328 Mr. J. N. Heardei* on a nbto Imtrument for Registering 



ducting wires in any portion of its length, between the terminal 

 and the discharger, with the outside coating of a Leyden jar con- 

 taining two or three square feet of surface, and by means of an 

 insulating handle, hold the wire proceeding from the other ter- 

 minal by the middle, or any convenient part of its length, so as 

 to be able to bring it in contact with the knob of the Leyden jar, 

 and thereby make it a part of the arrangement, and charge it. 

 If a current of sparks from the coil be made to pass thx'ough the 

 fine platina wire whilst the inner coating of the jar is \incou- 

 nected with the transmitting wire, no heating effect is produced, 

 as may be observed by including the wire in the bulb of the 

 thermo-electrometer ; but if, whilst the sparks arc passing, the 

 transmitting terminal wire be brought in contact with the knob 

 of the jar, the loud discharges are produced, and the platina wire 

 instantly becomes white-hot, elongates, and vibrates with great 

 rapidity. If the wire be too short, or the charge of the jar too 

 strong, it is melted ; or if too long and the charge too weak, it 

 merely becomes red-hot. This effect appears and disappears on 

 alternately making and breaking connexion with the jar. 



Whilst the jar is disconnected, the sparks in the discharging 

 interval instantly burn paper, wood, &c. ; but when connected, 

 the noisy sparks have scarcely any such power, though if the 

 discharging interval be made much shorter, this effect is con- 

 siderably increased. The coil which I have used for these and 

 the subsequent experiments, contains rather less than four miles 

 of fine wire, and the primary coil is usually excited with twelve 

 nitric acid cells having platina plates immersed, 2 inches by 4, 

 and used collaterally as a double set of six. The rationale of 

 these changes is not very obvious, nor have I much desire to 

 speculate upon the matter, as I hold the registration of facts 

 under present circumstances to be of much greater importance. 

 It has, however, suggested itself to my mind, that in each impul- 

 sive wave of the induced current, a certain quantity of electricity, 

 or rather amount of electrical force, is accumulated at the ter- 

 minals, and the attraction resulting from their opposite electrical 

 states causes them to induce upon each other, and determine the 

 discharge through the intei'val between them. Now in every 

 case of elecjtrical discharge, its character and appearance will be 

 materially influenced by the conditions of the conductors between 

 which it passes, viz. their extent of surface considered as sepa- 

 rate and independent conductors; and secondly, the extent of 

 the respective areas approximated to, and inducing upon each 

 other, and between which the discharge takes place. Every 

 freely-insulated conductor undergoes induction from the influ- 

 ence of surrounding bodies whenever an electrical charge is 

 thrown upon it, and I know of no condition in which a body 



