PKOCEEDINGS OF THE SOCIETY. 113 



Mr. Henry M. Sayers spoke on " lilumination in Micro-Metal- 

 lography." 



A full discussion of the subject of illumination is entered into. The 

 author concludes that improvement is desirable in the following items : — 



1. A transparent vertical illuminator reflector which shall get nearer 

 the theoretical perfection of reflecting 50 p.c. and transmitting 50 p.c 

 of the light incident on it at 45° without much coloration of the 

 transmitted light. An optically worked glass lightly platinised seems 

 the most promising. 



2. A source of light of uniform and steady high brilliancy presenting 

 an area of about half an inch square, to which a condenser of 2 in. 

 working distance can be focused without damage from radiant heat. 

 Either the " Pointolite " or the " half -watt " metal filament 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 f in. and the jV in., well-corrected for colour. If any- 

 thing can be done by computation to reduce glare by reflection from the 

 lens surface in 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. 



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 horizontal or vertical, to suit both 

 positions. 



Mr. Samuel Whyte, B.Sc, read a paper on "The Use of the 

 Microscope in Engineering Works." 



The microscope is of great practical use in controlling steel supplies 

 and their heat-treatment. Its uses are briefly that of : — 



1. Examination of raw materials, such as bars and especially small 



stampings for segregations and " laps " of oxide. 



2. An aid to arriving at the best heat-treatment, especially for high- 



speed steels. 



3. A means of detecting causes of failures, helping to work out the 



processes by which failures occur. 



Professor H. Le Chatelier, in a communication, suggested some 

 " Improvements in Metallurgical Microscopes." 



It would be an advantage to tvj and obtain good photomicrographs 

 with objectives corrected only for a single wave-length, say the highly 

 actinic blue line of the mercury vapour lamp, instead of using costly 

 apochromatics. 



Great errors frequently arise from the ignorance of observers. Thus 

 it is forgotten that every objective is intended to give an image at a 

 fixed point. Another mistaken procedure is to reflect the luminous 

 pencil by a total reflection prism, instead of by a mirror, forgetting that 

 the objective is calculated for working in air, not glass. 



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