1024 



SUMMARY OF CUURENT RESEARCHES RELATING TO 



head (1). A leather washer (5) is made to rest closely against the inner 

 surfaces of (1) and (4). It is held in position by another washer of 

 metal (6) which, by means of two screws passing throufjh it and (5), is 

 made fast to the milled head. A small tonsiou-wlieel (10) has a screw 

 passing through both washers, also binding them to (1), and when desired, 

 locking the coarse-adjustment by making the whole combination prac- 



Fio. 167. 



FiQ. 168. 



tically one wheel. When the coarse-adjustment is used the spindle (8) 

 holds (7), (6), (5), (4), so that they cannot revolve with the pinion. 



When the fine-adjustment is required the friction of the leather 

 washer makes the whole combination practically one wheel, which is 

 turned by means of the milled head (8), giving the entire range of the 

 coarse-adjustment. Both adjustments are always ready for use except 

 when the coarse one is purposely locked to prevent accidents. All wear 

 is taken up by the spring as shown in the fig. 



Fig, 168 shows the entire combination in proper position. 



Necessity for a Sub-stage.* — Mr. J. Mayall, junr., in the second series 

 of his Cantor Lectures on the Microscope at the Society of Arts, says 

 that, in his opinion, every Microscope with which it is intended to do 

 serious work should have a racking and centering sub-stage ; and if the 

 opticians would supply an adapter fitted with a pivoting diaphragm- 

 carrier, or even a disc of apertures, so that objectives could be conveni- 

 ently used as condensers, they would add much to the interest of popular 

 microscopy. 



As it is, it is to be feared that the great majority of possessors of 

 Microscopes are not aware of the immense advantages attendant upon 

 the use of condensers — achromatic condensers being, of course, far prefer- 

 able, for it is with them alone that it is really practicable to observe 



Jouin. Soc. Attn, xxxvi. (1888) p. 1169. 



