Mr. W. Sturgeon on Electro-Magnets. 197 



the horizontal arm, and terminates with a hook at its lower 

 end. A light copper wire, having a hook at one end, is by 

 this means suspended to the hook of the screw. The inferior 

 extremity of the pendent wire is pointed, and reaches into 

 the wooden vessel, but not sufficiently low as to touch its in- 

 ner surface. . , , - i. 



When an experiment is to be made with this apparatus, the 

 extremities of the helical wire which pass through the dish 

 and the lower cup, and also the extremity of the short wire 

 which passes through the bottom of the upper cup, are to 

 be well amalgamated. Mercury is now to be placed in the 

 two cups for the convenience of connection, and also in the 

 wooden dish, until the point of the pendent wire (which must 

 also be amalgamated) dips slightly into it. By this means 

 there will be formed a complete metallic connection between 

 the mercury in the upper cup, and that which is placed in the 



lower. r • 1 1 



If the connecting wire from the copper plate of a single gal- 

 vanic pair be now permitted to enter the upper cup, and that 

 from the zinc to enter the lower, then the direction of the electric 

 current through the system of conductors will be from the 

 upper to the lower cup. The cylindrical rod of iron, inclosed 

 in the spiral, will become highly magnetic, and the suspended 

 moveable wire will perform its revolutions round the upper 



pole. , . , 1 



With this arrangement the direction in which the pendent 

 wire performs its revolutions will entirely depend upon the 

 character of the spiral, or upon the direction in which that 

 part of the conductor passes round the iron rod from the up- 

 per to the lower extremity, and not upon any other circum- 

 stance whatever. For, it being an established laiv in electro- 

 magnetics that the direction of its revolutions is not cdtered by 

 simultaneously reversing the magnetic polarity and electric 

 current; and as, in the present arrangement, the character of 



small electro-magnets made in this way display the magnetic powers in a 

 very exalted degree. 



An electro-magnet of the above description, weighuig 3 ounces, and 

 furnished with one coil of wire, supported 14 pounds. The poles were after- 

 wards made to expose a larger surface by welding to each end of the cy- 

 lindric bar a square piece of good soft iron : with this alteration only, the 

 lifting power was reduced to about 3 pounds, although the magnet was 

 annealed as much as possible. 



It appears to inc that the suijcrior magnetic energies displayed by these 

 cylindric rods of iron whilst subjected to the electric influence, are owuig 

 in a great measure to the peculiar fibrous texture which the metal is made 

 to asbume by the process which brings it to their [)articular shape. 



the 



