NATURE OF THE GROUNDWORK OF SCIENCE 299

of what is physical and material, and (B) a division made up

of what is mental and ideal.

The first division includes all extended bodies and their

energies ; for no concrete existence can possibly be merely

passive, but must actively respond to stimuli (as iron to

the blacksmith's hammer) according to definite internal laws,

by which powers and activities it is we recognize the nature

of each such concrete existence.

Some readers may object to our subdivision of the matter

of science on the ground that we have assigned no place

to entities of such supreme importance as the various physical

energies.

\Ve have not, however, really omitted them, for we include

them amongst the active powers of material bodies. \Ve

have no experience of any physical energy save in connection

with some extended substance from which it is sometimes

said to emanate, and thence to be transmitted to others.

But the terms energy, force, light, heat, sound, etc., are but so

many abstract terms. We have no evidence that they can

really denote "substances," but only certain real actions

of real bodies considered in the abstract. Thus light and

heat are commonly thought of as set going on their radiant

but very unequal course by the fires of the sun (as one

source), and thence transmitted by the universally- disposed

ether to the surrounding bodies of the solar system beyond.

Similarly, the vibratory agitation of some sensuous body sets

going corresponding vibrations in the air, which may ultimately

cause similar agitations within the ears of men and animals,

so giving rise ultimately to what we know as " sounds."

This way of speaking of the transmission of energies has

not unnaturally arisen from the discovery of what was

originally termed ''the correlation of the physical forces,"

in other words, the discovery of the quantitative equivalence

which exists between the different kinds of actions which

of what is physical and material, and (B) a division made up

of what is mental and ideal.

The first division includes all extended bodies and their

energies ; for no concrete existence can possibly be merely

passive, but must actively respond to stimuli (as iron to

the blacksmith's hammer) according to definite internal laws,

by which powers and activities it is we recognize the nature

of each such concrete existence.

Some readers may object to our subdivision of the matter

of science on the ground that we have assigned no place

to entities of such supreme importance as the various physical

energies.

\Ve have not, however, really omitted them, for we include

them amongst the active powers of material bodies. \Ve

have no experience of any physical energy save in connection

with some extended substance from which it is sometimes

said to emanate, and thence to be transmitted to others.

But the terms energy, force, light, heat, sound, etc., are but so

many abstract terms. We have no evidence that they can

really denote "substances," but only certain real actions

of real bodies considered in the abstract. Thus light and

heat are commonly thought of as set going on their radiant

but very unequal course by the fires of the sun (as one

source), and thence transmitted by the universally- disposed

ether to the surrounding bodies of the solar system beyond.

Similarly, the vibratory agitation of some sensuous body sets

going corresponding vibrations in the air, which may ultimately

cause similar agitations within the ears of men and animals,

so giving rise ultimately to what we know as " sounds."

This way of speaking of the transmission of energies has

not unnaturally arisen from the discovery of what was

originally termed ''the correlation of the physical forces,"

in other words, the discovery of the quantitative equivalence

which exists between the different kinds of actions which