346 Posthumous Work of the late Col. Mark Beaufoy. 
ciety’s volume, gives us possession of the knowledge of a mass of 
_ facts, ascertained by most laborious and ingenious experiments, of 
immense value to every person engaged in hydraulic engineering. 
I cannot but hope that Mr. Beaufoy will continue the publication 
of the other volumes, thus increasing the debt which is already due 
to him from practical men as well as from scientific investigators. 
I am dear Sir, with great respect, 
your obedient servant. 
The second letter is from a gentleman much distinguished for his 
theoretical and practical knowledge of mechanics. 
TO PROFESSOR SILLIMAN. 
Dear Sir—I have with much pleasure given the first volume of 
Col. Beaufoy’s work a cursory examination. The Resistance of 
Fluids, to which this volume chiefly relates, is a subject of great in- 
tricacy, and one in which I have felt a deep interest. I had given it 
sufficient attention, theoretically, to satisfy my own mind fully, that 
what is said on the subject in the works, commonly received as sci- 
entifical and practical text books is not at all to be relied upon, and 
was pursuing my inquiries for something more satisfactory, when I 
was referred by a friend to this volume, which, on my application, 
you were so kind as to lend me. 
Before Col. Beaufoy commenced his experiments, the labors of 
philosophers and mathematicians in this department of hydraulics, 
had been chiefly directed to the deduction of a theory, a priori from 
the received doctrine of the percussion of fluids; and had for the 
most part contemplated only that portion of the resistance, which re- 
sults from the direct or oblique action of the fluid on the anterior 
disc of the moving body. Some experiments had been tried, but 
they were comparatively few in number, and having been instituted 
for the purpose of confirming some point in the theory, were shaped 
with sole reference to that object. Attempts, also, had been made 
to deduce the law of resistance directly from experiments; but the 
experiments were so few and so little diversified, that such an attempt 
could proceed only upon the false assumption that the resistance is a 
single force, or if made up of several forces, that these have a fixed 
relation to each other. 
Col. Beaufoy regards the resistance as made up of three distinct 
quantities, having no necessary dependence upon, or relation to each 
