22 On Mr. Ferrel's Theory of Atmospheric Currents. 
Section, where he connects pressure and wind, are derived from 
these equations ! He gives no equation of continuity. And 
in truth he does not want it. For his equations, as he had 
himself begun with observing, are the equations to the motion 
of a free projectile, not of a continuous fluid. 
Or, rather, this is what they would have been but for his 
fantastic treatment of them. Taking the case of an elastic 
fluid, he puts k=«P (in connexion with which I have men- 
tioned the blunder he subsequently makes); and then he 
separates the right-hand side of the equation for — -=- into 
two parts (sayU— g)\ and then the three equations become 
1 clY „ 1 tfP , , v 1 dP ._ 
Then he supposes H to be the complete integral of 
mUdr+aYdB+aWity, 
without attempting to prove that it is a complete differential : 
and then he asserts that P = H— yjadr, or say H + K : and 
then he applies his proposition as to the consequence of making 
P constant, and gets his wonder-working equations 
in which, moreover, we find that the r which maybe involved 
in a, and so in K, is treated as a function of 6 and of <f) in the 
differentiation, though and (f> are not treated as similarly 
interdependent. 
I think this is a sufficient specimen of Mr. Ferrel's way of 
dealing with symbols as soon as he leaves the beaten track, 
and that no one need attempt to follow him further. 
Kitlands, Dorking. 
Postscript. — Just as I was about to send this communication 
to the Philosophical Magazine I became acquainted with Mr. 
Scott's 'Elementary- Meteorology;' and I find from a passage 
in it that my warning against the misleading phraseology of 
the "old text-book," as quoted from Mr. Ferrel, is by no 
means superfluous. After explaining how the heated surfaces 
in the equatorial regions must cause an overflow of rarefied 
air northward and southward, he goes on (p. 241): — "As the 
form of the earth is spherical, the circumference of the equator. 
a great circle, exceeds that of the smaller circles of latitude, 
which gradually diminish to a point at the pole. The meri- 
