430 M. Poinsot on the Percussion of Bodies. 
coast. A steam-ship far out at sea was proceeding towards 
England, and the smoke was drawn by the gentle breeze into a 
streamer extending for miles behind the boat. The streamer of 
smoke appeared straight and perfectly horizontal over the surface 
of the water, until it arrived at a point about a quarter of a mile 
from the Hill of Howth, when it rose upwards with a gracefully- 
curved outline, and it appeared to be gradually diffused in the 
air situated vertically over the hill. 
The influence of vertical and oblique currents in the atmo- 
sphere is not only thus manifest in the comparatively limited and 
local phzenomena of sea- and land-breezes, mountain winds, and 
whirlwinds, but it has also been appealed to in order to explain 
the circulation of the great winds of the earth. Thus Maury, in 
his attempt to exhibit the general laws of the great winds, pre- 
sents a diagram in which ascending and descending currents are 
distinctly indicated over different regions of the globe. Their 
agency is also appealed to by other inquirers ; and their principal 
seats of action seem to be indicated as the calm regions, that is 
to say, the regions where horizontal winds blow with least in- 
tensity. Observations with the aid of the anemoscope in the 
regions of equatorial and tropical calms would therefore probabl 
serve to test the accuracy of the general views here alluded to. 
The systematic study of the non-horizontal movements of the 
atmosphere has scarcely been commenced ; but what little know- 
ledge we possess of such movements shows that they are so closely 
atactet with some of the most important phenomena of the 
weather, that their further investigation is certain to be attended 
with interesting and valuable results. 
LVII. On the Percussion of Bodies. By M. Potnsor*. 
[Continued from vol. xviii. p. 259.] 
Cuarrter V. 
i iG the very special cases hitherto treated+, we supposed 
that the motion of the body was. due to the impulse of 
a single force P having a certain direction, and we merely deter- 
mined the percussion Q which the body was capable of producing 
against a fixed point presented to it in a peculiar manner. 
It now remains to treat the general question where the motion 
of the body is due to the action of any given forces whatever, and 
where the percussion is required which this body can produce, 
by any one of its points, against any fixed obstacle which it may 
encounter, 
* From Liouville’s Journal, December 1859. 
+ See Phil. Mag. vols. xv. and xviii. 
