And still upon that face I look, And think 'twill smile again; And still the thought I will not brook, But when I speak-thou dost not say, If thou would'st stay, e'en as thou art, I still might press thy silent heart, But there I lay thee in thy grave- I do not think, where'er thou art, And I, perhaps, may soothe this heart, In thinking too of thee; Yet there was round thee such a dawn, Of light ne'er seen before, As fancy never could have drawn, And never can restore! SHORT PAPERS ON SUBJECTS CONNECTED WITH SCIENCE. No. V. HEAT. (Continued.) HEAT may be considered as a power opposed to attraction, for it tends to separate the particles of bodies; whenever a body is heated it is also expanded. Of all the effects of heat expansion is the most obvious and familiar, and it takes place, though in different degrees, in all forms of matter. Solids are least expandible; liquids are more expandible than solids, and gasses or æriform bodies more than liquids. When a body is expanded by heat it regains its former dimensions, or contracts, when cooled to its former temperature. However much we may have been struck with the apparent correctness of some or other of the Theories of Heat which Philosophers have proposed, however much we may have admired the beauty of their experiments and the force of their reasonings, we have, when arguments from an antagonist theory have been brought against them, been obliged to confess ourselves not yet fully convinced. If a thermometer is suspended in an exhausted receiver, it indicates changes of temperature while in such situation; this has been considered a proof of the material nature of heat, viz. its power of passing through a vacuum. Count Rumford made an experiment of this kind in the Torricillian Vacuum; he found the thermometer affected by changes of temperature; he imagined that the very subtle vapour which arises from quicksilver, and occupies the space called the torricillian vacuum, is too rare to transmit caloric by its vibrations in a short time; and concluded therefore, that heat being able to pass through such a space unaided by any elastic vibrating fluid must be material. One of the strongest arguments in favor of the material nature of heat is, probably, the fact of its radiation; any body heated above the temperature of the surrounding bodies, gradually parts with, or gives off its heat to the bodies around it, and heat so given off, passes through space in straight lines: it may be reflected by mirrors and condensed by lenses. Many experiments have been made with a view of discovering if there exists any difference of weight in the same body at different temperatures; the results have been various, at one time leading the experimenters to believe there was a difference, at other times no variation could be found; where the difference has been supposed to exist, it no doubt arose from some imperfection in the weighing apparatus, or some sudden condensation of the atmosphere in its immediate proximity. Count Rumford made a very ingenious experiment on this subject, he took equal weights of water and quicksilver and put them in bottles of the same size and shape, and adjusted their gross weights with a delicate ballance at the temperature of 610. he then kept them at 34°. for twenty-four hours, at the end of which time, no difference was perceptible in their weights. Now from the known capacities of the two fluids for caloric, it is very sure that the water must have parted with much more of the matter of heat than the quicksilver had done. The hypothesis by which Caloric is considered a subtle fluid, the particles of which repel each other, appears to give a plausible explanation of most of the phenomena dependant upon heat; we may suppose the expansion, fusion, and vapouration of bodies to arise when caloric is interposed between their particles in sufficient quantity. When a body is enlarged in bulk, it appears natural to suppose that it is enlarged by the introduction of particles of other matter, by which the particles of the leated body are repelled to a greater distance from each other; this repulsion being increased by greater quantities of heat being introduced, converts the particles of solid bodies either into the liquid or æriform state. There are some phenomena of heat which this hypothesis does not satisfactorily explain : the production of heat by friction and percussion; also, the explosion of gunpowder. Pieces of metal, gold, silver, and copper, have been acted upon by the stroke of the coining press, and the heat produced was ascertained by throwing the pieces into water and measuring the heat produced: it has been found that the increase of temperature produced in a piece of metal was greater at the first blow than at the second, at the second than at the third, after which the temperature was but little altered. Now this, no doubt, arises from the condensation of the metal being less at the second blow than at the first, from the texture of the metal being more close from the effects of the first blow; it appears therefore that the degrees of heat produced are in proportion to the condensation ; a bar of iron may be made red hot by hammering, but iron that has once been heated in this way cannot again be so made red hot unless it is previously heated in the fire to expand the particles. Lord Bacon's opinion of heat, was, that it consisted in motion among the particles of bodies, and that it is communicated through an apparent vacuum by the undulations of a very subtle elastic medium. Many experiments have been made on the production of heat by friction; Count Rumford made some on rather an extensive scale. Some made by Sir H. Davy were very ingenious, the bodies acted upon were so circumstanced as to prevent the possibility of their abstracting the matter of heat from the bodies around them. Notwithstanding this, the supply of heat liberated by friction was found to be inexhaustible; it is difficult to explain this fact on the hypothesis of heat being a subtle fluid. To review these points, the most general effect of the operation of Caloric is, expansion: If, then, caloric is mere motion or vibration of the particles of the heated body, how is this effect produced? Vibration is the alternate approximation and retrocession of the particles, therefore, from vibration no permanent and uniform increase of volume can take place. Again, How can we by this hypothesis account for the augmentation of volume which accompanies fluidity and vapourisation. When water is converted into vapour,it occupies 1800 times the space which it did while in the liquid form suppose vibration increased to any intensity, it cannot be shown how it can permanently separate the particles of a body to such distances. On the other side of the argument, it may be observed that, the production of heat by friction, appears to afford an unanswerable confutation of the doctrine of the materiality of heat. If heat is neither received from the surrounding bodies, which it cannot be without a depression of their temperatures, nor derived from the quantity already accumulated in the bodies themselves, which it could not be, even if their capacities were diminished in any imaginable degree; there is no alternative but to allow that heat must be actually generated out of nothing, it cannot be matter, nor anything of a material character. Heat is a subject which presents a boundless field for interesting speculation. I have endeavoured to lay the most popular theories before the reader, and have studied to avoid biasing his judgment, nor have I, that I am conscious of, allowed my own opinion to escape me. Altho' we do not understand the cause of heat, its effects are well studied, and, to a considerable extent, practically known. these will form the subjects of future papers. Some of THE FEAR OF BEING LAUGHED AT. BY JOIN FOSTER. S. THE attack of contempt and ridicule, is perhaps a still greater trial of courage. It is felt by all to be an admirable thing, when it can in no degree be ascribed to the hardness |