PHYSICS. 249 



battery in quantity and discharged in tension. Using ten 

 of these condensers charged with a secondary battery of 800 

 cells, as many as 15 brilliant sparks from 13 to 14 millimeters 

 long were obtained per second, giving the same noise, and 

 otherwise resembling closely the condensed spark from an 

 induction coil. The difference between the negative and the 

 positive spark is more marked in this machine than in the 

 ordinary ones. Its length appears to increase with the num- 

 ber of condenser plates, 40 condensers giving a spark 4 or 5 

 centimeters long, and 51 of 6 centimeters. In vacuo the 

 light is brighter than that of the coil, though no stratiii- 

 cation is observable with it in tubes in which the induction 

 spark gives it distinctly. Nor is there any difference be- 

 tween the poles in these tubes, the purple glow at the nega- 

 tive pole being absent. In proof of the minute quantity of 

 electricity in each spark, a secondary battery of 40 cells 

 was charged by 15 seconds contact with tw r o Bunsen cells, 

 and was then connected to the machine. It illuminated a 

 Geissler tube for more than 15 minutes. Contact for 10 

 minutes would therefore illuminate a tube for more than 10 

 hours. 



Jablochkoff has discovered and utilized the fact that if 

 one of the surfaces of a large condenser be connected with 

 one electrode of a to-and-fro current machine, an alternating- 

 current is obtained between the second condenser surface 

 and the other electrode, much more powerful than the cur- 

 rent given directly by the magneto-machine itself. 



Sabine has investigated the remarkable motions which are 

 produced by placing a drop of very dilute acid upon the 

 clean surface of a newly filtered and rather rich amalgam of 

 some metal which is positive to mercury. The drop does 

 not lie still, as it would do on pure mercury, but sets itself 

 into an irregular jerky motion. This is true of copper, tin, 

 antimony, zinc, and lead amalgams. If, however, amalgams 

 of metals negative to mercury be used, such as gold, plati- 

 num, and silver, the drop lies quite still. Sulphuric, hydro- 

 chloric, oxalic, and acetic acids were used, and all produced 

 the result, but in different degrees. In oxygen the move- 

 ments are increased ; in hydrogen they are arrested. The 

 author hence infers that the motions result from alternate 

 deoxidation of the mercury beneath the acid by electrolysis, 



L 2 



