114 



GLASS. 



the best reflector of light, it is, also, on that account, preferable 

 to any other. There are some considerations, however, in favor 

 of a dark color, which, as has been already stated, absorbs a 

 larger quantity of heat, and parts with it again on the cooling 

 of the atmosphere. A yellow color we consider the most objec- 

 tionable of all, both on account of its contrasting badly with the 

 glass of the house and the verdure of vegetation, as well as the 

 effects produced by it on the light, which, as will be seen from 

 the preceding investigations, exercises an injurious influence on 

 vegetation. The influence may not be so great in the reflected 

 light, as when permeating yellow or orange-colored media, but 

 the power is, nevertheless, exercised to some extent. The same 

 investigations show the beneficial influence of a blue, or dark 

 color, which perfectly accords with our observations on plants 

 growing against dark bodies, otherwise exposed to abundance 

 of light; and, when it is in accordance with the taste of the 

 proprietor, we think the interior walls of hot-houses should be 

 of a dark color. 



In England, where the rays of light are less powerful than 

 here, dark-colored walls are now very common. There, light is 

 a more important consideration than heat : the latter can be 

 applied by artificial means ; not so the former. This probably 

 tends to prevent the adoption of a dark color for the interior of 

 their hot-houses. Here, dark walls are more desirable than 

 white, as they absorb the heat-rays, during a powerful sun, and 

 prevent the atmosphere from becoming so rapidly hot. This 

 fact is sensibly felt on standing before walls of the different 

 colors during the mid-day sun. By a white wall, the rays are 

 reflected from the wall back into the air, or on any other body 

 which is near it, by which the temperature of the air and the 

 body is very much increased. A dark-colored wall, on the con- 

 trary, retains the heat which falls on its surface ; and though it 

 may feel colder, it contains more latent heat, which it only parts 

 with when it is abstracted by the reduced temperature of the 

 atmosphere. This, alone, is a good argument in favor of dark- 

 colored walls in lean-to hot-houses. 



The inner side of the rafters, astragals, and sash-bars, should 

 approach to the color of the glass. As the light-rays do not 



