Cavendish Laboratory : Maxwell's instrument for measuring the circumference of coils during winding
Cavendish Laboratory
<p style='text-align: justify;'>Photograph of Maxwell's instrument for measuring the circumference of coils during winding. Maxwell's instrument probably dates from 1881, two years after his death. This instrument was used to measure precisely the coils used by Rayleigh in his absolute determination of the Ohm. Glazebrook's precision coils (P2020 in colour) may have been measured by this device. These exact measurements were needed to estimate precisely the values of the self and mutual inductances of the pairs of coils.</p>