In the second half of the 1950s, as a college junior, I took the classic electrical measurements laboratory. The principal instrument was a Leeds and Northup wall galvanometer, which was sensitive to currents as low as 10 nA. This was the culmination of over a century of development of current-measuring instruments which relied on the interaction of currents with static magnetic fields. These instruments were mounted on a solid wall to prevent vibration, and a telescope and curved scale combination used to determine the deflection of the galvanometer. Because of its great sensitivity, you had to plan your measurements so that the coil did not burn out from putting currents of the order of tens of milliamperes through it. The coil had little natural damping, and it was standard procedure to use a key to short circuit the coil to provide electromagnetic damping to get the scale back to the zero reading.
All of the instruments below were made by either Morris E. Leeds or, after about 1900, the successor company of Leeds and Northrup, both of Philadelphia. The basic movement is that developed by D'Arsonval , with the long, slender coil moving between curved magnet pole pieces to ensure linearity. The first four instruments use a form of coil developed and patented by H.A. Rowland of Johns Hopkins.
The bottom instrument is the Type H galvanometer which
Leeds and Northrup sold for $45 in 1905.
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