162 
MOVING rORCE. 
materials ; that the superincumbent basalt or wacke is melted 
by this heat, and flows into these hollows, and that water rushe* 
in on the surface of this melted mass, and occasions its explo- 
sion*. 
(To be continued.) 
II. 
Cases of diffi- 
culty in the 
doctrines of 
moving force. 
On the Measure of Moving Force. By Mr. Peter Ewart. 
(Continued from p. gy.) 
I T should be observed, that a weight raised to a given height, 
and V docity generated in a given mass, are two very dif- 
ferent effects of mechanical power j but the measure, com- 
posed of the pressure into the space through which it acts, 
applies equally to both of them. When velocity is generated, 
the mass into the square of the velocity is always in the ratio 
of the pressure into the space ; but when a weight is raised 
with an uniform velocity to a given height, it has never, I be- 
lieve, been contended by any one, that the absolute quantity 
of mechanical power necessary to produce that effect, or the 
ascensional force, as it was denominated by Huygens, must 
be as the square of the velocity with which the weight rises. 
Such a conclusion would, indeed, be quite in contradiction to 
the principle of the mechanical force being as the square of the 
velocity generated. 
Mr. Smeaton’s meaning will appear still more distinctly, 
perhaps, if v'e attend to the particular case he was treat- 
ing of in the passage objected to by the reviewers. His 
object was to ascertain the mechanical power of a given 
quantity of water moving with a given velocity. In order 
to do this, be constructs an apparatus by w'hich it may be de- 
* Jameson III. p. 220, 
termincd 
