This is explained in the work cited above. (Du Calorique Rayonnant, § 121.) A good method of judging of this effect is to take an extreme case. Let us suppose the body to be a perfect reflector. In this case the internal cooling of the body would make no alteration in its radiation. The thermometer exposed to its influence would not be affected by it. In fact, before the cooling, the temperature being uniform, the body would radiate by reflection, and this radiation would be precisely equal to that of all the bodies in the same place and since it is supposed a perfect reflector, it would not emit any heat. Every thing continues the same after the interior cooling of this reflecting body. : I confine myself to these two objections. They are sufficient for pointing out the method of answering all the others. Thus it appears that in order to be able to refute objections of this nature, nothing more is necessary than to understand well the theory against which they are made. Those who have been struck with these objections without sufficiently examining this theory; and in particular the celebrated philosophers who have given them weight by inserting them in their works, will probably find it just and useful to insert also the answers to them, if they appear to them, as they do to me, perfectly satisfactory. IV. It is doubtless very useful that the objections which occur to philosophers against a probable theory should be explained at some length, and laid before those who are examining that theory. The consequence is a discussion which must be of advantage to the side of truth. It is therefore always with a kind of gratitude that I meet with such objections against the equilibrium of heat: and I experience a kind of dissatisfaction when I meet with mere indications of some difficulty, without its being possible for me to divine in what they consist. Time is lost in seeking for them. One runs the risk of being deceived; and it may easily happen that when we think we are untying the knot, we are only pursuing useless researches without an object. In my Treatise on Caloric (p. 93, note) I have given an example of this kind of uncertainty. More recently I have been in an equal state of uncertainty on reading a note in p. 105 of the excellent work of Dr. Wells on Dew. Few works have so much interested me; few, I believe, show more completely the genius for observation and the love of truth. I could not, therefore, be indifferent to the opinion of so distinguished an author respecting an explanation connected with the theory of the equilibrium of heat, which I still consider as corThe note to which I allude is as follows: rect. "I once intended to add here an explanation of some curious observations by M. Prevost, of Montauban,* on dew, which were published first by himself in the 44th No. of the French Annals of મ *The author has inserted here Besançon instead of Montauban. I have corrected this slight mistake. Chemistry, and afterwards by M. Prevost, of Geneva, in his Essay on Radiant Heat; but, fearing to be very tedious, I have since given up the design. I will say, however, that if to what is now generally known on the different modes in which heat is communicated from one body to another, be added the two following circumstances, that substances become colder than the air before they attract dew, and that bright metals when exposed to a clear sky at night become colder than the air much less readily than other bodies, the whole of the appearances observed by M. Prevost may be easily accounted for." Dr. Wells having under his inspection my treatise on radiant heat, the principles of which he has adopted, could not but have read my explanation of the curious phenomena observed by my relation, and which this last Gentleman has adopted. Since, then, in the above note, the author speaks of the explanation of these phenomena as still to seek for, it would seem that mine did not appear satisfactory to him. It is impossible for me to divine what fault he finds with it; and I mention the subject here in order to be informed of this particular, and to draw the attention of philosophers to it. What embarrasses me most is, that my explanation is founded on the very same principles which the author announces would have been his own. Though this subject be known and explained in works within the reach of every man of science, I trust I shall be excused for dwelling upon it a little here. The phenomenon is this. Two masses of air of unequal temperatures being separated from each other by a plate of glass, if we apply a leaf of metal on one of the faces of the glass plate, the face opposite to this leaf attracts or repels humidity according as the metallic leaf is on the hot or the cold side respectively. The explanation consists in conceiving the naked side of the glass thus covered as a vessel (un poële) destined to be dried, and the metal as a screen. If the screen is put upon the hot side, the vessel cools, and humidity accumulates on the naked glass on the cold side. If the screen is on the cold side, it prevents the heat from being dissipated after traversing the glass, and consequently the vessel becomes hot, and the humidity disappears from the naked glass on the hot side. I found this explanation on the property which metal has of reflecting seven or eight times more caloric than glass. (Du Calorique Rayonnant, §§ 195, et suiv.) If any attention be paid to this subject, it will be seen that the principles of this explanation differ in nothing from those of Dr. Wells. But no doubt he employs them in a different way from me; and I am really impatient to know in what this difference consists. V. I have nothing further to say on the principal object of this memoir, which was to reduce to very simple principles the answer to some objections against the equilibrium of heat. But I shall take an opportunity of making a remark on a set of experiments connected with this theory, published by M. Ruhland in the Jour. de Phys. for Nov. 1813. A part of these experiments proves directly the equilibrium of heat in a state of uniform temperature, as the author himself has observed. In fact, these experiments show us the evaporation of camphor by the radiation of different bodies proportional to the greater or smaller disposition of these bodies to radiate, even when the temperature is uniform; or, in other terms, even when the equilibrium of caloric exists. Hence it follows that radiation exists even in this state of equilibrium. This direct experiment seems to confirm in a satisfactory manner the numerous arguments in favour of the theory of the equilibrium of heat. The memoir of M. Ruhland contains several other interesting facts, which appear to me to flow directly from the general laws of heat. For example, lamp-black, which is known to be one of the most powerful radiators of heat, sublimes or evaporates camphor very rapidly. But if a metallic plate is placed over the lamp-black, the evaporation is immediately retarded. The caloric of the inferior strata is intercepted by this screen, or by this change of medium. I do not choose to enter into further details on this subject, which is beyond the particular point of theory that I was anxious to illus trate. ARTICLE IX. ANALYSES OF BOOKS. Hints for establishing an Office in Newcastle for collecting and recording authentic Information relative to the State of the Collieries in its Neighbourhood, and the Progress that has been made towards ascertaining the Nature and Constitution of the Strata below those Seams to which the Workings in this Country have been confined. By Wm. Thomas, Esq. To which are added Observations on the Necessity of adopting legislative Measures to diminish the probability of the recurrence of fatal Accidents in Collieries, and to prolong the Duration of the Coal Mines of the United Kingdoms. By Wm. Chapman, Esq. Civil Engineer. Being two Essays read at a Meeting of the Literary and Philosophical Society of New·castle-upon-Tyne, and published by order of the Society. 1815. THIS pamphlet contains a proposal to establish a Society in Newcastle-upon-Tyne, by whom all the facts respecting the collieries on the Tyne and Wear are to be collected and registered. When a colliery is abandoned, an exact plan of it is to be constructed, exhibiting those parts in which the coals have been wrought out, and those in which they have been abandoned. The consequence of this plan would be that by degrees a complete knowledge of all the underground workings would be acquired. It is obvious that all the abandoned collieries must be filled with water, and that unless an exact knowledge of them is obtained, it must become more and more difficult every year to sink new pits. Indeed the time must come when the mining for coals must be abandoned altogether, for want of such knowledge. Mr. Chapman gives examples of great expense already incurred in vain, merely from not knowing what part of the coal-bed had been wrought out. But when the whole high main shall have been exhausted, it will be necessary to have recourse to the low main. Now this will be hardly possible without an exact knowledge of the workings of the high main. Here and there considerable bodies of coal are left for the safety of the miners and the good of the mine. Through these bodies it would be possible to penetrate to the low main without the risk of being inundated by water; but this cannot be done unless the exact position of these bodies of coal be known. Mr. Chapman has shown that such a plan, though absolutely necessary for the good of the country, can never be executed without the interference of the Legislature. Indeed this is sufficiently obvious. The proprietors of the collieries, from mistaken views of self interest, are anxious to conceal every fact which they observe from the public. Hence it is quite obvious that they will never of their own accord form such a society as is described in the pamphlet before us; and that if such a society be formed by others, they will communicate no information to it unless compelled by an Act of Parliament. As to the coal viewers, they appear to be averse to all publicity and all changes in the present mode of working the collieries. This I conclude from a fact which I certainly should not have believed a priori. Though several hundred colliers lose their lives every year by explosions of carbureted hydrogen, and though they have been expressing a great anxiety to discover a mode of destroying this gas, not one of them has ever thought of trying the lamp of Dr. Reid Clanny, of Sunderland, though a model of it has been within their inspection for several years, and though there cannot be the least doubt that it would effectually prevent all such accidents. They may perhaps allege that it is more expensive than the present mode of lighting the mines. I should like to know at what they estimate the lives of 300 or 400 men; or what additional expense to the country it is to support the widows and children of so many workmen that have perished in their service, because they did not choose to increase the expense of lighting their mines. But setting this aside, if we consider the damage often done by these explosions, and the money requisite to put the mine in order again, I am not sure if the difference of expense would not be in favour of Dr. Clanny's lamp. Besides, nothing would be more easy than to substitute coal gas for oil; and a small steam-engine might easily be made to supply all the lamps with the requisite quantity of air. Such a substitution would make the lamps cheaper than the present mode of lighting the mines; and it would have the unspeakable advantage of preventing all deaths from the explosion of carbureted hydrogen gas. What excuse or apology can the proprietors of the mines and the coal-viewers make for never having made a single attempt to improve the present wretched and absurd mode of light ing their mines after other and better methods have been suggested to them? One would be tempted to suppose them entirely regardless of the lives of their workmen. The Literary and Philosophical Society of Newcastle-upon-Tyne should apply to the county inembers of Northumberland and Durham, and to the different members for boroughs within these counties, to lay the case before the House of Commons, and represent the necessity of legislative interference in order to preserve to the country the great benefits arising from the collieries on the Tyne and Wear. There can be no doubt that an Act of Parliament would be readily procured, establishing an institution similar to that posed in the pamphlet before us. It would be better that no fees were exacted for liberty of inspecting the plans, or at least they should be trifling; for such things are extremely liable to be abused, and to destroy the object in view. pro In all parts of Europe, where mining has been carried to a great degree of perfection, it has been under the inspection and controul of Government. That coal-mines should be in this predicament, and that exact plans should be preserved of all the excavations, and of all the coals left, is too obvious to require any illustration. ARTICLE X. Proceedings of Philosophical Societies. ROYAL INSTITUTE OF FRANCE. Account of the Labours of the Class of Mathematical and Physical (Continued from p. 229.) M. Risso, author of the Ichthyology of Nice, has sent to the Class a supplement to that work, in which he describes several fishes that he was not acquainted with when he published his work. Some of these are very interesting, by the peculiarities of their character. M. Lamouroux has extended and completed his great work on the polypi history, of which we have spoken two years ago, and it is to be hoped that he will soon publish it. M. Magendie's fine experiments on vomiting will be recollected, and the invitation by the Class to examine the part which the œsophagus may have in this disorderly movement of the stomach. Though these researches have not yet led to a decisive result, they appeared to him sufficiently interesting to be communicated. The alternate contractions and relaxations of the oesophagus |