the disturbance of the molecular arrangement, and it bears a very close resemblance to the magnetism induced by a blow on a bar of steel under the same circumstances.

The important part which Electricity performs in the great phenomena of nature, will, it is hoped, be now fairly understood. The practice, however, of referring every effect, which we cannot clearly trace to its cause, to electricity, is one which cannot be too strongly censured, since it leads to misconception, and stops the progress of inquiry. Electricity, galvanism, and magnetism stand as different forms of the same great power, and to these may be referred many remarkable results which have through all time excited the attention of man; our knowledge of them will be extended, but the probability is, that with the extension of our knowledge we shall discover physical agencies which stand far superior to any with which we are now acquainted.

The first great source of this important principle, or force, is undoubtedly the sun, and we find, upon examination of the solar beam, that the heat radiations do not obey precisely the same laws as those which we detect regulating the luminous rays. Sir William Herschel and Sir Henry Englefield were the first to examine the temperature of the solar rays. This examination was effected by placing very delicate thermometers across the prismatic rays they obtained the following results:

:

Quite out of visible light, below

the Red ray, the thermometer rose 18 degrees. In the Red ray,

15

In the Yellow ray,

Sir John Herschel, by more recent researches, has confirmed these results, and also proved an extension of the calorific spectrum beyond the limits of the luminous rays, far greater than had hitherto been suspected. His method of examination is as follows:-A piece of tissue paper is stretched on a frame, and blackened on one side only. It is then placed so that the prismatic image falls on the unblackened side. Being thus carefully adjusted, and a well-defined spectrum obtained, a wash of ether is passed, by means of a wide brush, fully over the paper. The ether, being very volatile, evaporates rapidly, the portion subjected to the greatest heat drying the most speedily, and marking, by spots whiter than the other parts of the

paper, the extension and defined limits of the calorific rays. This is shown in Fig. 2 of the frontispiece, which is adjusted, in its relation to the luminous spectrum, in such a manner as to convey a correct idea of the superior extent of the calorific radiations. The spot which corresponds with the crimson ray is the first which becomes visible from drying, thus marking the point of greatest heat; the larger spot dries more slowly, but it is always exceedingly well-defined; and the two lower and smaller spots are only made visible by a second copious application of ether. The appendage from the first heat-spot, which extends through the luminous rays up to the blue, marks in a very pleasing manner the gradual diminution of thermic influence, and fully confirms Sir William Herschel's thermometric examination.

The points for consideration here are, the difference between the calorific and the luminous rays, as it regards refrangibility; we detect heat-rays scarcely at all bent by the interposition of the prism;-the want of coincidence between the light-giving and the heat-producing rays, and the very rapid diffusion and diminution of the calorific rays, as soon as they become blended with the luminous bands. Out of this arises the question-Are light and heat identical? are they modified forms of the same force? It has been shown by Drs. Robinson and Draper, that all bodies become luminous at the same temperature. Every substance in nature, whether organic or inorganic, begins to emit light at about 1000° Fahrenheit, from which it

has been inferred that a certain degree of disturbance produces heat, which, being increased, gives rise to luminous vibrations.

Heat and light may, however, be separated from each other. Melloni has determined that although thin slices of obsidian and black mica obstruct nearly all the luminous rays, yet these bodies admit the free and full permeation of the calorific rays; whereas, a peculiar green glass, washed over on one side with a solution of alum, although perfectly transparent to light, is nearly opake for heat, most of the solar calorific radiations being cut off when such a glass is interposed as a screen. By coloured solutions we are enabled to produce similar results, and thus secure the isolation of heat and light.

The other sources of heat, which may be called by distinction the terrestrial ones, are summed up under the following heads.

Mechanical force, whether applied as friction or percussion. A piece of metal rubbed rapidly on any other body, soon becomes too hot to be held. Two pieces of dry wood, kept for a few minutes in a state of brisk attrition, will give rise to such a development of caloric as will occasion their ignition. The lucifer match is ignited by the heat produced by the friction of the chemical compound against a piece of sand-paper. Count Rumford found that the friction produced in boring a brass cannon of seven inches and a half diameter, the borers pressing with the force of 10,000, and making thirty-two revolutions a minute, de