This collection consists primarily of letters exchanged between Edison and Secretary of the Navy Josephus Daniels, along with related correspondence. Many of the typewritten letters are accompanied by drafts in Edison's hand. The documents in this folder are from March 1917. They pertain to tests on the absorption of light by sea water when different refrangibilities are used. There is also discussion of a scheme devised by Edison for ascertaining the depth of water under a ship (see Report 56).