S^O Mr Watts^ Ohservations on tlte Resistance of Flukh. 
nerally considered to be the most accurate of any yet given. 
This great diversity in the values which different authors have 
deduced from their experiments for the absolute resistance of 
water, is very remarkable ; and it should induce philosophers to 
exert their utmost efforts in endeavouring to detect any fallacy 
that may have crept into the principles or reasonings by which 
the result of the theory has been deduced ; and in multiplying 
experiments, with a view to obviate the great disparity that still 
exists in the absolute value of the resistance, as determined by 
different authors. I am well aware that this cannot be accom- 
plished, without incurring a considerable expence ; and it is this 
consideration alme^ that deters me from making the attempt, 
and not the difficulty of the undertaking ; for, however arduous 
it may appear, I imagine it might be overcome by a steady per- 
severance and attention. 
It may not be irrelevant to remark here, that when water es- 
capes from a vessel through a small orifice, perforated in one of 
its sides, the effective discharge is only about 0,6^ of the theore-> 
tical, owing to the contraction of the fluid vein, — a circumstance 
which has not been taken into the account in the preceding in- 
vestigation : this reduction being made in the value of R, when 
the mass M is assumed equal to unity, the resistance will he 
found NEARLY ccjual to the mass of a prism of water^ whose 
base is equal to b, the ai'ea of the fluid vein^ and whose height 
is equal to twice the fall producing the ejfluent velocity. 
It should also be remarked, that the result of the preceding 
investigation is not rigorously exact, because a portion of the 
fluid is thrown back on the sides of the plane surface, in conse- 
quence of which, it is neither so much urged, nor so continually 
impelled as before ; but notwithstanding this, it leads to an ap- 
proximation, at which, however, we are obliged to stop, on ac- 
count of the insuperable difficulties of the subject. This remark 
is due to Francceiir. Nevertheless, this approximation is the li- 
mit to which the real phenomena of the impulse and resistance 
of fluids continually approach. When, therefore, the law by 
wffiich the phenomena deviate from the theory, shall be once de- 
determined, by a well chosen series of experiments, this ap- 
proximate theory will become nearly as valuable as a true one ; 
for the rules and practice of computation are established even 
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