UPON PLANT-HOUSES. 85 



Bteam engine and steam printing. As yet our glass-houses are 

 mere make-shifts ; — science aloue, in the most extended sense of 

 tlie word, can perfect them ; and here, too, the Enghsh saying, 

 "Knowledge is power," will have its full application. The 

 researches of Dove convince us, that there exist influences in nature, 

 which those structures either do not admit at all, or only in a very 

 imperfect degree. Granting that we could introduce a due pro- 

 portion of heat, light, and moisture: still the real solar influence, 

 with all its thermic, chemical, and other powers, the radiation from 

 the soil, and its other properties of conducting heat and moisture, 

 &c., helonging to tropical countries, are impossibilities to us. Our 

 vegetable wards, properly speaking, have neither the proper loca- 

 tion nor soil, accorded to them in their own native climate, they are 

 doomed to a sort of anchorite life of solitude, in some tub or cask, 

 instead of the free expanse of land and air, to which they have been 

 habituated ; and how much they suffer in consequence, is proved 

 by the contortions of roots and stems, and the excrescences, &c, to 

 which they become subject. The sun's light conveyed to them 

 has to pass through panes of glass differing in colour and thick- 

 ness, placed at various inclinations towards the horizon and 

 ecliptic : all these are deviations from the natural state of things, 

 so great as not to be counterbalanced. A distinguished English 

 natural philosopher, whom I consulted on the best mode of con- 

 structing glass-houses, expresses himself in this manner ; " The 

 rays of heat pass through glass, as well as liquid substances, and 

 probably also through vapour in the atmosphere, in a veiy capricious 

 manner. If it is considered, besides, how small a portion of the 

 entire solar spectrum is luminous, and how extremely variable 

 is the absorbent action of the media, we are led to a belief, that 

 the question of the most appropriate construction for the recep- 

 tion of light still remains unanswered. We can only advance by 

 direct experiments." The problem receives further complications, 

 according to each locality, from latitude, clime, exposure of the 

 house, &c., and even from the chemical structure of the glass 

 used. Respecting this last article, a talented botanist, who has 

 at the same time a great degree of practical experience in 

 gardening, writes to me as follows : " Part of our house had 

 colourless, the other green glass ; the former we are now obliged to 

 paint white, and the latter has lost its colour, which has happened 

 .also at various other places. With all respect for the progress of 

 .chemical science, it must be admitted, that the old glass-manufac- 

 turers delivered articles of durable colour, while at present this 



