Heating or Cooling of Buildings by means of Currents of Air. 141 



of the receiver, into which, by the opening of another valve, it is 

 to be admitted in the reverse stroke; while the egress cylinder* 

 is to draw air freely from the receiver though the whole of each 

 stroke on one side or the other of its piston ; and in the reverse 

 strokes first to compress this air to the atmospheric pressure (and 

 so heat it as I'equired), and then dischai'ge it into a pipe leading 

 to the locality where it is to be used. If it be required to heat 

 the air from 50° to 80° Fahr., the ratio of expansion to the 

 whole stroke in the egress cylinder would be yq^q, the pressure 

 of the air in the receiver would be y^^-^^ of that of the atmosphere 

 (about 2*7 lbs. on the square inch below the atmospheric pres- 

 sure), and the ratio of compression to the whole stroke in the 

 egress cylinder would be y^^. If 1 lb. of air (or about 15- 

 cubic feet, at the stated temperature of 80°, and the mean atmo- 

 spheric 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 4 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 in- 

 gi'ess 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 inidoubtedly 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 connected 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 set a small auxiliary piston 

 to work beside the principal ingress cylinder, with which it is to 

 have free communication at each end. If it were required to 

 cool air from 80° to 50° Fahr., the auxiliary cylinder would be 

 required to have its volume yyth of that of each of the principal 

 cylinders ; and if its stroke be the same, its diameter would 



* In this case the egress cylinder acts merely as an air-pump, to draw 

 air from the receiver and discharge it into the locality where it is wanted, 

 and the valves required for this purpose might be ordinary self-acting 

 puni])-valves. A similar remark applies to tlie action of the ingress cylinder 

 Ml the use of the ajjijuratus for producing a cooling effect on tlie air trans- 

 mitted, which will then be that of a compressing air-jmmp to force air 

 from the atmosphere into the receiver. But in order that the same apiia- 

 ratus may be used for the double jjurpose of heating or cooling as may be 

 rccpiired at different seasons, it will be convenient to have the valves of 

 each cylinder worked mechanically, like those of a steam-engine. 



