38 Proceedings of the Asiatic Society. [ Frs. 
posed to be approaching the equator and to be moving under the 
influence of an initial velocity, would in consequence of the rotation, 
be such as to cut the successive parallels of latitude at continually 
diminishing angles on the eastern side; and the case would be 
reversed for a particle receding from the equator. Or to state the 
same proposition somewhat differently, a particle starting with a 
given velocity, in passing from the smaller circles of latitude to the 
larger would, asit went on, seem to observers at each successive 
point in its course to be coming froma more and more easterly 
direction, while conversely in passing from the larger circles to the 
smaller its apparent direction would grow to be more and more 
westerly. - It is true that the earth’s surface cannot be considered 
smooth even as regards its action upon such a mobile fluid as the 
atmosphere. The horizontal motion of masses of air over the 
earth is much checked by friction along the surface of contact or 
more correctly by the obstruction which is afforded by the earth’s 
inequalities of surface. Still the effect of this disturbing cause is 
upon the whole of a subordinate character; and speaking generally 
without regard to special localities or occasions, I may say that the 
law which expresses the motion of a free particle relative to the 
earth, also gives with some degree of approximation the course of 
moving portions of the atmosphere. The flow of polar air towards 
the equatorial belt, of which I have spoken, thus becomes an eas- 
terly wind in both hemispheres, while the upper outflow or anti- 
trade current is westerly aud in both cases with a certain exception 
the longer the course by which the current has reached a given 
point, the greater is its deviation from a polar direction. This 
explanation of the trade winds and of the intervening belt of calms 
was developed, more than a century ago, by Halley and all ob- 
servations since made have served most fully to demonstrate its 
truth. 
It is comparatively lately, however, that Dove and others have 
shown that the atmospheric phenomena of the trade and inter-trade 
regions are but simple cases of the air-movements which take place 
outside those limits. For instance, the well known veering of 
winds in the temperate zone is now held to be referable to precise- 
ly the same cause as is the peculiar constant direction of the trade- 
