Se — 
SEPTEMBER I1, 1913] 
have not extended our laboratory inductions too far. 
The conservation of energy, for instance: is it always 
and everywhere valid; or may it under some condi- 
tions be disobeyed? It would seem as if the second 
law of thermodynamics must be somewhere disobeyed 
—at least, if the age of the universe is both ways 
infinite—else the final consummation would have 
already arrived. 
Not by philosophers only, but by scientific men also, 
ancient postulates are being pulled up by the roots. 
Physicists and mathematicians are beginning to con- 
sider whether the long known and well established 
laws of mechanics hold true everywhere and always, 
or whether the Newtonian scheme must be replaced 
by something more modern, something to which 
Newton's laws of motion are but an approximation. 
Indeed, a whole system of non-Newtonian mechanics 
has been devised, having as its foundation the recently 
discovered changes which must occur in bodies moving 
at speeds nearly comparable with that of light. It 
turns out, in tact, that both shape and mass are 
functions of velocity. As the speed increases the mass 
increases and the shape is distorted, though under 
ordinary conditions only to an infinitesimal extent. 
So far | agree; I agree with the statement of fact; 
but I do not consider it so revolutionary as to over- 
turn Newtonian mechanics. After all, a variation of 
mass is familiar enough, and it would be a great 
mistake to say that Newton’s second law breaks down 
merely because mass is not constant. A raindrop is 
an example of variable mass; or the earth may be, by 
reason of meteoric dust; or the sun, by reason of 
radio-activity; or a locomotive, by reason of the 
emission of steam. In fact, variable masses are the 
commonest, for friction may abrade any moving body 
to a microscopic extent. 
That mass is constant is only an approximation. 
That mass is equal to ratio of force and acceleration 
is a definition, and can be absolutely accurate. It 
holds perfectly even for an electron with a speed near 
that of light; and it is by means of Newton’s second 
law that the variation of mass with velocity has been 
experimentally observed and compared with theory. 
I urge that we remain with, or go back to, Newton. 
I see no reason against retaining all Newton’s laws, 
discarding nothing, but supplementing them in the 
light of further knowledge. 
Even the laws of geometry have been overhauled, 
and Euclidean geometry is seen to be but a special 
case of more fundamental generalisations. How far 
they apply to existing space, and how far time is a 
reality or an illusion, and whether it can in any sense 
depend on the motion or the position of an observer : 
all these things in some form or other are discussed. 
The conservation of matter also, that main-mast of 
nineteenth-century chemistry, and the existence of the 
zther of space, that sheet-anchor of nineteenth-century 
physics—do they not sometimes seem to be going by 
the board? } 
Prof. Schuster, in his American lectures, commented 
on the modern receptive attitude as follows :— 
“The state of plasticity and flux—a healthy state, 
in my opinion—in which scientific thought of the 
present day adapts itself to almost any novelty, is 
illustrated by the complacency with which the most 
cherished tenets of our fathers are being abandoned. 
Though it was never an article of orthodox faith that 
chemical. elements were immutable and would not 
some day be resolved into simpler constituents, yet the 
conservation of mass seemed to lie at the very founda- 
tion of creation. But nowadays the student finds 
little to disturb him, perhaps too little, in the idea 
that mass changes with velocity; and he does not 
always realise the full meaning of the consequences 
which are involved.” 
NO. 2289, VOL. 92] 
NATURE 
ao 
This readiness to accept and incorporate new facts 
into the scheme of physics may have led to perhaps 
an undue amount of scientific scepticism, in order to 
right the balance. 
But a_ still deeper variety of comprehensive 
scepticism exists, and it is argued that all our laws 
of nature, so laboriously ascertained and carefully 
formulated, are but conventions after all, not truths; 
that we have no faculty for ascertaining real truth; 
that our intelligence was not evolved for any such 
academic purpose; that all we can do is to express 
things in a form convenient for present purposes and 
employ that mode of expression as a tentative and 
pragmatically useful explanation. 
Even explanation, however, has been discarded as 
too ambitious by some men of science, who claim only 
the power to describe. They not only emphasise the 
how rather than the why—as is in some sort inevitable, 
since explanations are never ultimate—but are satisfied 
with very abstract propositions, and regard mathe- 
matical equations as preferable to, because safer than, 
mechanical analogies or models. 
“To use an acute and familiar expression of Gustav 
Kirchhoff, it is the object of science to describe natural 
phenomena, not to explain them. When we have ex- 
pressed by an equation the correct relationship be- 
tween different natural phenomena we have gone as 
far as we safely can, and if we go beyond we are 
entering on purely speculative ground.”’ 
But the modes of statement preferred by those who 
distrust our power of going directly into detail are 
far from satisfactory. Prof. Schuster describes and 
comments on them thus :— 
““Vagueness, which used to be recognised as our 
great enemy, is now being enshrined as an idol to be 
worshipped. We may never know what constitutes 
atoms, or what is the real structure of the zther; why 
trouble, therefore, it is said, to find out more about 
them. Is it not safer, on the contrary, to confine our- 
selves to a general tallk on entropy, luminiferous 
vectors, and undefined symbols expressing vaguely 
certain physical relationships? What really lies at 
the bottom of the great fascination which these new 
doctrines exert on the present generation is sheer 
cowardice; the fear of having its errors brought home 
EGH EUs ae ok's 
““T believe this doctrine to be fatal to a healthy 
development of science. Granting the impossibility 
of penetrating beyond the most superficial layers of 
observed phenomena, I would put the distinction 
between the two attitudes of mind in this way: One 
glorifies our ignorance, while the other accepts it as a 
regrettable necessity.” 
In further illustration of the modern sceptical atti- 
tude, I quote from Poincaré :— 
“Principles are conventions and definitions in dis- 
guise. They are, however, deduced from experi- 
mental laws, and these laws have, so to speak, been 
erected into principles to which our mind attributes 
an absolute value... .« 
‘‘The fundamental propositions of geometry, for 
instance Euclid’s postulate, are only conventions; and 
it is quite as unreasonable to ask if they are true or 
false as to ask if the metric system is, true or false. 
Only, these conventions are convenient... . 
“Whether the zther exists or not matters little—let 
us leave that to the metaphysicians; what is essential 
for us is that everything happens as if it existed, 
and that this hypothesis is found to be suitable for the 
explanation of phenomena. After all, have we any 
other reason for believing in the existence of material 
objects? That, too, is only a convenient hypothesis.” 
As an antidote against overpressing these utter- 
ances, I quote from Sir J. Larmor’s preface:— 
“There has been of late a growing trend of opinion, 
