Miscellaneous Intelligence. 431 



without, not under the form of lightning, but under the form of a current 

 explosion.' Sir W. S. Harris then referred to some remarkable cases. 



5. On the Colored Glass employed in Glazing the new Palm House 

 in the Royal Botanic Garden at. Kew ; by R. Hunt, (Proc. Brit. Assoc., 

 1847, Athen., No. 1028.)— It has been found that plants growing in 

 stove houses often suffer from the scorching influence of the solar rays, 

 and great expense is frequently incurred in fixing blinds to cut off this 

 destructive calorific influence. From the enormous size of the new 

 Palm House at Kew, it would be almost impracticable to adopt any sys- 

 tem of shades which should be effective — this building being 363 feet 

 in length, 100 feet wide and 63 feet high. It was therefore thought 

 desirable to ascertain if it would be possible to cut off these scorching 

 rays by the use of a tinted glass, which should not be objectionable in 

 its appearance, and the question was at the recommendation Sir Wm. 

 Hooker and Dr. Lindley, submitted by the Commissioners of Woods, 

 &c. to Mr. Hunt. The object was, to select a glass which should not 

 permit those heat rays which are the most active in scorching the leaves 

 of plants to permeate it. By a series of experiments made with the 

 colored juices of the palms themselves, it was ascertained that the rays 

 which destroyed their color, belonged to a class situated at the end of 

 the prismatic spectrum which exhibited the utmost calorific power, and 

 just beyond the limits of the visible red ray. A great number of speci- 

 mens of glass variously manufactured were submitted to examination, 



and it was at length ascertained that glass tinted green appeared likely 



to effect the object desired most readily. Some of the green glasses 

 which were examined obstructed nearly all the heat rays— but this was 

 not desired — and from their dark color these were objectionable, as 

 stopping the passage of a considerable quantity of light, which was es- 

 sential to the healthful growth of the plants. Many specimens were 

 manufactured purposely for the experiments by Messrs. Chance of Bir- 

 mingham, according to s;iven directions, and it is mainly due to the in- 

 terest taken bv these gentlemen that the desideratum has been arrived 

 at. Every sample of glass was submitted to three distinct sets of ex- 

 periments— 1st. To ascertain, by measuring off the colored rays of the 

 spectrum, its transparency to luminous influence. 2nd To ascertain 

 the amount of obstruction offered to the passage of the chem.ca rays. 

 3rd. To measure the amount of heat radiation wh.ch permeated each 

 specimen. The chemical changes were tried upon chlor.d of silver, 

 and on papers stained with the green coloring matter of the leaves of 

 the palms themselves. The calorific influence was ascerta.ned by a 

 method employed by Sir John Herschel, in his expenments on solar ra- 

 diation. Tissue paper stretched on a frame was smoked on one side 

 by holding it over a smoky flame, and then while the spectrum was 

 thrown upon it, the other surface was washed with strong sulphuric 

 ether. By the evaporation of the ether, the points of calorific action 

 were most easily obtained, as these dried off in well defined circles long 

 before the other parts presented any appearance of dryness, ej ' nese 

 means it was not difficult, with care, to ascertain exactly the condmons 

 of the glass, as to its transparency to light, heat, and chemical agency, 

 (actinism.) The glass thus chosen is of a very pale yellow-green color, 



the color being given by oxyd of copper, and is so transparent that 



