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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 Excerpt: ...sweeping over a scale graduated in ohms, so that the value of the resistance connected to the instrument is read directly from the scale, no calculations being required. The Weston direct-reading ohmmeter, of which an external view is shown in Fig. 241 and its construction and circuits in Fig. 242, is an instrument belonging to the second type above mentioned. In mechanical construction, the instrument is practically the same as the Weston D. C. voltmeter or ammeter, that is, it contains a Fig. 241.--Weston Ohmmeter. Fig. 242.--Construction and Circuits of the Weston Ohmmeter. horseshoe permanent magnet, provided with soft iron pole pieces between which is pivoted the movable coil carrying the pointer. The winding of the movable coil is divided into two parts by means of a tap at the center of the winding, and these two parts are included one in each of two branch circuits, the deflection of the movable coil depending upon the currents flowing through the parts of its winding, which currents are proportional to the resistances connected to the branch circuits. By tracing the flow of current from the upper right-hand battery post of Fig. 242 it will be found that the current entering the coil at the top will divide and flow through the parts of the coil winding in opposite directions, a part of the total current flowing through resistance 1 and back to the battery, and the other portion of the current flowing through resistances 2 and 3 (if the plug is in the lowrange block of the plug switch) and through the unknown resistance back to the battery. Fig. 243 shows the same connections more clearly, all construction details being omitted. It will be seen, herefrom that the current through the upper portion of Fig. 243.--Electrical Scheme of the Weston Oncomete...