Fig. 2,583.—General Electric simultaneous record of three waves with common zero.
The desirability of a complete knowledge of the manner in which the pressure and current varies during the cycle, has resulted in various methods and apparatus being devised for obtaining this knowledge. The apparatus in use for such purpose may be divided into two general classes,
1. Wave indicators;
2. Oscillographs.
and the methods employed with these two species of apparatus may be described respectively as,
1. Step by step;
2. Constantly recording.
that is to say, in the first instance, a number of instantaneous values are obtained at various points of the cycle, which are plotted and a curve traced through the several points thus obtained. A constantly recording method is one in which an infinite number of values are determined and recorded by the machine, thus giving a complete record of the cycle, leaving no portion of the wave to be filled in.
Fig. 2,584.—General Electric simultaneous record of three waves with separate zeros.
