General Discussion. 



In inviting Dr. W. H. Hatfield to offer some remarks 

 on the metallograpliical side of microscopy, the Chairman 

 suggested that in view of the short time available for 

 general discussion of the many important papers presented 

 on this subject, the discussion be continued at Sheffield, 

 and, if possible, also at Glasgow. 



Vr. W. H. Hatfield: I should like to say that I know I should 

 be expressing the general feeling of the Council of the Metallurgical 

 Society at Sheffield in saying that we have great pleasure in accepting 

 your invitation. If you will let us have copies of these papers, 

 particularly the metallurgical section of them, we will have them 

 thoroughly discussed, and, if you desire it, we will send Mr. Spiers 

 a copy of the discussion. 



Speaking on the papers, I think one can safely say that we have 

 in Sheffield many large firms who have well equipped laboratories 

 where these different types of microscopes are in use every day. I 

 should like to congratulate the President on the interesting paper 

 by Mr. Elliot and himself. I think that the work contained in 

 this paper typically represents what we are able to do with the micro- 

 scope in our study of steel. We (Brown-Firth Research Laboratory) 

 have some photomicrographs upstairs; they are really on the same 

 lines as those of Sir Robert Hadfield, but we have gone as far as 

 8,000 magnifications. I think Sir Robert will probably agree with 

 me when I say that 1,000 diameters really represents the limit of 

 adequate resolution which we are able to obtain in our general prac- 

 tice, and that if we go in for these higher so-called magnifications — I 

 refer both to his illustrations and to ours — we are getting enlarged 

 pictures, but we do not obtain really much more information as to 

 the structure of our materials, and from that point of view it is 

 interesting to refer to the paper on Dr. Sorby which the President 

 has put before us. I notice there that Sorby made great advance 

 in the 'eighties because he was able to use sufficiently high magnifica- 

 tion' to see the structure of the pearlite. Every time that we have 

 been able to get a still higher resolution we have obtained more 

 fundamental knowledge with regard to steel, and whilst I feel that 

 1,000 is at present our practical limitation, I am certain that if 

 only you experts in the construction of the microscope can go still 

 further, we shall obtain still more fundamental information. For 

 instance, I remember studying what we know as black steel at 250 

 to 500 diameters, but we got inconclusive information, but as soon 

 as we got to 1,000 diameters we had definite information and a 

 complete solution of our difficulty. There are two problems which 

 I would like to point out to you microscopists, or rather to the makers 

 of microscopes, which are awaiting solution. One l3r. Aitchison 

 deals with very ably in his paper, i.e., notched bar brittleness. I 



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