DISCUSSION AT SHEFFIELD 221 



Discussion. 



Dr. W. H. Hatfield did not think that there was any point 

 on which he joined serious issue with the authors of the papers read 

 that evening. Mr. Mony penny said that many people used the 

 microscope and did not properly understand it. That was so. But 

 looking at it from another point of view, there were people who regar- 

 ded the microscope as a tool and looked to the manufacturers and tho 

 optician to further extend its usefiihiess. That was his position, and, 

 generally speaking, the position most metallurgical investigators would 

 take up. From that point of view one could tell the people who 

 were making a speciality of the microscope what the metallurgist 

 wanted. We might first of all tell them what we could do. From 

 his C'wn metallurgical experience he could obtain delightful micro- 

 photographs under ordinary conditions, and with ten magnifications 

 get excellent empirical microphotographs. This was also the case 

 with 50, 100, and up to 1,000 magnifications — excellent, almost per- 

 fect definition could be obtained. Beyond 1,000 diameters, how- 

 ever, we could not do so, and that was an essential thing to put 

 before the people who wore out to assist us in the use of the micro- 

 scope. 



There were a whole series of problems awaiting adequate solu- 

 tion, including the recrystallisation of cold-worked material, and 

 solutions could only come when we have better facilities for definite 

 and accurate information as to the internal architecture of the 

 material at magnifications, well above a thousand. We had produced 

 very pretty photomicrographs up to three thousand diameters — Sir 

 Robert Hadfield has produced excellent ones up to eight thousand — 

 but these magnifications did not give us much more information 

 than we could obtain by a. clear definite picture at a thousand. If 

 the Symposium had brought those facts before the notice of manu- 

 facturers of the rnicroscope, it would have served a great purpose 

 to metallurgists. 



Dr. P. Rogers thought that the theory of lens design had been 

 evolved much further than the theoretical side of metallurgy itself, 

 heretical as that might seem. In reference to the high, magnificatioji 

 work done by Sir Robert Hadfield and Mr. Elliot, he emphasised 

 that w^hilst magnifications of 8 to 10 thousand were interesting as 

 pictures, they did not contain any more detail ; they were, in fact, 

 of no greater value than enlargements. Nevertheless, he welcomed 

 this high magnification as a progressive step, even though the result 

 as regards detail w^as a negative one. 



He put in a jjlea to metallurgists that they should make their 

 pho'tomicrographs bigger; if they were, an advantage would be 

 gained. Such enlargements were better understood by the non-expert, 

 even if perhajDS as a record they were not so good. In regard to fuie 

 structures in the alloy steels — especially, for instance, in the study of 

 temper brittleness — he would welcome anything which would give 

 further resolution of detail. This information, he felt, was hidden 

 away from them just at the limit ^ of what the microscope could do. 

 He thought the microscope would ultimately contribute to the solution 

 of that problem. 



