396 



EEPORT — 1892. 



' Dr. Frolicli obtains the curves and renders them visible by means of a 

 mirror fixed to a soft iron diaphragm, and caused to vibrate vertically by 



ScaZe- of Tune^ 



the current. The horizontal motion is given by reflection from a set of 

 revolving mirrors, and a spot of light passing from them to a screen traces 

 the curve of the variation of the current. 



Fig. 24. 



12 MID 



IZ NOON 



SccxZc of TuTLey 



12 PM 



'A development of graphic methods for commercial purposes has been 

 recently brought into prominence in the plotting of the output of central 

 stations for supplying electricity to towns, giving the "load diagram." 

 For this purpose the output of the station with respect to time is made 

 into a curve showing the annual variations in the consumption. 



