Maker's Name: 
Cambridge Scientific Instrument Company Ltd, Cambridge England 178
Where made: 
47 × 68 × 22 cm

Central housing with removable wooden sides for suspended magnet and rotatable on tripod base with three levelling screws. Top of base contains scaled horizontal circle, two reading microscopes and spirit level. Telescope arm and deflection scale extending from central housing with focussing telescope, spirit level and mounted filters attached atop extension from central housing. From other end of central housing extends the platform for the mirror mount. Glass suspension tube, containing coupling on end of suspension fibre, screws into the top of central housing.

The base instrument (note attachment 158) alone only allows the strength of the Earth's magnetic field to be known. A magnet (see 157) placed in the coupling at the end of the suspension fibre is allowed to oscillate through some small angle. The angle of deflection is read from the deflection scale through the telescope are. From the period, the product of the Earth's field strength and the moment of the magnet may be found.

This same magnet is then placed parallel to and attached to a ruler which connects to the top of the base through the brackets and clamp pins and runs perpendicular to the central housing and telescope arm. From the deflection of a needle due to the competing magnetic fields the moment of the magnet may be eliminated from the above product and the Earth's field strength determined.