Moving Force. 157 
ever, found, that no such advantage was to be 
gained by that: means.* : 
It must be acknowledged, that the cele-. 
brated experiments of D’ Alembert, Condorcet, 
and Bossut, furnished results in confirmation of 
the common theory. But these were made 
under particular circumstances; they did not 
comprehend a sufficient variety of depths and 
velocities to afford satisfactory conclusions as 
to the general question, and various deduc- 
tions, of rather an arbitrary kind, were made 
from the actual pressure before the result which 
agreed with the theory was brought out. 
On the other hand, we have many experi- 
ments which are quite at variance with the 
theory. We may, in particular, refer to those 
of Don Juan and M. du Buat. ‘The former 
exposed to a current of water, moving with 
the velocity of two English feet in a second, a 
plane of one: square foot, immersed one foot 
under the surface, and found that it supported 
a weight of 152 lb. which is nearly four times 
the weight it should have supported, according 
to the theory.t M. du Buat exposed to a 
current, having the velocity of three French 
feet in a second, a plane of one square foot, 
* Philos. Trans. 1759, p. 124. 
+ De Prony Arch. Hydr. p. 304, 
