Mr Watts’ Observatims on the Resistance of Fluids. 
the author’s own experiments seem at least to support his con- 
clusion. 
2. It has been objected, that there is an essential defect in the 
investigation of the problem in question ; because, says the ob- 
jector, the equation (S) exhibits no resistance in the case of a 
liuid without weight, and because a theory of the resistance of 
fluids should exhibit the retardation arising from inertia alone, 
and should distinguish it from that arising from any other cause. 
In combating this objection, I remark, that this essential de- 
fect complained of above, is a mere nonentity ; for the fact is, 
that the equation in question does really exhibit a resistance, 
even in the case of a fluid destitute of weight ; because the va- 
lue of the mass M is independent of the weight; and the same 
is true of the difference of the two dead pressures, which diffe- 
rence constitutes the equation ( 2 ), notwithstanding it involves 
7 • ^ 
the quantity - 7 = 1 , 
which is nothing more than the expression 
of a ratio, that is, of an abstract quantity. Hence it follows, 
that this equation does bond fide exhibit the retardation which 
arises from inertia alone. 
3. Another objection is, that while the equation (2) assigns 
an ultimate sensible pressure, proportional, cateris paribus, to 
the simple velocity, it assumes as a principle, that the pressure 
p is as (u _+ vf. It will be sufficient to reply to this objection, 
that the ultimate sensible resistance has already been proved to 
be as the square (fithe velocity — a conclusion which is in unison 
widi the principle assumed, namely, that the pressure p is pro- 
portional to {u + vf. 
4. As to the objection, that the equation (2) gives a false 
measure of the statical pressures, which are affirmed to be 
made up of the pressure of the incumbent water, which is mea- 
sured by h, and the pressure of the atmosphere a constant quan- 
tity, it is of no force ; because it was never meant that it should 
give the complete measure of the statical pressure, but only 
the pressure of the incumbent water, which is measured by the 
height h, — not even when the value of v is such that a perfect 
vacuum is left behind the surface o, — a case which I believe 
