on 



the Electric A 



re. 



143 



If, instead of curving downward at their upper ends, they 

 are more properly straight throughout, we have 



A = at, and W = bt, 



where A = amperes, W = watts, t = t\me, and a and b are 

 constants. 



Using cored carbons, the arc was found to restart much 

 more easily. In fact it was difficult to make the current so 

 small that the arc would not restart after a time lapse of 

 0*3 sec. Observations were taken with constant time of in- 

 terruption to find the effect of variations of arc-length on 

 the current required to restart. The carbons were cored, 

 each 0*17 in. diam. 



Volts. 



Amperes. 



Arc Length 

 (in inches). 



Time 



(in sec). 



Watts. 



47 



1-2 



0-02 



0-3 



564 



45 



25 



0-05 



0-3 



1125 



49 



3-7 



o-i 



0-3 



181 



55 



5 



0-15 



0-3 



275 



50 



7 



0/2 



0-3 



350 



55 



8-5 



0-25 



0-3 



4675 



Plotting either amperes or watts against arc-length gives 

 practically a straight line (see fig. 13j. 



A cored carbon was bored out to a depth of about 

 1'5 inches, and packed with powdered potassium sulphate. 

 With this as positive and an ordinary cored carbon as 

 negative, a very low-power arc was obtained. The arc was 

 perfectly steady at 20 volts, 1*1 amperes and 0*05 in. 

 length. It was much more difficult to make this arc restart 

 than the preceding. The results agreed fairly well, however, 

 when the amount of energy consumed was the same. 



The following observations were taken with this arc. 



Volts. 



Amperes. 



Arc Length 

 (in inches). 



Fall 

 (in feet). 



Time 

 (in sec). 



Watts. 



12-5 



5 



0-05 



0-125 



0-089 



62-5 



12 



6 



005 



0-416 



0*162 



72 



12 



8 



0-05 



0-916 



0-239 



90 



11 



10 



005 



1-44 



0-3 



120 



12 



12 



o-i 



1-44 



0, 



144 



i 



