19G APPENDIX. 



" applies to such parallels of latitude only as have the amount of heat communi- 

 cated to the portions of air lying north and south of them nearly the same, or 

 along which the point of greatest heat, or of heat very little below the greatest, 

 may be supposed to travel from east to west. If," he proceeds, " the excess of heat 

 on one side be moderately increased, the plane of the vortex will be inclined in 

 that direction ; but if the excess become considerable, as through the greater part of 

 the temperate zone, the equilibrium will be established in a totally different way. 

 Thus, with regard to the United States, the point of greatest heat first passes south 

 of us, and an impulse is given to the under strata of the atmosphere in that direc- 

 tion, and when, some time afterwards, the columns in the meridians west of us 

 come to be expanded, the air that should have supplied the eastern or trade-wind 

 having passed off toward the equator, the upper or western current descends to the 

 earth, creating a westerly wind, or rather, by the composition of motions in conse- 

 quence of its mingling with the current that is proceeding southward, a north-west 

 wind, which may be regarded as the natural wind of the parts of the globe lying 

 on the north side of the equator beyond the thirtieth parallel. The same reason- 

 ing applies to the other hemisphere. As, however, the natural and gentle flow of 

 the air in this direction is interrupted by evaporation, condensation, and other 

 causes, the result is simply a predominance in those latitudes of winds from the 

 west, and the direction of the pole, over those from opposite quarters." 

 This whole reasoning appears to me obscure and unsatisfactory. 



3. The theory fails to account for the system of easterly winds which seems to 

 exist in high northern latitudes; for, if the above reasoning is sound for the tem- 

 perate regions, it will apply just as well all the way to the poles. 



4. The cause which Professor M. disregards must exist, and he makes no provi- 

 sion for it. We do certainly know that a body in motion tends to retain its motion j 

 and that if air, partaking of the easterly motion of the earth due to a higher latitude, 

 were, without any change in its motion, transferred to the equator, it must have a 

 relative motion as from the east. All this we should know even without observa- 

 tion or experiment, and if this cause does not produce appreciable effects, it is 

 incumbent to show how it is neutralized. 



The jpurely cosmical theory, on the other hand, runs to the opposite extreme, 

 and disregards the influence of heat altogether. The views of those who advocate 

 it may, if I understand them, be thus expressed. The absolute motion of a place 

 at midnight, say they, is equal to the sum of the annual and diurnal motions of 

 the earth, while, at noon, it is equal only to the difference ; and hence, that the air, 

 tending to preserve a uniform motion, travels slower than the earth in the former 

 case, and faster in the latter. But the same reasoning would apply if the earth had 

 no annual motion. The place would then move in one direction at midnight, and 

 in the opposite one at noon, making the difference the same as now. We all know 

 that a pail of water whirled around on board a steamboat or railroad car, when the 

 latter was in rapid motion, Avould present the same phenomena as when at rest. 

 The whole matter is easily understood by recurring to the first princii^les of central 

 forces. Motion in a circular orbit is neither accelerated nor retarded by a force 

 directed toward the centre of the orbit. Nor will a common motion, communicated 



