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The British Association Meeting at Dublin.

10th September 1908
Page 14
Page 14, 10th September 1908 — The British Association Meeting at Dublin.
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Which of the following most accurately describes the problem?

In his presidential address, given on Thursday last before the engineering section of the British Association at its meeting at Trinity College, Dublin, Mr. Dugald

F.R.S., M.Inst.C.E., F.C.S., told the story of the long battle which raged between the rival advocates of the " Materialistic doctrine of heat " and the "Kinetic theory of heat " in a very masterly manner. The first class of theorists argued that heat consisted of a subtle elastic fluid which they termed " caloric," and which fluid, they believed, penetrated through the pores or interstices of matter, whilst the latter group of scientists declared that heat was an internal commotion amongst the particles or molecules of matter. Under the " material," or " caloric " theory, work was supposed to be done by the fact of a fall in temperature. Carnot, in the yeoir 1824., stated :—" The amount of work done by a reversible heat engine depends only on the constant temperature at which the heat is received, and at which it is rejected, and it is independent of the nature of the intermediary agent (such as steam, air, etc.). Its efficiency is ronsequently a maximum." According to this principle, the amount of work which can be got out of a heat engine depends entirely on the absolute temperatures between which it is worked ; that is to say, in order to get out of the engine all of the work it would be necessary to cool the gas down to the absolute zero—a process beyond the reach of man. Carnot, however, stated Mr. Dugald Clerk, " although accepting the material ' theory, had his doubts as to its truth." New light was beginning to dawn, but the science of thermodynamics did not then exist.

Thomson (afterwards Lord Kelvin) in 1815 was attracted by Carnot's researches, and his brilliant intellect was brought to bear on the subject with the result that, in 18;r, we lind him delivering an address to the Royal Society of Edinburgh " On the Dynamical Theory of Heat "; but before this --at

the Cork meeting of the British Association in I843—Joule had spoken of a " Mechanical equivalent of heat." To these two great men—Joule and Thomson—stated the president, " Engineers dealing with motive power are deeply in debt for the secure position which they occupy to-day. . . . The ideas of Joule and Thomson now form so much of the basis of all reasoning upon motive-power engines that there is some danger to the present generation of forgetting what they owe to these two great men." Mr. Dugald Clerk then outlined some of the.work of other scientists and engineers, including James Stirling, Sir Geoge Cayley, C. XV. Siemens, Lord Armstrong, Dr. Faraday, and Captain Ericsson, and he wound up his very instructive and attractive address by stating :—

" The modern internal-combustion motor is the successor to the air engine so fully discussed by eminent engineers of .55 years ago, and the forebodings of so eminent a man as Faraday as to its ultimate success have proved unfounded. Great difficulties have been encountered and many discrepancies have had to be explained, but a minute study of the nature of the working fluid has rendered it more and more possible to calculate the efficienciesto be expected under practical conditions. At the present time we can deal with almost any cycle or any working fluid with some fair approximation to an accurate result. Much work, however, is required before all problems of the working fluid can be said to be solved with regard to any heat engine. Indeed, it may be said that under modern conditions of the use of steam even the properties of the working fluid—steamhave not yet been satisfactorily determined. The mere question of specific heat, for example, of steam and its variations of temperature and pressure is now under review, and important experiments are in progress in Britain and on the Continent to determine those properties. The properties of the working fluid of the internal-combustion motor are also the subject of earnest study by many Continental and British investigators."


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