154 On the Measure of | 
its centrifugal-force from the centre of the 
earth; but that exception does not apply to 
the case in question, for the centrifugal force, 
whatever it is, must, according to M. du Buat’s 
theory, be added to the non-pressure. In con- 
firmation of his theory of non-pressures, M. du 
Buat observes, “ Qu’ayant fait mouvoir, 4 une 
certaine profendeur, dans une eau stagnante, 
un tube vertical ouvert par les deux bouts, 
dont le supérieur étoit hors de l'eau, le fluide 
s'est maintenue dans le tube, plus bas que la 
superficie du réservoir, d'une quantité a~peu- 
pres égale a Ja hauteur die a la vitesse avec 
laquelle il étoit mu.”* But he has omitted to 
take into consideration the cohesion or the 
lateral action of the particles of the water 
upon each other, which has since been so well 
observed by M.Venturi; from whose experi- 
ments, and from those of Dr. Matthew 
Young,t made under the receiver of an air- 
pump, we may safely conclude, that, were it 
not for the pressure of the atmosphere, and 
the cohesion of the particles, there could be no 
depression in the tube as observed by M. du 
Buat; and, had he been aware of these cir- 
eumstances, he surely would never have 
reasoned as he has done on the subject of 
* Principes dhydraul. Vol. 2. p. 156. 
+ Irish Philos. Trans. vol. 7. p. 63. 
