544 Royal Society i — 



and disappeared in these experiments, first at one terminal and then 

 at the other, according as the cable was charged or discharged. 



After the cable had received the discharge to the greatest intensity 

 that could be obtained through the tube 219, the full charge of the 

 battery was then completed by cutting off the tube from the circuit 

 by means of a wire. On removing the wire, and substituting the 

 earth for the battery, a discharge took place ; but a residuary charge 

 was always found, which could not pass through the vacuum. If 

 this residuary was allowed to remain in the cable, and the battery 

 again substituted for the earth, no additional charge could be made 

 to pass from the battery through the vacuum-tube ; but so soon as 

 this residuary was discharged, the cable again became charged 

 through the tube as before*. 



We were particularly fortunate with these experiments ; for on 

 Mr. Wheatstone testing the capability or power of the battery, he as- 

 certained that on taking from it only 32 cells, thus reducing the num- 

 ber to 480, the discharge could not pass through the vacuum-tube. 



Grove's Nitric-Acid Battery, 



Each set of elements in the battery were inserted in a glass ves- 

 sel with a stem 6 inches long ; the stems were carefully cleaned and 

 dried. These precautions, with the high chemical affinity of the 

 elements, raised the tension of each terminal, as denoted by gold- 

 leaf electroscopes, to nearly that of the larger series of the water- 

 battery. A succession of spark-discharges could be taken between 

 the copper discs of my micrometer-electrometer, one disc being 

 attached to the zinc, and the other to the platinum end of the 

 battery. 



In the following experiments, the different vacuum-tubes were 

 introduced between one of the copper discs and the battery, as also 

 a galvanometer. By this arrangement the circuit could be gradually 

 completed without any risk of disarranging the apparatus, and the 

 spark discharged obtained before the copper discs of the micro- 

 meter-electrometer came into contact. 



" In 146, on the completion of the current, the discharge of the 

 battery passed with a display of magnificent strata of most dazzling 

 brightness. On separating the discs by means of a micrometer 

 screw, the luminous discharges presented the same appearance as 

 when taken from an induction coil, but brighter. On the copper 

 plate in the vessel there was a white layer, and then a dark space 

 about one inch broad; then a bluish atmosphere, curved like the, 



* If one of the wires of the vacuum-tube No. 219 is connected with the inner 

 coating of a Leyden jar, and the other with the prime conductor of an electrical 

 machine, when the machine is excited a luminous glow will be observed round 

 one of the balls, similar to that obtained during the charging of the cable by the 

 voltaic battery, and the jar will become gradually charged. On the excitation of 

 the electrical machine being stopped, if a pointed wire is presented to the prime 

 conductor, the jar will be gradually discharged, and the luminous glow appears 

 on the other ball of the vacuum-tube ; if several similar tubes are arranged in 

 series, and the jar is discharged through longer carbonic-acid vacua, the stria; 

 can be obtained in the latter. 



