MOVING FORCE. 
J67 
From that result, M. du Boat concludes, that the pressure at Cases of 
the circumference of the wheel is as After highly 
commending the experiments and observations of M. Bossut, moving force. 
M. du Buat continues ; “ Nous avouons ncanmoins, i regret, 
qiie, quelque iiombreuses et varices qu’elles soient, elles ne sent 
pas encore suffisantes pour etre applicables a tous les cas. Ce 
nc sera qu’apr^s en avoir fait de nouvelles sur le racm# plan, et 
eii avoir rappottc les resultats ^ quelque loi d’approximation 
simple, telle que celle que nous avons expos^e, qu’on pourra 
espcrer dedouner des regies pratiques propres ^ guider les arti- 
sans auxqufls ces sortes de constructions sont abandonneesf 
This observation well merits the atlentic'n of every writer on 
theories of hydraulics. Whether we contemplat* the number 
and diversity of the theories which have been proposed, or the 
still greater number of facts which appear to be beyond the 
reach of mathematical explanations, it must, I apprehend, be 
obvious, that approximation by experiment is all that can, in 
the present state of the science, bo reasonably expected in the 
comparison or estimation of hydraulic forces ; and we have 
a convincing proof of the great caution with which such ap- 
proximations should be sought, in the mistake into which this 
ingenious, persevering, and skillful 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 follow’s ; “ Si, 
par une cause quelconque, une colonne fluide comprise dans 
un fluide indetini, ou contenue dans' des parois solides, vient ^ 
se mouvoir avec une vitesse donnee, la pression qu’elle exer^oit 
lateralement avant son mouvement centre le fluide ambiaut, ou 
centre la paroi solide, sera dirainuee de toute celle qui est die i 
la vitesse avec laquelle elle se meut J” Now this doctrine is obvi- 
• Principcs d’liydraul. vol. 2, p. 336. 
t Ibid. p. 360. 
} Ibid, p, 175. 
•usly 
