Nikola Tesla Books
HOT WIRE METER CONSTRUCTION 135 the pointer does not describe a full-scale deflection, cut a narrow strip from the shunt and try again. Continue this paring operation until the needle sweeps to the end of the scale when the full amount of current is passing. For electro-therapeutic purposes, the meter will require no heavy shunt as the current is measured in milliamperes or thousandths of an ampere. The most practical scale is one reading from 0 to 2000 m.a. (or, 0 to 2 amps.). The adjustment for zero is effected by turning the Fig. 5.-The meter in its case spindle 4, within the coils of silk thread. This is a dainty operation but patience is rewarded by success. The thread will give some trouble owing to its propensity for absorbing moisture and changing its length in consequence. The only remedy is either to seal the case hermetically or, better still, to use a length of the fine tinsel known as "galvanometer suspension." This may be obtained from a maker of high-grade instruments if the builder is fortunate in being near one. The material is exceedingly thin and narrow phosphor bronze strip. The hot-wire element should be left just a trifle slack. Under no circumstances should it be taut. Before calibrat
