28 SIXTH REPORT. — 1836. 



Mr. M'Gauley wished to satisfy himself by experiment, that the 

 inverse ratio of the square of the distance is the law of the decrease 

 of magnetic attraction, but relinquished the idea for the present, 

 when he found that the same magnet would, with one keeper, lift 

 one quantity at -^ inch, with another the same quantity at 12 times 

 the distances, both keepers seemingly appropriate. 



In speaking of the nature of electro-magnetism, and its perfect 

 identity with electricity, he remarked, that we should if possible, in 

 comparing any agent with electricit)'^, discover some property of the 

 latter, not the measure of, nor dependent on either its intensity or 

 quantity, which may be so various. 



He attempted to show that the spark and shock obtained from an 

 electro-magnet, and which indeed may be obtained from a more 

 heap of wire, are not the spark and shock either of the battery or 

 the magnet ; that currents cannot circulate perpetually round a mag- 

 net, as the magnetism of a bar included in an hehx, so far from in- 

 creasing the effect of an helix, as it should by its current, may even 

 be made totally to prevent it, and ought to do so if it be mere in- 

 duced electricity, a supposition strengthened by the otherwise uni- 

 versal law of electrical induction. 



He mentioned that he never was able to believe that the effect of a 

 galvanic circle was the transmission of electricity from zinc to copper 

 in any way, and back along a wire from copper to zinc, since the force 

 which drove it through the fluid, an imperfect conductor, ought to 

 prevent its return ; and that he had frequently tried in vain with se- 

 veral pairs of plates, arranged singly in galvanic order in waterproof 

 cells, separated by glass plates, to deflect a needle. He believed it 

 was the arrangement of particles, impossible in insulating substances, 

 and not the transmission, which constituted galvanic excitement. 

 This supposition of electricity being mere inductive arrangement of 

 particles, he believed would unite and explain many different effects ; 

 amongst others, the agitation of the muscles of a frog, on breaking 

 connection with a single galvanic circle ; the danger of discharges 

 passing from cloud to cloud, and the shock obtained from a heap of 

 wire connected with a galvanic battery of a single circle. 



On aNew Compass Bar, with Illustrations, hy means of a recent Instru- 

 ment, of the Susceptibility of Iron for the Magnetic Condition. 

 By fAe Rev. W. Scoresby, B.D. F.R.S., Corresponding Member 

 of the Institute of France, &iC. 



Mr. Scoresby first exhibited to the Section a recent instrument 

 named a magnetometer, invented by himself in the year 1819^20, for 

 measuring minute magnetic attractions, and for finding the dip of 

 the needle by the observation of the plane of no-attraction. This 

 instrument has its principal recommendation in securing unity of 

 character in exj)erimcnts on the magnetic condition, by enabling the 

 experimentalist to try and compare the energy of magnetic bars or 



