ON ELECTRO-DYNAMIC INDUCTION. 307 



give the most brilliant deflagrations, and the loudest snaps from a sur- 

 face of mercury. The shocks, with this arrangement, are, however, 

 very feeble, and can only be felt in the fingers or through the tongue. 



16. The induced current in a short coil, which thus produces defla- 

 gration, but not shocks, may, for distinction, be called one of quantity. 



17. When the length of the coil is increased, the battery continuing 

 the same, the deflagrating power decreases, while the intensity of the 

 shock continually increases. With five riband coils, making an aggre- 

 gate length of three hundred feet, and the small battery. Fig. 1, the de- 

 flagration is less than with coil No. 1, but the shocks are more in- 

 tense. 



18. There is, however, a limit to this increase of intensity of the 

 shock, and this takes place when the increased resistance or diminished 

 conduction of the lengthened coil begins to counteract the influence 

 of the increasing length of the current. The following experiment 

 illustrates this fact. A coil of copper wire Ath of an inch in diame- 

 ter, was increased in length by successive additions of about thirty-two 

 feet at a time. After the first two lengths, or sixty-four feet, the bril- 

 liancy of the spark began to decline, but the shocks constantly in- 

 creased in intensity, until a length of five hundred and seventy-five 

 feet w^as obtained, when the shocks also began to decline. This was 

 then the proper length to produce the maximum effect with a single 

 batter}^, and a wire of the above diameter. 



19. When the intensity of the electricity of the battery is increased, 

 the action of the short riband coil decreases. With a Cruickshank's 

 trough of sixty plates, four inches square, scarcely any peculiar effect 

 can be observed, when the coil forms a part of the circuit. If how- 

 ever the length of the coil be increased in proportion to the intensity 

 of the current, then the inductive influence becomes apparent. When 

 the current, from ten plates of the above mentioned trough, was passed 

 through the wire of the large spool (10), the induced shock was too 

 severe to be taken through the body. Again, when a small trough of 

 twenty-five one-inch plates, which alone would give but a very feeble 

 shock, was used with helix No. l,an intense shock was received from the 

 induction, when the contact was broken. Also a slight shock in this 

 arrangement is given when the contact is formed, but it is very feeble 



VI. — 4 B 



