1344. The three properties of light have been defined by Mr. Hunt as producing colour, heat, and actinism or chemical action; and in a paper read before the Society of Arts on the 16th of February, 1848, he endeavoured to explain the principles on which tinted glass has been adopted in some hothouses. According to his theory, it appears that the full action of the chemical rays was secured by the use of glass stained blue by cobalt; that the hot rays were best obtained by the use of red glass; and that yellow glass abstracted the chemical and heat-giving rays without impeding those which contained only light; and, therefore, 'when there was any tendency to form too much stalk or leaves, and it was desired to produce more wood, it was done by admitting as much light as possible, with the smallest possible quantity of actinic power, and that might be effected by interposing glass of a yellow tint.'
