Prof. Olmsted’s Reply to Dr. Hare. 363 
‘The reasoning in my essay, which Professor Olmsted has 
overluoked, is as follows -—As, in order for on y 
bodies in motion, to resist another body or set of bodies in the 
same state, the velocity must be as much greater as the weight 
by any force arising from their motion, impart to the oe of a 
i I air should 
Has not Dr. Hare plainly fallen into a mistake here? It 
evidently is not heat which moves the piston of a steam-en- 
gine, but itis the elastic force of steam. ‘ But, (it may be — 
ed,) is not that elasticity caused by heat?” True; but the 
effect is not the same thing with the cause. It is difficult to 
see why heat should impart such wonderful power to steam, 
nor does our supposing it to be a material fluid diminish this 
difficulty. Has not the Doctor, committed a similar mis- 
take, in understanding Sir Humphrey Davy to assert, that 
heat is motion, whereas his doctrine is that motion is the cause 
of heat. The words are as follows: ‘‘ The immediate cause 
of the phenomena of heat, then, is motion.” (Ure’s Diction- 
ary, Hare’s Edition, Art. Caloric. 
Finally, I beg leave to repeat that, in my view, Gur rea- 
sonings on physical subjects must stop when we arrive at one 
of those principles denominated ultimate agents, namely, at- 
traction, heat, light, electricity and magnetism; that all at- 
tempts to ascertain the nature of these agents, have hitherto 
roved unsuccessful; and that, in the present state of our 
die 
, we have no means of ,Ww i 
severally depend on the operations of peculiar material fluids 
or not.. And though, to avoid cireumlocution, it may be 
convenient to speak of these agents as fluids, yet such a use 
of the term ougbt not to be understood as conveying any 
pinion respecting their specific nature. 
