236 



proposed that a method should be found of lovvenng the temperature 

 of the air in a room ; doing, in fact, there, the reverse of what is 

 effected in a cold room by lighting a fire. 



The principle of the plan which he brought forward was dependent 

 on the property of air to increase in temperature on compression, and 

 to diminish on expansion ; the air was to be compressed by a forcing 

 pump into a close vessel, then cooled or rather deprived merely of 

 its acquired heat of compression, and then being allowed to escape 

 into the room desired to be cooled, would issue at a temperature as 

 much below that of the atmosphere as it had risen above on com- 

 pression. 



That this was a vera causa there was no doubt ; the sufficiency and 

 the practicabiliti/ were the only mattei's of doubt. These the author 

 attempted to solve, by shewing the quantity of increase of heat due 

 to a certain amount of compression ; and by devising the most con- 

 venient form of the necessary apparatus, and concluded that a one- 

 horse power should supply a room with 30 cubic feet of air per 

 minute, cooled 20° below the surrounding atmosphere. The various 

 sources of mechanical power likely to be met with in warm countries, 

 were then described ; and particularly a new and simple, and at the 

 same time., a remarkably compact and effective form of windmill ; as 

 the wind is everywhere so cheap and abundant, and in the tropics so 

 certain a species of moving power. Methods also of ventilating the 

 cooled room, i. e., of keeping it constantly supplied with cooled fresh 

 air, and removing the vitiated, were explained, as well as a natural 

 principle for meeting the residual difficulty that might be expected to 

 arise in some cases, viz., the too great moisture of the cooled air. 



3. Notice of a Shooting- Star. By Professor C. Piazzi Smyth. 



The object of this notice was merely to call attention to the im- 

 poi'tance of observing the phenomena of shooting-stars more carefully 

 and rigidly, and of applying to them more correctly than has generally 

 been the case hitherto, the measurement of time and of space, and 

 to exemplify what may be done in this way by the calculation of a 

 recent instance. This instance, the rare one of an ascending shoot- 

 ing-star, was furnished by Captain W. S. Jacob, Bombay Engineers ; 

 and he having given the place where the body first appeared, that 



