It has departments of pharmacy, chemistry, electrical wiring, lithography, house-painting, printing, carpentry, moulding, tile-setting, bricklaying, machinery and applied science.
Suppose it is desired to measure the insulation-resistance of a system of electric house wiring; the ohmmeter circuits are then joined up as shown in fig.
1, where W represents a portion of the wiring of the building and I a portion of the insulating materials surrounding it.
In making the test, the whole of the copper wires belonging to any section of the wiring and the test must be connected together at some point and then connected through the series coil of the ohmmeter with one terminal of the dynamo.
The Evershed and Vignoles form of the instrument is much used in testing the insulation resistance of electric wiring in houses.
The branch is to be prepared by ringing or notching or wiring as in layering, and a temporary stand made to support the vessel which is to contain the soil.
On setting the dynamo in operation, a current passes through the shunt coil of the ohmmeter proportional to the voltage of the dynamo, and, if there is any sensible leakage through the insulator to earth, at the same time another current passes through the series coil proportional to the conductivity of the insulation of the wiring under the electromotive force used.