Galvanometers. - Third Paper
W E Ayrton, T. William Mather · Proceedings of the Physical Society of London · 1897
UNDER the above title the authors, in conjunction with Dr. Sumpner, read a paper before the Physical Society in January 1890 t, and gave a list of sensihility-records relating to a large number of instruments of various types.To facilitate comparison between different instruments, the results were reduced to a common standard as regards scaledistance, length of a scale-division, periodic time of vibration, and resistance, the values chosen for this purpose being, respectively, a scale-distance equal to 2000 scale-divisions, periodic time 10 seconds, and resistance 1 ohm.The sensibilities for steady currents were expressed as the number of scale-divisions deflexion a current of one microampere would produce (assuming proportionality) under the standard conditions, mid the sensibilities for quantity as the swing produced by the instantaneous discharge of one niicrocoulonib when the instruments were used ballistically.The resulting numbers give a measure of the relative sensitiveness of the various instruments when quickness of action is all important.For cases where time is of little consequence, and constancy of zero (as depending on the controlling forces) is of prime importance, the resnlts were modified by appropriately introducing the moment of inertia of the suspended systems.Our reasons for choosing a scale-distance of 2000 scdedivisions and a period of 10 seconds as standard conditions, were, that these conditions represented more nearly than any other round iiuinbcrs thoPe under which sensitive galvanoineters were generally used.For example, scales of half-* Read Xay 13,1898.