candlelight is nearly deficient of the chemical rays. How far they may influence crystallization and other molecular arrangements is unknown, but their power is universal wherever the solar beam falls, although their effect only becomes evident in cases of unstable molecular equilibrium. It is not by vision alone that a knowledge of the sun’s rays is acquired: touch proves that they have the power of raising the temperature of substances exposed to their action. Sir William Herschel discovered that rays which produce the sensation of heat exist in the solar spectrum independent of those of light; when he used a prism of flint glass, he found that the warm rays are most abundant in the dark space a little beyond the red extremity of the spectrum, that from thence they decrease towards the violet, beyond which they are insensible. It may be concluded therefore, that the calorific rays vary in refrangibility, and that those beyond the extreme red are less refrangible than any rays of light. Since Sir William Herschel’s time it has been discovered that the calorific spectrum exceeds the luminous one in length in the ratio of 42 to 25, but the most singular phenomenon is its want of continuity. Sir John Herschel blackened the under side of a sheet of very thin white paper by the smoke of a lamp, and, having exposed the white side to the solar spectrum, he drew a brush dipped in spirit of wine over it, by which the paper assumed a black hue when sufficiently saturated. The heat in the spectrum evaporated the spirit first on those parts of the paper where it fell with greatest intensity, thereby restoring their white colour, and he thus discovered that the heat increases uniformly and gradually throughout the luminous spectrum, and that it comes to a maximum and forms a spot at a considerable distance beyond the extreme red. It then decreases, but again increasing it forms a second maximum spot, after which it ceases altogether through a short space, but is again renewed and forms two more insulated spots, and even a fifth may be traced at a little distance from the latter. These circumstances are probably owing to the absorbing action of the atmospheres of the sun and earth. “The effect of the former,” says Sir John, “is beyond our control, unless we could carry our experiments to such a point of delicacy as to operate separately on rays emanating from the centre and borders of the sun’s disc; that of the earth’s, though it cannot be eliminated any more than in the case of the sun’s, may yet be varied to a considerable extent by experiments made at great elevations, under a vertical sun, and compared with others where the sun is more oblique, the situation lower, and the atmospheric pressure of a temporarily high amount. Should it be found that this cause is in reality concerned in the production of the spots, we should see reason to believe that a large portion of solar heat never reaches the earth’s