Lord Kelvin's mirror galvanometer with lamp and stand, 1858.

Made:
1858 in Strand
maker:
Elliott Brothers
Thomson mirror speaking galvanometer, made by Elliott Brothers 1925-179 Pt2: 
    
    Lamp cover for Thomson mirror speaking Scale on stand, for Thomson mirror speaking galvanometer Thomson mirror speaking galvanometer, made by Elliott Brothers 1925-179 Pt 1 (right hand object):
    
    Thomson mirror speaking Thomson mirror speaking galvanometer, made by Elliott Brothers 1925-179 Pt2: 
    
    Lamp cover for Thomson mirror speaking

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Thomson mirror speaking galvanometer, made by Elliott Brothers
Science Museum Group Collection
© The Board of Trustees of the Science Museum

1925-179 Pt2: Lamp cover for Thomson mirror speaking
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Scale on stand, for Thomson mirror speaking galvanometer
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Thomson mirror speaking galvanometer, made by Elliott Brothers
Science Museum Group Collection
© The Board of Trustees of the Science Museum

1925-179 Pt 1 (right hand object): Thomson mirror speaking
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Thomson mirror speaking galvanometer, made by Elliott Brothers
Science Museum Group Collection
© The Board of Trustees of the Science Museum

1925-179 Pt2: Lamp cover for Thomson mirror speaking
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Thomson mirror speaking galvanometer with lamp and stand, made by Elliott Brothers, Strand, London, 1858.

A mirror galvanometer is a particularly sensitive electrical indicating instrument and was used to detect the extremely weak currents received through long submarine cables. Instead of a needle indicator, a mirror with a bar magnet cemented on the back is suspended on silk threads within the coil. A beam of light shone on the mirror is reflected on to a scale card some distance away, thus magnifying any movement of the mirror. Instruments of this type were used on the Atlantic cable expedition of 1858. The mirror galvanometer became the standard instrument for receiving telegraph messages, but it did have a disadvantage in that it needed two operators - one to read and call the signal, and another to write the message down. This problem was solved by Thomson when he invented the siphon recorder, which used a glass tube dipped ink to record to movements of the cable on a moving tape, to then be read and decoded.

Details

Category:
Telecommunications
Object Number:
1925-179
Materials:
brass (copper, zinc alloy), glass, wood (unidentified), lead (metal), iron, cardboard and metal (unknown)
type:
galvanometer
credit:
Donated by the Eastern Telegraph Company

Parts

Lamp cover for Thompson mirror speaking galvanometer, 1858

Lamp cover for Thompson mirror speaking galvanometer, 1858

Measurements:
overall: 191 mm x 92 mm x 75 mm,
Materials:
copper (alloy) and paint
Object Number:
1925-179 Pt2
type:
lampshade
Oil lamp base for Thomson mirror speaking galvanometer, 1858

Oil lamp base for Thomson mirror speaking galvanometer, 1858

Measurements:
overall: 195 mm 104 mm, 1.14 kg
Materials:
metal (unknown) and textile
Object Number:
1925-179 Pt6
type:
oil lamp