a 
Feb. 27, 1873] 
Optical contact indicates only that the distance between 
the surfaces is much less than a wave-length of light. 
To show that the surfaces are not in real contact, I 
remove the weights. The rings contract, and several of 
them vanish at the centre. Now it is possible to bring 
two pieces of glass so close together, that they will not 
tend to separate at all, but adhere together so firmly 
that when torn asunder the glass will break, not at the 
surface of contact, but at some other place. The glasses 
must now be many degrees nearer than when in mere 
optical contact. 
Thus we have shown that bodies begin to press against 
each other while still at a measurable distance, and that 
even when pressed together with great force they are not 
in absolute contact, but may be brought nearer still, and 
that by many degrees. ‘ 
Why, then, say the advocates of direct action, should 
we continue to maintain a doctrine founded only on the 
rough experience of a pre-scientific age, that matter can- 
not act where it is not, instead of admitting that all the 
facts from which our ancestors concluded that contact is 
essential to action were in reality cases of action at a dis- 
tance, the distance being too small to be measured by their 
imperfect means of observation ? 
If we are ever to discover the laws of nature, we must 
do so by obtaining the most accurate acquaintance with 
the facts of nature, and not by dressing up in philo- 
sophical language the loose opinions of men who had no 
knowledge of the facts which throw most light on these 
laws. 
And as for those who introduce etherial, or other 
media, to account for these actions, without any direct 
evidence of the existence of such media, or any clear 
understanding of how the media do their work, and who 
fill all space three and four times over with ethers of 
different sorts, why the less these men talk about their 
philosophical scruples about admitting action at a 
distance the better. 
If the progress of science were regulated by Newton’s 
first law of motion, it would be easy to cultivate opinions 
in advance of the age. We should only have to compare 
the science of to-day with that of fifty years ago, and by 
producing, in the geometrical sense, the line of progress, 
we should obtain the science of fifty years hence. 
The progress of science in Newton’s time consisted in 
getting rid of the celestial machinery with which gene- 
rations of astronomers had encumbered the heavens, and 
thus “ sweeping cobwebs off the sky.” 
Though the planets had already got rid of their crystal 
spheres, they were still swimming in the vortices of 
Descartes. Magnets were surrounded by effluvia, and 
electrified bodies by atmospheres, the properties of which 
resembled in no respect those of ordinary effluvia and 
atmospheres. 
When Newton demonstrated that the force which acts 
on each of the heavenly bodies depends on its relative 
position with respect to the other bodies, the new theory 
met with violent opposition from the advanced philo- 
sophers of the day, who described the doctrine of gravi- 
tation as areturn to the exploded method of explaining 
everything by occult causes, attractive virtues, and the 
ike. 
Newton himself, with that wise moderation which is 
characteristic of all his speculations, answered that he 
made no pretence of explaining the mechanism by which 
the heavenly bodies act on each other. To determine the 
mode in which their mutual action depends on their 
relative position was a great s'ep in science, and this step 
Newton asserted that he had made. To explain the pro- 
cess by which this action is effected was a quite distinct 
_ Step, and this step, Newton, in his “ Principia,” does not 
- attempt to make, 
But so far was Newton from asserting that bodies really 
do act on one another at a distance, independently of any- 
NATURE 
SS Se ee ee eS eee eee eee 
325 
thing between them, that in a letter to Bentley which has 
been quoted by Faraday in this place, he says :— 
“ It is inconceivable that inanimate brute matter should, 
without the mediation of something else, which is not ma- 
terial, operate upon and affect other matter without mutual 
contact, as it must do if gravitation, in the sense of Epi- 
curus, be essential and inherent in it... . That gravity 
should be innate, inherent, and essential to matter, so that 
one body can act upon another at a distance, through a 
vacuum, without the mediation of anything else, by and 
through which their action and force may be conveyed 
from one to another, is to me so great an absurdity, that I 
believe no man who has in philosophical matters a com- 
petent faculty of thinking can ever fall into it.” 
Accordingly, we find in h’s “ Optical Queries,” and in his 
letters to Boyle, that Newton had very early made the at- 
tempt to account for gravitation by means of the pressure 
of a medium, and that the reason he did not publish these 
investigations “proceeded from hence only, that he found 
he was not able, from experiment and observation, to give 
a satisfactory account of this medium, and the manner of 
its operation in producing the chief phenomena of na- 
ture.” * 
The doctrine of direct action at a distance cannot claim 
for its author the discoverer of universal gravitation. It 
was first asserted by Roger Cotes, in his preface to the 
“ Principia,” which he edited during Newton’s life. Ac- 
cording to Cotes, it is by experience that we learn that all 
bodies gravitate. We do not learn in any other way that 
they are extended, mov able, or solid. Gravitation, there- 
fore, has as much right to be considered an essential pro- 
perty of matter as extension, mobility, or impenetrability. 
And when the Newtonian philosophy gained ground in 
Europe, it was the opinion of Cotes rather than that of 
Newton that became most prevalent, till at last Boscovich 
propounded his theory, that matter is a congeries of ma- 
thematical points, each endowed with the power of attract- 
ing or repelling the others according to fixed laws. In his 
world, matter is unextended, and contact is impossible. 
He did not forget, however, to endow his mathematical 
points with inertia. In this some of the modern repre- 
sentatives of his school have thought that he “had not 
quite got so far as the strict modern view of ‘matter’ as 
being but an expression for modes or manifestations of 
“force, at ; 
But if we leave out of account for the present the de- 
velopment of the ideas of science, and confine our atten- 
tion to the extension of its boundaries, we shall see that 
it was most essential that Newton’s method should be 
extended to every branch of science to which it was appli- 
cable—that the forces with which bodies act on each other 
should be investigated in the first place, before attempting 
to explain “ow that force is transmitted. Nomen could 
be better fitted to apply themselves exclusively to the first 
part of the problem, than those who considered the second 
part quite unnecessary. ; 
Accordingly Cavendish, Coulomb, and Poisson, the 
founders of the exact sciences of electricity and mag- 
netism, paid no regard to those old notions of “magnetic 
effluvia” and “ electric atmospheres,” which had been put 
forth in the previous century, but turned their undivided 
attention to the determination of the law of force, accord- 
ing to which electrified and magnetised bodies attract or 
repel each other. In this way the true laws of these 
actions were discovered, and this was done by men who 
never doubted that the action took place at a distance, 
without the intervention of any medium, and who would 
have regarded the discovery of such a medium as com- 
plicating rather than as explaining the undoubted pheno- 
mena O! attraction. 
(To be continued.) 
* Maclaurin’s Account of Newton's Discoveries. ak, 
+ Review of Mrs. Somerville’s “ Molecular Science,” Saiurday Review, 
Feb, 13, 1869. 
