98 



Prof. J. A. Fleming on the 



to the metal plate, recourse was had to the lamp ~Ro. 3, with 

 metal (aluminium) cylinders embracing without touching the 

 carbon at two different places. These cylinders, as before, we 

 will call X and Y (see fig. 22) . Cylinder X was the one near 

 the base of the positive leg of the carbon, and cylinder Y was 

 the one near the top of the negative leg. 



When the galvanometer was connected between the negative 

 electrode of the lamp and the cylinder X surrounding the 

 lower part of the positive leg, no perceptible current was found 

 to be passing when the carbon was rendered incandescent. On 

 inserting a single Clark cell in series with the galvano meter so 

 that the negative pole of the cell was in connexion with the 

 cylinder X and the positive pole of the cell through the galvano- 

 meter in connexion with the negative electrode of the lamp, 

 hardly any perceptible current was found to be passing (see 

 fig. 22). The Clark cell was then reversed, connecting the 



Fig. 22. 



positive pole of the cell to the cylinder X and the negative pole 

 through the galvanometer to the negative electrode of the 

 lamp. On bringing the lamp into action, a considerable 

 current of several milliamperes was found to be passing in such 

 a direction that a current of positive electricity was flowing 

 across the vacuous space from the metal cylinder to- the hot 

 carbon, or a negative current from the hot carbon to the cooler 

 metal cylinder. On switching-offthe lamp, there was a curious 

 - kick v or." throw " of the galvanometer, indicating a sudden 

 rusk of current in the same direction as the steady current 

 which the cell had been sending. These effects occurred also 

 when the cylinder Y was employed, and the galvanometer with 

 or without the cell in series joined in between the negative 



