September 24, 1908] 



NA TURE 



'■5 



power could be obtained. The data for such a theory were 

 accumulating ; and one of the most interesting circum- 

 stances connected with these Institution of Civil Engineers 

 Papers was a communication from M. Regnault to Colonel 

 Sabine, Treasurer of the Royal Society, dated April, 1853, 

 which was read at the Meeting, in which Regnault stated 

 that 



" He was about to publish immediately a series of 

 elaborate experimental researches on various subjects con- 

 nected with the effects of heat on elastic fluids, the results 

 of which would solve many questions long in dispute, and 

 by means of which engineers might accurately calculate 

 the effect of a given amount of fuel, in whatever way it 

 was applied. M. Regnault communicated in anticipation 

 that he had arrived at the number 0-237 for the specific 

 heat of air at constant pressure, and at 0475 for that of 

 steam under atmospheric elasticity, the specific heat of 

 water being taken in each case as unity." 



True to his word, Regnault produced his admirable 

 investigations, and succeeded in solving many problems ; 

 but he did not settle the questions to the extent he had 

 hoped. Even at the present time doubt arises as to the 

 very values he gave for the specific heat of air and steam. 

 The problem provrd much more difficult than he had 

 anticipated, and for modern engine purposes it cannot be 

 considered as whollv solved now — fifty-five years later. 



This description of the position of the hot-air engine, 

 as shown by the opinions of eminent engineers, is most 

 useful as proving how much practical men w'ere in need 

 of the work of Thomson and Joule. It is not surprising 

 that, of all the engineers present, Siemens appeared to be 

 alone in thoroughly grasping the new ideas. Thomson's 

 own conversion from the material theory of heat to the 

 dynamical theory was not complete until 185 1, and 

 although he had then succeeded in reconciling the ideas 

 of Joule and Carnot, it is not to be wondered at that 

 engineers two years later had not quite succeeded in grasp- 

 ing the combination of the two laws. This combination, 

 however, supplied engineers with a new and accurate 

 standard of measurement for studying and improving upon 

 their heat engines, and they were lay no means slow in 

 grasping the help thus offered them Ijy the abstract scien- 

 tific man. The broad laws of thermodynamics have placed 

 the theory of the heat engine in a position of certainty, 

 which was much needed. It would be a mistake to 

 assume, however, that even the determination of the 

 mechanical equivalent of heat and the second law of 

 thermodynamics expressed in terms of an absolute thermo- 

 metric scale had solved all the difficulties of the engineer 

 desiring to determine the efficiency of his heat engines. 

 Thomson, Joule, Rankine, and their great Continental 

 colleagues, it is true, settled once and for all the broad 

 laws of thermodynamics, but the Carnot cycle is a cycle 

 which is. as has been repeatedly shown, an impossible one 

 in practice. .Accordingly, actual engines have to operate 

 upon imperfect cycles. The theory of these imperfect cycles 

 has been worked out mostly during the last twenty-five 

 years, although Rankine made a beginning in dealing 

 with the theory of the Joule air engine. For the first 

 time he showed the existence of what may be termed a 

 cycle of constant efficiency in the case of the Joule air 

 engine. Assuming constant specific heat for the working 

 (luid, he calculates the efficiency of what we now call a 

 constant-pressure air engine between certain limits of 

 temperature, and he gives the efficiency of the fluid where 

 U = energy exerted and H|=heat received, and r = ratio of 

 compression and expansion ; — 



U _ l_. 



H,-' ,«-40S' 



that is, he indicates in this formula that the thermal 

 efficiency is independent of the maximum temperature so 

 long as that maximum temperature exceeds the tempera- 

 ture of adiabatic compression. He makes no statement, 

 however, that this engine is within a certain range in- 

 dependent of the maximum temperature ; that is, that 

 increasing maximum temperature does not increase 

 efficiency. Subsequent work has shown that, on a simple 

 assumption, such as constant specific heat, many engine 

 cvcles exist of a practicable nature having high theoretical 

 efSciencies where the theoretical efficiency depends on one 



NO. 2030, VOL. 78] 



thing only — the ratio of compression. Some misunder- 

 standing has arisen with regard to these imperfect cycles, 

 and it has even been thought that such imperfect cycles 

 would be contrary to the second law of thermodynamics. 

 Lord Kelvin himself was of this opinion in 1881. I vividly 

 remember a conversation I had with him at the Crown 

 Iron Works, in Glasgow, over the results I had obtained 

 from one of my early gas engines. I had then come to 

 the conclusion that the " Otto " cycle as ordinarily 

 operated was a cycle of constant efficiency, and I explained 

 this to Lord Kelvin. He had not followed such cycles, 

 and his view then was that no such cycle could exist, 

 because he thought it was contrary to the second law of 

 thermodynamics. Some idea of this kind has been held 

 by many scientific men, and has prevented the minute 

 investigation of imperfect cycles of different kinds, because 

 of the feeling that the whole question of efficiency was 

 entirely settled by the nature of the temperature limits ; 

 that is, by the maximum and minimum temperatures at 

 the disposal of the engineer. It is true that these values, 

 as has been shown, must always determine the e.xtreme 

 limit of possible efficiencies between certain temperatures, 

 and in cycles of constant efficiency the particular efficiency 

 of the cycle is always less than the efficiency of a Carnot 

 cycle engine working between the same limits of superior 

 and inferior temperature. The investigation, however, of 

 these imperfect cycles is much more difficult than the broad 

 investigation of the general thermodynamic laws, because 

 it requires accurate knowledge of the properties of the 

 working fluid dealt with under conditions rendering 

 observation extremely difficult. The modern internal- 

 combustion motor is the successor to the air engine so 

 fully discussed by eminent engineers of fifty-five years ago ; 

 and the forebodings of even 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 efficiencies to be expected under practical 

 conditions. -At the present time we can deal with almost 

 anv cycle or any w'orking fluid with some fair approxima- 

 tion to an accurate result. Much work, however, is re- 

 quired 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 — steam 

 — have 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 studv by manv 

 Continental and British investigators. Notwithstanding alt 

 the perplexities involved in the minute study of the 

 imperfect heat-engine cycles, we are in a very different 

 position to-dav compared with the engineer of 1S53. We 

 know all the broad laws as to the conversion of heat into 

 work or of work into heat ; and, numerous as are the 

 problems yet to be solved, we at least profit bv the guiding' 

 light set out for us by Kelvin, Joule, and Rankine. 



SECTION H. 



ANTHROPOLOGY. 



Opening Address by Prof. William Ridgf.«^\y, M.A., 

 F.B..'\., LiTT.D., LL.D., President of the Section. 



The Application of Zoological Laws to Man. 

 Thirty years ago in this very city I heard for the first 

 time a Presidential Address at the British Association, 

 and I was singularly fortunate in entering on my novitiate. 

 I had the privilege of hearing Prof. Huxley deliver his 

 Presidential .Address to the embryo of that Section over 

 which I, a very unworthy successor, have this day the 

 honour to preside. On that occasion Huxley dealt almost 

 exclusively with the physical evolution of man, and the 

 Neanderthal skull played an important part in his dis- 

 course. The anthropologists of that day and since have 

 severely criticised, and rightly so, the old teleological 

 doctrine that everything except man himself had been 



