| 17. Quelle fut la réponse du 18. Quelle résolution prit alors 19. Quelle promesse exigea-t-il? NOTES AND REFERENCES.-a. s'entretenait, was conversing; L. part ii., p. 90.—b. mille, thousand, does not take the form of the plural.- c. L. part ii., § 49, R. (1.)—d. L. part ii., § 49, R. (2).-e. L. S. 25, R. 2.-f. devez, must.-g. from plaire; L. part ii., p, 98, CORRESPONDENCE. THE PURSUIT OF KNOWLEDGE UNDER DEAR SIR,-Is it your intention to publish separately the I am striving to fit myself for a clerkship, as I think this is one of the few things which I should be able to manage. Before I became lame, I learnt a system of Phonography, so as to be able to report a sermon delivered at the rate of 100 words per minute, and to read it afterwards. Since my lameness I have studied French so as to be able to read it. I have gone through "Walkingame's Arithmetic," and have got as far as Equations of more than one unknown quantity, "Cassell's Algebra;" so that, one thing with another, and books when I can get them, I contrive to give old time a poke in the ribs, and thus get the better of him. You are welcome to use this letter as you like; and perhaps if some of your hard-up students saw it, they might be encouraged to proceed; for company is comfort, you know, sir.-I remain, JOHN F. ATKINSON. yours, etc. King's Cliff, Birkby, near Huddersfield, 29th June, 1854. ANSWERS TO CORRESPONDENTS. recommend penmanship that is legible, and so plain that he who runs may read. If we durst we would recommend a style which we feel assured would please his Lordship, viz. the nearest possible imitation of Italic printing, or of Printer's good Script. CERTIFICATED SCHOOLMASTER (Sheffield) will oblige us by applying his energies to the diffusion of the P. E. rather than a Gazetteer in embryo. DIFFERENTIAL CO-EFFICIENT (Keith): His solutions are correct, and his signature is forwarded. QUINTIN NASPUS (Southport): We wish our correspondent would study our Palmerstonian system of Penmanship in the P. E., vol. fi., for really we can hardly make out his writing. We did not answer his former letter because we could not read his name; and therefore it went under the table, a fate which has necessarily befallen many commu nications, and for the same reason. In answer to his question, "What are the sentiments most proper to be cultivated in order to render men happy we reply, in the words of Scripture, "Fear God and keep his commandments: for this is the whole duty of man," or, as our late excellent friend, Dr: Pye Smith, would have it, the whole of man; thereby meaning not only his duty, but his sole subject of thought and sentiment, his sole employment. in both time and eternity, and his sole enjoyment on earth and in heaven. To this may be added the words of Micah, "He hath shewed thee, O man, what is good: and what doth the Lord require of thee, but to do justly, and' to love mercy, and to walk humbly with thy God?"-ANXIOUS ONE (8pitalfields): The Greek letters are by no means unlike the English, and an approximation may be made to writing them easily by making them as like our script letters as possible. For instance, alpha, in the small cursive hand, is very like our italic and written a; beta is very like our written B gamma is very like the way in which many people write our g; and so on. J. ARMITAGE (Little Horton): Right in his solution; as yet there are no periodicals on the Phonetic System of Shorthand.-J. ELSON (Lambeth): His solutions are right.-A. EDWARDS (Long Crendon), and another correspondent, J. S. G., have called our attention to the fact that Zarah Colburn, the calculating boy, was "a useful though not extraordinary Wesleyan preacher."-C. NEWTON (Commercial-road East): His verses breathe a fine spirit, and were they a little more accurate would be acceptable; but we have no time to correct.-E. BROMFIELD (Elstead): His "Counsels to Young Men" on the "Frensham Tragedy" are very good; we strongly recommend them to the Anti-teetotallers.-J. A. MARSHALL (Sandyford) and, R. B. (Darlington): Right.-TAU (York): One striking reason for preserving the Geometrical Demonstrations of the second book of Euclid is, that they make a more lasting impression on the mind; another is, that algebraical products and squares are, after all, not geometrical rectangles nor superficial squares. The algebraic proofs may be added to the geometrical ones.-A. SCOT (Greenock): The classical subjects for 1855, are stated at p. 347, vol. iv.-ET. BERGHOLT: Pronounce the words as if they were met with in English; if you don't know how to do this, ask an intelligent native.-R. KERSLAKE (Carlisle): Received. LITERARY NOTICES. CASSELL'S FRENCH AND ENGLISH DICTIONARY: Composed from the French Dictionaries of the French Academy, Bescherelle, Landais, etc.; from the English Dictionaries of Ogilvie, Johnson, Webster, etc.; and from the Technological and Scientific Dictionaries of both Languages. By Professors DE LOLME and WALLACE, and HENRY BRIDGEMAN, Esq. The following are the distinctive features which render this Work superior to any of the same class now extant. It has been compiled with unusual care from the very best authorities. It contains correct renderings of all the most modern words and phrases-including those of science, art, manufac ture, commerce, law, politics, etc., as well as familiar conversation-which are indispensable to a knowledge of language, but yet are rarely, if ever, to be found properly translated in any Dictionary. The idiomatic usages of the two languages-the constructions of verbs, the force of prepositions, and the changes of meaning caused by different combinations of words-are more copiously and carefully illustrated than elsewhere within the same limits. The meanings are also classified and arranged in such a manner as to prevent the possibility of mistake. To crown all, the Work is as moderate in price as it is comprehensive in aim, accurate in detail, and superior in arrangement. Price 9s. 6d. strongly bound. CASSELL'S LESSONS IN FRENCH. Parts I. and II.-By Professor FASQUELLE. Price 28. each in paper covers, or 2a. 6d. bound in cloth. The Two Parts bound in One Volume, price 4s. 6d. A KEY TO CASSELL'S LESSONS IN FRENCH, containing Translations of all tho Exercises. Price ls. paper covers, or 1s. 6d. cloth. A COMPLETE MANUAL OF THE French Language.-By Professor Dz LOLME. Price 38. neatly bound. A SERIES OF LESSONS IN FRENCH, on an entirely Novel and Simple Plan, Beprinted in a revised form from "The Working Man's Friend." Price 6d. by post 7d. Above 30,000 copies of this work have been sold. D. JONES: We do not think that his mode of explaining the geological difficulty will answer the purpose intended.-AULD DONALD (Salisbury) must think again; every one else understands the query.-J. REDFERN: The books referred to cannot be had in the office of the P. E.-H. DRIVER (Tenterden): We entirely agree with Lord Palmerston, in reference to his opinion respecting modern penmanship; it is most detestable, especially the angular and spider-leg system-the so-called running-hand, which is a perfect sham; and we boldly and fearlessly maintain that the system of penmanship laid down in the second volume of the P. E. is by far the best we have seen in modern times: but we will admit that the machine-printing has prevented its beauty from being recognised; that, however, is not our fault, but the necessary result of the rapidity with which so many copies of the P. E. must be printed. Were the same lessons printed separately by CASSELL'S LATIN DICTIONARY. In Two Parts:-1. Latin and English, means of an ordinary hand-press, they would completely astonish our readers 3. English and Latin. BY J. R. BEARD, D.D., and C. BEARD, B.A. In by the difference in the execution. Our system may at once be denomi-Weekly Numbers, 3d. each, and Monthly Parts, 1s. The First Four nated the Palmerstonian System of Penmanship; and let our readers Monthly Parts are now ready, as also the First Sixteen Numbers. remember that it is all printed from types. His lordship, Viscount Palmerston, must have seen and admired, as we have done, the beautiful system of penmanship, published in London, by Joseph Champion, one of the most in cloth. beautiful writers of the last century, and not surpassed in any age or nation. But some of our own correspondents write a most beautiful hand; we wish our readers could see the penmanship of Mr. QUINTIN PRINGLE, of Glasgow, and even that of Mr. HENRY DRIVER, of Tenterden; we are sure they would be pleased, and so would Lord Palmerston. Emphatically we The Latin-English Division is now ready, price 4s. in paper covers, 58. CASSELL'S GERMAN PRONOUNCING DICTIONARY. ON PHYSICS, OR NATURAL PHILOSOPHY. No. XLIV. (Continued from page 258.) WARMING AND VENTILATING. Warming.-After the subject of Illumination, treated of in our last lesson, that of Warming and Ventilating naturally follows, as connected with the chemical sources of heat. The art of warming has for its object the proper employment of the sources of heat which nature presents to us, for the purposes of domestic economy and of manufacturing industry; in short, to warm our private dwellings and our public establishments so as to produce that degree of comfort necessary to the preservation of health. The chief sources of heat at present in use are the combustion of wood, charcoal, coal, coke, turf or peat, and anthracite. According to the apparatus employed in their combustion, we may arrange the subject under four distinct processes of heating :-1st, warming by the direct radiation of caloric, as in fire-places and stoves; 2nd, warming by hot air; 3rd, heating by steam; 4th, heating by the circulation of hot water. Let us consider these different processes of heating in their order. injurious. This mass of cold air which flows towards the fire, from without, cools the apartment in such a manner that only a very small portion of the heat is rendered of any use for the purpose intended. Moreover, the velocity of the air in the chimney being small on account of its great size, the draught is easily influenced by the winds, and it often produces in the chimney two opposite currents, which occasion the discharge of smoke into the apartment. Large fire-places and wide chimneys have been long abandoned in cities and towns; but those which are still in use are not sufficiently have still some of the inconveniences of the old ones. contracted in their dimensions, and our ordinary fire-places The proper theory of heating by means of common fires may be understood by reference to fig. 229, in our last lesson. If 斷 Fire-places. It is well known that modern fire-places are those in which open fires are placed against the walls of apartments, and furnished with chimneys through which the products of combustion are permitted to escape. Combustion cannot be continued without a constant renewal of the air in the apartment where it takes place. This renewal is carried on by the process of heating itself, which occasions a continual inward flow or motion of the air from without. There is, therefore, an essential and natural connection between warming and ventilation. It is remarkable that the houses discovered in Herculaneum and in Pompeii had no fire-places. Yet the invention of fire-places appears to be dated from the first century of the Christian era. In the times more remote, the fire was placed in the middle of the apartment to be heated, and the smoke escaped by an opening made in the roof of the house. Thus Vitruvius recommends that the winter apart-throws out its heat, and escapes in a heated state by the chimments should not be enriched with expensive works, because they would be injured by the smoke and the soot. The portable brasiers or chafing-dishes still in use in Spain, Italy, and France, indicate the manner in which the apartments of Pompeii and Herculaneum were heated; and the fires still to be found in the huts of the savages show their origin. These warmed the apartments more by radiation than by direct combustion. The dwellings of the Romans, in the first period of the empire, appear to have been heated by ovens or furnaces placed below the level of the ground, and the heat was distributed through the mass of the buildings; they were also heated by fixed fires open on all sides, set up in the middle of the apartments, and their smoke escaped by an orifice in the ceiling. Both these modes of heating required an enormous quantity of fuel, because the greatest quantity of the heat ascended into the open air along with the products of combustion. In the time of Seneca, flues or passages were first made in the walls of houses in order to convey the heat into the upper stories; and it is probable that this is the origin of the chimneys now in use. The first fire-places which were placed against the walls of houses were not surrounded with flues, but only surmounted with a sort of basket-funnel which gave a passage to the smoke. From an inscription found at Venice, we learn that in 1347, an earthquake threw down a great number of chimneys. This document, reckoned the most ancient in which mention is made of the existence of chimneys, coupled with the origin of chimney-sweepers in Piedmont, confirm the opinion that chimneys were invented in Italy. To the fire-places in which open fires were first made, as well as to the flues or chimneys for the smoke, a very disproportionate magnitude was given, and this disproportion still exists in country houses, especially in the chimneys. Too great an aperture for the fire-place and too great a width for the chimney are very serious inconveniences. The ventilation in such cases is enormous, and consequently the currents of cold air which are admitted by the apertures around the doors and the windows, acquire too great a velocity, and become very VOL. V. we take the flame of the candle, enlarge it, and maintain it by any proper means; in a word, place it in a fire-place, and it becomes a fire. The air which keeps up this fire reaches it from below, enters into the parts of the fuel, combines with it, ney, which discharges it into the atmosphere: all this heat is Jost; the only heat which is felt in the apartment is the lateral heat of radiation, which is at all times much less than the heat which ascends. Hence it is not surprising that a fire-place should give out to the room which it is intended to heat only two or three per cent. of the whole of the heat produced by the fire which is made in it. It has been even observed by experiment, that in some extraordinary cases, only one-half per cent. has been given out, and there are very few which give out more than six per cent. In our fire-places, therefore, we burn from twenty to thirty bundles of wood in order to obtain the quantity of heat which in reality is given out by a single bundle. The first work in which the true principles of the construction of fire-places were laid down, appeared in 1713, under the title of Mecanique du Feu, which was published anonymously by M. Gauger. This ingenious writer observed, first, that in order to reflect the heat the chimney, jambs should be of a parabolic form, and that the lower part of the mantelpiece should be horizontal. He next proposed to make under the hearth, behind the jambs, and close to the middle of the fire-place, a series of compartments through which the air might pass in succession, from a pipe or passage communicating with the exterior, into a mouth-piece which should throw it warm into the interior of the apartment. He discovered besides, that according to the testimony of the physician-architect Savot, in his L'Architecture Française des batimens particuliers, Paris, 1624, something analagous to this had already been done in the fire-place of the reading-room of the library of the Louvre. The only difference between the latter and his own plan was, that the cavity or mouth-piece was below the hearth and behind the middle of the fire-place, so that the air rushed into the apartment with less velocity and at a lower temperature. Besides, Gauger placed on the top of the chimney an apparatus for effecting the escape of the smoke, whichever way the wind might blow. Notwithstanding the excellence of these principles in heating of apartments, they were not duly appreciated; and it was not till the begin 122 ning of the nineteenth century that any improvements were made in our fire-places. The names of the earlier writers on this subject were Philibert de l'Orme and Gauger; the names of the latter writers, Franklin and Rumford. The latter philosopher narrowed the aperture of communication with the chimney, diminished the depth of the fire-place, and built inclined walls at the sides of it close by the jambs, a process which is called Rumfording a fire-place to this day. But he did not introduce hot air into the apartment, and his method is very incomplete in this respect. According to M. Peclet, in his Traité de la Chaleur considerée dans ses applications, experiment has shown that for the chimneys of fire-places in ordinary apartments, a circular opening of about eight or ten inches in diameter is almost always sufficient; and when this limit is exceeded, it is proper to supply the fire-place with a register, in order to diminish the size of the opening when necessary. Fig. 238 is the side vertical section Fig. 239. of a common fire-place furnished with a register or moveable wrought-iron plate, by means of which the draught can be increased. The direction of the air, when in motion, is indicated by the arrows. M. Peclet ascertained by experiment, that in a common fire, the volume of air required by combustion is 1,600 cubic feet for every pound of wood. He states that he had never seen apartments in which the apertures for the admission of air were of sufficient dimensions. The diameter of these apertures ought to be nearly the same as that of the chimney or of its upper orifice, when it has a diameter less than that of the chimney. The most effective arrangement consists in making the ventilator communicate with a tube which rises to the ceiling and pours into the room air heated by its contact with the metallic sides of that tube, and which is placed inside the chimney or passage for the smoke. Fig. 239 represents a vertical and side section of a fire-place and chimney arranged in this manner. The elevation of temperature produced by the combustion of 201bs. of wood in an ordinary fire-place and in a room whose capacity is about 3,200 cubic feet, or whose length is 20 feet, breadth 16 feet, and height 10 feet, is, according to the experiments of M. Clement, only 110 Cent., or 2°-7 Fahr. The same degree of heat thus obtained with wood burned in a common fireplace, was obtained, in an improved fire-place having a ventilator and register, with 10 lbs. of wood; in a fire-place improved by Desarnod, called the Prussian fire-place, with 6 lbs. of wood; in a Curendam stove of wrought-iron, with 4 lbs. of wood; and in a Desarnod stove of cast-iron or glazed earthenware, with 3 lbs. of wood. It is, therefore, often an easy matter to pay the price of an improved fire-place with the money saved in fuel during the course of a single winter. Whatever improvements, however, may have hitherto been made on our common fire-places, they are still the most imperfect and most expensive mode of warming apartments, seeing that they only yield in wood fuel about six per cent. of the whole heat developed by combustion, and about thirteen per cent. with coke or coal. Still open fire-places are, and always will be, the most agreeable and the most wholesome method of warming, in consequence of the presence of the fire and the continual renewal of the air in the apartments. Draught of Chimneys.-By the draught of a chimney is meant an upward current which is established in it by the ascent of the products of combustion; when the current is rapid and continued without intermission, we say that the chimney draws well. We have seen that the draught arises from the difference of temperature between the interior and the exterior of the chimney. In consequence of this difference, the gaseous matters which fill the chimney being less dense than the air of the apartment, a state of equilibrium becomes impossible; for the weight of the gaseous column in the chimney being less than that of the exterior column of the same height, an excess of pressure arises from the exterior upon the interior, which drives out the products of combustion with greater rapidity in proportion as the difference of weight between the two gaseous columns increases. The existence of the currents which arise in gases of different temperatures is easily proved by the following experiment: open a door which communicates between a heated room and one which is not so; then, holding a lighted candle at the top of the door, the flame will be seen forced in the direction from the warm room into the cold one. On the other hand, if the lighted candle be placed on the ground, the flame will be forced in the direction from the cold room into the warm one. In the Great Exhibition of 1851, we saw what was called a "registered conducting leaf-stove," adapted for heating large apartments in houses exposed to a north-eastern aspect. The following is the account given of this invention by the exhibitor, Mr. W. Keene : "The difficulty of heating large rooms to a comfortable temperature, in the depth of winter, led to the invention of the stove exhibited. In an apartment almost insensible to the action of the ordinary fire-place, and in which the thermometer indicated but a feeble tendency to rise two hours after lighting a fire, it was affected to the extent of twenty degrees in little more than as many minutes after lighting a fire in the leaf-stove. The sensitiveness of the leaves to the diffusion of heat is so great, that the combustion of a few shavings or a little paper in the fire-place is immediately and sensibly felt in the apartment. Such a result obtained not only without any sacrifice of, but in addition to, the comfort of an open fire-place, clearly demonstrates the value of the heat which we permit to pass up the chimney. By the leaf-stove, it is rendered available, and made to circulate in the apartment, or may be shut off at will. The conducting leaf-stove is formed of plates of metal so placed that each one is a conducting leaf, a portion of which goes down, as it were, into contact with the fire, and is exposed to the direct action of the heat. The heat thus received is rapidly distributed over the whole surface of the leaf. When it is desired to take advantage of the heat communicated by conduction, it is only needed to set the valves open, and permit the air to circulate around the leaves; by closing the valves, the circulation is suppressed or modified at pleasure. The rapidity of the conduction and radiation of the heat prevents the metal attaining a high temperature. The principle of this stove is to diffuse a large volume of air at a genial temperature by the conducting and radiating power of extensive surfaces. In ordinary stoves, masses of metal heat small volumes of air to a high temperature, by which it is rendered unwholesome. The principle of conducting leaves can be applied in a great variety of forms, and to the construction of stoves of any size, for heating vestibules, hospital wards, churches, and public buildings generally; and can be kept within the limits needful for the invalid bedroom or the smallest apartment." In order that a good draught may be established in a chimney, the following conditions must be satisfied : current of fresh air being obtained by giving great height an. little breadth to the conducting pipes. 3rd. To give a sufficient degree of humidity to the air heated by the stove, by placing a vessel full of water either upon the stove or on the pipes which convey the hot air, in the ratio of about half a gallon of water to an apartment containing upwards of 5000 cubic feet, or a room of 25 feet length, 20 feet breadth, and 10 feet high. 1st. The diameter of the chimney must be such as to admit of the necessary exit of the products of combustion. Otherwise, if this diameter be too great, it will create ascending and surface in wrought iron-plate, or less in cast iron, for every 4th. To reckon in practice about 10 square feet of stove descending currents, and the chimney will smoke. It is use-3,200 cubic feet of capacity in the room to be heated, or whose ful to place at the top of the chimney a conical chimney-pot, dimensions are 20 feet long, 16 feet broad, and 10 feet high. so that the smoke may escape with a velocity sufficient to resist the action of the wind. 2nd. The chimney must be raised sufficiently high to admit of an excess of pressure, powerful enough to expel the products of combustion; for the draught depending on the excess of the exterior pressure above the interior, this excess would be ineffectual were the column of heated air too short. 3rd. The outward air must be allowed to enter the apartment where the chimney is, in a manner sufficiently rapid to answer the demands of the fire. In an apartment quite close and free from the admission of air, the fire will not burn; or if it does so, it will create descending currents of air, which will drive the smoke into the apartment. The air in general enters in a sufficient quantity by the apertures round the door and the windows. 4th. A communication between the two passages to the fireplace, viz. that of the air and that of the smoke, must be carefully avoided; for if the one draws more than the other, there will be produced a descending current of air which will bring the smoke back again. Stoves.-An apparatus, placed in the middle of an apartment or at least at some distance from the wall, and in which fuel is burned for the purpose of heating the apartment, is called a stove. The air heated and altered by the combustion, issues from the fire either directly, or after having made certain revolutions in a pipe whose extremity is open to the external atmosphere. The doors of the fire and the ash-pit are sometimes made of the same piece as the stove, and sometimes of different pieces; and stoves are made of wrought-iron, castiron, earthenware, and bricks. The use of stoves is adopted to a great extent in the north of Europe; but in this country and in France, open fires are preferred. Sometimes the heat disengaged by the fuel passes directly into the room, through the iron of which the stove and the smoke-funnel are made; sometimes the air of the room is heated by the radiation of the fire through its cover, and is renewed by the exterior air, which, after having circulated in the interior of the stove, through pipes which multiply the quantity of heated surface, issues hot from these pipes into the apartment. In this case, the apparatus is called the caloric or hot-air stove. The common stove furnishes the most simple and economical method of heating, for almost the whole of the heat developed is employed in warming the room, and the smoke can be lowered to 100 Centigrade before it escapes into the atmosphere. But this advantage is accompanied with a great inconvenience; the ventilation is diminished, and it is even completely suppressed when the mouth of the fire is without the hall, as in the German and Swedish stoves. When a stove heats the air of an apartment to a great degree, the air is not saturated with moisture to the same amount as when it had the temperature of the exterior atmosphere. Accordingly an appreciable desiccation of the skin, and often a painful feeling in the respiratory organs, is experienced by persons immersed in this dry medium. This, however, is easily remedied by placing on the stove a vessel full of water; the evaporation of which soon restores the air to a proper degree of saturation. The following are the fundamental principles of the construction of hot-air stoves. 1st. To give the furnace the greatest possible surface, by constructing it with the greatest simplicity of form and adjust ment, and making the pipes which carry off the smoke as few as possible, and placing them vertically, so as not to alter the draught. 2nd. To make a passage over the furnace for a current of fresh air, in a direction opposite to that made for the smoke, which ought first to ascend and then descend vertically; the It is truly deplorable, says M. Peclet, to see, with very apparatus know of the simplest principles of their trade; it few exceptions, how little the manufacturers of warming seems as if they wished only to make an interior arrangement different from that hitherto employed; whether good or bad is of small importance, provided the exterior is of an elegant velocity and the high temperature of the jets of hot air which form. They only judge of the goodness of a stove by the issue from the heating orifices. He adds, that the orifices for the admission and emission of the air ought to be such that the hot air should not be emitted at a greater temperature than from 30° to 40° Centigrade, or from 86° to 104° Fahrenheit. Every stove which fulfils these conditions will produce the greatest useful effect; and the large body of air which passes through it will prevent the metallic surface from taking a temperature injurious to the heated air. It is also important to observe that an apparatus, which, under all circumstances, was arranged in the most advantageous manner, would not answer for the purpose of heating a room which should be occupied for a length of time by a great number of persons, because it would not produce a sufficient degree of ventilation. Fig. 240, represents a very simple arrangement for an hospital stove, which might be constructed of bricks and some thin cast-iron plates, heated by the smoke, for medicinal purposes. Stove-grates are metallic apparatus placed in the middle of a hall or in the centre of a fire-place, and arranged like stoves ture which can be closed by a vertical trap-door; when this for burning fuel and heating the air, but having a large aperis lowered, the apparatus becomes a stove, and when raised a fire-place. The Prussian and Desarnod fire-places are of this description. The latter, although old, are excellent; there are some of them which work well still, although they have been in use for fifty years. Warming by Hot Air.-An apparatus in which a fire, surrounded by an envelope, heats the air taken from the outward atmosphere, in order to transmit it to several apartments placed at various distances, is called a calorifer or hot-air stove. The difference between this and the stove properly so-called, is, that the latter is placed in the very apartments which are to be warmed. The following are the principles upon which the former should be constructed: 1st. It is necessary that a direction of constant ascent should be given to the hot air, and, therefore, the hot-air stove should be placed under the level of all the apartments to be heated. 2nd. The exterior envelope of the calorifer and its conduct ing-pipes should be thick, made of non-conducting materials, and have walls isolated by vacuums which are formed in the sides of the apparatus. 3rd. The whole interior of the apparatus must be made of metal, the parts which receive the first action of the fire in cast-iron, and the rest in wrought iron plate; the forms and adjustments must be so simple, that the parts may be easily made; they must be easily taken to pieces and put together again, in case of repairs; and, above all, easily inspected and cleaned. 5th. The smoke must be made to pass through metallic pipes, and the air heated all round; instead of being forced into the pipes and enveloped in the smoke. works at two atmospheres or upwards, the diameter of the conducting-pipe may be considerably diminished without inconvenience, according to the following practical rule given by M. Grouvelle: the interior diameter of the pipe must be equal at a minimum to one inch and four-tenths of an inch, increased by six-hundredths of an inch for every horse power of the generator, or of the steam which passes through this pipe. As to the generators, their dimensions must be determined by the following rule, the result of long practice, and confirmed by the experiments of M. Peclet: 10 square 4th. The smoke must not be reduced in temperature by feet of wrought iron plate, heated interiorly by steam and ex scattering it in all directions, and impeding its progress in posed to air at 15° Centigrade or 59° Fahrenheit, condenses various ways, but it must especially have a good draught, 4 lbs. of vapour, and is sufficient to heat and keep at this tem which must be encouraged by the issue of the flame in a verti-perature a room with walls and windows of an ordinary descrip cal column from the fire, and constructed so that the smoke tion, containing 2,400 cubic feet, that is, whose length is 20 shall not be lowered in temperature below 300° Centigrade, or feet, breadth 12 feet, and height 10 feet; or a workshop of 3,400 572° Fahrenheit. cubic feet, that is, 20 feet long, 17 feet broad, and 10 feet high, on the supposition that the latter does not require a high temperature; but if so, the preceding estimate will nearly answer the purpose. This rule was employed in the establishment of the heating apparatus for the Bourse, and the Institute at Paris, where it works well; but it must be modified when the premises contain a great number of people, where the temperature is raised, and a powerful ventilation is required. Thus, in a cotton-mill, the number of work-people employed. will raise the temperature by 3° Centigrade or 5°-4 Fahrenheit. The condenser is a hollow metallic vessel, into the interior of which the steam is introduced by a pipe raised some inches above the ground. Another pipe level with the ground is employed for the passage of the condensed water; and a third pipe proceeds from the upper part of the apparatus, and is employed to discharge the air when the steam enters the latter. These three pipes are furnished with stop-cocks: The alimentary pipes are always inclined towards the generator, so as to send back into it the water which has been condensed during the passage of the steam. One of these pipes, or the generator itself, is furnished with a small apparatus called the sniffer, which carries a valve opening inwards, and which allows the air to enter into the generators and the pipes, whenever the fire is low and a vacuum is created. In this way, the pressure of the atmosphere is prevented from destroying the whole apparatus. 6th. After the smoke has been made to ascend vertically in order to ensure a good draught, it must be made to descend in a direction contrary to that of the fresh air, which thus will come in contact with surfaces warmer in proportion to the elevation of the temperature. 7th. The surface of the parts nearest the fire must be made so large as to become only slightly red by heat, and that the air which passes over them may not contract a bad smell; at the same time, great apertures must be allowed for the escape of the hot air, in order that it may give out a very considerable quantity, without being too elevated in temperature; and a vessel full of water must be placed on the reservoir of hot air. In good calorifers, the useful effect may be raised to 75 per cent. of the calorific power of the fuel; but in plans, it is proper to reckon only on 50 or 55 per cent. In practice, one pound of coal will heat 1600 cubic feet of a house. As to the proportions of the apparatus, when 1 lb. of coal or 2 lbs. of wood are burned per hour, the surface of the stove should be ten square feet, the cross section of the smoke-pipes two square feet, and the fire-grate five square feet. The quantity of water for moistening the air may be estimated at about a gallon for every 8000 cubic feet of space. Heating by Steam.-The property which steam possesses of restoring its caloric of vaporisation when condensed, has been employed for the warming of baths, factories, public buildings, conservatories, and stoves. For this purpose, a generator or boiler such as that described at the beginning of our lesson on the Steam-Engine is required; also pipes of distribution and transport, and condensers with large exterior surfaces for condensing the steam and transmitting through their surfaces the heat disengaged by this condensation; a heat which is capable of raising 550 lbs. of water, 1° Centigrade by 1 lb. of condensed steam. The generators employed for the purpose of heating apartments are generally constructed to resist a pressure which does not exceed that of the atmosphere by a sixth or a third part; that is, the pressure varies from 35 to 40 inches of mercury. In manufactures, high-pressure steam is employed to heat the workshops; but it is employed first directly in the cylinder of a steam-engine, so as to make it perform double work, by which it is considerably diminished in force. The pipes of distribution, which convey the steam to distances amounting sometimes to several hundreds of yards, must fulfil the following conditions: 1st. They must have a diameter in their cross section sufficient to convey the steam to the greatest required distance, without occasioning a dangerous excess of pressure in the generator, and without causing the steam to condense too rapidly in its passage. 2nd. They must be placed in such a manner that they can be inspected and repaired at all times. Warming by Hot Water.-The heating of houses by the circulation of hot water in pipes was practised by the Romans, who employed it in their hot-air and hot-water baths. In some localities at the present day, as at Chaudesaigues in France, the water of hot springs is circulated in pipes in order to warm the houses; but the warming of apartments by hot water consists in the proper arrangement of an apparatus which transmits in a series of pipes the water heated in a boiler, and brings it back by another series of pipes, a continuation of the former, into the same boiler, so as to make it perform a continued rotation. This method was the invention of Bonnemain, who applied it to the artificial incubation of chickens, an operation which required a slow, moderated, and perfectly equable heat, and one with which the air of the stove would not become too dry. Invented in 1777, this process was brought to such perfection, that an apparatus set up by the inventor himself is in operation to this day at Pecq, in France. This method of warming was at last adopted in this country, and, between 1830 and 1836, was so extensively employed, that it took the place of steam in heating apartments. By itself, or combined with warming by hot air, it has been applied to public buildings, private houses, and conservatories, by the ablest engineers; and it received an extensive improvement from Perkins in 1837, by the invention of the circulation of hot water under high pressure; and this process has also been adopted in France. Fig. 241 represents the method of warming by the circulation of hot water. From the top of a boiler, a, placed on a fire, D, rises a vertical tube, F. The hot water tends to ascend towards F, in conseIn the heating apparatus set up by M. Grouvelle in the quence of its diminished density. But at r is commenced a palace of the Institute at Paris, the conducting pipes are 43 series of pipes, through which the water passes and succesinches in diameter; and the steam arrives in a few instants at sively heats the different parts of the building. During this the most distant points under a very small pressure. The passage it is cooled, and returns to the boiler at c, where it size of generators in general should not be less than that enters at the bottom; and thus a continued circulation of the adapted for engines of 10 or 12 horse power. When, for water is kept up in the direction AFC. M. Leon Duvoir has reasons independent of warming apartments, the generator | given to this apparatus the form in which it is now employed |