This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1910 edition. Excerpt: ...and the change of resistance of manganin and some other alloys will be of the same order. Both the foregoing may be neglected in all ordinary cases. The change of the elastic force of a spring will be several parts in ten thousand, and the change of resistance of a copper coil will be about 4 parts in a thousand. (b) Temperature Coeff1c1ents Of D1rect-current Voltmeters.--The effect of an increase of temperature of 10 C is to weaken a phosphorbronze spring about 0.04 per cent, and hence if no other part of an instrument was affected by the temperature change, the reading of the instrument would be increased by this percentage. In an instrument of the permanent-magnet moving-coil type, the strength of the magnetic field in the air gap will usually decrease by about 0.02 per cent25 for a rise of temperature of 10 C. This decrease in the field strength tends to reduce the reading of the instrument, and hence the reading will in general be increased by only 0.02 per cent by a rise of room temperature of 10 C. This figure applies to a permanent-magnet moving-coil instrument used as a milliammeter with This is an average of the values found by Sanford and Fearing for the magnetic fields of six instruments from three makers. The individual values ranged from--0.01 to--0.03 per cent. the whole current to be measured flowing through the moving coil. If the instrument is to be used, in connection with some added resistance, as a voltmeter, the effect of temperature change on the resistance of the instrument circuit must also be considered. It is evident that if the resistance of the voltmeter can be made to increase by about 0.02 per cent26. per degree C, the current taken by the voltmeter (when a definite voltage is applied to its circuit) will...