210 MEMORIAL OF JOSEPH HENRY. 



next communication to the Institute (made March 2nd 1825,) was 

 " On the PnxUiction of Cold by the Rarefaction of Air." As 

 before, he accompanied his remarks by several characteristic exhi- 

 bitions. 



'' One of these experiments most strikingly illustrated the great 

 reduction of temperature which takes place on the sudden rarefac- 

 tion of condensed air. Half a pint of water was poured into a 

 strong copper vessel of a globular form, and having a capacity of 

 five gallons; a tube of one-fourth of an inch caliber with a num- 

 ber of holes near the lower end, and a stop-cock attached to the 

 other extremity, was firmly screwed into the neck of the vessel; 

 the lower end of the tul)e dipped into the water, but a number of 

 holes were above the surface of the liquid, so that a jet of air min- 

 gled with water might be thrown from the fountain. The apparatus 

 was then charged with condensed air, by means of a powerful con- 

 densing pump, until the pressure was estimated at nine atmospheres. 

 During the condensation the vessel became sensibly warm. After 

 suffering the apparatus to cool down to the temperature of the room, 

 the stop-cock was opened : the air rushed out with great violence, 

 carrjang with it a quantity of water, which was instantly converted 

 into snow. After a few seconds, the tube became filled with ice, 

 which almost entirely stopped the current of air. The neck of the 

 vessel was then partially unscrewed, so as to allow the condensed 

 air to rush out around the sides of the screw: in this state the 

 temperature of the whole interior atmosphere was so much reduced 

 as to freeze the remaining water in the vessel." * 



Although the principle on which this striking result was based 

 was not at that time new, it must be borne in mind that this par- 

 ticular application, thus publicly exhibited, was long before any of 

 the numerous patents were obtained for ice-making, not a few of 

 which adopted substantially the same process. 



State Appointment as a Civil Engineer. — Through the friendship 

 and confidence of an influential judge, Henry received about this 

 time an unexpected offer of an apjjointment as engineer on the sur- 

 vey of a route for a road through the State of New York, from 



,,.,„o., * Trans. Albany Institute, vol. i. part 2. p. 36. 



