170 MOVING FORCE. 
Cases of diffi- confirmation of the common theory. But these were made 
doetriiles**of particular circumstances j they did not comprehend a 
moving force, sufficient variety of depths and velocities to afford satisfactory 
conclusions as to the general question, and various deductions 
of rather an arbitrary kind, were made from the actual pres- 
sure before the result which agreed with the theory was brought 
out. 
On the other hand, we have many experiments which are 
quite at variance with the theory. We may, in particular, 
refer to those of Don Juan and M. du Buat. The former ex- 
posed 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 15^1b. which is nearly four times the weight it should have 
supported, according to the theory*. M. du Buat exposed to 
a current, having the velocity of three French feet in a second, 
a plane of one square foot, immersed three inches under the 
surface, and found that it supported a weight of 19'45 liv. 
which, by the theory, should have been only 8'75 livf. M. de 
Prony attempts to account for the results obtained by Don 
Juan, by the additional pressure occasioned by the surface of 
the water over the plane being raised higher than the general 
level of the current. That circumstance, however, can ac- 
count for a small part only of the difference. M. du Buat 
explains his experiments by his theory of non-pressures, which 
I have already shewn to be fallacious. 
M. du Buat has described other experiments which are con- 
sidered by some to accord belter with the theory^. They 
were made upon insulated veins of water, spouting from the 
perpendicular side of a vessel against a surface not greater than 
the section of the vein ; and from their results he draws the 
following conclusions : “ II rcsulte des experiences qui prece- 
dent, que le choc d’une coionne, ou d’une veine fluidc centre 
• De Prony Arch. ITydr. p. 3P4. 
t Principcs (riiyilrnul. vol. V. p. 218. 
t Ibid, p. 142, A:c. 
wne 
