323 Intelligence and Miscellaneous Articles. 



changed. The absorptive action of air is known to be so weak that 

 it may be completely neglected. Lastly, comparing under several 

 conditions the absorptive action exerted by columns of coal-gas having 

 the same section and the same weight, I observed that they were the 

 same, although their length and their densities were very different. 



Tubes closed by plates of fluor-spar appear likely to be of great use 

 in demonstrating the laws of the absorption of obscure heat. 



In my experiments the galvanometric action produced by obscure 

 radiation transmitted through a tube full of air 064 metre in length 

 was 20° ; it sank to 1 1° when I used the coal-gas tube under a 

 pressure of 0*76 metre. The action of the vapour of ether is far 

 greater ; a tube half as long would be sufficient to render it very 

 distinct. 



I may be permitted, in conclusion, to add that troughs closed by 

 fluor-spar plates are, from their unalterability, very convenient in 

 investigating absorption by liquids. Using them, I have ascertained 

 that liquid chloride of carbon, with the same thickness, is more easily 

 traversed by obscure heat than bisulphide of carbon itself. 



Chloroform has great diathermaneity, but less than the preceding. 

 Benzole and glycerine, on the contrary, with a thickness of 0*01 

 metre, stop to a tolerably complete extent the heat from a plate of 

 blackened copper heated to 400°. — Comptes Rendus, September 10, 

 1867. 



CHANGE OF OBLIQUITY A CAUSE OF CHANGE OF CLIMATE. 

 BY J. CARRICK MOORE. 



In the August Number of the Philosophical Magazine, Mr. Croll 

 has pointed out a great inaccuracy which I had committed. Quoting 

 from memory, I had misrepresented the results of Melloni's experi- 

 ments, which show that when a ray of heat passes through a number 

 of transparent plates, the principal absorption is effected by the first 

 plate. But the main question to which I called attention, I submit, 

 remains as it was. Mr. Croll asserts, on the authority of Mr. Meech's 

 Tables, that if the present annual heat at the equator be represented 

 by 365*24, the heat at the poles will be represented by 151*59 ; and 

 if the obliquity were increased by 1° 22' 34", by 160*04, — these two 

 quantities being to each other as 18 to 19. What I contended for 

 was that each of these last quantities was necessarily erroneous, as 

 they make no allowance for the diminution of heat in passing 

 through the atmosphere, which is known to be very great, — and that 

 if we had the true quantities, their proportion might be very differ- 

 ent. Melloni's experiments show that the absorption for each trans- 

 parent substance that he tried was very different : he did not experi- 

 ment upon a mixture of oxygen, nitrogen, and watery vapour, such 

 as our atmosphere consists of. Mr. Croll says that whatever the 

 absorption be, it will be the same for each obliquity, and therefore 

 the proportion will be the same. But Tyndall has shown that watery 

 vapour is the greatest absorber of all gaseous bodies. Now increase 

 of heat is always attended by increase of vapour ; and the additional 

 thermal days at the poles from increased obliquity might therefore pro- 

 duce little or no change in the temperature of the poles, or in a very 

 different proportion from 18 to 19. 



