OF AETS AND SCIENCES. 



233 



obtained. These are given in Tables VIII. and IX., and are numbered 

 for convenience of reference. The length, Z, is expressed in terms 

 of the pitch of the micrometer screw, i. e. in thirty -seconds of an 

 inch. The current is expressed in amperes. Lengths of arc up to 



i| in. were observed. 



TABLE VIII. — Silent Arc. 



TABLE IX. — Whistling Akc. 



The fourth column of the table gives the inverse electromotive 

 force corresponding to each current, as found by multiplying the 

 intercept given in the equation by that current. It appears from the 

 results, that for the silent arc the mean value of the inverse electro- 

 motive force is apjaroximately 39 volts. There is, however, an evi- 

 dent diminution in this value as the current rises, and by reference 

 to the equations given in Peukert's paper, already cited, it will be 

 seen that they also indicate the probability of such a change. 



When the arc becomes very long there is an apparent tendency to 

 an abnormally small value of the equivalent resistance. This was 

 observed in the values of the resistance when the arc was ^| in. long, 

 with a current of 7 amperes, and when the arc was ^| in. long with 

 a current of 8 amperes. It was also noticed with very long arcs in 

 which metallic salts were volatilized. 



Table IX. also shows us an additional fact. Not only is the inverse 

 electromotive force of the silent arc the same for any given current, 



