HENRY M. SAYERS 173 



radiant heat. Either the half-watt or the Pointolite lamp may be 

 able to meet this. The limitation of bulb size is important. 



3. Oil immersion objectives intermediate in focal length and 

 aperture between the 2/3 inch and the 1/12 inch, well corrected for 

 colour. If anything can be done to reduce glare from internal 

 reflection in the objectives designed for metallography it will be an 

 advantage. 



4. An auxiliary condenser combination with a long working 

 distance compared with its focal length to be used to present a 

 magnified virtual image of the radiant to the objective. Suitable 

 specification would be: — 



Focal length, 1| inches to 2 inches, 



Working distance — anterior — 3 inches to 4 inches. 



Clear aperture, f inch to 1 inch. 



Well corrected spherically and chromatically. 



Mounted with a flange or a flanged collar. 



Cost reasonable. 



5. A simple firm optical bench or geometric slide arrangement 

 with carriers for lamp and condenser at heights corresponding to those 

 of usual microscopic axes when in the horizontal and vertical positions. 

 The whole bench or slide to be capable of movement parallel to the 

 microscope axis for 2 or 3 inches. 



