66 



POLMAISE METHOD OF HEATING HOT-HOUSES. 



perature ? Should we not expect most excellent results from 

 that system of heating which secures the greatest amount of 

 atmospheric agitation, — which not only warms a certain amount 

 of air, but by its motion secures that the whole of the air so 

 warmed shall be brought in contact with the foliage which it is 

 to nourish, — which, so far as motion of the atmosphere is con- 

 cerned, puts a plant in the hot-house in the same position as a 

 plant out of doors ? May we not reasonably hope that, with a 

 certain amount of fresh air charged with its proportion of car- 

 bonic acid gas, and this in motion, we shall always be able to 

 rival nature in the compact beauty of our specimens, as we have 

 done in the profusion of their bloom ? 



Having noticed the advantages of Polmaise heating, I have no 

 wish to conceal its dangers. Man may take the principles of 

 Nature, and when he reduces them to practice, he finds that he 

 has introduced some human imperfection, and so it is with Pol- 

 maise. A boiler may burst, or a pipe choke up with a hot water 

 apparatus, and a gaseous exhalation may escape from the stove 

 of Polmaise. The compounds of sulphur and oxygen appear, 

 even when much diluted, most prejudicial to vegetable life, and 

 the effects of the bursting of a flue are well known ; and this is 

 the point of danger. I prophesy that no winter, however severe, 

 will affect the operation of Polmaise ; but all the beauty of this 

 principle of heating must be sacrificed, unless we can secure the 

 chamber from gaseous exhalation. With this view, let me urge 

 upon all those who may employ the Polmaise principle to be 

 extremely particular in the manner in which the stove is built. 

 Let the outside be parged ; let it be constructed of at least nine- 

 inch brick-work ; and if the iron plate can be cast in one, with 

 a projecting rabbet on its under surface, and this rabbet dropping 

 into a sand groove thus : 









I 



























it appears that all possibility of exhalation must be precluded. 

 Indeed, if even this were insufficient, it is hardly probable that a 

 sound principle of heating should be lost for want of some inge- 

 nious mechanical contrivance to prevent exhalation. However, 

 I have thought it my especial duty to point out the weak points 

 of Polmaise ; and while I acknowledge that I think the form of 

 stove 1 have employed has many advantages, and especially the 

 retention of the heat, I by no means wish to prevent others 

 of a more complex and expensive, though probably of a more 



