power of producing wax, and obliterates the hollows in the thighs adapted for the transport of pollen.

The vital principle having accumulated force, can expend it either in animalism, sentiment, or reason. Every animal, except man, expends it on securing its own growth and conservation, and on transmission of vitality to another generation. Such reason as it has, is used to find its food, build its home, and seek out one of another sex. The caterpillar eats its own weight in a day, because it is accumulating the force which will develop it into a butterfly; but when in its imago condition, it scarcely eats, as it has reached the limit of its development. Its butterfly life is the expenditure of what was collected so diligently in its larva state.

Man can at his choice use up that force which he assimilates by his food in perfecting his vegetative life, or in the elaboration of brain matter. The country clown lives a life very little above that of the brute; he consumes a prodigious amount of force and material, and this he converts into muscle, flesh, blood, and sperm. He lives only to sustain his life and propagate his species.

Education tends to precipitate the force acquired upon the cerebral hemispheres; it sends a stream of blood over the whole surface, which oxidizes the grey vascular matter, and this oxidation is a manifestation of the production of thought. In sleep, nature builds up what has been pulled down during the day, adds cells, deepens the convolutions of the brain, and thus exposes more surface to oxidation. The waste and wear is carried off in the urine, as alkaline phosphates. The amount of earthy phosphates present in the urine is found to bear a constant relation to that which is contained in the food, but the amount of alkaline phosphates varies with different conditions of mental action; and

it is found that when severe intellectual exertion has impaired the nutrition of the brain, any premature attempt to renew the activity of its exercise causes the reappearance of an excessive phosphatic discharge.

But all the force absorbed is not at once expended in action. Mental exertion has produced ideas which remain in the mind, and the maintenance of these ideas consumes a large portion of the force received, which thus becomes latent.

Thus

It is not only through food that force passes to the brain; each sense is a force-conductor, as each muscle is a force-liberator. Sights, sounds, scents are modes of motion; nay, even qualities are so much more or so much less force. Thus ice takes up from the surrounding atmosphere a certain amount of heat, which is a form of force: this becomes latent in it when it assumes the state of water. And water absorbs more force to become steam. solidity, liquefaction, vaporization are modes of force. It is evident also that dimension is a modification of force; for dimension is due to the greater or less degree of cohesion in the mass, and this again is due to the amount of heat latent in it. Light is a modification of force. According to the theory now universally received, it consists of a vibratory motion of the particles of a luminous body propagated in waves, which flow in at the pupil of the eye, and, breaking upon the retina at the back, transmit their motion along the optic nerve to the brain, where they announce themselves as consciousness of light, and the perception retained becomes an idea. Sound is the undulation of the air. The force applied by the finger to a harp-string flings the air into agitation, and the ripples sweep in at the ear, vibrate on the tympanum, and are thrilled to the auditory ganglion, where the perception remains as a musical idea.

"The spectrum is to the eye," says Professor Tyndall, "what the gamut is to the ear; its different colours represent notes of different pitch. The vibrations which produce impressions of red are slower, and the ethereal waves which they generate are longer, than those which produce the impression of violet; while the other colours are excited by waves of some intermediate length. The length of the waves, both of sound and light, and the number of shocks which they respectively impart, both to the ear and the eye, have been strictly determined. Let us here go through a simple calculation. Light travels through space at a velocity of 192,000 miles a second. Reducing this to inches, we find the number to be 12,165,120,000. Now, it is found that 39,000 waves of red light, placed end to end, would make up an inch; multiplying the number of inches in 192,000 miles by 39,000, we obtain the number of waves of red light in 192,000 miles: this number is 474,439,680,000,000. All these waves enter the eye in a single second. To produce the impression of red in the brain, the retina must be hit at this almost incredible rate. To produce the impression of violet, a still greater number of impulses is necessary; it would take 57,500 waves of violet to fill an inch, and the number of shocks required to produce the impression of this colour amounts to six hundred and ninety-nine millions of millions per second. The other colours of the spectrum rise gradually in pitch from red to violet. But beyond the violet we have rays of too high a pitch to be visible, and beyond the red we have rays of too low a pitch to be visible.”

I have said that nervous action is a transmission of force. This statement is not merely hypothetical. Nervous 1 Tyndall: Heat as a Mode of Motion, p. 255.

force has been ascertained by experiment to bear a very striking resemblance to electricity, though its difference is also evident. A feeble galvanic current transmitted along the motor nerve of an animal recently killed will produce muscular contraction; whilst, on the other hand, a similar current transmitted along an afferent nerve will excite reflex movement through its ganglionic centre. "However strongly we may be convinced of the absence of identity between nervous and electric forces, it is impossible to be otherwise than impressed with the extraordinary analogy which exists between them. To use Professor Grove's term, they are mutually correlated, and that in the closest degree. Heat, in like manner, if applied to a motor nerve in its course, calls forth muscular contractions, and if applied to a sensory nerve it will occasion sensations, both common and special, precisely after the manner of electricity.

The same may be said of chemical affinity; for if certain reagents be applied to nerve-trunks they may be made to call into action their various endowments, whether these be motory or sensory; whilst, on the other hand, there is ample evidence that the chemical properties of secretions may be greatly changed under the direct influence of nervous force.2

In the brute, every impression through a sense produces a corresponding muscular discharge. We can thus complete the circle. But with man—and the brute which has cerebral hemispheres, and uses them in accumulating ideas -the circle is as yet incomplete. We can trace, say, the force of the impact on the retina of scarlet waves to the

1 Dr. Carpenter on Mattrucci's Lectures, in Medico-Chirurgical Review, 1848.

2 Philosophical Transactions, vol. cxl. (1850), p. 745.

brain, but we see no corresponding liberation of this force. It is therefore taken up, and becomes latent, just as the solar force has become latent in the beds of coal, and is only liberated when the coal is burnt. The force from the stroke of the waves of scarlet light is taken up by the brain, and there becomes a conception. In the formation of the notion the force becomes passive.

Where there is no perception, there is no notion to answer to it. The man blind from his birth can form no conception of scarlet; for the optic ganglia have not been charged with the force which forms the notion of scarlet, and ex nihilo nihil fit applies to notions as well as to material objects.

Thus we can form no notions of that which we have never seen, heard, smelt, or tasted.

Idealization is the accumulation of notions—that is, of fossil percepts. The notions received and the ideas formed out of them remain in the brain. Say an ideal of beauty is formed: the sculptor elaborates it in marble, and runs the pent-up force out of the storehouse where it had lain.

In the beast whose action is sensori-motrix, this action is instinctive; it can hardly be called yet reasoning; the creature receives an impression that awakes an emotion, which produces action. In man, the sensation transmitted to the cerebrum creates a corresponding concept. This, combined with more or less other concepts, produces an idea. Perception is the portal to intellectual action; for while in sensation the conscious mind feels intuitively the physical impulse of the outward object as it affects the consciousness through the sensorium, in idealization the nervous impression is carried a stage farther, and, by virtue of the harmony which exists between the percipient mind and the external world, the sensory impression is intuitively translated into