164 MICROSCOPIC ILLUSTRATIONS. 



penetrating genius) ; then let another piece of thin plane 

 glass be smeared with Canada balsam, and cemented 

 upon the divisions, which will preserve them for ever. 

 Now if corresponding black lines, of any scale required, 

 are placed under the paper on which we draw, we can 

 with great facility put in our outline in the most correct 

 proportions. Or if the paper is too opaque, a frame 

 with black silk threads stretched upon it may be laid 

 upon it till the sketch is completed. The contrivance 

 can be used with my microscope as well as with any 

 other. 



Mr. Lister has constructed the stand of a microscope 

 with a particular view to the use of the camera lucida : 

 accordingly his body is motionless and of considerable 

 length, so as to clear a large space on the table for the 

 field of view. The ocular end is, moreover, firmly lashed 

 to the legs of the stand, (which is very solid,) by means 

 of steadying rods, forming altogether the best construc- 

 tion for the use of long heavy bodies, and camerse lu- 

 cidae, which I have seen. 



It must be most evident that a single microscope re- 

 quires exactly the same powers, properties, and capa- 

 bilities as a compound one. I should, therefore, construct 

 its stand and apparatus precisely in the same manner as 

 that of a compound one, only it may be made on a much 

 smaller scale : as little strength is required for carrying 

 single magnifiers, triangular drawn tubes may be used 

 instead of the triangular gun-metal bar of the compound 

 (to be hereafter described). The drawing of triangular 



