IMPROVEMENT IN THE CONSTRUCTION OF HOTBEDS. 299 



the apparatus which I have above recommended. A, B, C, D, is a hot- 

 bed, resting upon an inclined plane of earth. E, the frame; F, G, a pipe, 

 made of a slender oak pole ; and H, I, K, smaller pipes fixed into the 

 larger one, through which the air which enters the latter at F ascends 

 into the hotbed. The tube of the large pipe is one inch and a half, and 

 that of the smaller three-quarters of an inch diameter. The smaller tubes 

 have near their upper ends two horizontal apertures, through which the 

 heated air passes laterally into the frame. I consider three of the large 

 pipes to be fully sufficient to give heated air to a bed twenty feet long ; 

 the heated air entering at all times very rapidly, and consequently always 

 keeping all within the frame in motion. The larger pipes might, I con- 

 ceive, be with advantage made of cast-iron. 



If the heat of the air be at any time excessive, it may be lessened by 

 opening the end of the tube at G, where it is usually kept closed. The 

 hotbed in which I have placed the above-described kind of tubes is 

 composed almost wholly of leaves ; but the mass of these is great, and the 

 temperature in consequence high. I immersed a deep pot into the leaves, 

 and caused the heated air of the tube K to ascend into it, having pre- 

 viously shortened the tube, and fitted it accurately to the aperture of the 

 pot, placing a thermometer, with some eggs of the common domestic 

 fowl within it, with the view of ascertaining whether these could be 

 hatched by such means. I have not yet seen the result ; but the temper- 

 ature of the ascending current of air which arises into the pot, and of 

 course into the frame, appears never to have varied during fifteen days 

 more than three degrees, the lowest temperature being 101, and the 

 highest 104 ; and it has, of course, been nicely adapted to both the pur- 

 poses for which it was intended. 



I have formerly ascertained, that the power of a current of heated air 

 when made to enter a pit, or chamber of any kind, \vas found greatly to 

 exceed the calculation which I had previously made; and in the last 

 winter, very contrary to my expectations, a very feeble current of air, the 

 temperature of which was below 50, proved sufficient to preserve gera- 

 niums which were placed close to the glass in the severest frost from 

 receiving the slightest injury. 



The operation of a hotbed into which a pipe is introduced in the 

 manner above mentioned has been observed by me only during the spring 

 and part of the summer of the present year ; but the results have been so 

 satisfactory, that I can, with the utmost confidence, recommend the 

 machinery which I have described, particularly when tender plants of any 

 species are to be raised in cold seasons of the year. 



