ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



107 



descent mantle — in all cases a surface of flame large enough to illuminate 

 every part of the lens E through the hole in F. 



The adjustments are made by bringing the object to the centre of 

 the field of a low-power objective and focusing it, then adjusting the 

 substage condenser so that the image of the hole in F is sharply focused 

 on the object, and then changing the objective for one of higher power 

 and re-focusing, but without interfering with the illumination. The size 

 of the hole in F should be such that its image in the field of view should 

 just fill the field of the eyepiece in use. As the flame is some distance 

 from the hole there is no danger of injuring the object by heat, even 

 with an exposure of two or three hours, and for the same reason the 

 threads of the Welsbach mantle do not show. With this arrangement 

 I have produced photomicrographs with a Beck eighth and astronomical 

 eyepieces giving a magnification of 3000 diameters with satisfactory 

 definition." 



Watson and Sons' Revolving Microscope Tray. — This is made to 

 the design of A. J. H. Brown and the suggestions of E. Harcourt Tyrrell. 



Fig. 26. 



An oak-framed tray (fig. 26) carrying a Microscope on a cloth base, has two 

 extended arms connected by a circular end, having on its under side a 

 centre-pin. The pin fits into an oak base, which is cloth-lined on the 



