PARABOLIC SPECULUM, 



123 



Beck's Parabolic Speculum. 



to a spring-clip that fits upon the Objectives (2 inch, li inch, 1 inch, 

 2-3rds inch), to which it is especially suited, and is slid up or down 

 or turned round 

 its axis, when 

 the object has 

 been brouglit 

 in to focus, until 

 the most suit- 

 able illumina- 

 tion has been 

 obtained. The 

 ordinary rays of 

 diffused Day- 

 light, which 

 may be consi- 

 dered as* falling 

 in a parallel 

 direction on the 

 Speculum turn- 

 ed towards the 

 window to re- 

 ceive them, are 

 reflected upon a 

 small object in 

 the focus of the 

 Speculum, so 

 as to illuminate 

 it sufficiently 

 brightly for 

 most purposes ; 

 but a much 

 stronger light 

 may be concen- 

 trated on it 

 where the Spe- 

 culum receives 

 its rays from a 

 Lamp placed 

 near the oppo- 

 site side of the 

 stage, a Bull's 

 Eye being in- 

 terposed to give 



parallelism to the rays. For the sake of Microscopists who may 

 desire to use this admirable instrument with Objectives to which it 

 has not been specially fitted, Mr. Crouch has contrived an Adapter, 

 by which it may be used with any objective of suitable focus. This 

 consists of a collar (Fig. 72, a) which is interposed between the lower 

 end of the body of the Microscope and the Objective ; on this collar is 



Crouch's Adapter for Parabolic Speculum. 



