242 Application of Terrestrial Heat 



more perfect developement of the particular crops or plants 

 under cultivation. 



Every cultivator knows what bad consequences result from 

 over-saturation, be the surface soil, or bed of the plant, ever so 

 good. The appellation of " cold," being applied to wet reten- 

 tive subsoils, well and fitly describes the lowering of tempera- 

 ture that arises from such a cause. Therefore, it becomes highly 

 important that, along with the application of manures, the prac- 

 titioner should fully understand this, and so endeavour suitably 

 to adapt the soil for the growth of the plant, by proper drainage 

 and a consequent raising of its temperature. This, in the course 

 of my experience, I have found very much to stimulate vegetable 

 growth, especially when means were taken, by surface mul- 

 chings, to counteract excessive evaporation in dry hot summers, 

 Nor is it difficult, I think, to obtain the requisite data to guide 

 us in this respect (sufficiently, at least, for all practical pur- 

 poses); for we have only chiefly, I conceive, to ascertain the cir- 

 cumstances of climate and the nature of the localities, as to soil, 

 subsoil, and exposure, where the plants we wish to cultivate grow 

 in greatest perfection, in their respective countries and habitats : 

 and seeing that, so far as has been gone in such investigation, 

 we have always, more or less, a mean terrestrial temperature of 

 from 1° to 2° above the mean of the atmosphere, both with 

 regard to these and other latitudes, as so ably set forth in Pro- 

 fessor Lindley's admirable Theory of Horticulture, I think, 

 with such facts before us, and the experience we are obtaining, 

 that there is quite sufficient to guide the persevering practi- 

 tioner in the application of this important principle. 



In a paper written by me in 1841, and subsequently pub- 

 lished in this Magazine, I ventured to throw out certain hints 

 relative to the matter in question. I then submitted a distinct 

 plan and statement of the method I proposed of supplying 

 terrestrial heat to vine borders ; and I also went so far as to 

 express the strong interest I felt as to its important bearing on 

 the practice of horticulture generally, but especially in the cul- 

 tivation of exotic plants and fruit. 



Having, since the paper alluded to was written, had various 

 opportunities of testing the correctness of my anticipations rela- 

 tive to the subject before us, I proceed at once from the premises 

 to the results already obtained. 



In the spring of the year above noted, in a range of pits I had 

 erected for the growth of the pine-apple plant, I had arrange- 

 ments made, by the formation of a suitable bed of soil over a 

 moist hot-air chamber, as the section shown \v\Jig. 1 7. will more 

 fully explain. In Jig- 17. a a are hot-air tubes, or open pilasters, 

 that can be opened or shut at pleasure ; b is the bed of compost, 

 &c, as hereinafter described; c c are hot-water pipes; d is the 



