1885.] “ Solar Light and the Earth's Atmosphere 649 
point, and atomic volume no longer return to the type of 
the alkali metals. But although there is no recurrence of 
the former monad type, there is distinct evidence that the 
fall in atomicity is not without influence. The atomic 
volume rises, the melting-point falls, and the expansion by 
heat becomes greater at this point. Copper and its analogues, 
silver and gold, are in each cycle the elements of least che- 
mical activity, and are by far the best conductors of heat 
and electricity. Malleability and conductivity are properties 
possessed by positive elements, and by positive elements of 
low activity, to a greater extent than by positive elements 
ot high activity. The elements of the intermediate groups 
preceding copper and its analogues are held together by 
more poles, and are harder, more brittle, and more rigid; 
copper and its analogues are held together by poles fewer in 
number, but of higher cohesive power, and these metals 
possess more malleability and softness, and are better con- 
ductors. The atoms, while strongly cohesive and close 
together, are more capable of relative motion. 
In the elements of the series commencing with copper 
(silver and gold) the transition proceeds in the opposite di- 
rection, — that is, to the occurrence of poles of the first 
order. Atomicity rises and then falls to the monad halogen 
type, the change being accompanied in a rise and fall of the 
melting-point, and by a small but sensible depression in the 
curve of atomic volumes. 
III. “SOLAR LIGHT AND THE EARTH’S 
ATMOSPHERE.” 
By the Count O. Reichenbach. 
t LECTURE on the above subject was delivered on 
April 17th, 1885, by Prof. J. P. Langley, at the 
Royal Institution. 
Speaking of his observations during his expedition to 
Mount Whitney, the lecturer said : — “ The results, stated 
in the broadest way, mean that the Sun is blue ; but mean 
a great deal more than that, this blueness in itself being 
VOL. vii. (third series. 2 x 
