that the facts occur as if the principle existed.

The manner in which Faraday himself habitually deals with his
hypotheses is revealed in this lecture. He incessantly employed
them to gain experimental ends, but he incessantly took them down,
as an architect removes the scaffolding when the edifice is complete.
'I cannot but doubt,' he says, 'that he who as a mere philosopher
has most power of penetrating the secrets of nature, and guessing by
hypothesis at her mode of working, will also be most careful for his
own safe progress and that of others, to distinguish the knowledge
which consists of assumption, by which I mean theory and hypothesis,
from that which is the knowledge of facts and laws.' Faraday
himself, in fact, was always 'guessing by hypothesis,' and making
theoretic divination the stepping-stone to his experimental results.

I have already more than once dwelt on the vividness with which he
realised molecular conditions; we have a fine example of this
strength and brightness of imagination in the present 'speculation.'
He grapples with the notion that matter is made up of particles, not
in absolute contact, but surrounded by interatomic space. 'Space,'
he observes, 'must be taken as the only continuous part of a body so
constituted. Space will permeate all masses of matter in every
direction like a net, except that in place of meshes it will form
cells, isolating each atom from its neighbours, itself only being
continuous.'

Let us follow out this notion; consider, he argues, the case of a
non-conductor of electricity, such for example as shell-lac, with
its molecules, and intermolecular spaces running through the mass.
In its case space must be an insulator; for if it were a conductor