

1861.] 235 



copper wire. The presence of an iron core in the coil, therefore, has 

 a similar effect to the coil itself, i. e. it makes the vibrations wider 

 and the pitch of the sound lower ; and in making the crispations 

 wider, up to about T ^th of an inch, the sounds also become louder, 

 and beyond that width the sounds become more feeble ; and the 

 presence of a closed secondary coil has the reverse effect, it makes 

 the vibrations narrower, and the pitch of the sound higher. These 

 effects of an iron core diminished on increasing the number of ele- 

 ments to ten, and decreasing their depth to fths of an inch, and ceased 

 entirely on employing 20 Smee's elements 2^ inches wide, immersed 

 1 or 2 inches, the same as with the closed secondary (38) . 



4 1 . The effects of a closed secondary coil and of an iron core upon 

 the vibrations produced by a current from a battery of low intensity 

 being of opposite kinds, if the two are suitably adjusted, they neu- 

 tralize each other's effects. The moveable secondary coil containing 

 4243 feet of " No. 26 " copper wire was arranged with the iron core 

 and primary coil of the previous experiment (40), and six of the 

 large Smee's elements (4) connected as three : with the core and 

 without the closed secondary coil, the crispations were very wide ; 

 with the closed secondary and without the core, they were very 

 narrow ; and with the core and closed secondary acting together, 

 they were of medium width, about the same as if neither the core nor 

 the closed secondary were present : the effects were very conspicuous. 

 These opposite effects of an iron core and closed secondary coil upon 

 the phonetic vibrations are analogous to their opposite effects upon 

 the brightness of the spark at the break-hammer of an induction- 

 coil ; the iron core increases, and closing the secondary coil decreases 

 that brightness. A cylindrical core of antimony 9 inches long and 

 2^ inches diameter, employed instead of the iron core, had no per- 

 ceptible effect upon the vibrations. 



42. A pole of a strong electro-magnet (34) was applied to the end 

 of the iron core of the Ruhmkorff's coil whilst the primary wire (with- 

 out a break-hammer) was in circuit with a phonetic liquid and three 

 Smee's elements (4) immersed 8 inches : with the secondary coil 

 closed, and small crispations occurring, magnetization of the electro- 

 magnet slightly raised the tone of the sounds if the magnetic poles in 

 contact were dissimilar, and lowered it if they were similar ; and with 

 the secondary circuit open and large crispations occurring, the chief 



s2 



