the planes 

 of orbits, turned towards the July sun, was that at which the moon 

 rises to the north of the ecliptic, the latter when it is that at which 

 the moon is descending to the south of the ecliptic. But the prin- 

 cipal cause of the difference is this ; that the former eclipse occurred 

 early in the morning, the latter in the afternoon : on placing a 

 terrestrial globe in the proper position for July, with its north pole 

 inclined considerably towards the sun, it is seen that, even if the 

 moon moved precisely in the ecliptic, the path of her shadow across 

 Europe before Europe came to the meridian would trend from the 

 south to the north ; but if Europe had passed the meridian it would 

 trend from the north to the south. 



Quitting the geometrical explanations, the Lecturer then pro- 

 ceeded to describe some peculiar phaenomenawhich had been observed 

 in eclipses, and first, one which had been observed most distinctly 

 in annular eclipses, and which is known by the name of " Daily's 

 beads and strings." When the preceding limb of the moon, tra- 

 versing the sun's disc, approaches very near the sun's limb, or when 

 the following limb of the moon is in the act of separating from the 

 sun's limb to enter on the sun's disc, the two limbs are joined for a 

 time — (no one has estimated the duration with accuracy) — by alter- 

 nations of black and white points or strings. Phsenomena, evidently 

 of the same class, have been observed in the transits of Venus and 

 Mercury over the sun's disc ; the black planet, when just lodged on 

 the sun's disc, being pear-shaped, with its point attached to the black 

 sky. The Lecturer was able to state, in his own experience at the 

 Royal Observatory, that at the same transit of Mercury this phseno- 

 menon was seen with some telescopes and was not seen with others. 

 In the annular eclipse of 1836 observed at Konigsberg, where the 

 moon's limb but just entered completely on the sun's, and where con- 

 sequently it grazed along the sun's for many seconds of time, the 

 phsenomenon appeared to resolve itself simply into points of light 

 seen between lunar mountains. The Lecturer expressed himself 

 generally satisfied with Professor Powell's explanation, that the phse- 

 nomenon originates in that inevitable fault of telescopes and of the 

 nervous system of the eye which tends to extend the images of lumi- 

 nous objects (producing what is generally termed irradiation), and 

 thus enlarges the sun's disc towards the sky, towards the moon or 

 planet, and towards the bottoms of its hollows. 



In describing the total eclipse of 1842 (which perhaps was better 

 observed than any one preceding it), the Lecturer insisted on our obli- 

 gation to M. Arago, who had prepared the preliminary notices, and 



