﻿Notices respecting New Books. 331 



see that, mainly on account of the volume of 1 lb. of steam being 

 nearly inversely proportional to the pressure, the curve connecting 

 W and H is very nearly straight within the limits of such ordinary 

 pressures as are used in engines. It is unfortunate that there are 

 engineers who forget that the law is an empirical one, and who 

 are already speculating on the meaning of the "Williams law when 

 the H is negative. The useful horse-power given out by the crank- 

 shaft and the electrical horse-power given out by the driven 

 dynamos are known to be linear functions of the indicated horse- 

 power H with considerable accuracy ; and hence W is a linear 

 function of each of these powers also. 



Any general law like this which simplifies calculations is of 

 enormous use to practical men. It is of importance to note that, 

 from theoretical considerations, it is probably to be relied upon 

 as being generally true ; for the practical man is very provincial, 

 and he is a little too apt to assume a general law from his own 

 restricted experience. 



On the subject of gas- and oil-engines Prof. Ewing has given 

 just enough to make us wish that he had devoted three times the 

 space to it. Except in the noisy Otto-Langen of 1866 — now 

 seldom seen — no one except Mr. Atkinson has made a serious 

 attempt to get rid of the enormous waste due to the water-jacket. 

 In the usual working of gas- or oil-engines the water-jacket carries 

 off just half of the total available energy of the gas or oil. The 

 average velocity with which each part of a cycle is performed is pro- 

 bably now as high as it conveniently can be made to be, consistently 

 with certainty that each operation shall be properly performed. But 

 after ignition of the charge, if there is not too much inert matter 

 present, and if the mixture of air and gas was sufficiently intimate, 

 we have no reason to believe that four times the present velocity 

 in the expansion-stroke would do any harm, whereas the cooling 

 due to such a rapid expansion would probably do away, almost 

 altogether, with the necessity for a water-jacket. It is known, 

 indeed, that exceedingly rapid cooling of red-hot, and therefore 

 dissociated, carbonic acid allows it to remain partially dissociated 

 at the lower temperature, like the carbon in steel (possibly) ; 

 but experiment would easily settle the rate of expansion which 

 produced maximum economy. 



Besides Mr. Atkinson's method of giving rapid expansion, we 

 might effect the same object by the use of a springy attachment of 

 the fly-wheel to the crank-shaft. It is unfortunately the difficulty 

 of balancing reciprocating masses which now troubles the gas-engine 

 maker, as it troubles also the steam-engine manufacturer ; and it 

 is possible that the large gas-engine of the future will consist of a 

 pump pumping a mixture of air and gas or oil at great pressure 

 into a white-hot firebrick chamber from which it will issue, driving 

 a turbine on the Parson's steam-turbine principle. 



The steam-engine constructor seems rather to dislike statements 

 of the actual thermodynamic efficiency of his engines. Sightly 

 enough, his standard of comparison is a perfect steam-engine 



