the Effect of Magnetic and Electric Injluence, S^c. 269 



for more than a minute to the glass cover, and then gradually 

 losino- such power, it declined again to its horizontal and di- 

 rective positions." This I invariably found to be the case 

 when any apparent variation took place, which may he pro- 

 duced by giving the compass-box the slightest motion during 

 thetime'that the glass cover is excited: this causes the needle to 

 oscillate ; and when the glass becomes sufficiently electrical, it 

 attracts one point of the needle ; and if that point be 20° or 

 40° on either side of the magnetic meridian, at the moment 

 when it becomes stationary by the attraction of the fluids, it 

 gives not a real but only a7i apparent variation of the needle. 

 When the glass cover of the compass-box is rubbed with a 

 silk handkerchief, positive electricity is produced upon its up- 

 per surface, consequently negative electricity will pervade the 

 opposite surface ; which, I observed, invariably attracted the 

 sonth pole of the needle ; and when left undisturbed, this mu- 

 tual attractive force of the two fluids generally continues for 

 the space of one minute. 



Lieut. Johnson likewise states, " that the rubber (the silk 

 handkerchief), and various other substances, as the metals, &c. 

 when presented to the glass cover, have the power and pro- 

 perty of repelling both poles of the needle." This effect I 

 have reason to doubt, as I have not been able to produce it 

 in a sinole instance. No small substance which I yet have 

 tried that is not magnetical, with the exception of the finger 

 {a curious fact), will immediately neutralize the effect produced 

 by the attraction of these mysterious and powerful agents. 



A bar of warm or hot iron has not the same effect as the 

 finger, in immediately neutralizing the attractive power of the 

 two fluids; but when the needle by repulsion, or saturation 

 by contact, recedes from the glass plate, the austral pole will 

 be attracted and the boreal repelled on having a bar of hot 

 iron presented to them. Being anxious to ascertain whether 

 the boreal fluid and positive electricity are similar in their 

 effect to what was witnessed with the austral fluid and nega- 

 tive electricity, I adopted the following experiment : 



Having charged a Lcyden jar positively, I placed a hori- 

 zontal needle upon a stand, so as to be on the same plane with 

 the knob of the jar, and within the influence of the electrical 

 atmosphere. The north pole, as I anticipated, vyas instantly 

 influenced and drawn from the magnetic meridian ; and it 

 pointed to the brass knob of the jar, which was situated due 

 west, or in the line of the magnetic equator. The needle was 

 removed from the stand and placed on the table, about five 

 or six inches from the jar, and the south pole was immediately 

 attracted to the negative side of the jar, confirming what I 



have 



