32 THE MICROSCOPE, ETC. 



To the largest hole of the diaphragm a short tube, 

 1, fig. 16, lined with cloth is attached, another tube 

 2 of sufficient length to reach the under surface of 

 the condenser, slides within it, at the upper extremity 

 of the inner tube and a short distance from its ori- 

 fice a slight rim projects into the interior, on which 

 brass discs having different sized central apertures 

 may be fitted. 



Another tube E carrying a disc of blue glass may 

 be made to slide within the tube 2. If the tint of 

 this glass is properly chosen it obviates the neces- 

 sity of using a part of the spectrum to produce 

 monochromatic light. The intensity of the colour is 

 increased or diminished by increasing or diminishing 

 the distance between the blue glass and the aperture 

 of the slot or back of the condenser. 



The description of this substage arrangement was 

 originally given to enable anyone possessing a cheap 

 instrument, or unable to afford an expensive one 

 already "fitted with an achromatic condenser, to con- 

 struct an apparatus which would answer that pur- 

 pose, and whose chief advantages were that no 

 light could reach the object or enter the objective 

 except through the diaphragm and condenser them- 

 selves, the ease and simplicity with which the several 

 adjustments are made, and the possibility of adapt- 

 ing it to any existing microscope stand. 



