“Moving Force. — 153 
convincing proof of the great caution with 
ewhich such approximations should be sought, 
in the mistake into which this ingenious, per- 
severing, and skilful experimenter has himself 
been led, by attempting to generalize too far 
the results of some of his experiments—I 
allude to his peculiar theory of non-pressures. 
After very reasonably concluding, that, in 
cases where water is descending, as it were 
upon an inclined plane, the bottom of the 
channel does not sustain the whole weight of 
the water, he extends that principle as follows : 
“Si, par une cause quelconque, une colonne 
duide comprise dans un fluide indéfini, ou 
contenue dans des parois solides, vient a se 
mouvoir avec une vitesse donnée, la pression 
quelle exercoit latéralemeut avant son mouve- 
ment contre le fluide ambiant, ou centre la 
paroi solide, sera dimimuée de toute celle qui 
est. due a la vitesse avec laquelle elle se 
meut.”* Now this doctrine is obviously 
untenable. For, when water is moving upon 
a horizontal plane, we cannot doubt that the 
plane must support the whole weight of the 
water. It is never supposed that.a ball loses 
a part.of its weight by rolling upon a hori- 
zontal plane, excepiing indeed the amount of 
* Principes @hydraul. vol. 2. p. 175. 
. UD . 
