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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[September, 



in adjudicationss of rails. It is asserted now that France is fully able to sup- 

 ply the quantity required, and in consequence of the custom house union with 

 Belgium being considered impossible, several of the Belgian capitalists have 

 taken establishments on French s'de, four new forges having been set up in 

 the department of the North for manufacturing iron with coke. These estab- 

 lishments are extending, one is being built in the coal fields of Commentry, 

 another at Montlufon, and four blast furnaces either at the gates of Lyon or 

 at Lavoulte on the Rhone. All these works are for manufacturing rails, and 

 it is calculated they will supply 25,000 tons. The eleven old works, it is said 

 in the official mining returns, can supply 75,000 tons of rails yearly, which 

 we should doubt. After all a hundred thousand tons a year only just supply 

 2500 miles yearly, or one-fifth of the total length of railway authoiized by 

 the legislature. 



Sheet Iron. 

 Sheet iron was little attended to in France thirty or forty years ago, about 

 two-thirds being imported from abroad and now not a plale. In 1834 the 

 produce was 12,000 tons, in 1841 it was 26,200 tons, valued at £040,000. This 

 increase arises from the great demand for machinery, steam boilers, boats, 

 buildings, &c. Formerly sheet iron was only made with charcoal, now it is 

 often made with coke. The High Saone and the Vosges ate the chief depart- 

 ments tor this branch. M. Richard exhibited boiler plates made out of four 

 blocks of iron united by the hammer and then rolled. M. Blanc, jun., of 

 Versailles, exhibited pipes of sheet iron. 



Drawn Theing. 

 This manufacture, derived from England, is extending in France, and is 

 chiefly carried on at La Briche, near St. Denis, and at Abainville, in the 

 Meuse. La Briche was founded by 11. Gaudillot for drawing and soldering 

 tubing hot, he imported the prucess. and exhibited his first specimens in 1839. 

 His tubes or pipes are all tested to 300 atmospheres, and are principally used 

 for gas and hot water pipes. M. Gaudillot supplied last year 16,000 yards to 

 M. Duvoir Leblan for heating the Luxembourg Palace, the Blind School, and 

 other large establishments. He also makes large tubing for pumps, boiler 

 pipes, waggon axles, columns, &c. He is trying, in consequence of the expe- 

 riments in England, to get a demand for hollow axles for locomotives and rail- 

 way carriages. M. Gaudillet asserts that he can produce 9 inch pipes, while 

 in England none have been made beyond 4f in. outside diameter. The use of 

 hollow iron for large gates is extending. He has supplied a good many at 

 Paris within the last 15 years. M. de Viney exhibited tubing drawn cold, 

 proved to a pressure of 10 atmospheres, and galvanized by Sorel's process. 



PROFESSOR FARADAY ON HEAT. 



A course of eight Leetures delivered at the Royal Institute. 



Lecture VII., June I, 1844. 



(Specially reported for this Journal,) 



When light falls on a polished opaque substance, it is reflected from it, or 

 thrown ofl in an opposite direction, the angle of reflection being always equal 

 to the angle at which it falls on the surface. If the body is transparent, the 

 greater part of the light pasaes through it, and if the light falls angular on it, 

 it is refracted, or bent from its course, and «hen the transparent substance 

 is prism-shaped, the light is thrown completely in another direction. Such 

 substances as ice and glass allow light to pass through, and refract it, but 

 polished metals reflect, and do not allow i t to pass. The same facts have been ob- 

 served with respect to heat, and although it cannot be seen in its passage, its 

 transfer can be proved. When the hand is held towards a fire, heat is felt, 

 which is due to its being radiated, or thrown equally, as from a centre, in all 

 directions. The eilects of radiated heat may be watched by using a red-hot 

 ball, which will be fouud to give oil' heat equally in all directions, and will 

 readily light a piece of phosphorus placed at a great distance below it. A 

 flat mirror, held in the path of the rays of heat, will reflect them, and the 

 rays may thus be thrown on any required spot. If, instead of one mirror, 

 300 or 400 are employed, and so placed that the heat reflected from each 

 should fall on the same spot, the effect of course is greatly augmented. A 

 concave mirror maybe considered as such an assemblage of myriads of flat 

 mirrors, and its focus as the spot where their reflected heat is accumulated. 

 With two parabolic reflectors, the eflects of radiated and accumulated heat 

 are very striking. A red-hot ball placed in the focus of one will fire com- 

 bustibles held in the focus of the other, though they m;iy be far apart, and 

 ice produces in a similar manner, cooling eflijcts. 



The rays of heat and light are not hot, and it is an error in thought and 

 word to call them so. The rays of heat are heating rays but not iiot rays. 

 This is beautifully illustrated by the experiments of Mclloni, who found that 

 various transparent substances allowed heat to pass through them in various 

 proportions ; that those bodies that allow it to pas.s freely through them 

 do not become heated, and that those that stop the rays become heated ex- 

 actly in that proportion. He ,placcd a red-hot ball on a stand, and the two 



substances he wished to compare on opposite sides of it, and by a frame pre- 

 vented any heat from passing excepting through the two bodies ; beyond 

 these he placed two pieces of metal with phosphorus on them, and by com- 

 paring the time it took to fire the phosphorus, he learnt the comparative 

 freedom with which heat passed through the bodies experimented on 

 Through a piece of rock salt the heat passed with facility, but through glass 

 it scarcely passed at all. Passing through the salt, it leaves it CGUl,lbut being 

 stopped by the glass it makes it hot, thereby proving that when as rays it is 

 not hot, but only when stopped, and then they lose their character as rays. 

 In the same manner the rays from a luminous body are not light, until 

 stopped by a solid body. If they were, the light from the sun should be seen 

 passing through space to the planets or to the moon, but they give no light 

 until stopped by them, and therefore are invisible. 



When reflectors are used with the sun's rays, of course both the light and 

 heat are reflected. Wood or paper held in the focus of a large reflector, are 

 immediately fired by the sun's heat. The course of the rays travelling from 

 the reflector to its focus is made beautifully evident by holding a smoking 

 piece of paper underneath. 



The rays of heat passed through a lense, are conveyed in a similar manner 

 by refraction to a focus, but in this case the focus is on the opposite side to 

 the source of heat. With the action of a burning glass every one is familiar, 

 but it will now be seen that the property of refracting to a centre does not 

 depend upon the nature of the body, but upon its transparency and shape ; 

 for ice, if melted in a hot tin mould until it is lense- shaped, acts equally well 

 with glass. By it the sun's rays may be concentrated so as to burn paper 

 and other combustibles, and yet the ice does not become melted. This could 

 not be done with common heat, for instance, that from a fire, as ice will not 

 allow its rays to pass, and stopping them, becomes melted. In Melloni's 

 experiments on this subject he found that there were different kinds of rays 

 of heat, just the same as there are different coloured rays of light, and that these 

 rays were mixed in various proportions according to the source from whence 

 they emanated. Thus some will pass through ice and salt, and not through 

 glass. The rays of heat from the sun pass through almost every substance 

 whilst those from a common fire are stopped to a certain extent by almost 

 every thing, and the substances themselves become heated. That no heat is 

 produced until the rays are stopped is seen bypassing the sun's rays con- 

 centrated by a lense through a glass tube filled with ether, when no efl'ect is 

 produced ; but put into it something which will stop the rays, such as a piece 

 of black paper, and the ether is seen to boil immediately. The great elTects 

 produced by concentrating the sun's rays from afevv feet on to one spot, gives 

 a great idea of the immense quantity of heat which is continually being 

 poured on this earth, and of the fearful eflects were this heat withheld but 

 for one season. These rays are not obstructed by the glass of the window, 

 but allow it to pass on to carpets, SiC, and heat them, but were they the 

 same rays as from a fire, the effect would be very different. 



The reception and emission of heat, though depending principally on the 

 nature of the body, is found to be very greatly influenced by the state and 

 texture of the surface. Of two radiating bodies, for instance, tin canisters 

 filled with hot water, one blackened or roughened on the surface will be 

 found to get cold sooner than that which is left bright, one appearing like a 

 good conductor, the other like a bad one. though the only diflTerence is in the 

 state of the surface ; or the experiment may be varied by black-washing or 

 white-washing only one side of the vessel ; a thermometer will then indicate 

 more heat being given off from that side than from the others. In the same 

 way the reception of heat is affected by surface, those absorbing the best 

 which radiate the best. The application of this pnncipie to useful purposes 

 is carried out to a great extent; for steam engines, and boilers, which are 

 required to retain the heat, are kept bright, whilst those from which the heat 

 is required to be delivered, as in warming buildings by hot water pipes, the 

 surface is kept rough. In domestic economy the china teapot is now super- 

 seded by polished metal, which is found to keep the infusion hotter, and a 

 difi'erence even would be found whether a silver teapot were kept clean or 

 dirty. Every substance is continually radiating heat to any other body near 

 it which is colder than itself, and ice, even, will send out radiant heat to 

 solid carbonic acid. The emissive power is not always in proportion to the 

 amount of heat, for the flame of a candle, though consisting of particles far 

 hotter than a red-hot iron ball, does not radiate nearly so much heat as the 

 latter. The power of a bright reflective surface to protect from radiant heat 

 is well shown by placing a slip of gold leaf on a sheet of paper, and holding 

 over it a red-hot ball ; the uncovered paper is scorched, whilst the thin metal, 

 itself an excellent conductor, entirely protects the paper below. 



It has, then, been shown that bodies differ in their power of transmitting 

 heat, some, like rock salt, transmitting it readily, or being an easy diathermal 

 body, whilst others, such as alum, transmit it but slightly, and that the rays 

 of heat difl'er, depending upon the source from which they emanate, for the 

 facility with which they penetrate transparent media ; thereby confirming 

 the probability of the analogy that Melloni has drawn between the various 

 rays of hght and those of heat. 



