172 Professor Tyndall, on the Influence of [Jan. 20, 



been more or less invoked by theorists, to account for the effects 

 observed. ]Mr. G assiot was the first to urge, with a water battery of 

 3500 cells, a voltaic spark across a space of air, before bringing the 

 electrodes into contact : with the self-same battery he had obtained 

 discharges through exhausted tubes, which exhibited all the pheno- 

 mena hitherto observed with the induction coil. He thus swept away a 

 host of unnecessary complications which had entered into the specula- 

 tions of theorists upon this subject. 



8. On the present occasion, through the kindness of Mr. G assiot, 

 the speaker was enabled to illustrate the subject by means of a battery 

 of 400 of Grove's cells. The tension at the ends of the battery was 

 first shown by an ordinary gold-leaf electroscope ; one end of the 

 battery being insulated, a wire from the other end was connected with 

 the electroscope ; the leaves diverged ; on now connecting the other 

 end of the battery with the earth, the tension of the end connected 

 with the electrometer rose, according to a well-known law, and the 

 divergence was greatly augmented. 



9. A large receiver (selected from Mr. Gassiot's fine collection), 

 in which a vacuum had been obtained by filling it with carbonic 

 acid gas, exhausting it, and permitting the residue to be absorbed by 

 caustic potash, was placed equatorially between the poles of the large 

 electro-magnet. The jar was about six inches wide, and the distance 

 between its electrodes was ten inches. The negative electrodes con- 

 sisted of a copper dish, four inches in diameter, the positive one was a 

 brass wire. 



On the 16th of this month an accident occurred to this jar. Mr. 

 Faraday, Mr. G assiot, and the speaker had been observing the dis- 

 charge of the nitric acid battery through it. Stratified discharges 

 passed when the ends of the battery were connected with the electrodes 

 of the receiver ; and on one occasion the discharge exhibited an extra- 

 ordinary eftulgence ; the positive wire emitted light of dazzling bright- 

 ness, and finally gave evidence of fusion. On interrupting the circuit, 

 the positive wire was found to be shortened about half an incli, its 

 metal having been scattered by the discharge over the interior surface 

 of the tube. 



10. The receiver in this condition was placed before the audience 

 in the position mentioned above. When the ends of the 400-cell 

 battery were connected with the wires of the receiver, no discharge 

 passed ; but on touching momentarily with the finger any portion of 

 the wire between the positive electrode of the receiver and the positive 

 pole of the battery, a brilliant discharge instantly passed, and continued 

 as long as the connexion with the battery was maintained. This 

 experiment was several times repeated : the connexion with the ends 

 of the battery was not sufficient to produce the discharge, but in all 

 cases the touching of the positive wire caused the discharge to flash 

 through the receiver. 



Previous to the fusion of the wire above referred to, this discharge 

 usually exhibited fine stratification : its general character now was 



