The magneto‐chronograph and its application to magnetic measurements

Abstract

The period of a magnet oscillating under the directive force of the Earth's magnetic field is a function of the strength of that field. Heretofore the estimation of the period has been accomplished by eye‐and‐ear readings but in the present method the personal equation is entirely eliminated. Light from an intense source such as an automobile headlight lamp is condensed on the glass‐scale end of a magnetometer‐magnet and after reflection is focussed on a slit in front of a photo‐electric cell. The reflected beam acts as an optical lever whose period is the same as that of the magnet but whose amplitude is twice as great. At each transit of the image across the slit current is passed by the cell and after passing through amplifiers is made to operate a pen on a chronograph. A chronometer in the circuit marks seconds on the record by the same pen. In this investigation the method was applied in the determination of the moment of inertia of a magnetometer‐magnet, estimation of personal equation in eye‐and‐ear readings, and in preliminary tests of the relative absolute magnetometer.