Moving Force. 233 
circumstances ; but the amount of it may in 
© sone instances be estimated with considerable 
exactness. When a jet of water issues from 
an orifice of a particular construction, it has 
very nearly the same velocity which a body 
‘would acquire in falling freely through a 
height equal to the depth of the orifice under 
the Famaetties of the water.—In that case there- 
fore, a very small part only of the moving force 
is expended in changing the figure of the 
water before it reaches the most contracted 
part of the orifice.—But if the orifice be con- 
structed so that any separation of the particles 
of the water from each other takes place, 
although they may be brought together again 
and completely fill the most contracted part of 
the orifice, yet there is invariably a consider- 
able loss of moving force. In other words, a 
portion of the moving force is expended in 
producing this separation of the particles of 
the water; and that portion may be estimated 
by deducting from the whole moving force 
‘which the water would acquire in falling 
freely through the height of the head, that 
portion of moving force which is found to 
remain with the water after it has issued. 
The following important proposition re- 
‘lating to this subject, is laid down by Daniel 
Bernoulli in his Hydrodynamics, page 278. 
Gg 
