118 
without involving the idea of its correlate, depth ; the idea of 
parent cannot exist without involving the idea of offspring. 55 
But, notwithstanding this, he almost immediately after says it 
is “ a necessary reciprocal production. 55 It is manifest that the 
idea of parent cannot exist without the idea of child, and that 
consequently they are correlates ; but it is equally manifest that 
they are not reciprocally productive, for while the parent pro- 
duces the child, it would be difficult for the child “ in its turn 55 
to produce the parent : it may become a parent to another child, 
but it cannot produce the parent from whom itself has de- 
scended. According to Mr. Grove’s own definition, the im- 
ponderables may be, in certain cases, the condition of each 
other’s existence ; but they may not become each other. He 
again confounds production and conversion when he says, 
speaking of heat, light, &c., “ that either may produce, or be 
convertible into, any of the others. 55 Production is not con- 
version ; the parent produces the child, but surely he is not 
converted into the child. A seed of com produces a full head 
of corn, but it is not converted into it. But his language on 
this point is so confused, he at one time making distinctions 
without differences, and at others confounding things that 
differ, that it is impossible to arrive at any distinct conception 
of the nature of his own belief. It seems, however, to partake 
more of the nature of conversion than of correlation ; but in 
spite of that, we have sufficient grounds to justify the assertion 
that while the physical forces no doubt, in certain cases, con- 
dition the existence of each other, there is not sufficient evidence 
to enable us to say that they are convertible into each other. 
38. The theory of the Dissipation of Energy is held by Mr. 
Moore to be inconsistent with that of its Conservation. But here 
I am reluctantly forced to differ from him. The theory is, that 
while one mode of motion produces certain other modes, such as 
electricity, electricity can reproduce motion, but not the exact 
amount of the original motion. Some has been rendered incapable 
of reconversion, because it has become heat, and been radiated 
by earth into space, and thus lost for all practical purposes, or, 
as it is called, dissipated. Still the theory of conservation 
is theoretically consistent, inasmuch as, although allowing the 
departure of the motion from the earth, it asserts its con- 
tinuance in the ethereal medium filling space. While, how- 
ever, allowing all this, we are hereby taught that “ conservation 
of energy 55 in reference to the earth, really means nothing more 
than that energy is conserved, till it is finally lost ; for Pro- 
fessors Tait and Thomson tell us that, in consequence of the 
energy of all the planets eventually losing its kinetic form, they 
must creep in age by age towards the sun to a fiery end. But 
