62 



THE MICROSCOPE. 



aperture, place No. 1 aperture of the wheel of dia- 

 phragms in tlie field, then, looking through the eye-piece, 

 centre the aperture accurately; then bring No. 11 aper- 

 ture in the field, and again centre the lamp flame, and be 

 careful that it corresponds with the axis of the pupil of 

 the eye. 



" Should we wish to examine hairs, scales, or morbid 

 structures, use "No. 3, 4, or 5 apertures of the wheel of 

 diaphragms without a stop, the |th, iVth, to^h, ^fth, or 

 object-glasses, and the A, B, or C eye-piece as 



Fig. 36. Powell ami Lealand's Microscope arranged for LoWs illumination. 

 A. Secondary Stage carrying Achromatic Condenser. 



thought proper ; now bring the object into focus, and by 

 racking up the condenser for the best light, very clear 

 and satisfactory definition will be obtained. Nothing 

 more is required when examining these objects than the 

 selection of the most suitable aperture, and focussing the 

 condenser for the illumination which defines the best ; too 

 much and too little light being equally bad. 



" If we wish to examine objects such as Pleurosigma 



