o have an atmosphere of elastic fluids phosphorescent in their nature; and these, by decomposition, become the means of light and heat. Q. By what terms are these rays known? A. As colorific and calorific rays: the first affect the sense of sight, and are the medium of what we term vision; the second refer to the sense of feeling, and lead to what we term heat. Q. What is heat? A. Heat and cold are sensations which lead us to state our feelings; they are terms by which we describe our state in relation to objects by which we are surrounded. These words are commonly used as if they were causes, whereas in truth they are more effects. Q. Illustrate what you say. 4. Two persons come into the same room, the one from air at a low temperature, the other from some situation where it is high. The first says, How warm this room is ! The other declares it shivers him with cold. One person descending from a high mountain, meets another ascending from the vale: at the place of meeting, he that has descended speaks of the warmth of the spot; he that has ascended, notices the cold he endures. Place on a table three basins of water; let the temperature of the water in the left basin be 33°, the middle 60°, the right 100°. Put the left hand in the first, the right hand in the third; when the hands have remained in these basins some two or three minutes, take them out, and place them both immediately in the middle basin: the right hand will feel cold, and the left hand warm. By the same body different sensations will be felt at the same moment, and in the same temperature. Q. Tell me the cause of this. A. The sensation which we term heat is caused by receiving caloric from some near warm body; as the left hand from the warm water. The sensation which we denominate cold is the effect of parting with caloric to some colder body; as when we go from a valley, or room of a high, to another room or on a mountain of a lower, tem liable to be forgotten as soon as uttered, does he maintain it; but by every mode that could give his expressions publicity, and ensure them perpetuity, he longs that his confidence in God to vindicate him might be recorded, whatever might be the issue of those evils to himself, even though he were brought down by them to death and corruption, descending not only with sorrow, but with ignominy, to the grave; for, saith he, "I know that my Redeemer liveth, and that he shall stand at the latter day on the earth: and though after my skin worms destroy this body, yet in my flesh shall I see God: whom I shall see for myself, and mine eyes shall behold, though my reins be consumed within me." (Job xix. 25—27.) Had these words of the Patriarch been indeed " engraven with a pen of iron on the rock for ever," yet without some more certain medium of transmission to posterity, they would have been unknown at this day, or only speaking in the desert with the voice of silence, which no eye could interpret, no mind could hear. But, being inscribed on materials as frail as the leaves in my hand, yet capable of infinitely multiplied transcription, they can never be lost; for though the giant-characters enchased in everlasting flint, would ere now have been worn down by the perpetual foot of time, yet, committed with feeble ink to perishable paper, liable "to be crushed before the moth," or destroyed by the touch of fire or water, the good man's hope can never fail, even on earth; it was 66 à hope full of immortality ;" and still through all ages, and in all lands, whilst the sun and moon endure, it shall be said by people of every kindred and nation, and in every tongue spoken under heaven, "I know that my Redeemer liveth."-Montgomery. CHRISTIAN PHILOSOPHY. (Continued from p. 342.) Q. Is there any supposed connexion between light and heat? o have an atmosphere of elastic fluids phosphorescent in their nature; and these, by decomposition, become the means of light and heat. Q. By what terms are these rays known? A. As colorific and calorific rays: the first affect the sense of sight, and are the medium of what we term vision; the second refer to the sense of feeling, and lead to what we term heat. Q. What is heat? A. Heat and cold are sensations which lead us to state our feelings; they are terms by which we describe our state in relation to objects by which we are surrounded. These words are commonly used as if they were causes, whereas in truth they are more effects. Q. Illustrate what you say. A. Two persons come into the same room, the one from air at a low temperature, the other from some situation where it is high. The first says, How warm this room is! The other declares it shivers him with cold. One person descending from a high mountain, meets another ascending from the vale: at the place of meeting, he that has descended speaks of the warmth of the spot; he that has ascended, notices the cold he endures. Place on a table three basins of water; let the temperature of the water in the left basin be 33°, the middle 60°, the right 100°. Put the left hand in the first, the right hand in the third; when the hands have remained in these basins some two or three minutes, take them out, and place them both immediately in the middle basin: the right hand will feel cold, and the left hand warm. By the same body different sensations will be felt at the same moment, and in the same temperature. Q. Tell me the cause of this. A. The sensation which we term heat is caused by receiving caloric from some near warm body; as the left hand from the warm water. The sensation which we denominate cold is the effect of parting with caloric to some colder body; as when we go from a valley, or room of a high, to another room or on a mountain of a lower, tem placed in the warm water,-a portion of caloric is abstracted: we express the effect, by saying that we feel cold. Q. Are these the uniform causes of these sensations? A. Yes to every substance which feels cold, a portion of caloric is given; from every substance that gives the sensation of heat, a portion of caloric is received. Q. What is caloric? A. The ideal meaning of the term is heat; and here it would seem to express the cause, as well as the effect produced. But what the substance is, of which the word is the sign, it is difficult to say. By some, caloric is taken as a real and a distinct substance, everywhere diffused; with others the term stands for some specific and peculiar vibration of the particles of bodies, or the effect supposed to be produced by this. Q. Have both the parties attempted to support their opinions by facts? A. They have the one by various chemical operations, and the effects produced by combination, condensation, &c.; as the mixing sulphuric acid and water, for example, in a glass phial, by which heat will be evolved. The latter appeal to the effects of friction; as by two pieces of wood, the wheel of a coach, the drag on that wheel, &c. Q. Seeing that in this case, as in a thousand others, we must believe facts, without being able to comprehend the agent and the agency, can you tell me any uses of caloric? A. They are many: "the verdure of the earth, the lustre of the waters, and the freshness of the air, are connected with heat. Without the presence and effects of heat, the earth would be an impenetrable rock, incapable of supporting animal or vegetable life; the waters would be for ever deprived of their fluidity and motion, and the air of its elasticity and utility together." Caloric appears to be the great instrument employed to control the operation of attraction. By the latter, all substances tend most closely to each other, and would by cohesion form solid bodies: by the former this tendency to adhesion is so counteracted, that have the state, the consistence, and the proper solidity or fluidity of the bodies around us. Q. Would caloric by increase cause solid bodies to become fluid? A. Yes; and in some cases so completely dissolve them as to render them invisible. Q. Is it a general law, that bodies become either more solid or fluid as their caloric is diminished or increased? A. It is; and generally bodies are expanded by caloric. Q. How may I assure myself of this? A. Begin with air: take a bladder ; let it contain a small portion of air; tie the neck very close, so that no air can escape; then place the bladder near a fire, and the air will so expand as to burst it. Pass to liquids: take a Florence flask; put therein water up to the neck; colour it with port wine, red ink, or what else, that it may the more easily be seen; then place the flask in a vessel of hot water, and the expansion will cause the water in the flask to rise up in the neck. Look to solid substances: take an iron rod; fit it exactly to any ring, mould, or cavity; make the rod very hot, and it will not then pass. The wheelwright, to make his wheel as compact as possible, takes his iron while red hot and in a state of expansion, quickly places it on the wheel, then turns it in the water, that by the contraction of the iron the parts may be brought more closely together. The difference in temperature in tropical regions and ours, and in cur own in summer and winter, causes the variation of clocks and watches: by heat the pendulum and spring dilate, by cold they contract; this causes the vibrations to increase or diminish in a given portion of time. Glass also, and especially when thick, if suddenly exposed to heat, the surface immediately expands, while the inner part remains comparatively unaffected; the expansion is unequal, and the glass cracks. The same effect is produced by suddenly cooling some hot bodies, as throwing cold water on hot iron; the contraction is sudden on the surface, and unequal as to the whole, and it cracks. To this contraction, being first heated, granitic rocks are said to yield and split, in any |