Johnston Optical Company's Ametropometer
 Catalogue Number: 4272 Johnston Optical Company's Ametropometer Category: Equipment Sub-Category: Optometer Designer/inventor: George Johnston Year Of Publication/Manufacture: c1902 Time Period: 1900 to 1939 Place Of Publication/Manufacture: Detroit, Michigan, USA Publisher/Manufacturer: Johnston Optical Company Description Of Item: A tabletop device to subjectively measure refractive errors. Upright column of cast iron with screw fitting to mount device on table. Large disc of nickel plated brass with raised lettering: 'JOHNSTON OPTICAL COMPANY'S AMETROPOMETER, DETROIT, MICHIGAN/ PATENT APPLIED FOR OCTOBER 1902'.Rear of disc has axis increments. A viewing tube looks through 2 glass prisms mounted within the rotating disc and the separation of the images seen is used to determine refractive error and astigmatism. H: 440mm, W: 193mm, D: 140mm Historical Significance: George Johnston's patent application for his 'Sight Testing Apparatus' was filed on October 9, 1902. The United States Patent Office granted him Patent No 742329 on October 27, 1903. This instrument works upon the same principle as Culbertson's Prisoptometer, patented September 21, 1886, Ref Kett Cat Nos 202, 570, 1177. How Acquired: Donated by Pamela Sutton Date Acquired: August 2022 Condition: Good, but missing chin rest Location: Documents Room West Unit Bay 3 Shelf 4 |