Lord Rayleigh on the Induction- Coil. 593 



provided by a pot of mercury well drowned in oil and con- 

 denser, only about one break in fifteen succeeded. On the 

 other hand, of three bullets fired so as to cut the primary wire 

 (no condenser) two succeeded ; while for the failure of the 

 third there was some explanation. The bullet without con- 

 denser was now distinctly superior to the best ordinary break 

 with condenser. 



The next step was the substitution of a rifle-bullet, fired 

 from a service rifle. Here again the bullets were reduced to 

 about one-half, and after cutting the wire were received in a 

 long box packed with wet sawdust. At 60 mm., while the 

 mercury-under-oil break with condenser gave only feeble 

 brush-discharges, good sparks were nearly uniformly obtained 

 from the bullet working without a condenser. At 70 mm. the 

 bullet without condenser was about upon a level with the 

 mercury-under-oil break with condenser at 60 mm. As 

 regards the strength of the primary current, if there was any 

 ■difference, the advantage was upon the side of the ordinary 

 break with condenser, inasmuch as in the case of the bullet 

 the leads were longer and included about 8 cm. of finer copper 

 wire where the bullet passed. 



In the next set of experiments upon the same Apps' coil 

 excited by three Groves, the bullet was used each time, and 

 the comparison was between the effect with and without the 

 usual coil condenser. At ~ri mm. the bullet without condenser 

 gave each time a fair or a good spark, while with the con- 

 denser there was nothing more than a feeble brush scarcely 

 visible in a good light. 



'fhe single pane of coated glass was next substituted for the 

 usual condenser oi' the coil, with the idea that possibly this 

 might be useful although the larger capacity was deleterious. 

 But no distinct difference was detected when the bullet was 

 tired with this or without any condenser. 



In the last .set of experiments now recorded the primary 

 current was raised, six Grove cells being employed partly in 

 parallel, and the wire was cut each time by a rifle-bullet. At 

 90 mm. no spark could be got when the coil condenser was 

 in connexion ; when it was disconnected, a spark, good or fair, 

 was observed nearly every shot. 



Altogether these experiments strongly support the view- 

 that the only use o( a condenser, in conjunction with an 

 ordinary break, i^ to quicken it by impeding the development 

 of an arc, so that when a sufficient rapidity of break can be 

 obtained by other means, the condenser is deleterious, ope- 

 rating in fact in the reverse direction, and prolonging the 

 period o( decay of the primary current. It is hoped that the 

 establishment of this fact will inspire confidence in the theory, 



