320 



Anniversary Meeting. 



[Nov. 30, 



surface temperature was small ; while the greatest difference be- 

 tween the two temperatures was observed on nights when the deposi- 

 tion of dew was scanty. The explanation offered by Tyndall is this : 

 — copious dew indicates abundant vapour ; and abundant vapour, by 

 arresting the terrestrial rays, prevents the refrigeration observed in 

 drier air. Strachey's able discussion of observations made at Madras, 

 point distinctly to the action of aqueous vapour on the radiation both 

 of the sun and of the earth ; while the experiments of Leslie, 

 Hennessey, Hill, and other distinguished men, which were long con- 

 sidered enigmatical, are readily explained by a reference to the 

 varying quantities of vapour with which the atmosphere is charged, 

 on days of equal optical transparency. The interesting observations 

 of Desains and Branley, made simultaneously on the Rigi and at 

 Lucerne, are well worthy of mention here. The difference of level 

 between the two stations is 4,756 feet, and within this stratum 17*1 

 per cent, of the solar heat was proved to be absorbed. This absorp- 

 tion being due to aqueous vapour, is tantamount to the transmission 

 of the sun's rays through a layer of water of a definite thickness. A 

 sifting of the rays would be the consequence, and on a priori grounds 

 we should infer that the percentage transmission through water at 

 Lucerne must be greater than on the summit of the Rigi. This was 

 the exact result established experimentally by Desains and Branley. 

 Mr. H. Wild, Director of the Central Physical Observatory, St. Peters- 

 burg, basing his statement on experiments made by himself according 

 to Tyndall's method, has expressed the opinion " that meteorologists 

 may, without hesitation, accept this new fact in their endeavours to 

 explain phenomena which hitherto have remained more or less enig- 

 matical." The correctness of this statement is illustrated by the fore- 

 going examples, to which, if necessary, many more might be added. 



At the recommendation of the Committee on Solar Physics of the 

 Science and Art Department, a grant of £350 was made from the 

 Society's Donation Fund to Captain Abney and Mr. Lockyer in aid of 

 their proposed observations of the total eclipse of the sun at Thebes in 

 May last. Unfortunately the state of Captain Abney's health precluded 

 his taking part in the expedition ; but Dr. Schuster generously under- 

 took the conduct of his observations, and, notwithstanding the short 

 time remaining for preparation, he carried them out in the most 

 satisfactory manner. 



Three photographs of the corona itself were obtained during the 

 eclipse. They show that the corona had the characteristic features 

 observed during the time of the maxima of sun-spots. The long 

 streamers in the plane of the ecliptic seen during sun-spot minima 

 were absent, and the corona showed much disturbance. A bright 

 comet appeared in all the photographs at a distance slightly less 

 than a solar diameter. 



