These fourteen letters, which cover the period November 1903-October 1904, were selected from three letterbooks in box 10 in Series 1 of the William J. Hammer Collection. The twelve selected items from the first letterbook are all addressed to Edison. They pertain primarily to Hammer's interest in radium and radium-luminous materials and to the spinthariscope, a radiation measuring device invented by William Crookes in 1903. There is also a letter regarding possible purchasers of Edison's patent "on the use of pressure in connection with electrical furnaces," along with a letter concerning Edison's interest in purchasing a White steam car manufactured by Hammer's father-in-law, Thomas H. White. The one selected item from the second letterbook is a description an illustration (not included) of the first commercial incandescent lamp fixture. The one selected item the third letterbook is an incomplete letter to Francis Jehl regarding Hammer's return from the Louisiana Purchase Exposition (World's Fair) in St. Louis. Courtesy of the NMAH Archives Center.