twenty millimeters. This will work as well on a wet day as 

 on a dry day. In fact it works with as much certainty as any 

 experiment in voltaic electricity. The glass rod must be dry 



however as it loses its charge easily. We have thus a means 

 for using the galvanometer to measure static electricity with 

 as much certainty as we measure voltaic electricity. 



In the light of this experiment the Indict charged posi- 

 tively in the morning and negatively in the afternoon instead 

 of the opposite and this is in line with what we might expect. 



This result is also in accord with the flow of ions in a 

 voltaic cell and an electrolytic cell. In Fig. 6 let C he a voltaic 

 cell composed of copper and zinc for electrodes, and hydro- 

 chloric acid, ten per cent solution for an electrolyte. The zinc 

 plate charges negatively and the copper plate charges posi- 

 tively. In order to accomplish this result the hydrogen ions 

 travel to the copper plate and charge it positively. The uega- 



& 



T 



- + 



+ - n 



Ho 



c, 



Figure 6. 



B^ 



tive chlorine ions travel to the zinc plate and charge it nega- 

 tively. Thus the negative charges in the battery are traveling 

 from the positive pole to the negative pole of the cell. Let ('1 be 

 a cell containing a dilute solution of sulphuric acid and water. 

 Let the water in this cell be decomposed by t he current from t he 

 cell ( '. It is well known that the positive hydrogen ion of the 

 water travels to the negative electrode Pt. and the negative 

 oxygen ion travels in the opposite direction to the positive 

 pole Pt'. therefore the negative ions are traveling in the 

 electrolytic cell in the same absolute direction in the circuit 

 in which they are traveling in the voltaic cell C. Now if the 

 electric current from the cell C which consists of a stream of 

 negative charges is traveling from the copper to the zinc out 

 side of the cell, it is traveling from zinc to copper inside of 

 the cell and opposite to the direction of travel of the negative 

 charges in the cell; but, if on the contrary, the current is 



69 



