340 MAGNETIC LINES OF FORCE. SECT. XXXIV. 



magnet. He placed two bar magnets of the same length, size, 

 and intensity with their similar poles together, so that they might 

 act as one magnet. A copper wire was then passed between 

 their axes, which after extending through half their length was 

 bent up equatorially and turned back along the outside, so that 

 the whole wire formed a loop, the two ends being connected with 

 a galvanometer. When the whole wire was made to revolve, no 

 effect was produced, although it crossed the lines of magnetic 

 force ; but when it was cut in two, so as to separate the external 

 from the internal part, electrical currents of equal intensity, but 

 in contrary directions, were induced in each portion of the wire as 

 they were made separately to cross the lines of force, for the 

 apparatus was so constructed that that could be done. The ex- 

 terior wire crossed the lines of force which issued from the 

 magnets at right angles to their axes, while the equatorial part 

 of the interior wire traversed the returning lines of force. It is 

 evident that these forces neutralized each other when the whole 

 wire revolved : consequently the internal and external lines of 

 force must have been of equal intensity and opposite in direction, 

 so as to balance one another. By this and a very great number 

 of other experiments Dr. Faraday has proved that the magnetic 

 lines of force are continuous closed curves alike in shape, size, 

 and power. They extend indefinitely beyond the magnet, and 

 undergo no change by distance. 



Thus the magnetic force pervades the interior of the mass ; if 

 electricity does the same, a compensation must either take place, 

 or it also must move in lines of force, sensible only at the sur- 

 face. Electricity has a perpetual tendency to escape, and does 

 escape, when not prevented by the coercive power of the air, and 

 other non-conducting substances. Such a tendency does not 

 exist in magnetism, which never leaves the substance containing 

 it under any circumstances whatever. There must be some 

 coercive force, analogous to friction, which arrests the magnetic 

 forces, so as first to oppose their separation, and then to prevent 

 their reunion. In soft iron the coercive force is either wanting 

 or extremely feeble, since iron is easily rendered paramagnetic by 

 induction, and as easily loses that quality ; whereas in steel the 

 coercive force is extremely energetic, because it prevents the steel 

 from acquiring the paramagnetic properties rapidly, and entirely 

 hinders it from losing them when acquired. The feebleness of 



