Complex sentence: Roosevelt decided that the letter required action, and authorized the creation of the Advisory Committee on Uranium, chaired by Lyman James Briggs, the Director of the Bureau of Standards, with Adamson and Hoover as its other members.
Split into simpler sentences: Roosevelt decided that the letter required action, and authorized the creation of the Advisory Committee on Uranium. The committee was chaired by Lyman James Briggs, the Director of the Bureau of Standards, with Adamson and Hoover as its other members.