210 IMPORTANCE OP 



of an external covering in the other, it ■would be found that the balance 

 would turn in favour of the latter. The trouble of covering a house 

 with mats, every night, is no doubt the main obstacle to their employ- 

 ment. Long ago. Sir Joseph Paxton used moveable thatched roofs 

 running in a sort of groove or rail, capable of being pushed over a house 

 every night, and pushed off again at one end every morning ; and this 

 device left nothing to be desired in principle. But it demanded space. 

 For every fifty feet run of glass house fifty more feet were required at 

 the end of it to receive the moveable roof during the day, and it is only 

 here and there that so much space can be afforded. Ifor is the plan 

 applicable at aU to houses of any considerable dimensions. It therefore 

 still remains for some ingenious person to show how glass houses may 

 be covered every night cheaply, and mithout trouble, by a moveable 

 roof. 



It is to the attention that, since the appearance of Daniell's 

 paper, in 1824, upon this subject, has been paid to the 

 atmospherical moisture of glazed houses, that the great 

 superiority of modern gardeners over those of the last genera- 

 tion is mainly to be ascribed : there are, however, traces of the 

 practice at a much earlier period, although, from . not under- 

 standing its theory, no general improvement took place. In 

 the year 1816, an account was laid before the Horticultural 

 Society of a successful mode of forcing Grapes and Nectarines, 

 as practised by Mr. French, an Essex farmer, with rude 

 materials, and under unfavourable circumstances. It is not a 

 little remarkable, that, although Mr. French himself correctly 

 referred his success to the skilful management of the atmo- 

 spherical moisture of his forcing-houses, the subject was so 

 little, understood at that time that the author of the account 

 not only shrank from adopting the opinion, but evidently, from 

 the manner in which he speaks of the explanation, had no idea 

 of its justness. 



" About the beginning of March, Mr. French commences his forcing 

 by introducing a quantity of new long dung, taken fromimder the cow- 

 cribs in his straw yard ; being principally, if not entirely, cow dung ; 

 which is laid upon the floor of his house, extending entirely from end to 

 end, and in width about six or seven feet, leaving only a pathway 

 between it and the back waR of the house. The dung being aE new at 

 the beginning, a profuse steam arises with the first heat, which, in this 

 stage of the process, is found to be beneficial in destroying the ova of 



