_Sixthly:_ The laws of reflection are the same in light and heat. Other coincidences might be established, and other celebrated names added. If this identity should be established finally, it would not effect the doctrine of the foregoing pages in the least. It would only be necessary to say, the luminiferous fluid of this essay is the well established substance now called caloric. _Addenda on Light._ 1. It is now generally admitted that the real body of the sun is surrounded with a peculiar set of clouds, _phosphorescent_ in their nature. It is also allowed that these clouds do not emit heat. And as it is well known that no one of the _planets_ has such clouds, but receive their light from the sun, _it is extremely probable that these phosphorescent clouds are intended by the Creator, to be the great dispenser of light to the solar system, by operating as the exciting cause to put the luminiferous ether in motion throughout the solar system_. By a parity of reasoning, each centre of a system may be invested with similar clouds, which operate in the same way in reference to the planets which belong to it. 2. If light were a real substance, _as commonly understood_, solar light must proceed from the sun by _impulsion_, and artificial light from burning bodies by _evolution_. Take the case of burning bodies. A single candle placed two miles above the surface of the earth in the air, and lighted up in that position, will _instantly illuminate a space of two miles in every direction from itself, or a spherical space four miles in diameter_. In this case a sufficient quantity of light is instantly evolved to fill this space, and the evolution continues as long as the candle burns. The question upon this fact is this: Can it be supposed that there is a sufficient quantity of light, in combination with a single candle, or the oxygen necessary to keep up its combustion, to fill a spherical space four miles in diameter for several hours together? This would indeed be almost incredible in view of the space filled by light evolved from a single candle. But this difficulty would be satisfactorily solved upon the supposition that light is the _effect_, produced by a luminiferous ether, universally diffused, and put in motion, by which it becomes visible, by the sun, burning bodies, &c. Because, the motion which renders the luminiferous ether visible, commences instantly upon the commencement of combustion, and is propagated from the point of combustion _in right lines_, under the appearance of rays of light: but the motion ceases instantly on the cessation of combustion, and of course darkness instantly ensues.]