122 LEADING AMERICAN MEN OF SCIENCE 



ing from a boiler as measured by a thermometer under various 

 circumstances. 



Placing the thermometer in steam-jet at a distance of four 



4 inches from the outlet, and then applying more and more heat to 



the water in the boiler, he found that the steam, instead of being 

 hotter, actually grew cooler the hotter the fire was made. At 

 the highest pressure the steam at a little greater distance would 

 not scald the hand at all although it would scald it when the 

 pressure was lower. The explanation was that the great expan- 

 sion caused by the increased temperature of the steam when it 

 first escaped produced a stronger cooling effect, which more 

 than made up for the higher temperature. Carrying out the 

 same idea of the production of cold by the rarefaction of air, 

 N^ he published the principles by which to-day ice is manufactured 

 by the condensation and rarefaction of 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 number 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 dipped into the water, but a 

 number of holes were above the surface of the liquid, so that a 

 jet of air mingled with the water might be thrown from the foun- 

 tain. The apparatus was then charged with condensed air, by 

 means of a powerful condensing-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, carrying 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 tempera- 

 ture of the whole interior atmosphere was so much reduced as to 

 freeze the remaining water in the vessel. 



His delicate constitution now suffered so much from confine- 



