Letters Received to H.H. Barker, April 9, 1931

UNIVERSITY OF MINNESOTA SCHOOL OF CHEMISTRY MINNEAPOLIS April 9, 1931 OFFICE OF THE DEAN Mr. Howard H. Barker Vice President of the United States Radium Corporation APR 11 1931 535 Pearl Street New York City Dear Barker: Dr. Paul D. Berrisford, 810 Lowry Building, St. Paul, who is also a member of the staff of our University Hospital, called today to get information about radium paint and I have referred him to you. His problem is the following. He wants to do some experimentation toward devising an instru- ment for testing the sensitivity of the human eye to weak light sources. He would like to make up discs, possibly of different sizes, and to time the eyes of different individuals in adjusting the sensitivity so that the source just becomes visible in the dark. I have warned him that the luminosity of radium paint does not remain constant. He would like, to have, a paint that would become visible the sucjes in about two minutes in changing from ordinary room conditions to complete darkness. I have told him that the weaker the paint, the slower its rate of decay and that a paint after application with a binder has a slower rate than the dry paint. I have suggested that possibly an aged paint which has reached its neerly light minimum might be most useful to him. I suggested that he should inquire whether you could make up such dials for him and give him the luminosity in lamberts and any information about the rate of decay that you might have. I am not sure whether his method is feasible at all. Possibly, you have already considered this proposition and can advise him. I think that if he succeeds in getting a satisfactory device, he would make them up in fairly large quantities through some medical supply house in St. Paul for distribution to the profession. With best regards, Very sincerely yours, s. C. Lind S. C. Lind, Director. scl:en