and its Effects. 203 



Appendix II. 

 On a new method of increasing the Induction Current^. 



Amongst the reasons which induced me to construct Neef's 

 hammer as an independent instrumentfj I may mention that I 

 intended to use it under the air-pump, because I anticipated 

 that the induction current would be influenced by interrupting 

 the inducing current in a partial vacuum, instead of in free air. 



Recent experiments have fully satisfied my anticipations, by 

 proving that the partial vacuum increases the action of the cur- 

 rent-breaker to such an extent, that in those classes of phseno- 

 mena wherein the action of the condenser was greatest, the latter 

 may now be dispensed with. 



As the eflPects produced by this manner of using NeePs ham- 

 mer are in other respects interesting, I may here be allowed to 

 enter into a few particulars. 



I placed the hammer upon the extra plate, before described, in 

 an atmosphere of about 1 or ] t lines of mercury pressm-e, and 

 connected it with the inducing apparatus in such a manner that 

 the galvanic current could traverse the wires of the primary coil 

 (which were 100 feet long and 1 millim. thick, and encircled a 

 core of soft iron), either alongside or behind one another in the 

 same direction. The current was excited sometimes by one, and 

 sometimes by two of Grovels elements, and allowed to act alter- 

 nately upon the shorter and upon the longer of my induction 

 wires. Arrangements were made, lastly, to connect the hammer 

 vibrating in the partial vacuum with the large oiled-silk con- 

 denser, if necessary. 



The same hammer was afterwards employed in air under the 

 same circumstances, and also supported by the same condenser, 

 so that its action here could be compared with that which was 

 observed when it worked in a vacuum J. 



* From Poggendoi'ff's Arinalen for May 1855, p. 156. 

 t Phil. Mag. vol. X. p. 12. ' 



X In order to make this comparison with two different hammers, it is 

 necessarj- that they should l)e exactly alike. Under otherwise equal cir- 

 cumstances, the sparks, and particularly the spark-distance, of the induc- 

 tion coil are very much influenced by the motion of the hammer ; it is not 

 80 essential that it should vibrate (piickly as that it should vibrate with a 

 certain force, i. e. that the tongue should separate itself quickly from the 

 pin, and that the amplitude of its oscillation should not be too small. For 

 this purpose it is therefore convenient to have a rather heavv armature at 

 the end of the tongue ; in one of my instruments, where the armature is 

 too light, I usually attach a piece of Ijrass to it by means of wa.\. On the 

 other hand, in order to obtain very strong galvanometric or voltametric 

 actions, when the induction current is interrupted by a piece of dry blotting- 

 paper, it is convenient to employ a light arnuitnrc, so that the tongue may 

 vibrate verv quickly. 



