404 Intelligence and Miscellaneous Articles, 



Amongst all the metals which have hitherto been tried for the arma- 

 ture of these points of contact, platinum has succeeded best ; its high 

 fusing-point and its slight tendency to oxidation indicating it as pre- 

 ferable to the ordinary metals for presenting long resistance to the 

 corrosive action of the spark which passes at each interruption. 

 Nevertheless when the apparatus is in action for a certain time, pla- 

 tinum itoelf is at last attacked ; the surfaces of contact become de- 

 formed, presenting hollows, or enlargements at each other's expense, 

 the texture of the metal alters, and at length the interruptor ceases 

 to perform its functions. This tiresome result arrives sooner in pro- 

 portion to the strength of the current, and when this acquires an 

 intensity above a certain limit, the pieces of the interruptor are sol- 

 dered together at the first contact, and become quite useless. 



In attempting to increase progressively the phsenomena of induc- 

 tion, I met with a difficulty which appeared to be rather serious in 

 this imperfection of solid contact, and like many others no doubt, I 

 thought of having recourse to mercury. 



In my first essays I perceived that it would be impossible to distri- 

 bute an intense current continuously with naked mercury ; by this 

 means the interruption is never sufficiently sudden, the inductive ac- 

 tion remains weak, the surface of the metal becomes oxidized in a few 

 moments, and it emits abundant vapours which in course of time do 

 not fail to exert their deleterious action. I was thus led to cover the 

 mercury with a stratum of distilled water, or better still, with a stra- 

 tum of alcohol, which at once remedies the inconveniences attending 

 the employment of mercury alone. Thus the interruption of the 

 current is produced under alcohol with a dry sound which indicates 

 a sudden stop ; it gives rise to a strong spark of induction, the alco- 

 hol soon becomes turbid, but it does not cease condensing the vapours 

 given off from the point of rupture, at the same time that it protects 

 the surface of the mercury from oxidation. The apparatus thus con- 

 tinues to act with regularity as long as the battery is capable of 

 maintaining the inducing current. 



Regarded in a mechanical point of view, the employment of a liquid 

 conductor such as mercury introduces a happy modification into the 

 constitution of the interruptor. The oscillating piece known as 

 the hammer being no longer limited in its movements by the firm 

 obstacle which it met with in its anvil, may be replaced by an elastic 

 plate, which vibrates by its own spring under the influence of an 

 electro-magnet. This plate, being curved at its extemity and ter- 

 minated by a platinum point, closes the circuit of the inductive cur- 

 rent sixty times in a second, by penetrating more or less into the 

 mercury. The contact thus established, notwithstanding its short 

 duration, is nevertheless perfect ; in itself it only presents a resist- 

 ance which may be neglected in comparison with those spread 

 through the circuit, and as the elastic piece vibrates in perfect liberty, 

 the contacts succeed each other at regular intervals of time, as may 

 be seen from the uniformity of the sound given by an apparatus in 

 action. The series of sparks at the extremity of the induced wire 

 participates in the same character, and in the crepitating sound which 



