84 Mr. H. H. Howorth on 



it of moisture, and therefore force it to descend and come 

 to the ground long before it can reach the poles. 



The polar cold, therefore, cannot affect the circulation 

 of the trade winds. The hotter the equator, the hotter and 

 more charged with vapour will the air be that rises there. 

 That is true, but this will only make it more buoyant and 

 rise higher to a colder stratum, and thus the greater heat of 

 the furnace will be compensated by the greater cold of the 

 stratum to which the air will rise, that is of the refrigerator. 

 It is well known that the equatorial current discharges its 

 great mass of moisture in the shape of very heavy rain — 

 (that is to say, has its moisture condensed) before it reaches 

 the two tropics. 



This makes it clear that the trade winds belong to a 

 circulation of air outside of polar influence altogether, and 

 are not affected, as Dr. Croll argues, by a greater or less 

 temperature at the poles. 



Let us now advance another step, limiting ourselves 

 strictly to the trade winds. If the earth were still, the trades 

 would move directly towards the parallel of greatest heat, 

 while the anti-trades would move directly away from it, 

 and their motion would be at right angles to the equator. 

 This direction, however, is interfered with by the rotation of 

 the earth, for although this rotation will not induce a move- 

 ment in anything placed upon the earth, it will, as we have 

 seen, deflect the direction of anything already in motion. 



"In virtue of the rotation of the earth," says Mr. Buchan, 

 " objects on its surface at the equator are carried round 

 towards the east at the rate of about 17 miles a minute on 

 receding from the equator. This rate of velocity is being 

 continually diminished, so that at 6o° N. L. it is only about 

 8*4 miles a minute, and at the poles nothing. From this it 

 follows that a wind blowing along the earth's surface, in the 

 direction of the equator, is constantly arriving at places 

 which have a greater eastward velocity than itself. As the 



