WITH THE MICROSCOPE.' 21 



ful light be employed, it is necessary to concentrate the rays upon 

 the surface of the object placed in the focus of the object-glass by 

 the aid of one of the following instruments. 



27- Bull's Eye Condenser. This instrument is provided with all 

 microscopes, and needs no description. Different modes of mounting 

 the plano-convex lens are represented in figs. 51 and 52, pi. XI, and 

 the position of the microscope, condenser, and light in fig. 43, pi. X. 



28. Metallic Reflector. A concave metallic reflector may also be 

 used to bring the rays of light from a lamp to a focus on the object. 

 This instrument is fitted to the side of the microscope. I do not, how- 

 ever, think it possesses any advantages over the bull's eye condenser. 



29. Beck's Parabolic Reflector, pi. XI, fig. 50. This instrument 

 is made to fit on and rotate round the object-glass ; it answers ad- 

 mirably for condensing the light on the surface of objects, and by 

 throwing the rays in any particular direction across the surface 

 enables the observer, by the assistance also of the shadows, to deter- 

 mine the nature of irregularities upon some objects in a very satis- 

 factory manner. By the adaptation of a little reflector, arranged as 

 represented in fig. 50, pi. XI, Mr. Sorby gained great advantage in 

 the examination of the fractured surfaces of iron and steel. See 

 Microscopical Journal, Oct. 1865, p. 117. 



so. Lieburkuhn. The rays of light reflected from the mirror 

 and passing round the circumference of the object placed in the field 

 impinge upon a concave annular reflector or Lieberkuhn adapted to 

 the object-glass, from which the rays are reflected downwards, and 

 brought to a focus upon the surface of the object itself, pi. XII, 



fig- 53- 



If a transparent object is to be examined by reflected light, a 

 piece of black paper, rather larger than the aperture of the object- 

 glass, should be placed behind it to prevent the passage of light 

 through it, or one of the stops, fig. 53 <?, supplied with some instruments 

 may be inserted in its place beneath the stage. The stops, however, 

 are not furnished with many of the modern microscopes. 



31. Arrangement for examining Opaque Objects with very High 

 Powers. Prof. H. Lawrence Smith, of Kenyon College, Gambia, 

 Ohio, U.S., has introduced a plan by which the object-glass is made 

 its own illuminator. The rays of light are admitted at the side of 

 the lower part of the tube of the body, received upon a small silvered 

 mirror set at the proper angle, and cutting off a portion of the aper- 

 ture, by it thrown down through the objective to the object, and 

 returned through the object-glass and aperture of the mirror to the 

 eye-piece. 



Messrs. Powell and Lealand substituted for the silvered mirror a 



