CHARLES H. WILLIAMS. 517 



In 1895 he returned to Boston and began again the regular practice 

 of his profession, not, however, leaving but rather further cultivating 

 the special field of his endeavors. The impression that his work up 

 to this time had made on his colleagues is well noted in a letter received 

 by him from Snellen, in which that great ophthalmologist, recalling 

 pleasant days which he had spent with Dr. Williams abroad, said of his 

 return to general practice, " I am glad that you have come back to the 

 old flag." 



While industriously following the daily routine of his profession 

 Dr. Williams kept on with his stud}^ of vision and of signalling, and 

 devoted no little time to the improvement and testing of railway 

 signal lights, in which he was most expert and resourceful. He 

 served on many committees of the American Ophthalmological Society 

 and had a large share in the preparation of their test cards and recom- 

 mendations for improved methods, and wrote many papers before 

 professional societies dealing with the general problem of the critical 

 diagnosis of imperfect vision. 



As an incident to his work upon signal lights he devised an extremely 

 simple and useful modification of the photographic wedge photometer, 

 a pocket instrument working on the extinction principle and capable 

 in careful hands of remarkably useful work. This instrument came 

 into considerable use among railway signal experts as well as among 

 those interested in scientific photometry, to whom it has great use as 

 an auxiliary for the quick investigation of photometric conditions. A 

 little later he devised still another photometer of the equality-of- 

 brightness type, employing as before the photographic wedge, which 

 proved particularly useful in comparing the brightness of surfaces and 

 estimating the density of smoke and cloud. He became an early 

 member of the Illuminating Engineering Society and frequently took 

 useful part in its discussions, and was beside a member of many socie- 

 ties and clubs. He was elected to our Academv Januarv 14, 1914, 

 and until very recent years was a frequent attendant at its meetings. 

 The stud\- of color \'ision he kept up, as far as strength permitted, 

 almost to the end and was for a score of years a frequent lecturer on 

 the problems connected with color blindness at the Harvard Medical 

 School and elsewhere in professional gatherings. In a practical way 

 no American ophthalmologist has done more toward the investigation 

 of this curious and mysterious condition. 



