OF ARTS AND SCIEIsCES. 



243 



dow set in the side of the receiver allowed observation of the arc. 

 The exhaustion could be read by an attached gauge. The rubber 

 screw plug, through which the rod passed, was covered with oil or 

 glycerine to diminish the leakage. The construction of the apparatus 

 was greatly delayed by unforeseen circumstances, so that up to the 

 present date we have been able to make only a very few experiments. 

 Some difficulty has also been met with from the heating and vaporiza- 

 tion of portions of liquid which have leaked into the receiver. This 

 was partially avoided by immersing the receiver in water. In the 

 experiments thus far made with this apparatus, the pressure was 

 4 inches of mercury. Currents were employed of 5, 7.95, and 9.86 

 amperes respectively, with lengths of arc from ^^ to 3% int-h. In 

 all the experiments the positive carbon was uppermost. The arc 

 was found to be a whistling one up to the extreme limits obtained. 

 The results of the experiments are given in Table XXV. 



TABLE XXV. 



Current = 5.00 amperes. Current = 7.95 amperes. Current = 9.86 amperes. 



These results, when plotted as before, give straight lines, repre- 

 sented by the following equations. 



TABLE XXVI. 



* These values deviate greatly from the curves. 



