1835] WRITINGS OF JOSEPH HENRY. 95 



7. In order to increase if possible the intensity of the 

 spark while the battery remained the same, larger spirals 

 were applied in succession. The effect was increased until 

 one of ninety-six feet long, an inch and a half wide and 

 weighing fifteen pounds, was used. The snap from this was so 

 loud that it could be distinctly heard in an adjoining room 

 with the intervening door closed. Want of materials has pre- 

 vented me from trying a larger spiral conductor than this, 

 but it is probable that there is a length which, with a given 

 quantit}' and intensity of galvanism, would produce a maxi- 

 mum effect. When the size of the battery is increased, a 

 much greater effect is produced with the same spiral. Thus 

 when the galvanic apparatus, described in the first article, is 

 arranged as a " calorimotor" of eight pairs, the snap produced 

 on breaking contact, with the spiral last described, resembled 

 the discharge of a small Leyden jar highly charged. 



8. A handle of thick copper was soldered on each end of 

 the large spiral at right angles to the ribbon similar to those 

 attached to the wires in Pixii's magneto-electric machine for 

 giving shocks. When one of these was grasped by each hand, 

 and the contact broken, a shock was received which was felt 

 at the elbows, and this was repeated as often as the contact 

 was broken. This shock is rather a singular phenomenon, 

 since it appears to be produced by a lateral discharge, and 

 it is therefore important to determine its direction in reference 

 to the primary current. 



9. A shock is also received when the copper of the battery 

 is grasped by one hand, and the handle attached to the cop- 

 per pole of the ribbon with the other. This may be called 

 the direct shock, since it is produced by a part of the direct 

 current. It is however far less intense than that produced 

 by the lateral discharge. 



10. When the poles were joined by two coils, connected by 

 a cup of mercury between them, a spark was produced by 

 breaking the circuit at the middle point, and when a pair of 

 platina wires was introduced into the circuit with the large 

 coil and immersed in a solution of acid, decomposition took 

 place in the liquid at each rupture of contact, as was shown 



