358 
NATURE 
[August 19, 1886 
exist in both departments of research is a statement 
equivalent to the as yet undisputed assertion that human 
faculties are limited and human knowledge imperfect. 
Nevertheless, some of the difficulties raised by him are 
well worthy of thoughtful consideration. There can be 
no doubt, for instance, that the results of M. Gustav 
Hirn’s experiments on the resistance to motion of air at 
different temperatures are gravely embarrassing to the 
kinetic theory of gases. The resistance ought to vary 
as the square root of the absolute temperature ; it con- 
tinues, nevertheless, practically unchanged at all temper- 
atures, so long as the density remains the same (Comptes 
Rendus, t. Xciv. p. 379)- 
Our author's strictures, however, although couchedin 
terms of praiseworthy moderation and fairness, are some- 
what too indiscriminate. His respect for thoroughgoing 
scientific work is evident and unfeigned ; but it is almost im- 
possible to take up the position of a sceptic ex frufesso, with- 
out at times incurring the reproach of perversity. Weare 
totally unable to see the force of his reasons for preferring 
the obscure notion of a threefold spectrum containing 
chemical rays specifically distinct from thermal, and 
thermal from luminous, to the simple and intelligible view 
which substitutes for intangible differences of quality in 
radiations, measurable differences of wave-length. Nor 
ean we believe that he would, on mature consideration, 
attempt to maintain the opinion that the planetary move- 
ments would remain unaffected by the progressive trans- 
mission of gravity. It is demonstrable that a species of 
aberration would thence ensue involving accelerative 
effects the insensibility of which so far proves (as Laplace 
has shown) that gravitative influence travels at /east fifty 
million times faster than light. We owe the remark to 
Mr. William B, Taylor (S7zthsontan Report, 1876, p. 212), 
that if one minute were spent on the journey from the 
sun to the earth, the consequent slight obliquity of trac- 
tion, represented by an angle of 24, would produce a 
shortening of the year perceptible while the sun was 
finishing a single round of the Signs. 
Prof. Zanon appears to have bestowed much intelligent 
study on spectroscopic science. He carefully examines 
Mr. Lockyer’s discovery of the independent “ behaviour ” 
of iron lines (amongst others) in spots and prominences, 
and though rejecting the inference of dissociation, he 
admits the necessity of assuming an ad /zbztum number 
of allotropic forms of the substance in question in order 
to explain anomalous appearances. He published more- 
over in 1880 a detailed analysis of Mr. Lockyer’s “Studies 
in Spectrum Analysis,” deriving therefrom confirmation 
in many particulars of his own views as to the nature of 
matter. Whatever we may think of these, there can be 
no doubt that our hope of penetrating the mysteries of 
molecular constitution must in future rest on the dis- 
closures of the spectroscope. We do not in the least 
believe that these point towards the conclusion depre- 
cated by Prof. Zanon of a fundamental unity of substance. 
On the contrary, Mr. Lockyer’s striking observations 
indicate (if we may be allowed the expression) divergent, 
rather than convergent, simplifications. 
It is perhaps inevitable in a work of the character of 5 
that now under consideration that the value to science 
of “working hypotheses ” should be taken little account 
of. Yet the story of man’s progressive knowledge of 
nature is a story of tentative efforts to represent facts to 
thought. Without some method of provisionally co- 
ordinating phenomena, indeed, the advance from a lower 
to a higher stage of induction, which we call discovery, 
could scarcely at all be effected. The true investigator is 
he who is never weary of collecting particulars to fit into 
his framework of theory, and of reconstructing his frame- 
work of theory to match fresh particulars. Without the 
power of thinking appearances into shape, no diligence 
in amassing the details of those appearances is of the 
slightest avail. 
There is, it is true, the danger of a working hypothesis 
hardening unduly or prematurely into a theory—of a mere 
track, struc’: out for surveying purposes, turning into a 
fenced highway, without exit save in a quagmire. Against 
this peril the activity of such critics as Prof. Zanon is a 
very effectual safeguard. Their assaults may sometimes 
appear vexatious, but are really directed in the best in- 
terests of science, as hindering false security, and leading 
to a juster estimate of probabilities. 
A. M. CLERKE 
A MANUAL OF MECHANICS 
A Manual of Mechanics; an Elementary Text-Book, 
designed for Students of Applied Mechanics. By 
T. M. Goodeve, M.A. (London: Longmans, 1886.) 
HIS little work is evidently meant for readers whose 
knowledge of mathematics is small. The amount 
of mathematical knowledge supposed may, perhaps, be 
best inferred from an example quoted from the book 
itself. In p. 32 we have the problem to find the resultant 
of two equal rectangular forces, P. If A is the resultant, 
es ay ie FEN By 50 _ 4/49, Re 2 
R= PV2. Now V2 ae 8 very nearly; .-. 
J2 = 7 very nearly. Whence ? at PP.” When the 
5 
angle between the lines of action of the forces is 120°, 
R should be equal to P; but it is proved in p. 33 to be 
equal toP 3, by an unaccountable error in the application 
of an elementary formula. However, 3 is found by 
= 48, 49 
the same process as before. Thus 3 = cae = af, 
SRG a 
very nearly, 7 
Now what naturally strikes one about beginners who 
have to be spoon-fed in this fashion is that it would be 
very much better to spend some time in teaching them 
trigonometry and algebra, than to push them into 
dynamics with the very slender knowledge of arithmetic 
and geometry which they possess. In our system of 
national education there is far too much effort employed 
in bringing branches of dynamics and physics dows te 
the level of the ignorant, and too little in bringing students 
up to the standard of mathematical attainment required 
for a really intelligent knowledge of these subjects. The 
result of this system is that nearly all our elementary 
scientific books are very scrappy in character, presenting 
to their readers conceptions which they cannot possibly 
realise, and which must therefore be crammed into the 
mind as mere definitions devoid of real meaning. 
In elementary scientific treatises it is necessary to 
insist, above all things, that the information given to the 
