RECENT PROGRESS IN PHYSICS. 



421 



This table shows that with an equal number of jars s, and for equal 

 distances d of the knobs of the spark micrometer, the value of q re- 

 mains very nearly constant, whether the platinum wire, the copper 

 wire or the tube of water be interposed. With equal charges, then, 

 the striking distance is the same however the connector may be com- 

 posed. 



The striking distance of the electrical battery, consequently, is per- 

 fectly independent of the nature of the closing substance, provided the 

 surfaces between which the discharge takes place remain unchanged. 



Though the striking distance is not changed by the nature of the 

 circuit, the latter has a great influence upon the sparks themselves. 

 Five jars of a battery, with a certain charge, and using the copper 

 wire, produced sparks of dazzling brilliancy, 1^ lines long with a 

 rattling report ; while by using the platinum wire, with an equal 

 charge, a spark of equal length was obtained, but the light was feeble 

 and the report faint ; and with a tube of water the spark was scarcely 

 perceptible. 



§ 3.3. Quantity of electricity disappeaeing by discharge at the 

 STRIKING distance.' — When the battery is discharged at the striking 

 distance, a perceptible charge remains behind, which produces a 

 second spark on bringing the knobs nearer together. This fact can 

 be easily shown by the measuring jar. Place its knobs about two 

 lines apart, and charge until a spark passes ; now approach the knobs 

 towards each other and a second spark will pass. 



Riess has shown in the last mentioned memoir, that the quantity 

 of electricity disappearing on discharging the battery at the striking 

 distance, is always in the same ratio to the entire charge, and that it 

 is the same whether the closing circuit is composed of better or worse 

 conducting metallic wires. 



The experiments were arranged precisely like those whose results 

 are given in the last table ; in one of the series a copper wire, and 

 ip the other a platinum wire was used with Henley's discharger. 

 After the discharge had taken place at the striking distance, and a 

 part of the battery's charge had thus disappeared, it was recharged 



