2058. The introduction and management of light is the most important point to attend to in the construction of hothouses. Every gardener knows, that plants will not only not thrive without abundance of light, but will not thrive unless they receive its direct influence by being placed near to, or at no great distance from, the glass. The cause of this last fact has never been satisfactorily explained. (Sowerby on Light and Colours, 1816.) It seems probable that the glass acting in some degree like the triangular prism, partially decomposes or deranges the order of the rays. It is an important fact, also, that light in nature is always accompanied by heat; and, therefore, it should not only be an object to admit the sun's direct rays in clear weather, when he is visible, but even when the rays are refracted and deranged by clouds and vapours, when he is invisible.