OP THE MICROSCOPE. 



113 



vents the use of the Lieberkuhn, condensing lenses, reflectors, 

 etc. Several different arrangements are used. The first was a 

 small annular silver reflector, placed just above the back lenses 

 of the objective. A hole in the side of the brass mounting 

 admitted the light, which was thus thrown down through the 

 lenses of the objective, on to the object, and back again to the 

 eye. For the silver reflector, some manufacturers substitute a 

 thin plate of glass, and with excellent results. This illuminator 

 has been used with immersion objectives of high power, and 

 with very good results. 



The Parabolic Reflector was first made by Messrs. 

 Beck for Mr. Sorby, who employed it to examine the micro- 

 scopical structure of iron and 

 steel. As ordinarily constructed, 

 it consists of a parabolic mirror 

 attached to the end of a rod fur- 

 nished with universal joints, so 

 that it may be placed in any 

 position. It answers admirably 

 for condensing the light on the 

 surface of objects, and by throw- 

 ing the rays in any particular 

 direction across the surface, the 

 observer is enabled, by means of 

 the shadows, to determine the 

 nature of irregularities upon some 

 objects in a very satisfactory man- 

 ner. It is in general used in con- 

 nection with a large bulls-eye 

 condenser, which is thus made to throw parallel rays on it. 



There are two ways of mounting the parabolic reflector. The 

 usual, and where applicable, the best method, is to attach it to 

 the arm of the microscope. Many microscopes, however, have 

 no arrangement for attaching this accessory, and to meet such 

 cases Mr. Crouch has devised the adapter shown in Fig. 23. 

 The jointed arm which carries the reflector is attached to an 

 adapter, which fits between the nose-piece and the objective, 

 and may thus be used on any stand. 



Fig. 23. PARABOLIC EEFLECTOB. 



