432 Miscellaneous Intelligence. 



scarcely any light is intercepted. In examining the spectral rays 

 through it, it is found that the yellow is slightly diminished in intensity, 

 and that the extent of the red ray is affected in a small degree, the 

 lower edge of the ordinary red ray being cut off by it. It does not ap- 

 pear to act in any way upon the chemical principle, as spectral impres- 

 sions obtained upon chlorid of silver are the same in extent and char- 

 acter as those procured by the action of the rays which have passed 

 ordinary white glass. This glass has, however, a very remarkable ac- 

 tion upon the non-luminous heat-rays, the least refrangible calorific 

 rays. It prevents the permeation of all that class of heat-rays which 

 exists below and in the point fixed by Sir William Herschel, Sir H. 

 Englefield, and Sir J. Herschel, as the point of maximum calorific action. 

 As it is to this class of rays that the scorching influence is due, there is 

 every reason to conclude that the use of this glass will be effective in 

 protecting the plants, and, at the same time, as it is unobjectionable in 

 point of color, and transparent to that principle which is necessary for 

 the development of those parts of the plant which depend upon external 



chemical excitation, it is only partially so to the heat-rays, and it is 



opaque to those only which are the most injurious. The absence of 

 the oxyd of manganese, commonly employed in all sheet glass, is in- 

 sisted on, 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 any tint of this character would com- 

 pletely destroy the peculiar properties for which this glass is chosen. 

 Melloni, in his investigations on radiant heat, discovered that a peculiar 

 green glass, manufactured in Italy, obstructed nearly all the calorific 

 rays ; we may, therefore, conclude that the glass chosen is of a similar 

 character to that employed by the Italian philosopher. The tint of 

 color is not very different from that of the old crown glass ; and many 

 practical men state that they find their plants flourish much better 

 under this kind of glass than under the white sheet glass, which is now 

 so commonly employed. 



6. On the Application of Gutta Percha for Modeling ; by Mf- 

 Busk, (Proc. Brit. Assoc, Athen., No. 1027.)— After alluding to his 

 experiments, he described the mode he followed in obtaining his 

 moulds :— u It is to be rolled out on a smooth surface in sheets of ^any 

 convenient size suitable to the object to be taken, and varying in thick- 



ness according to the size. 



A 



inch is thick enough. The sheet is dipped for a moment or two into 

 boiling water, and placed warm upon the object, upon the surface o^ 

 which it is to be carefully pressed with the finger point, or a conven- 

 ient elastic pad, so as to insure its close and uniform adaptation, 

 moulding soft objects it is, of course, necessary that they should P ^. 

 elasticity or resiliency, as is the case with living or recently dead a ^ 

 mal bodies. The gutta percha does not seem to be applicable 



— such 



wn, "8 mvuiua iiuiu vciy tragi ie OOUies, SUCH as iua.it j *— .^ 



would not bear the requisite pressure nor admit of the removal ot 

 mould when rigid without risk. The most delicate objects, howe » 

 and slender projections, if firm enough in the original, may in 

 plaster cast be removed from the matrix without any difficulty w 

 the latter is softened by momentary immersion in hot water. 



