266 Proceedings of the Eoyal Society 
and implies the existence of Law in the wider sense. An observed 
order of facts — assuming, of course, that the order is constant 
under the same conditions — implies the action of some force of 
which that order is the index and the result. But the mere 
general idea that some force is at the bottom of all phenomena 
which are invariably consecutive, is a very different thing from 
knowing what that force is, in respect to the rule or measure of its 
operation. It is, indeed, the great object of pure science, to 
ascertain the measures of force. Mr Lewes, in the very curious and 
interesting work which he has lately published on the philosophy 
of Aristotle, has maintained that the knowledge of measure — or 
what he calls the “verifiable element” incur knowledge — is the 
element which determines whether any theory belongs to science, 
or to metaphysics ; and that any theory may be transferred from 
metaphysics to science, or from science to metaphysics, simply by 
the addition or withdrawal of its “verifiable element.” In illus- 
tration of this he says, that if we withdraw the formula “ inversely 
as the square of the distance, and directly as the mass,” from the law 
of universal attraction, “ it becomes pure metaphysics.”* If this 
means that, apart from ascertained numerical relations, our concep- 
tion of law loses all reality and distinctness, I do not agree in 
the position. I think the idea of natural forces is quite separate 
from any ascertained measurement of their energy ; that, for 
example, the knowledge that all the particles of matter exert an 
attractive force upon each other, is, so far as it goes, true physical 
knowledge, even though we did not know the farther truth that this 
force acts according to the numerical rule ascertained by Newton. 
That matter attracts matter is a definite idea, — although it is less 
definite, or less complete than tbe idea that the measure of that 
attraction is “ directly as the mass, and inversely as the square of 
the distance.” This is undoubtedly the highest, or perhaps I ought 
to say, the ultimate, conception of a scientific “ law,” — force 
ascertained according to some method and measure of its operation. 
But now we must go a step farther. What is force ? What is 
our conception of it ? What idea can we form, for example, of the 
real nature of that force, the measure of whose operation has been 
^ Aristotle. By G. H. Lewes. P. 84. 
