302 Royal Society, 



rent is also manifested by the occurrence of a shock, at the same mo 

 ment, to a person who grasps with wetted hands the two ends of the 

 wire; whereas no such effect, nor even any sensible impression on the 

 tongue, is produced by the electromotor, when a short wire is em- 

 ployed. 



All these effects of exaltation are produced at a time when the ac- 

 tual current of electricity from the electromotor is greatly diminished; 

 as the author shows by many experiments on the ignition of a fine 

 wire, and the deflection of a galvanometer. He also proves that the 

 effects of the spark and the shock, at the moment of disjunction of a 

 long wire, are due to a current far more powerful than that which 

 passes through the short wire at the same instant ; or indeed than 

 that which passes through either the long or the short wire at any 

 other instant of time than when the disjunction takes place. 



That this extraordinary effect is not due to any species of inertia, 

 is shown by the fact, that the same wire will produce it in a greater or 

 less degree, under circumstances incapable of influencing any effect 

 depending on inertia : thus, if 1 00 feet of wire, when extended, 

 produce a certain effect, a greater effect will be produced by coiling 

 the same wire into a helix, and a still more powerful one by employ- 

 ing it as the helix of an electro-magnet. 



The author ultimately refers these phsenomena to an inductive ac- 

 tion of the current, analogous, or perhaps identical, v/ith that described 

 in the First Series of these Experimental Researches : for he found 

 that when a second wire was placed parallel to the long conducting 

 wire, the ends of this second wire being connected together so that a 

 current of electricity could circulate round it, then the spark and shock 

 did not take place at the first wire at the moment of disjunction, but 

 a current was induced at the second wire, according to the law ori- 

 ginally described in the First Series. The moment the current in the 

 second wire was interrupted, the spark and shock appeared at the 

 first. These and many other experiments were adduced to prove 

 that these effects, namely, the shock and the spark, result from an in- 

 ductive action of the original current, producing, at the noment it is 

 stopped, a current, in the same direction as itself, in the same wire 

 which serves to convey the original current. 



The author,lastly, considers the reverse effect produced upon mak- 

 ing contact J and concludes his paper by some general views of the 

 consequences resulting from this inductive action in various cases of 

 electric discharge; pointing out the important influence it must have 

 in magneto-electrical machines of the ordinary construction. 



The reading of a paper was then commenced, entitled, '* Geome- 

 trical Researches concerning Terrestrial Magnetism." By Thomas 

 Stephens Davies, Esq., F.R.S., &c. 



February 12. — Mr. Davies's paper, entitled "Geometrical Re- 

 searches concerning Terrestrial Magnetism," was resumed and 

 concluded. 



The object of this paper is to exhibit methods of conducting the 

 mathematical inquiries which are applicable to the magnetism of the 

 earth, by the aid of the coordinate geometry of three dimensions. 



