288 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Julyj 



votiient distance they are obliged to walk or ride by an oninibu'!, 

 which occupies as inucb time as travelling by railway a distance of 

 20 miles. To wliat are called short passengers, this delay is a most 

 serious inconvenience. Hence it will be observed that particular 

 lines more favourably situated in populous localities, enjoy a quasi- 

 monopoly of this class of traffic, persons will go to London Bridge or 

 Fenchurch Street, who will not undertake the expedition to Pad- 

 dington or Nine Elms, consequently these latter termini must in 

 the end be extended into town. One of the circumstances most to 

 be regretted in considering the subject is, that every year of delay 

 enhances the difficulty of obtaining a clear line. Such is the rapidity 

 with which house building in the metropolis extends, that what was 

 lately a vacant space soon gets covered with brick and mortar. A 

 very excellent plan is now before us for a Metropolitan junction rail- 

 way, with a terminus at Waterloo Bridge. We understand that it is 

 proposed to take the West London Railway which now communicates 

 the Birminghan and Great Western, and terminates at Kensington, as 

 part of the line, and then to carry the Railway to the Thames, oppo- 

 site Battersea, thence across the river by a bridge, and join the South 

 Western Railway near Battersea, afterwards to carry the line across 

 the Vauxhall and Westminster Bridge roads by a viaduct, terminating 

 at Waterloo Bridge, on a level with the roadway. Ultimately it is 

 contemplated to carry the line to Southwark Bridge, and have a 

 branch to Richmond. Waterloo Bridge may be considered as the 

 centre of the metropolis, it has good roads to the south, and a road is 

 now being made to give it as good access to the north by the con- 

 tinuation of Wellington Street, which runs in a line nearly straight 

 across Holborn to the Hampstead Road. Thus from Waterloo Bridge 

 will there be convenient access and good omnibus accommodation to 

 every part of London. We trust there will be no difficulty in the 

 question of feasibility or expense, while most certainly sooner or later 

 something must be done to carry this or a similar line into eft'cct. 

 Such aline will be a great boon to those railways with which it may 

 be connected, as it cannot fail to cause a great increase of passengers 

 to such places as Richmond, Hampton Court, Windsor, Harrow, Sec, 

 and a great accommodation for conveying goods direct from the river 

 Thames to all parts of the manufacturing districts. 



PROFESSOR FARADAY ON HEAT. 



J course of six Lectures (leliiieicd nt flic Royal InstiUUc. 



Lecture HL, May 4, 1844. 



(Spechdhj reported for this jommit.) 



When bodies are heated at one part, they gradually give up their heat to 

 the other parts, till they are equally hot all over. This, which is called the 

 power of conduction, exists to some extent in all substances, in solids to the 

 greatest extent, in gases to the least. The law of conduction, or the rate at 

 which heat travels through the substance, is found to he uniform with all 

 solid bodies, and is expressed by saying that as the distances increase in arith- 

 metical progression, the heat decreases in geometrical progression ; thus, a 

 bar heated to 800° at one end, if at one foot distance it was reduced to 400°, 

 would at 2 feet be at 200°, at 3 feet 100°, at 4 feet 50°, and so on, as in the 

 diagram. 



800=" 400° 200° 100° 30° 



I 



I 



I 



I I I I I 



• 1 2 3 4 feet 



But bodies differ from each other very greatly in their degree of conducti- 

 bility, some being excellent conductors, others very bad conductors. A rod 

 of metal will serve best to illustrate this travelling of heat. A series of balls 

 fixed on the under side of a bar of copper heated at one end, by their falling 

 one after the other, indicate its progress. If a bar of iron be heated under 

 the same circumstances, it will be seen that three balls will fall from the 

 copper to one on the iron, showing the great conducting power of the former. 

 This point is of great importance in many arts, particularly in building, as on 

 a hot day all the materials employed expand in different proportions, or con- 

 tract with cold. A frequent mode of illustrating this is to have a series of 

 cylinders of copper, iron, glass, wood, and brick, and to place them on a hot 

 plate of metal, and a paper indicator fixed on the top of each by means of a 

 little wax; the indicators will be found to fall in the order in which they are 

 named. German silver, which is being so much used for domestic purposes, 

 is not nearly so good a conductor as silver, therefore hot substances can he 

 eaten with it without fear of burning. The relative conducting power of 

 various substances is shown in the following table : 



13ad conductors arc frequently employed to stop conduction. Thus the 

 smith who punches a hole through red hoi iron, protects liis baud from the 

 heat his tool acquires, by fixing it in a wooden handle. The handles of 

 domestic articles, such as curling tongs, are for this purpose covered with 

 string. In the manufacture of coal gas, the men in the retort house are ex- 

 posed to an intense heat ; at first they wore canvass shirts, hut they soon 

 found that it was more judicious to work in flannel shirts, flannel being a 

 much worse conductor than canvas, and therefore better suited to the pur- 

 pose. It is true, it was not philosophy that pointed it out to these men, but 

 liracticc. The accumulation of badly conducting matter is occasionally very 

 injurious. Fur should never be allowed to accumulate in kettles or boilers, 

 as the heat then has to penetrate a thin stratum of stone, and not being 

 rapidly enough absorbed, destroys the metal of the boiler. From salt water 

 the accumulation is much more abundant than from fresh, and instances have 

 been known where, owing to the deposit in the boiler, holes have been burnt, 

 during one journey, large enough for a man to crawl through. 



Want of continuity lessens very much the conducting power of substances. 

 Owing to this, hot metal may be carried on chains with impunity. At Gib- 

 raltar advantage was taken of this property of non-continuous bodies, for it 

 is said that red-hot balls were carried in wheelbarrows merely by interposing 

 a layer of sand between the wood and the ball. The band, even, can sup- 

 port a red-hot ball for a short time, by laying some sand on it, taking care to 

 protect the other parts of the hand from the heat of radiation. Aldini, Gal- 

 vani's nephew, introduced into this country the use of the filamentous sub- 

 stance asbestos, as a protection against heat, a ])erson clothed in a dress of 

 this kind being able to withstand for a short time the action of flames. Ob- 

 sidian, which is lava in a state of glass, is a tolerable conductor of heat, but 

 when frothed up into pumice, it is one of the worst conductors known. If 

 continuity is broken by the interposition of a bad conductor, the effect is 

 very great, as may be shown by a metallic vessel with three handles, one 

 continuous, the second in two pieces fitting on to each other, the third the 

 same as the second but with a piece of paper interposed. Phosphorus being 

 placed on each handle, and boiling water poured into the vessel, it will be 

 found that that on the continuous handle will soon fire, that on the handle 

 in two pieces will be some little time after, and that with the paper inter- 

 posed perhaps will not light at all. 



All bodies conduct heat, but fluids do so with difficulty. A red-hot ball 

 may be brought to touch the surface of a small vessel full of water, and yet 

 a delicate air thermometer at the bottom of the liquid will not be affected. 

 Count Ruinford showed that water may be kept boiling at the surface, whilst 

 ice remained at the bottom. Indeed so slightly does it conduct, that plulo- 

 sophers once thought that fluids did not conduct at all. But the effect of 

 the mixture of hot and cold water, shows that they do. Food frequently 

 surprizes us by its conducting power ; whilst one kind cools very quickly, 

 another maintains its heat for a long time. In the water foot bath, heat can 

 be borne by keeping the feet still which cannot if they arc moved about. 

 This is because the feet abstract the heat from the water next to it, but the 

 remainder of the water gives up its heat hut slowly and therefore it can be 

 borne. The same thing takes place with porridge, one part becoming cool 

 whdst the other parts are hot. This may be shown strikingly by substituting 

 a copper tube with ether in it, for the spoon. When first put into the por- 

 ridge the ether is vaporized and may be lighted, but the flame soon lessens 

 and is nearly extinguished, because it has deprived the surrounding part of 

 its heat ; but move it to another part, and the flame of the ether is vastly 

 increased, indicating greater heat. 



Air is almost a non-conductor. The flame of a spirit lamp communicates 

 great beat to air, but owing to its being so bad a conductor, gunpowder may 

 he dropped through the flame without inflaming, whilst iron filings, which 

 require much more heat to burn, are consumed in this manner ; but here the 

 efli'ect is increased by the good conduction of the iron. The warm of wadding 

 or eider down arises from its non-conduction, but this is not due to the sub- 

 stance of the material, but to the air which is enclosed. Count Rinnford 

 showed that if these porous substances are twisted tight, they beconie far 

 better conductors. The small quantity of solid matter that many of these 

 textures contain is truly surprising. If a jar be filled with alcohol, wool may 

 be gradually inserted till several times the bulk of the jar, without the level 

 of the alcohol being materially affected. 



Metals are said to he colder than wood, hut they arc not so. To the hand 

 they feel colder, but that arises from their conduction, as they carry away 

 the heat much more quickly than wood does. When heated, on the con- 

 trary, they are said to be hotter than wood, because they give uj) the heat 

 they have acquired, more quickly. This is well illustrated by roiling a slip 

 of paper round a rod of wood, and another round one of copper ; that on the 

 wood is soon charred, whilst that on the copper remains unhurt, because the 

 beat is conducted away so quickly. Effects exemplifying these facts are 

 often seen in daily life. A very hot cinder falling on to water, causes but: 

 little steam until it has become somewhat cooler, when its action is violent .; 

 this is because it forms, when very hot, a vapour of steam all around it, 

 which by its non-conduction protects the water from actual contact, until, by 

 its cooling down, its atmosphere of steam is removed. Exactly similar to 

 this is the curious phenomena attending the pouring a drop of water on a 

 very hot silver basin ; the water runs over the surface like a beautiful pearl, 

 with no perceptible evolution of steam, until the basin becoming cooler, the 

 water touches the surface, and is suddenly converted into steam. Potassium, 

 thrown on the surface of water, acts in a similar manner ; for after combus- 



