88 HOW TO SEE WITH THE MICROSCOPE. 



the purpose of a micrometer for measuring small inter- 

 vals, or for the measurement of cover glasses, etc. In 

 this adjustment the same security against lateral dis- 

 placement is provided for by means of the " T" angle- 

 pieces, as applied to the rack and pinion movement. 



The lower end of main tube carries a nose-piece fitted 

 with the " society screw." This piece can, however, be 

 detached so that the broad-guage objectives now in pro- 

 cess of construction can be used on this instrument. 



The main stage consists of a circular metal plate, 

 three and one-quarter inches in diameter, firmly bolted 

 to the heel of the limb, and in such a manner as to be 

 isolated from the movements of the sub-stage apparatus; 

 four holes are drilled through the main stage plate, 

 and so arranged that the spring clips may be adjusted 

 to hold the object-slide in either a vertical or horizon- 

 tal position. The spring clips may also be tiansferred 

 to the under surface of the stage, holding the object- 

 slide in contact therewith, when very oblique illumina- 

 tion is to be employed. The well-hole is of the usual 

 size and is provided with a standard screw-thread, by 

 means of which the Woodward prism and other acces- 

 sory pieces can be readily placed in position. The stand 

 is thus fitted for such emergencies as required a fixed 

 and central sub-stage, separate from the movements of 

 the mirror ; the polariscope is also nicely provided for. 



(NOTE. It has lately come to the surface that the diameter of the 

 * society screw" Is not sufficiently large to meet the requirements of the 

 optician when low powers of the widest apertures are demanded. Mr. 

 Sidle is now making for the author a one -inch glass having a diameter of 

 over one inch, and the Acme has been designed to meet such requirements). 



