CH. XIII] CANDLE-POWER OF ARC LAMPS 555 



face forward as is shown in figure 297 for the inclined electrodes and 

 in figures 294-296 for the right-angle arc. The results of these 

 measurements are shown in curve form in fig. 302. These curves 

 show that the greater the current the greater is the amount of light 

 given by the arc. The increase in light is, however, more rapid 

 than the increase in current and no simple mathematical statement 

 of the relationship is possible. The crosses indicate the individual 

 measurements with the right-angle arrangement and the circles, 

 measurements with the inclined carbon arc. The upper curve is for 

 the right-angle arc with direct current. In this case the highest 

 candle-power for the same current (amperage) is obtained. The 

 next curve is for the inclined carbon arc with direct current. The 

 light is not quite as much with this arrangement as with the right- 

 angle arc. 



The two lower curves are for alternating current. It will be 

 noticed that there is a greater difference in candle-power depending 

 on the electrode arrangement with alternating than with direct 

 current. The short dotted part of the curve for the right-angle 

 arrangement is for 6 mm. carbons and small currents, while the 

 main part of the curve is for larger carbons. 



A table showing the results of the individual measurements 

 might be misleading, as large variations in the light of the arc are 

 continually occurring and a given measurement might be made 

 when the arc was giving its greatest or its least light. For this 

 reason the values given in the table ( 756) for the candle-power of 

 the arc with different currents were taken from the curve instead of 

 being from individual observations. These values are good 

 averages and may be accepted as close enough to the actual candle- 

 powers for all practical purposes in projection. 



