39° SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



I may here remark that so far as I can see as yet the values of /3 

 vary about a mean that is to be found between 35 and 40 . 



If now we designate the total quantities of heat received and lost 

 in the equatorial zone by radiation during the whole year by O a and 

 O a> respectively, and the similar quantities for the two polar zones 

 by O p and O p respectively, then we have 



o - o a + o p 



and 



O = O ffl + Op 

 whence recalling that by assumption O = O, we obtain 



O a - O a = Qp - Q p (9) 



that is to say, the excess of insolation received in the equatorial 

 zone is counterbalanced by an exactly equal excess of radiation 

 outward lost from the two polar zones and this counterbalance is 

 effected by the convection into the polar zones of the excess attained 

 in the equatorial zone. 



Hence the difference O — O a is equal to the quantity of heat that 

 by convection (in the broadest sense of the word including the 

 kinetic energy of moving masses of air) flows through the two neutral 

 sections from the equatorial zone into the two polar zones. 



Moreover, the quotient 



O a — O a _ Op — Op 

 T T 



expresses the average intensity of the currents of heat entering into 

 the equatorial zone and flowing toward the poles, as we can imagine 

 them in our scheme replacing the counterbalancing interchanges 

 that are actually occurring within the atmosphere. 



This quotient will therefore be designated by J a So that we 

 have 



O — O 



\ r -=/« (10) 



On the other hand, we divide the quantities representing the two 

 polar caps into two parts relating to the northern and southern 

 hemispheres, respectively. 



If we give the index n to the quantity relating to the northern 



