318 On the Resistance of Fluids. 
producing a supposed primary north and south current, or in any 
other manner, I entertain no doubt that, if it were possible to pre- 
serve the atmosphere at a uniform temperature over the whole sur- 
face of the globe, the general winds could not be less brisk, but 
would become more constant and uniform than ever. 
New York, April 8th, 1835. 
Art. X XII.—On the Resistance of Fluids ; by Gro. W. KEEty, 
Prof. of Natural Philosophy, in Waterville College. 
TO PROF. SILLIMAN. 
Srr—lI perceive in No. 55 of the Journal, that Prof. Wallace has 
announced a new measure of the resistance of a fluid m a direction 
perpendicular to a plane surface moving init: viz. That it is as the 
sine of the inclination of the plane. Permit me to state my rea- 
sons for adhering to the old doctrine, that the perpendicular resist- 
ance is as the square of the sine of inciination. It is well known 
that the latter measure has been deduced from the alleged facts that 
the number and the force of the resisting particles vary as the sine 
of the inclination. If it be true that the resistance to a plane sur- 
face moving in a fluid is as the number of particles it strikes in its 
course, and that the number of particles in any indefinitely thin fluid 
lamina is as the area of that lamina, (nel- 
ther of which we think Prof. W. will de- 
ny,) it follows that, if BD be a section of 
a plane inclined to the direction BA of 
its motion, and BF an equal section of 
an equal plane perpendicular to the same 
direction, the number of particles BD will strike is to the number 
that BF will strike in the same time as the parallelogram ABCD is 
to the parallelogram AEF'B; and the resistances are therefore, on 
this account, as BG is to BD, or as the sines of the inclinations of 
the sections ; the resistances to the planes are of course in the same 
ratio. 
Now this familiar demonstration would seem to settle the ques- 
tion; but Prof. Wallace argues, ‘‘ that the number of particles stri- 
king the plane does not depend on the breadth of the fluid column 
BG BF, but on the surface of the plane, because the particles that 
act on the plane are those in contact with it, and therefore their 
