August 5, 1909J 



NA TURE 



171 



TiiE Solar Eclifsk of June 17, 1909. — Observations of 

 the contacts, during tile solar eclipse of June 17, were 

 made by Father Rigge, at the Creighton University 

 Observatory, Omaha, and showed that the phenomena 

 actually occurred a second or two earlier than the com- 

 puted times. At first contact the difference was 2-025., 

 and is trustworthy, but at the last contact a difference 

 of 18-43. was observed, and may largely be due to the 

 extremely bad conditions under which the observation was 

 made, the sun being within fourteen minutes of setting 

 {kslronomisdxe Nachrichteit, No. 4340). 



RECENT IMPROVEMENTS IN THE INTERXM.- 

 COMBUSTION ENGINE. 

 I. 

 A SURVEY of the progress made during the last twcnty- 

 "^ five years in almost any field of engineering work 

 would show an immense advance. Even during the past 

 ton years very considerable progress has been made in 

 certain br.anches of applied science, and in none of them 

 to a greater extent than in the internal-combustion engine. 

 We need not in this- comparison claim the gun as a form 

 of internal-combustion engine, though we are naturally 

 entitled to do so. Wo may leave lethal weapons aside, and 

 thinlc only of the remarkable development of the reciprocat- 

 ing internal-combustion engine, and of the many changes 

 it has brought about in our times. It has revolu- 

 tionised cross-country transit. It has given us the long- 

 deferred, but now actually achieved, victory called the 

 " conquest of the air." It is extraordinary to think of the 

 numbers of men who have spent ingenious years in seeking 

 a ■ solution of the problem of flight. The solution has 

 come in the unexpected form of a pair of long, sail-like 

 arms, driven forward by a small high-speed internal-com- 

 bustion engine. This simple form of design, which, owing 

 to the relation between centre of pressure and angle of tilt, 

 seems to be naturally stable, bids fair to be adopted in a 

 great output of flying machines shortly to be constructed. 

 The hardly less novel, but less interesting, dirigible balloon 

 owes the whole of its diriglbility, whatever that may 

 amount to, to the internal-combustion engine. 



Less startling, but of considerable material imixirtance, is 

 the utilisation of '* waste heat " in our coal- and iron- 

 producing areas. Our coal supply !s admitted to be limited, 

 and there seems to be at least an indication that at the 

 present rate of consumption mankind would, in a few 

 centuries, have to be prepared to turn its attention to the 

 unlocking of some other form of stored-up energy, perhaps 

 a radio-active one. It is not too much to say, however, 

 that if the power available from the waste gases of blast- 

 furnaces and coke-ovens in this country — and the amount 

 can hardly be less in the aggregate than 1,000,000 h.p. — 

 were put to use, the saving in the coal consumption might 

 perhaps give us another half-century or two in which to 

 look about lor some substitute for coal. 



In writing of what has been already achieved, w'e have 

 to remember that we are only yet at an intermediate stage 

 in the development of the intern.al-combustion engine. The 

 internal-combustion engine gives us a bigger return for heat 

 put in than any other known form of engine. We cannot 

 imagine the development of the future " going hack," so to 

 speak, on such an advance as that. The internal-combus- 

 tion engine must come, and existing steam engines be re- 

 placed. This means the supersession of the steam turbine, 

 and may therefore seem to suggest a retrograde step, since 

 the rotary engine is mechanically an Improvement on the 

 reciprocating one. \A'e have to remember, however, that 

 evolutionary processes sometimes take a step backwards to 

 an earlier form in bringing forward the latest and most 

 developed creation. \o one would look on any reciprocat- 

 ing engine as a final Improvement on a rotary one, even 

 although, as Is now the case, large gas engines are capable 

 of so uniform a rotary motion that alternators are easily 

 driven by them In parallel — the standard test of excellence 

 In this respect. The day of the gas-engine turbine must 

 come. Numbers of men are working at the problem which 

 It presents ; hut little has as yet been published as to the 

 result of their labours — an Indication that the many dlfiicul- 

 ties are not yet mastered. 



N'O. 2075, VOL. St] 



The present stage in the development of the internal- 

 combustion engine Is a convenient one at which to sum- 

 marise briefly what has been done in regard to its 

 improvement. We therefore propose in this and the suc- 

 ceeding articles of the series to state the problem and the 

 lines on which, with such a striking measure of success, 

 its solution has been attempted. 



The problem can be stated In a very simple form. Given 

 one pound of carbon of, say, 12,000,000 ft. lb. calorific 

 value, which Is a. normal estimate, find how to obtain the 

 largest possible amount of useful power. So far this- 

 energy has always been liberated In the form of heat. 

 This heat has been given to some body which, by its sub- 

 sequent cooling, can give out mechanical energy — such a 

 body is a mass of gas or vapour. Let us assume that a- 

 mass of gas is chosen as the working medium. It Is 

 obviously desirable that the heat liberated should be 

 absorbed as completely as possible by the gas, but in 

 investigating whether this has been effected one at once 

 meets with a check. To tell whether the whole of the 

 12,000,000 ft. lb. of heat energy has reached the gas, we- 

 may either look out for possible chances of heat leakage 

 or may measure the amount of energy in the gas at the 

 end of the operation. But to do the latter is practically 

 impossible, for we do not know the specific heat at high 

 temperature of any gas, and to do the former Is extremely 

 difficult, owing to the very short time the heat transfer- 

 ence usually takes, and owing also to our lack of know- 

 ledge as to the temperature of metal or other surfaces In , 

 contact with, and enclosing, the gas. Many attempts 

 have been made to ascertain what happens to the heat 

 liberated, and" much has been written on such topics as 

 " dissociation," " after-burning," and " increasing specific 

 heats." There would be no diftlculty in filling the whole 

 of the allotted space with a discussion of the various 

 experiments that have been made and theories that have 

 been built on this subject, but as many other matters have 

 also to be dealt with, and as the author has already written 

 on this topic elsewhere,' he does not now propose to go 

 into the matter at length. 



Briefly summarised, the result of gas-engine experiment 

 is to establish that only about 50 to 55 per cent, of the 

 heat energy known to be liberated Is accounted for by 

 multiplying the measured rise of temperature by the 

 commonly accepted figure for the specific heat at constant 

 volume. The same ratio of 50 to S5 per cent, was found 

 for all sizes and shapes of containing vessel, and for all 

 mixtures of gas. This constancy at once disposed of the 

 theory that the " suppression of heat " was due to dissocia- 

 tion, as such an effect would naturally be dependent upon, 

 and increase with, the Increasing temperatures due to the 

 richer mixtures. Equally It showed that the cooling of the 

 gas by convection currents, radiation, and conduction to the 

 walls of the containing vessel was an Inadequate explana- 

 tion. The suggestion of the French physicists, MM. Mallard 

 and Le Chateller, that the effect must be due to Increase of 

 specific heat with temperature was open to precisely the 

 same objection as that of dissociation, and Involved values 

 of the instantaneous specific heat much In advance of what 

 was then thought likely. It is now generally rcognlsed that 

 the real explanation of the apparent suppression of energy 

 Is due to a combined cooling effect and rise of specific heat. 

 " After-burning " is now generally believed, as a result of 

 many tests, not to occur In normal circumstances. With 

 a weak mixture the time of explosion, and therefore of 

 cooling. Is a long one, so that the cooling loss has time 

 to become considerable, and this compensates for the lesser 

 degree to which the theory of increasing specific heats is 

 effective for these weak mixtures and low temperatures. 



The constancy of this apparent " loss " made it clear 

 that no great improvement in the internal-combustion 

 engine could be looked for in any Increase of pressure and 

 temperature in a gaseous mixture of given strength. We 

 cannot alter the specific heat law of a substance. We 

 might, perhaps, alter our working medium, which now for 

 the most part is nitrogen, but no other gas is so cheap 

 or so easily obtained ; but we may vary the part of the 

 temperature scale over which we work, and, within limits, 

 we may affect the cooling loss bv altering the shape of 

 the containing vessel or cvlindcr. Experiments have shown 

 1 " The Internal-comtustion Engine " (Constable and Co.) 



