spread of the Gospel as well. Many, indeed, talk as if a diffused taste for books and pictures and music were a sure mark of social and moral progress; and with them the approved nostrum for humanizing and elevating a people is to cover a land with museums and libraries and picture-galleries; but does past history prove such things to be any real boon to a community in the absence of Christian truth and Christian principle? Ancient Greece was resplendent all over with the choicest triumphs of literature and art; but did that prevent the Greeks from being a byword among the nations for perfidy? Modern Paris, on the eve of the first revolution, had its academies of science, and its galleries of painting and sculpture, and its magnificent Versailles, where thousands upon thousands assembled every Sunday to gaze on fair statuary, and yet fairer fountains, and to keep holiday amid gay parterres of flowers and orange-trees; but did that prevent Paris from becoming a very Aceldama? did that blunt the edge of the guillotine, or shorten the duration of the Reign of Terror? Literature and science and art will doubtless promote men's true progress, when they are underlaid by that public and private virtue which the Gospel produces and sustains. But, in the case of a people devoid of moral and religious principle, they are only an intoxicating cup to prepare men more speedily for ruin. Nations are great, not in the measure in which they live amidst flowers and fountains and statuary, but in the measure in which they will not lie, will not cheat, will not act a mean and selfish, but a generous and noble part. It is only through the knowledge and belief of the Gospel that a people can be trained to that love of truth and of righteousness which is the true source of national strength and greatness. And hence, with all our admiration of the triumphs recently achieved in the fields of science and invention, we should count them but an equivocal sign of the times, were it not that they are accompanied by a correspondent outspread of Christianity. PROPERTIES OF HEAT. THE chief properties of Heat, or Caloric as it is sometimes called, are Radiation and Conduction. Radiation.-Heat always tends, not only to diffuse itself, but to diffuse itself equally. When two bodies are of different temperatures, the warmer gradually parts with its heat to the colder, till both are brought to the same temperature. Thus, when a thermometer is applied to a hot body it receives heat, when to a cold one it communicates part of its own heat, and this communication continues until the thermometer and the body arrive at the same temperature. Cold is not a positive quality, but merely the abstraction of heat. When you lay your hand on a marble table you indeed feel it positively cold; but the cold you experience consists merely in the loss of heat that your hand sustains while its temperature is being brought to an equilibrium with the marble. If you lay a piece of ice upon the table, you will find that the contrary effect will take place,—the ice will be melted by the heat which it abstracts from the marble. And not only do the hotter bodies emit rays of heat to the colder, but there seems to be a reciprocal radiation among bodies. All bodies whatever appear to be constantly radiating or emitting heat; the hotter emitting to the colder, and the colder to the hotter; nor is it more extraordinary that a hot body should receive heat from a cold one, than that a candle should send forth rays of light to the sun, which yet must necessarily happen. Different bodies-or different surfaces, rather-possess the power of radiating heat in very different degrees. From experiments made on this subject, it appears that black surfaces radiate most, white next, and polished surfaces the least of all. Hence it is that light-coloured clothes, in cold weather, keep us warmer than black ones; hence also a metallic vessel preserves the heat of the liquid within better than one of any other materials; silver teapots, for instance, make better tea than those of earthenware. The property which different surfaces possess of radiating in different degrees may appear to be at variance with the doctrine respecting the equilibrium of heat, inasmuch as it would seem to imply that those bodies which radiate most must ultimately become coldest. But it is to be recollected that the power of absorbing heat is always proportionate to the power of radiation; so that, in equal temperatures, bodies compensate, by their greater absorption, the loss which they sustain by their greater radiation. Conduction. In establishing an equilibrium of temperature, heat is conveyed to surrounding objects, not only by radiation -or by an interchange from a distance-but also by conduction through intermediate bodies. Heat passes through bodies with different degrees of velocity. Some substances oppose very little impediment to its passage, while it is transmitted slowly by others. Daily experience teaches, that though we cannot leave one end of a rod of iron for some time in the fire, and then grasp its other extremity, without danger of being burnt, yet this may be done with perfect safety with a rod of glass or of wood. The heat will speedily traverse the iron bar, so that, at the distance of a foot from the fire, it is too hot to be handled; while we may hold a piece of redhot glass two or three inches from its extremity, or keep a piece of burning charcoal in the hand, though the part in combustion is only a few lines. removed from the skin. The observation of these and similar facts has led to a division of bodies into conductors and non-conductors of heat. The former class includes bodies which allow heat to pass freely through their substances: the latter comprises bodies which do not give an easy passage to heat. It has been ascertained by experiment, that the metals are the best conductors of heat, and that of the metals silver is the best, copper the next, gold the third, and bismuth the worst. Next to the metals, though far behind them, crystals, glass, and stones are the best conductors; but these differ as much among themselves as the metals do. Substances which belong to the animal and vegetable kingdoms, such as furs, wool, silk, cotton, etc., are extremely imperfect conductors, a property which, doubtless, serves, not only to guide us in the choice of our clothing, but also, in some degree, to protect animals and vegetables from the injurious effects of sudden changes of temperature. Abridged from TURNER. EFFECTS OF HEAT. THE principal phenomena which accompany the passage of heat into substances, are Expansion, Liquefaction, and Vaporization. The phenomena that attend its escape from them, viz., Contraction, Solidification of Fluids, and Condensation of Vapour, are merely the converse of these. Expansion. The effect of heat is directly contrary to that of the attraction of cohesion-the one drawing the particles together, the other driving them asunder-and from the continual struggle between these two forces result all the various degrees of consistence which bodies assume. Different bodies dilate in very different proportions,-liquids being much more dilatable than solid bodies, and gases much more dilatable than liquids. It is in consequence of the great expansibility of liquids that they are used for filling thermometers. A thermometer consists of a tube, with a bulb containing a fluid, whose degrees of dilatation are indicated by a scale to which the tube is fixed. The fluid generally used is mercury, because its dilatations and contractions are found to correspond more exactly to the additions and subtractions of heat than those of any other fluid. The degree on the scale that indicates the boiling point simply means that, when the mercury is sufficiently dilated to rise to this point, the heat is such, that water exposed to the same temperature will boil; and when the fluid is so much condensed as to sink to the freezing-point, we are to understand that water will freeze at that temperature. The extreme points of the scale are not the same in all thermometers, nor are the degrees always divided in the same manner. Fahrenheit's scale, which is gener ally used in Great Britain, is di- 100-212 Water boils. vided into 212 degrees, in which 32° 45 -114 86 -98 Greatest natural heat. Blood heat. corresponds with the freezing-point, 78174 Alcohol boils. 16-61 0--32 -17-0 Mean temperature of July in England. Ice melts. Water freezes. Zero, Fahrenheit. -28-20 Strong wine freezes. -39-39 Mercury freezes. Cold experienced by -51-61 Captain Ross. Thermometer, with the mercury standing at mean summer heat, and a scale of the chief points of temperature. On the right side, the scale is that of As liquids expand more readily than solids, so aeriform fluids are more expansible than liquids; and one circumstance respecting their dilatation deserves to be particularly noticed—they all undergo the same degree of expansion from equal augmentations of temperature, though they vary in density more than either liquids or solids. This uniformity of expansibility, extraordinary as it may appear, is readily accounted for; for if bodies owe their different susceptibilities of expansion to their various degrees of attraction of cohesion, no such difference can be expected in permanently elastic fluids, since in these the attraction of cohesion does not operate. Fahrenheit: the corresponding degrees, on the left side, are those of the Centigrade scale. Liquefaction. All bodies are either solid, liquid, or gaseous; and the form which they assume depends upon the relative force of cohesion and heat. As it is easy to increase or diminish the quantity of heat in any substance, it follows that the form of bodies may be made to vary at pleasure; that is, by a sufficiently intense heat every solid may be converted into a fluid, and every fluid into the aeriform state. This inference is justified by experience so far that it may safely be considered a general law. The converse ght also to be true; and, accordingly, various gases |