POLMAISE METHOD OF HEATING HOTHOUSES. 55 



Moreover, the temperature of the house was assisted by there 

 being a separate boiler in another chamber to supply the bottom 

 heat, and the external temperature was singularly high ; had 

 this table been taken February twelvemonth, it is probable the 

 loss would have been far more apparent ; however, it is sufficient 

 to prove the hot- water system extremely wasteful in its use. 

 Another serious objection attaches to hot water, or any other 

 mode which introduces any radiating surface within a building 

 which we desire to heat uniformly, or nearly so — for the very 

 terms radiation and equal diffusion are a contradiction ; radiation 

 is a power the effect of which diminishes as the squares of the 

 distance from the heating body increase, so that the instant 

 radiation is introduced, uniformity of temperature is necessarily 

 sacrificed. Are not hot-water pipes radiating surfaces? And 

 that of very unequal temperature in their circuit ? Will they not 

 of necessity, therefore, heat bodies unequally, especially since 

 these bodies cannot be all at one uniform distance from them ; 

 the result being, that the atmospheric uniformity will conse- 

 quently become deranged ? I do not wish to deny that I consider 

 hot water far preferable to smoke flues ; I will admit the heat to 

 be more uniform, the chance of smoke and exhalation got rid of ; 

 I acknowledge it to be a step on the road to truth, but it has not 

 gone far enough ; it stopped at the water ; it should have gone 

 onward to the wind. 



While pointing out the errors of our present modes of heating, 

 I would remark that there are other plans of air heating quite 

 different from Polmaise, and which I consider essentially erro- 

 neous. I will endeavour to explain them, and show their errors. 

 The principle on which they act is this — to place a stove either in 

 a separate building or in some portion of the building it is 

 desired to heat, and to provide a current of air either from the 

 external air or elsewhere to blow over the stove, to become 

 heated, and then by flowing into the building to warm it ; but 

 in this arrangement we apparently forget that the air is material ; 

 that gases, though very compressible, still enjoy the property 

 common to all matter, namely, bulk, and consequently, that hot 

 air will not flow into a building to any great extent until some 

 means are employed to remove the air at present within it. 

 This is not only theoretically but practically true ; for in a 

 dwelling-house in my own neighbourhood, heated on this prin- 

 ciple, the hot air would not flow into one room unless there were 

 a window open, or into another unless there were a fire in the 

 grate, proving that the ingress of the hot air depended on the 

 egress of the cold, and was in exact proportion to it ; this is 

 truly what one of its advocates has called it, a system of heating 

 based on ventilation ; but a moment's reflection will convince us 



