1905.] Oscillations into Continuous Currents. 485 



This dynamometer was placed in series with a shunted movable coil 

 galvanometer of Holden-Pitkin pattern, and the two together placed in 

 series with a variable section of an inductionless coil through which an 

 alternating current was passing. A vacuum valve as above described 

 was in series also with the galvanometer and dynamometer. The 

 alternating current was derived from an alternator giving a nearly true 

 sinoidal electromotive force. The form factor of the electromotive 

 force curve of this alternator was determined and found to be 1 -115, 

 that for a true sine curve being 1-1 11. 



The vacuum valve sifted out the alternating current flow and allowed 

 the currents in one direction to pass, but nearly stopped those in the 

 opposite direction. The indications of the electrodynamometer were pro- 

 portional to the root-mean-square (R.M.S.) value of the sum of the two 

 opposite currents, and that of the galvanometer to the true mean value 

 (T.M.) of their difference. The galvanometer and dynamometer were 

 both calibrated by a potentiometer by means of continuous current, and 

 curves constructed to convert their scale readings to milliamperes. 

 Then with various alternating current electromotive forces, their 

 readings were taken when in series with a vacuum valve and recorded 

 in the following tables. The letter D denotes current in milliamperes 

 as read by the so calibrated dynamometer and G that read by the 

 galvanometer. The ratio D/G is denoted by a, and the rectifying 

 power, viz., 2//a+/by /3. 



The table shows that the value of a is not constant, but for each 

 state .of incandescence of the filament reaches a maximum which, 

 however, does not greatly differ from the mean value for the range of 

 currents used. If we set out the mean values of ft in a curve (see 

 fig. 4), in terms of the power expended in heating the carbon filament, 

 we see that the rectification is less complete in proportion as the 

 temperature of the carbon filament increases. This is probably due 

 to the fact that as the filament gets hotter, it heats the enclosing 

 cylinder to a higher temperature and enables negative electricity to 

 escape from the latter. 



Hence, I feel convinced that if the metal cylinder could be kept 

 quite cool by water circulation the rectification would reach 100 per cent, 

 or be complete. 



An ideal and perfect rectifier for electric oscillations may, therefore, 

 be found by enclosing a hot carbon filament and a perfectly cold metal 

 anode in a very perfect vacuum. With a bulb such as that used for 

 the above experiments all we can say is that the current passed 

 through the vacuum is from 80 to 90 per cent, continuous, 100 per cent, 

 implying that the vacuum is perfectly non-conducting in one direc- 

 tion and permits the flow of negative electricity only from the hot to 

 the cold electrode. The necessity for keeping the cathode cold is 

 shown by the following experiment : An alternating-current arc was 



