1898.] 



MICROSCOPICAL JOURNAL. 



133 



about half an inch internal measurement. Such tanks 

 may be bought from any photographic dealer, as they are 

 designed for use with the optical lantern. The action of 

 the litmus solution is to cut out or absorb all the yellow 

 rays, by which in the ordinary way focussing is eJEfected, 

 and leave only the blue and violet, to which the plate is 

 most sensitive. Any old objectives can, however, be 

 corrected by an optician. 



It is essential that the microscope should have a fine 

 adjustment and one that works steadily, so that when in 

 use the image of the object will not shift from side to 

 side. If this is underneath, as shown in Fig. 1, and, as 

 is usually the case, it has a groove in the milled head, a 



piece of fine silk twist or catgut should be passed over it 

 and then carried round two ordinary cotton reels with 

 grooves cut in them, as shown exaggerated in Fig. 3. 

 One of these reels should be provided with a cross saw 

 cut, as in Fig. 2, into which can be fitted a square-sided 

 rod of brass fastened to a long handle, which is sup- 

 ported on wooden pillars, to the back of the camera. At 

 this point it ends in a milled head, which enables the 

 operator whilst examining the focussing screen to manip- 

 ulate the fine adjustment. If the fine adjustment has no 

 groove, then a small collar of brass lined with a couple 



