136 MR. JOSEPH BAXENDELL 



is, I believe, now generally admitted by meteorologists 

 that the many valuable series of thermometrical observa- 

 tions which have since been made in various localities 

 have hitherto failed to afford any decided indication of a 

 periodical change in the element of mean annual tempera- 

 ture. The question therefore naturally arises, if the in- 

 tensity of solar radiation varies in a period corresponding 

 with the period of solar- spot frequency, why does not the 

 element of mean annual temperature exhibit a similar 

 periodical change ? For the present, I will merely suggest 

 that a clue to the correct explanation of this apparent ano- 

 maly may perhaps be found in the conclusion at which 

 Professor Forbes arrived from a discussion of his observa- 

 tions made in Switzerland, in conjunction with Professor 

 Kaemtz, on the intensity of solar radiation at different 

 elevations in the atmosphere, namely, that the heating 

 rays of the sun consist of two kinds, — one kind of high 

 intensity, which suffers little or no loss in passing through 

 the atmosphere; and the other of much lower intensity, 

 and therefore much more absorbable. Now, if we suppose 

 that the relative quantities of the two kinds of rays undergo 

 periodical changes, such that the maximum of the one 

 corresponds to the minimum of the other, it will be evident 

 that when the lower strata of the atmosphere receive less 

 heat by absorption, owing to a diminished supply of the 

 rays of low intensity, the ground will receive more from 

 the simultaneous increase in the quantity of the rays of 

 high intensity, and this being communicated to the lower 

 atmosphere by conduction and convection, as well as by 

 radiation upwards, will restore the equilibrium, and tend to 

 produce uniformity in the mean annual temperatures. 



On a former occasion I urged the desirability of giving 

 more attention than has hitherto been done to the oscil- 

 lations of mean daily temperature, and have shown, in 

 the present discussion, their importance in connexion with 



