272 llr. Ure on Ventilation. 



ratio of corapression to the whole stroke in the egress cylinder would be 

 j^Q. If 1 lb. of air (or about 15i cubic feet, at the stated temperature 

 of 80°, and the mean atmospheric pressure,) be to be delivered per second, 

 the motive power required for working the machine would be "283 of a 

 horse power, were the action perfect, with no loss of effect, by friction, by 

 loss of expansive power due to cooling in the ingress cylinder, or otherwise. 

 If each cylinder be four feet in stroke, and 26 '3 inches diameter, the 

 pistons would have to be worked at 30 double strokes per minute. 



On the other hand, if it be desired to cool air, either the ingress 

 piston must be worked faster than the other, or the stroke of the other 

 must be diminished, or the ingress cylinder must be larger, or an auxiliary 

 ingress cylinder must be added. The last plan appears to be undoubt- 

 edly the best, as it will allow the two principal pistons to be worked 

 stroke for stroke together, and consequently to be carried by one piston 

 rod, or by a simple lever, without the necessity of any variable connecting 

 gearing, whether the machine be used for heating or for cooling air ; all 

 that is necessary to adapt it to the latter purpose, besides altering the 

 valve gearing, being to connect a small auxiliary piston to work beside 

 the principal ingress cylinder, with which it is to have free communi- 

 cation at each end. If it were required to cool air from SO" to 50° Fahr., 

 the auxiliary cylinder would be required to have its volume ^j of that 

 of each of the principal cylinders ; and, if its stroke be the same, its 

 diameter would therefore be a little less than a quarter of theirs. The 

 valves would have to be altered to give compression in the ingress cylin- 

 der during the same fraction of the stroke as is required for expansion 

 when the air is heated through the same range of temperatui-e, and the 

 valves of the egress cylinder would have to give the same proportion of 

 expansion as is given of compression in the other case ; and the pressure 

 kept up in the receiver, by the action of the pistons thus arranged, would 

 be li| atoms, or about 3'2 lbs. on the square inch above the atmospheric 

 pressure. The principal cylinders being of the same dimensions as those 

 assumed above, and the quantity of air required being the same (1 lb. per 

 second), the pistons would have to be worked at only 24-G double strokes 

 per minute instead of 30, and the horse power required would be '288, 

 instead of as formerly •283, when the same machine was used for giving 

 a supply of heated air. 



Mr. John Ure then exhibited a Model Ventilating Apparatus which 

 had been constructed by him. He explained its stnicture and illustrated 

 its action, (Lc. It consisted of an oblong case, about 2 feet long, 1 foot 

 broad, and 15 inches high, with sides and top, but no fixed bottom. The 

 interior of this case represented that of an apartment to be ventilated. 

 The sides and ends were glazed, so as to enable the observer to ascertain 

 the changes which might occur within. The case (see drawing, No. 1) 

 was provided with a moveable bottom, around the margin of which was 

 a gutter or groove filled with water (see drawing, No. 2), into which tho 



