travel with a rotation of about twenty-five thousand miles. every minute.

Again: if, with Newton, we call the sun a body of fire, the language is harmless, so long as we use it to designate the phenomena merely which the sun exhibits; but if we intend to deduce consequences, the phraseology is essential thus, as the planet Saturn is ten times further from the sun than our earth, and as fire dispenses heat and illumination in a degree which distance diminishes in a ratio equal to the square of the distance, we enjoy a hundred times more light and heat than Saturn. This piteous conclusion is accordingly predicated of Saturn. The poor inhabitants of that planet are, however, not permitted to exist with these privations only, but more adventurous theorists urge the deductive process further, and prove that water exists among them in solidity only, and consequently they know not the luxury of fish. Humanity must rejoice, that these distressful consequences are avoidable, by the simple contrivance of a late philanthropist, who has extinguished the solar fire, and converted the sun into a radiating fluid, which becomes hot only when it falls on solid bodies. The heat is produced by a combination of the fluid with the bodies on which it falls, precisely as water evolves heat, when thrown on unslaked lime. We need, therefore, no longer wonder why comets are not vitrified. Mercury is made salubrious, and even Herschel a pleasant

retreat.

Again: the phenomena exhibited by the barometer and air pump, were formerly reconciled to our operations, by asserting that nature abhors a vacuum. Latterly we say that they are produced by atmospherical pressure. It is immaterial which expression we adopt, so long as we in

tend to designate the phenomena only; but the expression becomes important when we design to deduce consequences beyond the phenomena: thus, if a column of water ascends in a vacuum by reason of atmospherical pressure, we can calculate, by the ascended water, the force of the pressure; and prove that a man of ordinary dimensions sustains a pressure of fourteen tons. This immense burden was first imposed on us about two centuries ago, and it may now be removed if we return to the old phraseology of nature's horror of a vacuum. However, it is better to continue the burden, (as we carry it with great convenience) and it accords with more phenomena than the discarded theory.

I might accumulate deductions which, like the foregoing, depend for their significance on the name by which speculative men designate their premises; but I have probably produced enough to disclose the principle on which such speculations are founded. Every person may find as many further examples as he desires, for he can resort to no science in which they are not prodigally scattered.

It may be proper to remark that, while I descant so freely on received theories, I do not wish to depreciate their usefulness. My whole object is to illustrate the nature of language. If theories are beneficial to science, it is also beneficial that we should discriminate between theoretical agents and the realities of nature: for example, when we say that water ascends in a vacuum, by means of the pressure of the atmosphere, the word pressure is the theoretical agent by which we account for the ascent of the water. Now, if we would escape from the delusions of language, we must steadily distinguish that

this theoretical agent is wholly different from the feel to which the word pressure is ordinarily applied. The feel is a reality of nature, but the pressure, which is attributed to the atmosphere, is merely verbal. It cannot be felt or seen, nor is it palpable to any of our senses. We see the water ascend in the vacuum, but the pressure, which we say causes the ascent, is merely the verbal machinery by which we account for the ascent.

The word pressure, like every other word, has no invariable signification, nor has it any inherent signification. It is a mere sound, whose signification is governed by the phenomenon to which we attach it. When it is applied to the effort of my hand against this table, it names a feel; and when applied to the ascent of water in a vacuum, it names the ascent. If we suppose it names also some insensible operation of the air on the water, this is merely our theory, which signifies nothing; or rather it signifies all the phenomena to which we refer in proof of the pressure: beyond these the word pressure returns again to its pristine insignificance, as a mere sound.

If we keep in view this distinction between theoretical agents and the realities of nature, we shall at once discover the absurdity of continuing the employment of these agents beyond the uses which they subserve to science. If the attribution of a pressure to air enables us to systematically embody numerous phenomena which are exhibited by the air pump and barometer, &c., the attribution is valuable; but there is no use in continuing the verbal machinery beyond this utility, and in deducing therefrom that every man sustains a pressure of fourteen tons ;-a conclusion which I believe is not subservient to

any use, and is therefore only an evidence that the persons who make the deduction are ignorant of the nature of theories, and do not discriminate between the verbal agents of a theory, and the phenomena of nature.

That we may better understand these verbal agents, I will examine the principle which governs us in the selection of them. They are creatures of our own fabrication, as their mutability evinces. At one time we prop up the heavens by the shoulders of Atlas, or support the earth on the back of a tortoise; at another we remove both the props and support, and sustain the earth by attraction and propulsion. The character of all these instruments is alike, though they vary in usefulness. The shoulder of Atlas would be preferable to the attraction and propulsion of Newton, if it would apply consistently to a greater number of phenomena.

I wish then to direct your attention to the principle that governs us in the selection of the verbal agents which we employ in our theories. This shall constitute our next Lecture, lest, by a union of different subjects in the same discourse, the understanding should become perplexed.

LECTURE XI.

In my last Lecture, I showed that theorists deduce consequences from names, without regarding the fact, that names vary in signification with the objects to which they are applied. The word Cæsar, which, in one application, is an emperor; becomes, by another application, a quadruped. Even thus varies the signification of round, when applied to the earth, from what the same word signifies when it designates an artificial sphere.

This error is most effective in the verbal agents with which we construct our theories. The earth's motion around its axis, at the rate of 700 to 1000 miles an hour; and its motion around the sun, at the rate of 58000 miles in the same period, are the theoretical agents by which we account for the phenomena exhibited by the heavenly bodies. Few persons estimate this motion as a word which is significant of nothing but the phenomena that it is applied to elucidate, but they estimate it as possessing