The Sub-Stage 



19 



Simple and obvious tests will quickly demonstrate that this 

 is quite fallacious. 



THE UNDER-FITTING. In the cheaper instruments, instead 

 of the sub-stage as above described, an ordinary plain- 

 tube, termed the under-fitting, is screwed into the under 

 side of the stage, and in this tube the condenser or other 

 apparatus is moved up and down to focus. It is shown 

 fitted to the microscope figured on page 8. This must be 



FIG. 3. VIEW OF DIAGONAL FIG. 4. SECTIONAL VIEW OF 



KACKWOIIK ATTACHED TO ONE ADJUSTABLE FITTINGS OF RACK 



OF WATSON AND SONS' MICRO- AND PINION. 



SCOPES, SHOWING DOVETAILED 

 FITTINGS TO RECEIVE FINE 

 ADJUSTMENT SLIDE AND AD- 

 JUSTING SCREWS (MARKED A). 



truly centred with the optical tube, and it is well to test it 

 by placing a small diaphragm in the under-fitting, and 

 with an objective in the body to focus the diaphragm. If 

 it be not central its practical importance is annulled. The 

 additional convenience and necessity of the centring sub- 

 stage cannot be too fully impressed upon the beginner who 

 contemplates doing thorough work. Swift and Son, of 

 Tottenham Court Eoad, in their new series of ' Students' 

 Microscopes,' and Watson and Sons, of High Holborn, in 



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