Henry Craig

Henry Craig was working as a janitor of the Western Homeopathic College in Cleveland, Ohio when he patented a new form of microscope. His patent (no. 34,409) of 18 February 1862 was the fourth microscope patent issued in the U.S. It described his construction of a lens formed by a heated rod of flint glass drawn out to a diameter of 1/8 inch and then fused to a disc of crown glass, 1/2 inch in diameter. As heat was increased, the flint glass formed a spherical drop of 1/8 inch diameter. The focal plane of the lens was at the bottom of the crown glass disk.

In outward appearance, Craig's microscope resembled a drum microscope. However, the lens assembly was mounted in a collar and rested in contact with the specimen slide, which was inserted into a slot near the top of the microscope. A mirror at the bottom of the tube directed light at the specimen.

Three models of Craig-type microscopes were made: one of brass; one of hard rubber; and another version of the rubber instrument that could be folded flat.

Henry Craig's 1862 advertisement stated that his microscope had won a silver medal at the Ohio State Agricultural Fair. The Craig microscope was advertised in many agricultural magazines in late 1862 and 1863 and later offered as a premium.