Vickers Microplan 10X, Microscope

This is an objective lens—part of a microscope optical system—
rather than an entire microscope unit.
The specific lens in question is marked
"Vickers England MICROPLAN 10/0.25 + PH.1",
indicating a 10× magnification
and a numerical aperture (NA) of 0.25.
The “PH.1” denotes that it includes phase-contrast capabilities

Typical length around 37–39 mm,
and weight in the range of 58–63 g