150 PRACTICAL TREATISE ON THE MICUOSCOPE. 



a conical frame-work of wire, are exceedingly useful, and 

 perhaps more so than those of metal. The shades answer 

 two purposes, the one to keep away superfluous heat and 

 light from the eyes, and the other to throw a good light 

 on the table. The heat is not entirely prevented by the 

 metal shade, and is very annoying when the head is kept for 

 some time in the neighbourhood of it, but by the paper one 

 this is obviated, which renders it certainly the best for all 

 purposes. The method of making these shades is described 

 by Mr. Gwilt.* He takes half a sheet of good foolscap paper 

 and strikes thereon two semicircles, as in fig. 106, the longest 

 diameter being thirteen inches, and the 

 shorter one four inches, fitting and adapt- 

 ing it to a skeleton-shding frame as the 

 case may require, and then glueing or 

 Fig. 106. pasting the superfluous edges together. 



When once properly fitted, another pattern 

 may (previously to the glueing of the edges) be traced out 

 and kept at hand, from which any number may at any time 

 be drawn, and a new shade made when wanted, in less than 

 ten minutes. 



The head and eyes are more effectually protected from the 

 heat by a contrivance of Mr. Nasmyth, who uses two shades 

 instead of one. The outer one is made about a quarter of an 

 inch in diameter larger than the inner one, and both have 

 tubes proceeding from them, which are raised so high as to 

 cover the upper part of the chimney of the lamp. By this con- 

 trivance, a current of cold air is continually passing between 

 the two shades, and the outer one is, consequently, kept cool. 



When it is wished to illuminate the room, and at the same 

 time not to have the light in the eyes, one half of the shade 

 may be dispensed with, the remaining part being supported by 

 a ring of wire at the top and bottom, as in the frame which 

 supports the paper shade. 



By far the best lamps for burning, are those on the bird- 

 fountain principle, in which the oU is always presented to 

 the wick at a certain level, and whether the reservoir be 



* Microscopic Journal, vol. i. p. 58. 



