OF ATMOSPHERICAL TEMPERATURE. 147 



quantity when the leaves have pushed forth. In a 

 few days, the violence of the steam abates as the buds 

 open, and in the course of a fortnight the heat begins 

 to diminish ; it then becomes necessary to carry in a 

 small addition of fresh dung, laying it in the bottom, 

 and covering it over with the old dung fresh forked 

 up : this produces a renovated heat, and a moderate 

 exhalation of moist vapour. In this manner the 

 heat is kept up throughout the season, the fresh sup- 

 ply of dung being constantly laid at the bottom in 

 order to smother the steam, or rather to moderate the 

 quantity of exhalation ; for it must always be remem- 

 bered, that Mr. French attaches great virtue to the 

 supply of a reasonable portion of the vapour. The 

 quantity of new dung to be introduced at each turn- 

 ing must be regulated by the greater or smaller 

 degree of heat that is found in the house, as the sea- 

 son or other circumstances appear to require it. The 

 temperature kept up is pretty regular, being from 65 

 to 70 degrees." {Hort. Trans., i. 245.) 



In this case, which attracted much attention at the 

 time, it is evident that the success of the practice 

 arose principally out of two circumstances ; firstly, 

 the moisture of the atmosphere was skilfully main- 

 tained in due proportion to the temperature ; and, 

 secondly, a suitable amount of bottom heat was 

 secured. This is, as will be elsewhere remarked, the 

 principal cause of the advantages found to attend the 

 Dutch mode of forcing. The reporter upon Mr. 

 French's practice speaks with surprise of the rudeness 

 of the roof of his forcing-houses, and of the nume- 



