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unphilosophical to assign new causes when those before 
accepted clearly meet the case. Yet we have seen two elabo- 
rate essays, by Dr. W. J. M. Rankine and Professor Tyndall, 
each based on th e. force heat assumption, but without affording 
any solid proofs of its application to the phenomena adduced 
by them. 
Mr. Rankine states that u Heat produces an increase of 
temperature and of expansive force in bodies ; that the changes 
from the solid and liquid states to the gaseous state is accom- 
panied by an increase in volume ; that heat which produces 
those effects is known by the name of sensible heat, as attain- 
ing the form of heat, and in short making the body hotter.” 
Again, that <f changes of volume are attended with changes 
of molecular arrangement, perceptible or imperceptible, and 
that the latent heat of expansion or evaporation consists of 
heat that disappears in overcoming pressure and the attrac- 
tion of the particles of the body.” In reference to the non- 
production of heat by the moving force exerted in waterfalls, 
the following solution is offered, viz. : “ It is natural to 
suppose that the motion during this phenomenon (the falling 
of a mass of water) has not been destroyed, but has been con- 
verted into revolutions of the particles in vortices or eddies too 
small to be perceptible by any of our means of observation, 
and that the centrifugal force of such eddies is the cause of 
the tendency of hot bodies to expand, melt, and evaporate.” 
The first class of phenomena above cited are plainly 
accounted for by the doctrine of latent heat, but the latter 
explanation about waterfalls passes Mr. Dyer’s comprehension. 
He submits that what is said to be natural to suppose con- 
cerning the revolutions of particles in vortices and eddies too 
small to be perceived is too obscure and questionable to be 
accepted in explanation of anything. If Mr. Rankine has 
no better mode of accounting for the nonappearance of heat 
from the force expended in waterfalls than the above, his 
defence of the generation of heat by force fails, and the 
