The United States Army Hospital Model microscope was manufactured by the optician and scientific instrument maker Joseph Zentmayer of Philadelphia. It was first introduced in 1862-1863 for use by the U.S.A. Medical Department during the Civil War. It continued to be sold to the government as well as to the civilian market until the end of the 19th century. Over that time span, the microscope incorporated a number of modification and improvements. The four examples below are illustrative of some of these changes.

Monocular:  serial no. 975
prior to 1876

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Binocular: serial no. 723
prior to 1876

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The Army microscopes made after 1876 incorporated the swinging substage and, later, the new fine adjustment described in the Zentmayer patent of  Aug. 15, 1876       

Monocular: serial no. 1867
c. 1877

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Binocular: serial no. 3773
after 1876

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