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LIV. On the Relation of Mechanical Strain of Iron to Magneto- 

 Electric Induction. By G. Gore, Esq., F.R.S.* 



FOR making experiments on this subject I have constructed 

 the following apparatus : — A A' is a strong base or plank 

 of oak about 120 centims. long, 18 centims. wide, and 7*5 cen- 

 tims. thick (the thinner part of which, marked A, may with ad- 

 vantage be left of the same thickness as that of A r ). B is an iron 

 lever about 72 centims. long, and 1*5 centim. thick at its lower 

 end, capable of moving in a vertical plane upon a strong hori- 

 zontal rod or axis of steel C, about 2 centims. diameter, driven 

 tightly into a hole in the wooden base ; the lever has a piece of 

 iron D (shown in section in fig. 2) welded upon its upper sur- 



Fig. 2. 



face, with a hole 6 millims. in diameter drilled through it for the 

 reception of one end of the iron wire. E is a slot cut in the 

 wood for the reception of the lever. The wire to be strained 

 cannot be shown in fig. 1, because it lies in a narrow groove F F, 

 about 8 millims. wide and 3 centims. deep, cut in the base-board, 

 the wire being at a distance of about 1*5 centim. below the sur- 

 face of the board ; its position is shown by the horizontal dotted 

 line in fig. 2. G is a coil of insulated copper wire; it is about 

 18 centims. long and 4*3 centims. in diameter, with a hollow axis 

 of glass tubing of about 8 millims. internal diameter ; it contains 

 about 3295 turns of wire 0*54 millim. thick ( = No. 26 Bir- 

 mingham brass wire-gauge), the two ends of the wire being 

 attached to the binding-screws H, H. The coil lies tightly fixed 

 by wedges of wood in a rectangular space in the wood, with its 

 axis coincident with that of the iron wire. The iron wire is kept 

 in the same horizontal plane by passing over two brass rollers 

 (without axles) I, I, shown in section in fig. 2 ; these rollers 

 are about 2*5 centims. long and 1*5 centim. in diameter, and lie 

 upon the bottom of the hollow rectangular spaces in the wood 

 shown at J, J. K, K are two moveable rectangular pieces of 

 oak which slide vertically and tightly in narrow grooves formed 



* Communicated by the Author. 



