DISCOURSE OF W. B. TAYLOR. 209 



societies; with General Stephen Van Rensselaer as its President:* 

 and young Henry became at once an active member: though with 

 his modest estimate of his own attainments, he preferred the part 

 of listener and acquirer, to that of seeming instructor, till urged by 

 those who knew him best to add his contributions to the general 

 garner. 



Henry's first communication to the Institute was read October 

 30th, 1824, (at the age of about twenty-six years,) and was "On the 

 chemical and mechanical effects of steam : with experiments de- 

 signed to illustrate the great reduction of temperature in steam of 

 high elasticity when suddenly expanded."")" From the stop-cock 

 of a strongly made copper vessel in which steam could be safely 

 generated under considerable pressure, he allowed an occasional 

 escape; and he showed by holding the bulb of a thermometer in 

 the jet of steam, at a fixed distance (say of four inches) from the 

 orifice, that as the temperature and pressure increased within the 

 boiler, the indications of the thermometer without grew lower; 

 the expansion and consequent cooling of the escaping steam under 

 great pressure, increasing in a higher ratio than the increased tem- 

 perature required for the pressure. And finally he exhibited the 

 striking paradox, that the jet of saturated steam from a boiler will 

 not scald the hand exposed to it, at a prescribed near distance from 

 the try-cock, provided the steam be sufficiently hot. J 



Prolific and skillful in devising experiments, Henry delighted 

 in making evident to the senses the principles he wished to impress 

 upon the mind. Extending the law of cooling by expansion, from 

 steam at high temperatures, to air at ordinary temperatures, his 



*The Albany Institute resulted from the fusion of "The Society for the Pro- 

 motion of Useful Arts in the State of New York," organized Feb. 1791, (incorporated 

 April 2nd, 1804,) and the "Albany Lyceum of Natural History" formed and incorpo- 

 rated April 23rd, 1823 : of which latter society, HENRY had been a member. See " Sup- 

 plement," NOTE A. 



t Trans. Albany Institute, vol. i. part 2. p. 30. 



% While it requires a temperature of 250 F. to generate a steam-pressure of two 

 atmospheres (i. e. one additional to the existing), 25 higher will produce a pressure 

 of three atmospheres, and 100 higher, (or 355 F.) will produce a pressure of nine 

 atmospheres: the curve (by rectangular co-ordinates of temperature and pressure) 

 resembling a hyperbola. The increased velocity at high pressure produces a mole- 

 cular momentum of expansion carrying the rarefaction beyond the limit of atmos- 

 pheric pressure; and in the case of the exposed hand, the injected air current 

 doubtless adds to the cooling impression. 

 14 



