Born in Germany in 1826, Joseph Zentmayer immigrated to the US as a young man, already trained in optics and instrument making. He incorporated his business in Philadelphia in 1853, making his first large model in 1858. For decades he made models with different bases and supports, from the "American Centennial" to the small "American Histological" or previously the highly successful "United States Army Hospital" . The business survived, on Zentmayer's death in 1888, until the middle of the following decade run by his sons.
This rare microscope is signed on the base "J Zentmayer, Phila, Pat'd Aug 15 76." . The instrument is about 30 cm high in the closed position. The focus is by rack and pinion and has a fine adjustment mechanism. The optical assembly is made up of three objectives and two eyepieces, all of them in perfect condition and housed in a small drawer inside the box. It has a mechanism to facilitate the exchange of objectives that seems later, since it was patented on December 1, 1882. The system under the observation platform is tiltable to facilitate observation with oblique light. The mirror, concavo-convex, and the sub-base are also in perfect condition. The gold lacquer is very well preserved, with hardly any signs of use. The whole set is housed in a beautiful box that has perfectly stood the test of time.
References: "Billings Microscope Collection" pag 71, fig. 133
"Billings Microscope Collection" pag 84, fig. 157