17-4 THERMOTICS. 



Prony, in liis Architecture Hydraulitjue (1796). established a mathe- 

 matical formula, 19 on the experiments of Betancourt, who began his 

 researches in the belief that he was first in the field, although he 

 afterwards found that he had been anticipated by Ziegler. Gren com- 

 pared the experiments of Betancourt and De Luc with his own. lie 

 ascertained an important fact, that when water boils, the elasticity of 

 the steam is equal to that of the atmosphere. Schmidt at Giessen 

 endeavored to improve the apparatus used by Betancourt ; and Biker, 

 of Rotterdam, in 1800, made new trials for the same purpose. 



In 1801, Mr. Dalton communicated tc the Philosophical Society of 

 Manchester his investigations on this subject ; observing truly, that 

 though the forces at high temperatures are most important when 

 steam is considered as a mechanical agent, the progress of philosophy 

 is more immediately interested in accurate observations on the force 

 at low temperatures. He also found that his elasticities for equidis- 

 tant temperatures resembled a geometrical progression, but with a ratio 

 constantly diminishing. Dr. Ure, in 1818, published in the Philoso- 

 phical Transactions of London, experiments of the same kind, valua- 

 ble from the high temperatures at which they were made, and for the 

 simplicity of his apparatus. The law which he thus obtained ap- 

 proached, like Dalton's, to a geometrical progression. Dr. Ure says, 

 that a formula proposed by M. Biot gives an error of near nine inches 

 out of seventy-five, at a temperature of 266 degrees. This is very 

 conceivable, for if the formula be wrong at all, the geometrical pro- 

 gress rapidly inflames the error in the higher portions of the scale. 

 The elasticity of steam, at high temperatures, has also been experi- 

 mentally examined by Mr. Southern, of Soho, and Mr. Sharpe, of 

 Manchester. Mr. Dalton has attempted to deduce certain general 

 laws from Mr. Sharpe's experiments ; and other persons have offered 

 other rules, as those which govern the force of steam with reference to 

 the temperature : but no rule appears yet to have assumed the charac- 

 ter of an established scientific truth. Yet the law of the expansive 

 force of steam is not only required in order that the steam-engine 

 may be employed with safety and to the best advantage ; but must 

 also be an important point in every consistent thermotical theory. 



[2nd Ed.] [To the experiments on steam made by private phy- 

 sicists, are to be added the experiments made on a grand scale by 

 order of the governments of France and of America, with a view tc 



Architecture Hydraulique, Seclude Partie, p. 163. 



