Proceedings of tee Polttecunic Association. 943 



'U'as M'orked ; and that as hoth engines were intended to work the 

 steam very expansively, under all eonditions, with a view to obtain 

 its greatest possible effect, the pressure at the end of the stroke was 

 always quite low. It is hardly necessary to remark here, that the 

 actual quantity of steam used, or rather the whole quantity of water 

 disappearing from the boiler, never corresponds with the amount of 

 pressure existing in the cylinder at the end of the stroke, but always 

 exceeds it; in other words, although in theory the quantity of steam 

 in the cylinder at the end of the stroke can be very accurately ascer- 

 tained, b}' comparing the terminal pressure with any good table of 

 j^ressures and densities, the amount tlius ascertained is always much 

 less than the quantity of water disappearing from the boiler. An 

 important field, for the investigation of savans, is connected with this 

 sul;)ject. It should be much better understood than it now is, what 

 proportion of the water disappearing from a boiler, disappears in the 

 form of vapor, and what of simply minutely divided water. It is 

 probable that the discrepancy in the amounts indicated by the meas- 

 urements at the two points, i. e., by measuring the quantity forced 

 into the boiler, and by measuring the qu^J^ity of steam, thrown out 

 as steam., from the engine, is due to three causes: First, to the escape 

 of unevaporated water, mingled with the steam from the boiler ; sec- 

 ond, to the condensation of vapor, by the radiation of heat from the 

 pipes and cylinders ; and third (a ]»oint never yet alluded to, so far 

 as I am aware, in this connection), to the annihilation of heat, or its 

 change into mechanical effect in the cylinder. It has been proved, 

 by the investigations of Holtzman, Manhiem, your Mr. Joule, of 

 Manchester, and M. "V. Regnault (the latter acting under the French 

 government), that in the performance of any work, or, in other 

 words, in the production of mechanical power by any form of heat- 

 using engine, a quantity of heat proportionate to the power disap- 

 pears ; being either annihilated, or actually changed into mechanical 

 work. In a former number you have published a paragraph of much 

 interest, giving some of the latest results ascertained in relation to 

 this subject. The quantity of heat corresponding to a given (juantity 

 of mechanical power has not yet been ascertained with absolute pre- 

 cision ; but that there is such a relation, and that a quantity of heat 

 does thus disappear, is beyond question. If steam is generated in a 

 boiler, and blown off' through a safety valve, all the heat disa])pearing 

 through the boiler will be found either in a sensible or latent state, 

 in the vapor ascending through the escape pipe ; but if the same 



