1870.] Astronomy. 521 



Commander Ashe endeavours to show that the Council of the 

 Astronomical Society were not justified in expressing the opinion 

 that " in photographs 3 and 4 " (of his set of 4, illustrating the 

 American eclipse) " there is evidence of the disturbance of the tele- 

 scope during the exposure of the sensitive plate. But there seems 

 every reason to accept the opinion of the very able committee ap- 

 pointed by the Council to consider the matter, and the members of 

 this committee " unanimously report that in their opinion there was 

 a decided movement of the instrument at the time the photograph 

 was taken; a conclusion arrived at from an examination of the 

 chromosphere close to the moon's limb, as well as from an examina- 

 tion of the prominences." 



In a description of the occultation of Saturn by the moon on 

 April 19, 1870, Captain Noble dwells on the exceeding sharpness 

 of Saturn's definition; the most delicate details being perceptible, 

 even in contact with the moon's limb. The crape ring C was seen 

 most perfectly where the dark limb of the moon crossed it. " I 

 never was more impressed," remarks this skilful observer, " with the 

 absolute absence of a lunar atmosphere of any appreciable density 

 than I was on this occasion." 



Mr. Penrose, from observation of the star Algol, concludes that 

 the period of 2 ■ 86727 days assigned to this remarkable variable in 

 Herschel's ' Outlines of Astronomy ' requires to be slightly corrected. 

 The minima occurred nearly three hours earlier than the epochs 

 calculated with the above period from a minimum which occurred 

 on January 3, 1844. The shortening of the period of this variable 

 is certainly a remarkable and interesting circumstance. Observers 

 should watch from time to time the occurrence of the well-marked 

 minimum, in order to see whether the reduction of the period is 

 steadily progressing, or to detect signs of its being eventually trans- 

 mitted into the reverse process, as in the case of planetary pertur- 

 bations. 



Mr. Proctor, in a paper " On the Besolvability of Star-groups 

 regarded as a Test of Distance," points out that there is good reason 

 for doubting whether we can form any opinion whatever respecting 

 the distance of a cluster of stars from the telescopic power necessary 

 to completely resolve it. He shows that a star-group may be so 

 constituted that let its distance be ever so great it cannot appear 

 nebulous, or again that conceiving its distance to be increased so 

 that it passed eventually beyond the range of our most powerful 

 telescopes, it would pass from irresolvability to resolvability and 

 again to irresolvability through the mere effect of a continually in- 

 creasing distance. The question of the resolvability of a star-group 

 depends not on distance alone, but on the relation between the 

 magnitudes of the component stars and the distances separating 

 them. If the magnitudes are such that the stars would vanish in- 



