(1835 - 1910) American physician and scientist. In 1864 he undertook experiments to produce electric light by passing the current through a resisting filament which he claims “was the first steady electric light generated in Pittsburg, if not in the country”. Barker was a vital academic ally to Thomas Edison and helped Edison bridge the gap between Edison's inventive world and the formal scientific community. Rare A.L.S., 1p. 8vo., New Haven, May 18, 1872. Barker discusses his findings in the analysis of a substance submitted to him which he determines to be calcium carbonate. Some erosion to left side of letter causing the loss of a few letters of text, else very good.