APPLICATIONS OF THE MICROSCOPE. 133 



To explain this, and to meet the difficulties 

 connected with these various currents meeting 

 and crossing at the equator, the Calms of Cancer 

 and Capricorn, and the North and South Poles, 

 Maury, with the help of diagrams, traces the 

 course of a hypothetical " particle of northern 

 air" (or a particle of air supposed to pass from 

 the north), and follows it in a round from the 

 North Pole, onward across the equator to the 

 South Pole, and back again to the North. This 

 particle of air (" for reasons," says Mr. Maury, 

 " not very satisfactorily explained by philoso- 

 phers"), instead of proceeding on the surface all 

 the way from the pole to the equator, travels in 

 the upper regions of the atmosphere, until it 

 gets near the parallel 30 N. Here it meets a 

 "hypothetical particle" also in the clouds, that is 

 passing in similar fashion from the south toward 

 the pole. Here these two particles must press 

 against each other, and produce a calm (the 

 Calms of Cancer). From under this bank of 

 calms, two currents of air are ejected, one to- 

 ward the equator as the north-east trades, the 

 other toward the pole, as the south-west passage 

 winds. The barometer, it is noticed in support 



