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vention of this beautiful instrument, a prepared frog was considered the most delicate test of galvanic electricity. But it has been found, that the multiplier is not only a far nicer test of electricity, but that it is also the most delicate thermoscope ever invented-that part of a degree of Fahrenheit's thermometer produces a sensible movement of a small needle suspended by a fibre of silk. From which it follows, that magnetic phenomena are not confined to the action of electricity, but also result from the agency of caloric in quantities too small for measurement by any other test.

It is therefore not a little surprising, that when Dr. Faraday offered as a proof, that all the varieties of electricity are essentially the same, because they all produce magnetic effects, that he did not recognize the identity of caloric and electricity.

Guided by the general fact discovered by Ersted, that a magnetic needle placed over the wire connecting the poles of a battery in action has a tendency to arrange itself at right angles to the conducting wire, Schweigger covered a common brass wire with silk thread, for the purpose of insulating it. This wire was then lapped round a piece of wood, 50, 100, or 200 times. When its two extremities were connected with the poles of a battery in action, the galvanic current passes through all the windings of the wire, by which the magnetic effects are multi

plied with every turn of the wire; so that when a magnetic needle is suspended in the middle of the hank of wire, it is placed at right angles to it. In this way the power of the multiplier was made to detect, not only minute portions of electricity that could not be otherwise appreciated, but the smallest changes of temperature, as before observed.*

By an improvement of this important instrument, MM. Nobili and Melloni were enabled to detect the heat of phosphorescent wood, dead fish, living insects, and that of the different coloured rays of the solar spectrum. But it was previously discovered by Dr. Seebeck of Berlin, that when a circuit is formed by soldering together two metals, and applying the heat of a lamp to one of the junctions, a needle placed within it was deflected from the magnetic meridian, and placed at right angles to the metals forming the circuit. It was afterwards found by Dobereiner, that the heat of the hand was sufficient to cause a deflection of the needle, when applied to the junction of the two metals—and by others, that the same effect was produced by applying ice, æther, or any thing which alters the temperature in one part of the circuit from that of the

It was also by wrapping a piece of soft iron, bent in the form of a horse shoe, with insulated copper wire, and connecting its extremities with the poles of a galvanic battery, that Professor Moll of Utrecht was enabled to convert it into a temporary magnet of great power.

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rest. M. Becquerel found, that when one end of the multiplying wire was heated and brought in contact with the other end, the needle was deflected. Hundreds of similar experiments might be adduced, all of which demonstrate the agency of caloric in producing magnetism, where there is no sign whatever of electric tension; and that the magnetic needle is a true test of the smallest quantities of caloric that have ever been measured.

Some of the most delicate experiments on record were performed by Dr. Locke of Cincinnati. By interposing one quarter of a grain of antimony between the two copper wires of a multiplier, and applying the warmth of his finger, the needle was deflected 22o. In another experiment, one of the copper wires was laid upon the other, without the interposition of any other metal, and the warmth of the hand applied as before, when the needle was deflected 6°. The same results were obtained by substituting the warmth of the breath instead of that of the hand. The temperature of the room in which the experiments were made was 65°. F. (American Journal of Science, April, 1834.)

But the most decisive proof that caloric and electricity are only modifications of one and the same agent is, that they are mutually convertible into each other; and that the electric fluid obtained from a permanent natural magnet, fuses, volatilizes, and ignites charcoal, metals, and

other solids, like ordinary caloric, as may be daily witnessed at the Adelaide Gallery in London.

From a general review of the foregoing chapters, the following conclusions have been deduced:

1. That the latent caloric of aqueous vapour is the true and only basis of lightning:

2. That the latent caloric of liquids is the basis of voltaic electricity in all its various forms:

3. That they are both governed by the same universal law of attraction for ponderable matter, and repulsion of their own particles:

4. That the essential properties of positive and negative electricity are the same under all cir

cumstances:

5. That when metals are made red hot by electricity, whether it be disengaged from a galvanic battery, a common machine, or from a magnet, it immediately loses its peculiar power of darting through conductors and producing a shock, being transformed into caloric, when it excites the sensation of heat, and converts solids into liquids, vapours, and gases, which present the same properties as if generated by the action of ordinary caloric:

6. That if caloric and electricity be not modifications of one power, and the cause of all mechanical and chemical action, the whole of modern science is a perfect chaos of contradictions.

455

'BOOK IV.

CHAPTER I.

Life.

"First then, if any one think that the secrets of nature remain shut up, as it were with the seal of God, and by some divine mandate interdicted to human wisdom, we shall address ourselves to remove this weak and jealous notion; and, relying on simple truth, shall bring the inquiry to this issue, not only to silence the howl of superstition, but to draw religion herself to our side."

BACON.

WHETHER in a theoretical or practical point of view, the animating principle is the most important problem that ever engaged the attention of mankind; for it connects all that is profound and fascinating in physics, with the science of preserving health and prolonging life. Never can the healing art take its appropriate rank among the exact sciences until the cause of vital force and animal motion is distinguished from the operations which it produces; but must remain, as in all the ages that are past, a mere collection of empirical rules. If it be true that every deviation from health is immediately connected with some derangement of the vital principle, there cannot be a doubt, that a clear comprehension

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