Description
A compendium is the name given to a small holder for more than one instrument. Here the case holds a sundial, a magnetic compass, and a mercury thermometer. With the case suspended from its ring, the thermometer hangs vertically. It is graduated in degrees Fahrenheit and Celsius over the normal range of temperatures. The compass and sundial are removed from the case and set up to find the time of day. Instructions for use with the Equation of Time are pasted inside the box lid.

The Fahrenheit scale, which takes 32 as the freezing point and 212 as the boiling point of water, is named after the instrument maker Daniel Gabriel Fahrenheit (1686-1736), who spent many years perfecting thermometers.

The Celsius scale is named after the Swedish scientist Anders Celsius (1701-1744). He is best known for the scale ranging from 0 for the freezing point and 100 for the boiling point of water, but nowadays this scale is generally known as Centigrade.

The Equation of Time is the difference between clock time and sundial time on any day. Because the tilt of the Earth’s axis and the fact that its orbit is not exactly circular, solar days vary throughout the year. Between January and March and again at midsummer the sundial lags up to 15 minutes behind the clock; between September and December, and again in May, the sundial will advance to be about 16 minutes ahead of the clock.

26/03/2008
Created by: Dr. Anita McConnell on 26/03/2008