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energy, that lias been expended in burlesqueing physical energy 
had been devoted to obtaining a fuller comprehension of the 
subject, the cause of truth might not have been more efficiently 
promoted. 
59. Two further points only of Dr. McCann’s paper will here 
be remarked upon. The quotation (§ 20) from Mr. Spencer’s 
First Principles is an elaborate but, to my mind, confused 
statement of the perfectly distinct and definite ideas of absolute 
and relative motion. He writes — “ A body impelled by the 
hand is clearly perceived to move, and to move in a definite 
direction/’ i. e., relatively to the perceiver and surrounding 
objects, beyond which perception cannot extend, for the per- 
ception must obviously be the same whether the observer were 
absolutely at rest in space, or whether he and the observed 
body partake alike of the earth’s rotation on its axis and 
revolution round the sun, and the progression, if any, of the 
entire solar system in space, and any other motion or motions, 
conceivable or inconceivable — and that is the whole question. 
60. In reference to Mr. Spencer’s gratuitous assumption (§ 1) 
that the various forms of physical and mental energy are recip- 
rocally convertible, he writes (§41): — “That such is a fact 
may be assumed but can never be proved till some instrument 
be constructed capable of measuring the velocity of thought ; ” 
evidently not being aware that such an instrument had been 
constructed some years since, and satisfactory experiments made 
by Drs. Hirsch, De Jaager, and Donders ; * but they afford no 
confirmation of Mr. Spencer’s assumptions, beyond the fact 
that time is an element in mental operations ; but until the 
precise train of physical changes in the brain and nerves which 
accompanies perception and thought can be fully ascertained 
(an amount of knowledge obviously beyond the reach of man), 
the hypothesis in question must be held to be insusceptible 
of proof. 
61. It may, in conclusion, be remarked with much regret that 
the principle of the conservation of energy has by some been 
misapplied to questions far beyond its legitimate scope, in a 
fruitless endeavour to supersede the necessity of an omniscient 
Creator. To the mind of the writer, and, it is earnestly hoped, 
to that of most of his hearers and readers, the indisputable esta- 
blishment of this principle conveys only a more exalted idea of 
that infinite wisdom by which the perpetually recurring trans- 
formations and interchanges, not only of the materials, but also 
of the powers, of Nature are rendered subservient to predeter- 
mined laws, which govern the comfort and welfare of all created 
* Elements of Natural Philosophy , sixth edition, p. 568. 
