196 THE SCIENTIFIC PAPERS OF 



them attached to a second piston 4 inches in diameter, working in 

 the barrels of double-acting pumps, which inject at each stroke 

 their fluid contents into one extremity and the other of their 

 respective air cylinders. The larger air cylinder (of 21 inches 

 diameter) compresses atmospheric air into an upright receiver, 

 where it is allowed to separate from the injected water, the water 

 issuing from the bottom through a ball-tap, and the comparatively 

 dry air proceeding through a pipe leading from the tap into a 

 larger horizontal receiver or reservoir, which is provided with a 

 mercurial pressure-gauge indicating 55 Ibs. effective pressure per 

 square inch when the apparatus is at work. 



"A copper pipe (of 3 inches diameter, and provided with a stop- 

 valve) leads from the receiver to the second air cylinder of 19 

 inches diameter, wherein the compressed and cooled air is allowed 

 to expand again down to atmospheric pressure, and being mixed 

 in the expanding cylinder with a spray of injected brine (by 

 means of the second injection pump) it is expelled into a large 

 cistern containing about 500 gallons of brine. The injected brine 

 here subsides, and the expanded air escapes freely into the atmo- 

 sphere. It appears from records of experiments made on the 28th 

 and 29th of April, and on the 13th of May last, that the water 

 injected into the compressing cylinder was raised uniformly from 

 2^ to 3 Fahr. in temperature, whereas the brine in the cistern 

 (500 gallons) fell gradually in temperature from 2 to 3 per hour at 

 first, but diminishing gradually, as the temperature descended gradu- 

 ally below that of the atmosphere, until it reached the temperature of 

 18'5, which appears to be the lowest degree ever attained. The 

 speed of the main shaft was, during the first-named experiment, 

 twenty revolutions per minute, when the injected water was raised 

 3, and the brine in the cistern reduced only 2 per hour at the 

 commencement of operations, and during the second experiment 

 the speed varied from fourteen to sixteen revolutions per minute, 

 when the injection water was raised only 2^, whereas the brine in 

 the cistern was lowered 3 Fahr. per hour, until it descended corre- 

 spondingly below atmospheric temperature. The water to be 

 frozen had been filled into cans of copper and dipped into the 

 brine, after the greatest depression of temperature had been 

 attained, which caused a rise of temperature from 18'5 to 22 

 or 23. 



