On angular aperture of objectives for the microscope : read before the Microscopical Congress at Indianapolis, Ind., August 15th, 1878
A late nineteenth-century technical pamphlet by George E. Blackham, read before the National Microscopical Congress at Indianapolis in 1878 and published in New York in 1880 for microscopists and optical students. Its pictures are plain black-line optical diagrams of a semicircular aperture, a glass slide with cover, and light rays refracting through glycerine and air, with one decorative scroll-and-vine ornament at the end. A designer could take the clean geometric construction of radiating lines and angle labels as a restrained, diagrammatic motif.
