and its Effects. f 



tions being ao arranged that the current must pass alternately 

 along the one and along the other wire^ in the same or in oppo- 

 site directions. 



I have often employed the second pin, and a thick, angular- 

 shaped wire, which could be screwed to it and made to press 

 against the tongue in order to displace its fulcrum, to shorten 

 the vibrating part, and thus quicken its motion. Too quick a 

 motion of the tongue, however, combined with an amplitude so 

 small that the vibrations are scarcely perceptible, and the noise 

 similar to that of the humming of a bee, is prejudicial to the 

 action of the induction wire. 



This instrument also possesses a contrivance, by means of 

 which, besides the first current, a second can be simultaneously, 

 and at equal intervals, interrupted. 



Another instrument was employed to break the current within 

 a liquid. For this purpose the small electro-magnet was placed 

 above the armature of the tongue. The tongue carries the pin 

 or hammer ; the anvil (a thick platinum wire) is placed in the 

 middle of a small glass cylinder which rests on a brass pedestal. 

 The platmum wire is screwed into this pedestal, and around it 

 the glass cylinder is cemented with a layer of sulphur, which is 

 well adapted to this purpose, because, when cold, it resists the 

 greatest number of liquids*. In other respects this current 

 breaker is constructed in the usual manner, and, as in the first 

 instrument, the parts which strike against one another are of 

 platinum, though for certain purposes I have used silver and 

 other metals instead of platinum. 



In most, if not all, induction apparatus the current-breaker 

 forms an inseparable part of the whole ; and in some, as in 

 RuhmkorfF's, it is set in motion by the same soft iron core which 

 increases the action of the inducing current. I preferred not 

 only to produce this motion by a small separate electro-magnet, 

 as in Halske's apparatus, but also to have the current-breaker 

 constructed as a separate instrument, in order to connect it at 

 will with other instruments, and, if need be, to use it under the 

 air-pump. 



NeePs hammer is, perhaps, the simplest contrivance for pro- 

 ducing periodic interruptions of a galvanic current ; but for 

 certain purposes, of which I intend to speak another time, it has 

 one imperfection, — it does not produce uniform interruptions, 

 the time during which the circuit is. broken is longer than that 

 during which it is closed, and that because the tongue vibrates 

 with its whole length downwards from the pin, and only with a 

 part of its length upwards. In this respect Neef 's hammer dif- 



* For this reason I have for many years used sulphur for cementing the 

 platinum in the covers of my Grove's battery. 



