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 
