Dating vintage rotary watches
The long shunt pin with knurled nut allows connection as a potentiometer if desired.Morris Leeds and Edwin Northrup started Leeds & Northrup in 1903 in Philadelphia, PA to supply precision instruments for scientific experimentation within laboratories, colleges and universities and precision test and calibration instruments for industrial applications.
A Standard Cell provided a reference voltage for calculation of various circuit values or a specific voltage supplied for precision measurement type comparisons.Various types of laboratories also purchased L & N equipment.L&N was a major supplier of various types of devices that were used for industrial calibration of temperature sensors and associated temperature monitoring instruments.The large knob is original and has JAGABI embossed on it - JAGABI was the trade name for James G. The JAGABI rheostat shown is 52 ohms total R, rated at 5.0 Amps. The small German rheostat shown is 48 ohms, only rated at 1.5 Amp - six inches long.Central Scientific Company was located in Chicago, IL and generally built various types of devices for laboratory experimental use, mainly for schools, colleges and universities.These types of boxes were used in DC Resistance bridge circuits for precise measurements of an unknown resistance (Wheatstone Bridge circuits) or in other circuits for calculating current flow, low voltage levels or comparison evaluations.
Both of these Otto Wolff resistance boxes were used a Mount Wilson Observatory in Southern California. Wilson and the facility there had (has) a lot of very early test gear.
To select a R value one first has to know the total resistance of the box.
In the case of the Central Scientific box shown, the total R is 1100 ohms.
I was given these boxes by my old Virginia City friend, Maynard Clark who worked at Mount Wilson Observatory (Maynard designed much of the computer software for the various telescope drive systems at Mt.
Wilson.) These large, adjustable wire-wound rheostat-potentiometers were generally used in college and university physics laboratories when performing experiments in electricity where fairly large currents were involved.
With the box shown, each junction is a different value of R starting at 400 ohms and reducing in value down to .01 ohm.