93'2 Traasactioxs of the American Institute. 



The great value of this invention is, that, as an instrmnent, for 

 testing the duty of steam engines, it is altogether free from the objec- 

 tions that have been urged against the indicator. While practically 

 engaged in my duties, as an engineer, I have noticed several errors 

 in the formulas universally accepted by the profession, and have 

 become satisfied that we have much to leam in regard to the steam 

 eno;ine and boiler. I will mention one case where I have observed a 

 serious error in the usual method of estimating tlie advantage of a cut- 

 off. Some years ago, I had charge of a propeller engine, of about 

 250 horse power. The boiler was rather small for the engine, and the 

 performance of the boat was not at all satisfactory. My predecessor 

 had been carrying from ten to fifteen pounds of steam, the cut-off was 

 permanently fixed at half-stroke, and he run an open throttle. The 

 steam pipes and parts were of the ordinary dimensions. I concluded 

 to carry thirty-five pounds of steam in the boiler, and throttle so as 

 to keep the steam in the boiler always at this point. On doing so, the 

 speed of the boat was considerably increased, and the coal account 

 reduced far more than any formula with which I am acquainted, would 

 account for. 



In the case mentioned, it was impossible to tell exactly the course 

 of this gain, but 1 soon determined that no reliable results could be 

 arrived at, without an instrument that would average fluctuating 

 powers, and hence the invention I submit to the society. It is not 

 patented, mid will not be. I see no reason why it should not 

 be applied to the main driving shaft of all factories, and thus do for 

 the factory engine, what the counter has done for the pumping engine. 

 At the same time it will be an excellent means of deciding on the 

 merits of the hosts of fimcy cut-offs and boilers, that claim the pat- 

 ronage of the public, and serve as a sure guide to the factory owner, 

 in regard to the value of his coal, and the ability of his engineer. 

 Where two engines are used to drive, the duty of each can be obtained. 



Before closing, I wish to point out a singular error into which 

 Regnault and others have fallen in regard to the changes that take ]»lace 

 when a gas expands without resistance. Two receivers, A and B, 

 are immersed in a proper liquid. A has a pressure of ten atmos- 

 pheres, and B is exhausted. A stop-cock which connects the two, 

 being opened, the gas rushes from A to B. It is found that no 

 decrease of heat takes place. Hence when gases expand without 

 doing work, they do not absorb heat ; now it is plain that it is impos- 

 sible for gases to expand without doing work. In the case mentioned, 



