27 



upon by the reflected and radiated heat of the sun, in a manner 

 so much in accordance with a uniform sequence of physica 

 effects, that the periodic movements of the gases composing- 

 it would have been as regular as the planetary motions them- 

 selves. In the northern parts of our hemisphere, it appears 

 by Mr. Baxendell's valuable paper, read before the General 

 Meeting of this Society on the 13th ult., that the barometric 

 oscillations are least in amount when the sun is on or near 

 the equator. This fact points to the inference that if the plane 

 of the earth's orbit had coincided with the plane of its equator 

 the disturbance of the barometric column would have been 

 comparatively small and nearly uniform throughout the year. 

 The coincidence of these two planes not existing, it is found, 

 that as the sun retreats from the equator towards the southern 

 tropic, the sum of the oscillations of the mercury gradually 

 increases for a considerable time, and then rapidly mounts up 

 so fast as to form a prominence in Mr. Baxendell's curves 

 resembling a mountain peak. This peak or summit of the 

 "dynamical curve" occurs above different points of its axis — 

 that is, at different periods of time — according to some peculi- 

 arity in the position — different from the latitude or the 

 longitude — of the locality from which the data for constructing 

 the curves were derived. 



Speaking of the northern hemisphere, as the sun withdraws 

 southward from the equator, less or greater portions of the 

 northern part of the terraqueous surface becomes cooled down 

 gradually to the freezing point, according to various peculiari- 

 ties of substance, elevation above the sea-level, proximity to 

 the open ocean, or to far-inland mountain ranges, and to other 

 analogous causes. In similar latitudes, from the varying 

 conditions just mentioned, there will exist, side by side, spots 

 differing, or having a tendency to differ, very much in 

 temperature, and where consequently currents of different 

 density — set in motion by the constant struggle going on in 

 the air to attain a state of equilibrium— will cause frequent 



