i 



May i8, 1893] 



NATURE 



67 



correctly proportioned to the stresses imposed by a rolling load. 

 This comparatively small bridge was followed by the Boyne 

 viaduct at Drogheda, which must ever rank as a signal illustra- 

 tion of the successful application of abstract principles to a great 

 work by men who were capable, not only of appreciating them, 

 'but of following their guidance in a practical manner. 



The wrought-iron portion of the viaduct consists of three 

 spans, the main girders of which are continuous ; and the points 

 of contrary flexure in the middle, and larger span, were deter- 

 mined by direct calculation, the correctness of which was de- 

 monstrated in the actual structure by setting free the plates of 

 the flanges at the points indicated, and by observing the opening 

 and closing of the plates so disunited when the land ends of the 

 girders forminjg the side spans were raised or lowered. 



Mr. Wild appears to have been the first to demonstrate 

 correctly the distribution of stresses under any disposition of 

 load in the Warren girder, a form of beam in which the web is 

 composed of a single system of diagonal bracing inclined at an 

 angle of about 60°. In the museum of Trinity College, Dublin, 

 there has existed since, I believe 1854, a model of a Warren 

 girder, 12 feet 6 inches long and 12 inches deep, in which the 

 tension members both of the flanges and diagonal bracing are 

 so arranged and articulated that any one section can he taken 

 out and a spring balance inserted, by means of which it can be 

 demonstrated that the stresses calculated for any disposition of 

 load do actually arise. 



The history of scientific research teems with instances of dis- 

 coveries which at first seem to have had no practical value, but 

 which nevertheless have ultimately proved to be ofthe utmost 

 importance to the engineer. For example, the changes of tem- 

 perature which occur in many chemical reactions were merely 

 noted at first as interesting accompaniments to such reactions ; 

 but, by degrees, it was perceived that the amount of heat evolved 

 or absorbed in each change was a constant and definite quantity, 

 capable of exact measurement, and in process of time the ther- 

 mal values which characterised a vast number of chemical 

 changes were determined, and are now considered of cardinal 

 importance in many industrial operations, and constitute the 

 science of thermo-chemistry, and render it possible to judge of 

 the efficiency of a boiler, for instance, when the rate of fuel com- 

 bustion and that at which the water was heated or evaporated 

 were known, by calculating the proportion which the heat im- 

 parted to the water bore to that produced by the combustion of 

 any fuel of which the chemical composition had been ascertained, 

 and from which the heat capable of being developed could be 

 ■calculated by general rules. 



One practical effect ofthe exact knowledge which every com- 

 petent engineer now possesses on this subject, or can easily 

 obtain, is that inventors have ceased to squander their time and 

 their means in seeking for impossible high boiler duty, and the 

 public is no more entreated to try contrivances which are to save 

 at least 50 per cent, of the fuel they use, because inventors know 

 that the testing of boilers is now usually carried out by ex- 

 perienced and educated men, who, by very simple and inexpen- 

 sive trials, obtain the data by means of which they can calcu- 

 late with certainty how much scope for improvement actually 

 -exists. 



Still more remarkable perhaps is the application of thermo- 

 chemistry to the complicated reactions in the blast and regenera- 

 tive furnace, and the valuable conclusions arrived at in conse- 

 <iuence by such thorough and patient investigators as Sir Isaac 

 Lowthian Bell, Sir William Siemens, Charles Cochrane, and 

 others who have succeeded in equating the heat-units resulting 

 from the oxidation o( fuel to the ultimate thermal results ofthe 

 decomposition ofthe ore and fluxes, showing thereby the limits 

 of economy which the ironmaster may hope to reach, and 

 the proportions of the furnaces in which his expectations may 

 be realised. 



No less valuable have been the fruits yielded by the discovery 

 ofthe great law of the Conservation of Energy, and by the 

 recognition of the fact that, though energy cannot be destroyed, 

 it may be made to assume various forms, and may be rendered 

 cither dormant or active. The sun's rays, aeons of ages ago, 

 during the dense vegetation which characterised the period of 

 the coal measures, expended their energy in tearing asunder the 

 carbon and oxygen of the carbonic acid distributed through the 

 atmosphere, and in .storing the carbon, thus endowed with 

 potential energy, in the deposits whence we now derive our 

 coal supplies. By suitable arrangements this dormant energy 

 is quickened into that quality of motion which we recognise 



NO. 1229, VOL. 48] 



as heat, and which, setting into sympathetic vibrations the 

 material of the furnace-plates and smoke-flues of boilers, 

 operates on the surrounding water, the molecules of which, 

 under this influence, assume the more extended movements 

 of the highly elastic substance which we know as steam. 

 The products of combustion, on the one hand, are restored 

 to the atmosphere, their remaining store of heat is slowly 

 dissipated, while the carbonic acid gas produced in combus- 

 tion is again ready to present itself, in the green leaves of 

 plants, to the decomposing action of the sun, and by that 

 means the carbon and the oxygen become once more 

 sources of heat. The steam produced, on the other hand, 

 communicates its molecular motion to external bodies in various 

 heating operations, in the visible motion and force of the 

 steam-engine or into the slower dissipation through space or 

 over the earth, whereby it is again condensed to water and 

 returned to its normal condition, while the energy, for the 

 exhibition of which, Carnot has taught us, steam was the mere 

 agent, becomes transformed into masses of water lifted, into 

 air compressed, into electrical currents generated, into mechan- 

 ical work done, or into the heat developed by friction ; but the 

 general tendency is towards dissipation under the form of heat 

 into space, the waste being made good by the stores of heat 

 poured on to our planetary system by the huge and mysterious 

 body which is its centre. 



But modern investigators, and, most of all, engineers, are 

 not content with vague statements such as I have just made ; 

 they hold with the motto of the ancient Society of Civil 

 Engineers, " Omnia in numero pondere et mensura," and they 

 are therefore greatly indebted to Rumford, Carnot, Davy, 

 Mayer, and Joule, who not only showed that heat was a "mod* 

 of motion," but determined by tedious and delicate experiments 

 its mechanical equivalent. 

 And what is now the result? 



When examining heat-engines or other applications of heat 

 in the arts, the engineer collects the apparently aimless work 

 of half a century, and of many minds, and finds himself able 

 to construct a balance sheet by which he can show on the Dr. 

 side, to a fraction, the quantity of heat he has received, and on 

 the Cr. page, with astonishing precision, the manner in which 

 that heat has been expended. This method of treatment is 

 not only lucid, but it is self-checking, and it points out exactly 

 how much heat has been uselessly dissipated, and consequently 

 in what direction improvements may be made, and it indicated 

 further, the limits within which it is alone possible to make 

 advances in economy. 



These general principles apply even to the conversion of heat 

 into the work done in the bore of a gun. The enormous 

 pressures which require to be developed in order to impress 

 high velocity on the projectile in the necessarily limited length 

 of the barrel, the shortness of the time of action, and its 

 violence, render it extremely difficult to obtain accurate and 

 trustworthy records of pressures along the chase of a gun by 

 direct methods ; but by invoking the aid of the chemist and of 

 the physicist in first ascertaining the properties of the explosive, 

 that is to say, the specific volume of the gases, the quantity of 

 heat evolved during combustion, and the specific heat of its 

 products at high temperatures, it becomes possible to calculate 

 curves of mean pressure which will account for the energy im- 

 parted to the projectile and to the expelled gases, although the 

 question of abnormal local pressures, due apparently to the 

 mode of ignition of the charge and the rate at which explosion 

 is propagated through it, will not be revealed. This process is 

 made the easier, in the case of smokeless explosives, because 

 the products of combustion are wholly gaseous and retain that 

 condition till expelled from the bore. 



One of the loftiest of abstract conceptions relating to the 

 structure of the universe, the product of many acute minds of 

 this century, is the imagining of a substance of infinite tenuity 

 but of immense elasticity, which permeates all space and every 

 substance. It cannot be seen, or felt, or weighed, its com- ' 

 jjosition is unknown, it cannot be pumped out of a closed 

 vessel, it does not appear to offer any resistance to the motion 

 of planetary bodies, and its existence is only made manifest by 

 its property of transmitting chemical rays, light, radiant heat, 

 electricity, and probably some more recondite forms of energy, 

 at enormous velocity from the remotest regions of the universe 

 and by means of vibrations the nature of which, the astounding 

 frequency and minute pitch, have been determined by mathe- 

 maticians. It is pardonable in human beings to disbelieve in 



