Notices respecting New Books. 511 
of expression occurs here and there. Thus the opening lines 
run :— 
“We give the name of matter to that which we regard as the 
permanent cause of any of our sensations.” 
This definition would surely include heat, light, railway accidents, 
&e. Again the term velocity nowadays has surely the unique 
definite meaning of “space described (or capable of description) in 
a time-unit ;” but the term is used in several places as if it had 
a simply spatial meaning, e.g. (p.-28) “a velocity of 400 feet,” 
(p. 29) ‘‘ the velocity per minute,” and similar instances in many 
other places. AtLan Cunninenam, Major, AL. 
Energy and Motion. A Textbook of EKlementary Mechanics. 
By W. Patcr, M.A. Cassell and Co. (Pp. 114.) 
THIs is one more of the legion of small textbooks of elementary 
science the razson d’étre of which it is hard to discover. The pre- 
face states that there “‘ appear to be no good books on the subject 
which approach it from a sufficiently elementary standpoint ;” but 
we fear that this book put into the hands of ordinary schoolboys or 
schoolgirls, unless supplemented by good oral teaching, will make 
too large demands upon their intelligence. ‘There are a few good 
points of more or less novelty to be noted, but these are more than 
counterbalanced by erroneous teaching upon certain important 
matters. A few instances will suffice. The specification of an 
acceleration as “23 feet per second per second,” or as ‘‘ 24,000 
yards per minute per minute,” is no doubt to be commended; but 
such unusual accuracy contrasts, unfortunately, with such state- 
ments as that “‘ 1 horse-power is equal to 550 foot-pounds ” (p. 61) ; 
or that “to produce a velocity v in m units of mass, or to stop the 
mass m if moving with a velocity v, would require mv units of 
force” (p. 44). 
The author seems to be of opinion that the formula s = 3 ft.’ 
does not admit of rigorous proof, but always involves some assum p- 
tion. Certainly he makes an assumption (p. 13); but using the 
word “therefore,” he gives his readers no hint of this when he says, 
“When a moving body is uniformly accelerated the increase of 
velocity is the same throughout for every equal small portion of 
time, therefore the distance passed over will be the same as if the 
body moved uniformly with the average velocity for the whole 
number of small spaces of time—that is, for the whole time.” 
The statement on p. 39, “Ifa bullet of lead and another of 
wood of the same size be thrown at the same time with the same 
velocity, the bullet of lead wili go further than the bullet of wood ” 
needs no comment; it is sufficient to quote it. The meaning of 
“mass” is not explained by saying that there is more of ‘“‘ some- 
thing” in a leaden bullet than in a wooden bullet of equal size; 
and the statement that there is more “matter” or “stuff” in a 
cubic inch of gold than in a cubic inch of water has simply no 
meaning at all. Until it is proved that gold is a compound of 
hydrogen and oxygen, in the proportions in which they occur in 
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