2092. In consequence of the experiments of Mr. Hunt, a very clear pale yellowish green glass, the colour of which was given by oxide of copper, was selected for glazing the great palm-house at Kew; that house being so large that it was almost impossible to adopt any system of blinds for shading the plants that was likely to be efficacious. The green glass chosen was so transparent, that scarcely any light was intercepted. On examining the spectral rays through it, it was found that the yellow was slightly diminished in intensity, and that the lower edge of the ordinary red ray was cut off. It also appeared to have a remarkable action upon the non-luminous heat rays. 'The absence of the oxide of manganese, commonly employed in all sheet-glass, was insisted upon, it having been found that glass into the composition of which manganese enters will, after exposure for some time to intense sun-light, assume a pinky hue; and it was found that the slightest approach to redness would allow the passage of those heat rays which were found to have so remarkably scorching and injurious an effect.