A portable transit instrument by Dollond of London. Circa 1775.

2 inch objective lens.

With original fitted case with accessories, striding level, and 3 eyepieces.

Case dimensions:
Height: 20.5 cm. – 8 in.
Width: 88 cm. – 34. 5 in.
Depth: 43 cm. – 17 in.

For a similar instrument see The Science Museum, London. Object number 1939-390.

Dollond & Co., established 1750, Hatton Garden, London. Optical, Mathematical & Philosophical Instrument Makers.

A transit instrument is a telescope pivoted on a stand so that it can only move in one plane. Normally this would be aligned north-south so that as the Earth turns, every star visible from the latitude of the telescope can be seen to rise and fall over the course of a year. These types of telescopes can be used to create star charts, since every star can be viewed and so plotted. The time at which each star crosses the north-south line, or meridian gives one co-ordinate, the angle the telescope must point at to see it (its angular height) gives the other. It can also be used to find the time by the stars. Ref: National Maritime Museum, Greenwich, London.