"There is a power in natural philosophy, of an influence universal, and yet withal so obscure, in its nature so unobtrusive, that for many ages no idea of it existed. It is called _inertia_. It tends to retain every body in its _present_ state, and seems like the spirit of constancy impressed upon matter. Whatever is in motion is by it retained in motion, and whatever is at rest remains at rest under its sway. It opposes every _new_ influence, strengthens every _old_ one. Is there nothing in the human mind which seems analogous to this power?... "Inertia is an essential property of matter; is it a never-failing attendant on the mind? I hope it is; for as it seems to be in full force whenever the mind is passive, I trust it is also in power when she is actively engaged. Was the idle mind ever yet pleased to be placed in activity? Was the dolt ever willing to resign inanity for perception? Or are they not always found contented to remain as if they were satisfied with their situation? They are like the shepherd Magnus: although on a barren rock, their efforts to remove are irksome and unpleasant; and they seem chained to the spot by a power over which they have no control, of which they have no perception. Again: in activity, what intellectual being would resign his employment? Who would be content to forego the pleasures hourly crowding upon him? Each new thought, perception, or judgment is a sufficient reward in itself for his past labours, and all the future is pure enjoyment. There is a labour in thought, but none who have once engaged in it would willingly resign it. Intermissions I speak not of; 'tis the general habit and tenor of the mind that concerns us, and that which has once been made to taste the pleasures of its own voluntary exertions will not by a slight cause be made to forego them. "Inertia, as it regards matter, is a term sufficiently well understood both in a state of rest and of motion. As it is not my intention to attempt a description of functions of the mind according to strict mathematical terms, I shall resign the exclusive use of the word at present, and adopt two others, which, according to the sense they have acquired from usage, will, I believe, supply its place with accuracy. Apathy will represent the inertia of a passive mind; industry that of an active mind. "It is curious to consider how we qualify ideas essentially the same, according to the words made use of to represent them. I might talk of mental inertia for a long time without attaching either blame or praise to it--without the chance even of doing so; but mention apathy and industry, and the mind simultaneously censures the one and commends the other. Yet the things are the same, both idleness and industry are habits, and habits result from inertia....