in the Air and in the Sea, 103 



where C denotes the centrifugal force of the equator, and <£ the 

 latitude of the parallel circle. Consequently BF = C . cos cf> . sin <f>, 

 and therefore reaches its maximum quantity when 0=45°, 

 amounting then to sin 2 45° x 0*11124 foot =0*05563 foot in a 

 second, or 4806*4 feet in 24 hours (which makes 1^ verst^ 

 nearly j of a German, or almost exactly i-9 of a British statute 

 mile). This inconsiderable tendency toward the equator is 

 further diminished by friction, and therefore cannot possibly be 

 thought of as the motive force of a current. Yet it may per- 

 haps contribute something to this — that in each of the oceans 

 the current flowing, in the middle latitudes, from west to east 

 gradually inclines in its direction a little to the equator. 



The earth's centrifugal force, acting in an opposite direction 

 to that of gravity, occasions over the entire earth, with the 

 single exception of the two poles, a more or less perceptible di- 

 minution of weight. This is greatest at the equator, amounting 

 to nearly the 290th part. Thence to the poles the quantity to 

 be deducted from gravity diminishes in the ratio of the squares 

 of the cosines of the latitudes. Now, as all bodies (air and water 

 not excepted) are somewhat lighter in the vicinity of the equator 

 than in higher latitudes, one would think that this must produce 

 currents in the ocean and atmosphere equal to those arising from 

 the lightening of the water and air by heating. These currents 

 must flow beneath to the equator, and as upper currents from 

 the equator to the poles. But in reality this does not appear to 

 be the case ; for degree-measurings and pendulum-observations 

 have shown that the surface of the sea has the form of an ellip- 

 soid slightly compressed at the poles, the long diameter of which 

 (measured in the plane of the equator) is 295 of its length 

 greater than the shorter diameter (measured in the line of the 

 earth's axis). Erom this we see that the level of the ocean at 

 the equator is nearly as much raised as the weight loses there 

 through the action of the centrifugal force; hence probably 

 none, or a scarcely perceptible portion of the lighter water at 

 the equator can flow off. 



It is, perhaps, just the same with the atmosphere; yet it is 

 probable that, with diminished pressure, the strong elasticity of 

 the air will produce by expansion a greater raising of its level 

 (if such an expression can be used) than the centrifugal force 

 requires. If it is so, certainly the upper, much rarefied air 

 must flow off from the equator, and be replaced by an under- 

 current. Now, since the mass of the inflowing and of the out- 

 flowing air must be the same, the dense undercurrent will be 

 considerably less perceptible than the upper strongly rarefied 

 one. The centrifugal force may thus, combined with the differ- 

 ence of temperature, generate the currents in the upper strata 



