Letters Sent to Dr. S.C. Lind, October 20, 1939

October 20,1939 Dr. S. C. Lind, University of Minnedota, Minneapolis, Minn. Dear Dr. Lind: Wie were glad to receive your letter of October 13th and shall attempt to give you the information requested. (1) The luminous material industry as a whole is not growing, since the tendency on the part of many of the watch and clock concerns to cheapen qualityhas resulted in less demand for those dials. However, so far as the aviation field is concerned the industry is expanding quite rapidly due largely to the increased building program adopted by our owm Government. (2) There is probably a greater use for luminous dials today than during the last World War due to the faot that many new type instruments have beon developed which were not then known. In other words, there are many more instruments per plane now than during the World War, and each instrument is supplied with a luminous dial. (3) I cannot give you exact figures but the average small plane would have 12 or 15 luminous treated dials. Aircraft like the "Clipper Ships" and large Bombors have 3 sets of controls, and probably each ship has from 60 to 75 luminous treated instruments. Aircraft such as Trans- continental planes with dual controls probably have anywhere from 24 to 50 dials, depending on the type ship. There is no set rule, as each type ship differs from the other both in design and amount of equipmente (4) The use is not limited to military planes, as all commercial transport planes are equipped with luminous treated dials. (5) In our opinion the present waz abroad will not incroase the use of luminous material in thi s countay unless there is a change in the present embargo law which will permit large scale purchases of aircraft by foreign governments. If this change is made, which is certainly indicated, there is no doubt but that the use of luminous material will be greatly enlarged. (6) No new worth while uses for luminous material have been developed during the past fow years. However, both the Army and Navy have written Specifications which require a higher grade material than previously used, and also require it to be applied with a much heavier application. So far as the industry is concerned, this alone will cause a large increase in volume. (7) Nesothorium is not generally used in luminous material at the