74.a – Einthoven String Galvanometer – A large heavy instrument with a thick solid black steel framework supported by 3 adjustable brass feet. Two horizontal cylindrical holders protrude from both the left and right sides of the front of the instrument. These hold thick steel rods with brass ends. The framework of the instrument has two thick solid arms extending horizontally to the back of the instrument which support either end of a large leather-covered galvanometer coil.
74.b – String Carrier Attachment – This part of the instrument fits vertically at the front of the Einthoven String Galvanometer with the “Sensitivity Wheels” at the top. A wooden box with 2 clasps on the front, the inside has been constructed with felt-covered wooden supports made specially to house a metal instrument. The instrument consists of a black metal bar with a brass bar mounted parallel underneath it. At one end of the instrument, there are vertical dials which turn parallel to the central bars, one black and one brass, approximately 4 cm in diameter. These lie on either side of the central brass bar and are used to adjust screws that can touch the bar. Both dials read “to increase sensitivity” with an arrow pointing clockwise. There are 2 terminals, one black and one brass, on top of the instrument at this end. At the other end of the instrument are 2 terminals on top of the black metal bar, one brass, one black metal. There is also a smaller brass knob.
Older UTMuSI entry reads: “Insertable brass centre piece (fibre carrier) and tension adjustment (micrometer screw); Two terminal connections to fibre at front of carrier; tension adjustment has arrow and reads “to increase sensitivity”; telescopes on either side of fibre carrier; an extremely heavy electromagnet with coils covered by red leather…”
Note: This instrument is accessioned with one fibre carrier, although there were likely at least two more associated with this instrument. A third is indicated by an empty box clearly meant to house a fibre carrier as it is similar in construction to the box housing 74.b. Neither surviving fibre carrier match this box precisely.
Accession Number: 2012.psy.74
Primary Materials: Steel, Brass, leather
“The Cambridge and Paul Instrument Co. Ltd. England”, “No. 48451”, “Made in England””S & J? Beck, London”, “This terminal to be earthed”
Dimensions (cm): Height = 28.5, Width = 31, Length = 48
Invented by Willem Einthoven in 1903 to provide highly accurate records of heart currents. The Electrocardiogram and String Galvanometer was by far the most sensitive instrument of its time. Improved by William Duddell in 1907 and manufactured by the Cambridge Scientific Instrument Company. The fibre changed position in the strong magnetic field. These movements were viewed through the microscope or projected onto a screen. The experimenter changed the period and sensitivity of the fibre by adjusting the micrometer screw. “The sensitivity of the galvanometer was very high; a current of only 0.1 microAmps would cause the fibre to deflect 1 mm. Since the mass of the fibre was only about 1 microgramme it had a very low moment of inertia and the period was about 0.005 seconds.”[Cattermole & Wolfe, 1987].
Good. Some wear and damage, especially to leather material covering cylinder.
Associated Instruments: 2011.psy.74.a, .b
The Cambridge and Paul Instrument Co. Ltd. England
Date of Manufacture: c. 1919-1924
Department of Psychology, University of Toronto
Additional Information and References:
1) Cattermole, M.J.G and A.F. Wolfe. <i>Horace Darwin’s Shop: A History of the Cambridge Scientific Instrument Company 1878 to 1968</i>, Adam Hilger: Bristol, Boston. (1987). p. 224