Ojpaque Illuminators for Sigh Powers,, 



467 



OPAQUE ILLUMINATORS FOR HIGH POWERS. 



In the September number of Siltiman's Journal, Mr. H. L* 

 Smith, of Kenyon College, U.S., described a new illuminator 

 he had contrived for the examination of objects under high 

 powers by reflected light. His plan is to throw light through 

 a lateral aperture on to a small silver reflector, so situated as 

 to reflect the rays down through the object-glass on to the 

 object. An instrument of this sort was recently sent by Mr. 

 Smith to Mr. Lobb, accompanied by a request that he would 

 invite Messrs. Powell and Lealand to make and introduce it 

 to the English public. Those gentlemen did not read the 

 description in Silliman's Journal, but, after experiment and con- 

 sideration, modified Mr. Smith's plan in a way which they 

 considered an improvement. The apparatus as made by them 

 will be understood from the following diagrams. Fig. 1 repre- 

 ss, i. sents its external appearance, and Fig. 2 

 gives a sectional view. The upper part 

 of this apparatus screws into the body of 

 the microscope like an adapter, and its 

 lower part carries the object-glass. Light 

 entering one of the round holes in the 

 circular diaphragm strikes against a 

 piece of glass B, which reflects a large 

 portion of it downwards in the direction 

 C, where the object-glass is placed. The 

 object-glass condenses the light upon 

 the object beneath it, and the return 

 rays from the object pass up again through the object-glass, 

 through the piece of glass at B, and on to the eye of the ob- 

 server in the direction D. 



The inclination of the piece of flat 

 favourable for the reflection of the in- 

 cident light down to C, and the rays on 

 their return through the object-glass 

 strike D at a different angle, which per- 

 mits a much larger proportion to pass 

 straight through, while another portion 

 is reflected back again and lost. 



Mr. Richard Beck,who, like Messrs. 

 Powell and Lealand, had not seen Silli- 

 man's Journal, heard that Mr. Smith's 

 plan was to throw the light down through 

 theobject-glass bymeans of a mirror that 

 cut off a portion of its aperture, and he, c 



without any concert with Messrs. Powell and Lealand, hit upon 



glass 



B 



is 

 "Eia. 



D 



the most 

 2. 



