Page:On Radiation.djvu/58

 from the downs of Epsom, from the hills and seabeach of the Isle of Wight, and also by experiments on air in the first instance dried, and afterwards rendered artificially humid by pure distilled water. It has also been established in the following way. Ten volatile liquids were taken at random and the power of these liquids, at a common thickness, to intercept the waves of heat was carefully determined. The vapours of the liquids were next taken, in quantities proportional to the quantities of liquid, and the power of the vapours to intercept the waves of heat was also determined. Commencing with the substance which exerted the least absorptive power, and proceeding upward to the most energetic, the following order of absorption was observed:—