] 12 Proceedings of the British Association. 



whether in the combining of several series of short bars, the elemen- 

 tary bars be of the same or of unequal lengths. — 2. That the relative 

 powers of magnets, whether single or compound, when different in 

 mass, but proportional in all their dimensions, are not in the ratio of 

 the masses, the large masses being less strong proportionally then the 

 smaller. — 3. That whilst magnets of large dimensions are less power- 

 ful with respect to their masses, than small magnets to which they are 

 exactly proportional in all their dimensions ; and whilst the increase 

 of the dimensions continually deteriorates from the energy due to the 

 mass : yet magnets may be combined in such proportional dimensions 

 with a constant increase of power ad infinitum. From this last result, 

 it follows, that magnets indefinitely small must be indefinitely strong ; 

 and may indicate that the mutually attractive forces of the ultimate 

 magnetic elements may be as strong as that by which the metallic 

 elements are themselves combined. It must, also, be kept in mind, 

 that the steel should be perfectly hard ; and the elementary plates of 

 the magnet should be made of steel, converted out of one or other of 

 the very best qualities of common iron. All the conditions, with the 

 exception of thinness, were attended to in the large magnet construct- 

 ed by Dr. Scoresby. A magnet on this principle, of the size of the 

 lower mast of a first-rate ship of war, would produce a deviation of 

 nearly 1' at the distance of a mile, and a sensible effect much beyond 

 that. The electrical effects of Dr. Scoresby' s magnet with a very 

 imperfect armature were — it decomposed water, rapidly producing 

 about one cubic inch of the gases a minute ; with about sixty-five 

 yards of coiled wire, the effervescence seemed as violent as during the 

 action of dilute sulphuric acid or zinc. Copper was deposited from 

 a solution of sulphate of copper at the rate of about 1*2 grain per 

 minute. Shocks and scintillations were thrown out ; and sparks were 

 visible in daylight, and emitted audible sounds when the armature 

 revolved, so slowly as one in sixteen seconds. 



Prof. Forbes had little doubt that Dr. Scoresby could construct 

 very powerful magnets ; but he thought that as electro-magnets, so 

 much more powerful, were so readily made, it was almost useless to 

 incur the expense of the others — Mr. Roberts described a magnet 

 which he had constructed some four or five years since — but as an 

 account was published at the time in the ' Annals of Electricity,' we 

 need not report it again. 



