70 TOLMAISE METHOD OF HEATING HOT-HOUSES. 



the advancement caused by your encouragement, — whatever they 

 may owe to your exertions in bringing- into and spreading through 

 this country many of the plants which now adorn our gardens 

 and hot-houses, — in no way could your Society more effectually 

 increase this obligation than by devoting some portion of your 

 means and attention for the purpose of investigating the relative 

 merits of different modes of artificial heating. 



Now that the cost of glass structures has become so much 

 lessened, and consequently their erection so much more general, 

 this subject is daily increasing in importance. A series of care- 

 fully-conducted experiments made under like circumstances, in 

 buildings similarly situated, and constructed with a view to de- 

 termine the relative merits of different modes of heating, espe- 

 cially as to their economy both of first cost and use, the amoun 

 of artificial temperature produced, its regularity, the uniformity 

 of its diffusion, and their general effects on vegetation, would be 

 of extreme value to horticulturists, who, for the want of some 

 standard of the kind, are daily imposed upon by designing people 

 for their own individual gain ; and one thing at least will be 

 admitted by all, that it is much to be wished that some cheaper 

 means should be devised than at present exists for horticultural 

 heating. Brick flues (may they not be said to be the most eco- 

 nomical means of all?) seem to be generally abandoned on the 

 score of various imperfections, especially their unequal diffusion 

 of heat and their liability to exhalation. Hot water (even ad- 

 mitting all its fondest admirers can say of it) is limited in its 

 usefulness by the cost of erection. Surely, under these circum- 

 stances, it well behoves all lovers of gardening to try the merits 

 of Polmaise. The soundness of its principles who can dispute ? 

 Hostile opinions have been plentiful, but arguments few : it 

 remains for individual ingenuity to exercise itself as to the most 

 effective mode of reducing them to practice. 



Since the above observations were in type a sudden change 

 has taken place in the atmospheric temperature. At the be- 

 ginning of the present month the external temperature at night 

 was as low as 21° Fahr. ; there was no difficulty in keeping up the 

 temperature of the house to its usual point, 57° or 58°, during 

 the night— the fire, as usual, being only supplied night and 

 morning. It will be found necessary to employ some means of 

 lessening the bottom heat at the end nearest the furnace — 94° at 

 the winter season being, I apprehend, out of all proportion to 

 the atmospheric heat and light. This may easily be effected by 

 employing at this portion of the bed a double bottom, with an 

 area, say of one inch, for air between the two, or by using some 

 non-conducting material. Another practical point to which at- 



