Description
In the nineteenth century accurate watches were available, but it was difficult to check that your watch was showing the right time. Instrument makers made transit instruments that helped people to do this by observing the sky. They were cheap, and easy for someone without much knowledge of astronomy to use.

The transit instrument is a telescope that can only move in one plane and has cross-wires in its eyepiece. This one was made in London in 1884, and is designed to be set up on a window-sill. If you set it up facing South, you can observe the exact point at which the sun, or a star, crosses the observer’s meridian (a line imagined to run north to south across the sky directly above the observer’s head).

Before the nineteenth century, most people used local time (so noon in Plymouth, for example, would be a few minutes later than noon in London). Standardised and precise timekeeping became more important as the railways and telegraph systems ran to exact schedules all across the country. Railway stations and telegraph offices had clocks set to Greenwich Mean Time, but if you lived in the country you still had to use the sun or stars to regulate your watch. If you used the transit instrument to measure local noon precisely, you could then add the difference between noon at your location and noon in Greenwich to set your watch to the exact time as used all over Britain.
02/05/2008
Created by: Dr. Jenny Downes on 02/05/2008