18 Prof. E. Edlund on the Path of Electrical Induction- and 



On one of these caps was screwed a brass tube with a stopcock, 

 the other end of which was provided with a screw-thread by. 

 which it could be screwed to an air-pump. The brass tube was 

 bent at right angles, so that during the experiments the glass 

 cylinder was in a horizontal position. 



To convince myself whether the bridge acted efficiently when 

 the spark was formed in rarefied air/ the glass cylinder was in- 

 serted between the points c and e, and the air rarefied until it was 

 at a pressure of 15 inillims. ; the spark, therefore, at fg was 

 formed in rarefied air. 



Experiment 7. — The German-silver wire in the circuit : — 



Deflections. 

 15-7 

 15-7 

 Mean . . 15*7 



Experiment 8. — C inserted along with the German-silver wire, 

 the latter as bridge to the former : — 



Deflections. 

 13-8 

 13-0 



Mean . . 13*4 



Experiment 9. — The same as No. 7 : — 



Deflections. 

 12-0 

 12-7 

 15-5 



Mean . . 13-4 



Hence a distinct action of the induction-currents could not be 

 observed; and the same result was obtained when the air was 

 exhausted to a pressure of 6 millims. In all the subsequent ex- 

 periments the bridge remained in the same position in front of 

 the galvanometer ; and thus the deflections obtained were inde- 

 pendent of the induction-current of the galvanometer-coil. When 

 in the sequel nothing is said to the contrary, the poles consisted 

 of two equal-sized brass knobs. 



2. Comparison between dry air and air saturated with aqueous 

 vapour* 



The air was dried before entering the cylinder by being passed 

 slowly through two glass vessels which were filled with pieces of 

 pumice impregnated with concentrated sulphuric acid, and then 

 through a tube filled with chloride of calcium. The air was 

 moistened by having to pass through a long glass tube which 

 contained pieces of wetted paper. 



