3 1 British Association for the Advancement of Science. 



Five magnets, each 8 inches long and -f- diameter, were coiled 

 with 7-J- yards of wire, and the same battery was used with each 

 magnet. 



No. 1. The wire was coiled only on the ends, and crossed 



straight from one pole to the other 1 



2. Wire coiled on the ends, but connected by a spiral 



round the magnet 11 



8. Wire divided, and each half placed as a helix on 



one end of the magnet 6 



4. Wire coiled equally over the whole magnet 7 



5. Wire divided into 4 equal parts, each coiled on one 



fourth of the magnet 5 



6 yards of wire were coiled on a magnet 74- inches 



long, i square 7 



1-j- yard of wire were coiled on a magnet 7-f inches 



long, ± square 3 



Hence the power of the magnet increases far more rapidly than pro- 

 portionately with its size. 



Remarks on the Nature of Magnetism. The author in this part 

 of his paper discusses the prevalent theories of magnetism, and 

 compares them with a variety of experiments corresponding to the 

 analysis which he presents of the subject. It would be nearly 

 impracticable to do justice to Mr. M'Gauley's views on the nature 

 of magnetism in the compass of an abstract. The following brief 

 notice will serve to convey some idea of his mode of reasoning. 



Magnetism does not arise from the circulation of electrical cur- 

 rents, but from the electrical excitation of the mass or the particles 

 in the magnet : not from currents, because it can begin to exist 

 without them, can continue to exist without them, and because cur- 

 rents can be generated in conducting substances of sufficient quan- 

 tity, velocity and intensity, without the development of magnetism. 

 Magnetism is mere electrical excitation, provided that by mere elec- 

 trical excitation we can cause its existence, and its various phaeno- 

 mena are such as we should expect from mere electrical excitement ; 

 and provided not electrical currents but electricity at rest be always 

 coexistent with it. Such, the author contends, are the facts, and he 

 proceeds to prove his position by appropriate experiments. 



He then offers explanations in agreement with these views of se- 

 veral leading phaenomena, as terrestrial induction, the mutual at- 

 traction of conjunctive wires, the position of the poles, of a perma- 

 nent magnet, and of an electro-magnet, the retention of magnetism 

 in steel, the destruction of magnetism by heat, the development of 

 it by percussion, &c. He finally observes: 



If magnetism be merely electrical excitation it is probable that, 

 cheap as their production is at present, a more ceconomical mode of 

 forming powerful magnets may yet be discovered. Though it may 

 be said that magnetism is not now for the first time applied to ma- 

 chinery, the author believes it will be acknowledged that the attempt 



