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Simple compass microscope

Year/Period	1690-1750
Maker	VAN MUSSCHENBROEK
Country	The Netherlands
Signature	Punched with the Van Musschenbroek trade mark (oil lamp and crossed keys)
Category	Microscopes
Optical 1	Simple
Optical 2	Non-achromatic
Size of the microscope (h x w x d)	4 × 3.5 × 15 cm
Provenance	Dr. J.J. Beijer (1898-1986), Lisse (the previous owner)
Inventory number	SM 32

Description

Compass type microscope with a set of exchangeable lenses, coarse and fine adjustment, adjustable specimen grips, and a box which fits over the specimen in order to regulate the amount of light by means of a revolving stop. Unfortunately this box is missing.
With the microscope goes a chamois wallet for six lenses in their holders. The lenses are mounted between two thin pieces of brass in which a small recess is hammered to contain the lenses.
There is one unmounted lens, it is obviously a molten glass bead, there still remains a short part of the original stem from which it was once molten. Its diameter is 4.62 mm, the focal length is 3.36 mm. A simple calculation learns us that the refractive index of the glass is 1.52, common crown glass.

There are still four original mounted lenses:
‘…’: f = 17.7 mm, magnification 14×.
‘…’: f = 12 mm, magnification 21×.
‘….’: f = 8.3 mm, magnification 30×.
‘..’: f = 4.3 mm, magnification 58×.

Accessories: three specimen holders.