On the Temperature of the N. and S. Hemispheres. 443 



opposite, and in such terms I have in fact expressed them 

 long since as follows : — The effect of land under sunshine 

 is to rapidly throw off the heat it receives into the upper 

 regions of the atmosphere and the interplanetary spaces both 

 by day and by night ; and thus, although it causes a consider- 

 able increase of temperature in the strata of air over it by day, 

 it is not well adapted for storing up and retaining heat. 

 Water is much more effective in this respect ; the heat pene- 

 trates to a greater depth within it than on dry land, and it 

 becomes more completely absorbed, owing to the far higher 

 capacity for heat of water and the difference between its 

 diathermanous action on the luminous heat-rays entering it 

 from the sun compared with its action on the obscure rays 

 quitting the particles in the interior of its mass. 



Among the consequences following from my theory of 

 terrestrial climate was one which seemed difficult to recon- 

 cile with the facts accumulated at the time this theory was 

 brought forward. I refer to the supposed higher temperature 

 of the northern as compared w T ith the southern hemisphere. 

 This was formerly attributed to the heating-power of the 

 great masses of land north of the equator. I could not 

 account for this inequality unless by supposing that oceanic 

 and aerial currents w-hich had not been as yet fully examined 

 transported some of the heat absorbed south of the equator to 

 its northern side. This supposed superiority of temperature 

 in the northern hemisphere was employed as an argument 

 against my conclusions. 



In 1875, at the meeting of the British Association at 

 Bristol, I brought forward my views for the purpose of estab- 

 lishing my priority in regard to some of the conclusions which 

 had been frequently reproduced at different inquiries in Great 

 Britain without any reference to their original source. In 

 the discussion which followed one of the speakers, Prof. 

 Everett, is reported to have asked, " How, assuming Professor 

 Hennessy's theory without acknowledgment to be correct, it 

 could be reconciled with the generally accepted fact that the 

 temperature of the northern hemisphere was greater than that 

 of the southern. Professor Hennessy denied that this was a 

 fact, but supposing it were so, he w T ould attribute it to oceanic 

 currents." 



It now appears that the notion of any superiority of mean 

 temperature in the northern as compared to the southern 

 hemisphere must be abandoned. When this opinion gained 

 currency the number of temperature-observations made south 

 of the equator was very small compared to the number 

 recorded in northern latitudes. Of late years a considerable 



