Physics and Chemistry. 143 
there is derived entirely from the temperate regions. In July we 
have the northern trades coming from a hemisphere with a mean 
temperature as high as 70°°9, and the southern trades coming 
from a hemisphere with a mean temperature not under 53°, while 
in January the former trades flow from a hemisphere as low as 
50°, and the latter from a hemisphere no higher than 60°. Con- 
sequently the air which the equatorial regions received from the 
trades must have a higher temperature in July than in January. 
The northern is the dominant hemisphere ; it pours in hot air in 
July and cold air in January, and this effect is not counterbal- 
Consequently cool the equatorial regions more during the former 
than the latter season. The general tendency of the trades to 
g will eccentricity have a counteracting effect upon the tem- 
perature of the air at the equator, which but for that would be 
