694 AMPERE'S LAWS. 



The last of these laws may be stated somewhat 

 differently. Let ab and cd in fig. 350 represent two 

 currents flowing in directions indicated 

 by the points of the arrows. The con- 



ductors tend to move until a coincides 



with c arid b with d, in other words, at- 

 o traction takes place between the portions 



FIG. 3oO. a e an( j c ^ an( j a j go between e b and e d, 



while repulsion takes place between a e and e d, and c e 

 and e b. Now in a e and c e, the currents flow towards 

 the point of intersection e, in e b and e d they flow from 

 the point of intersection. Hence we may express the 

 third law by two statements : 



A. Two currents, the directions of which intersect, at- 

 tract one another when both flow towards or away from the 

 point of intersection. 



B. They repel one another if one flows towards the point 

 of intersection and the other away from it. 



When strong currents can be used for the experiments, a simple 

 conductor, suspended so that it can move freely, and a second con- 

 ductor, also simple, which can be brought near the other, are quite 

 sufficient for manifesting appreciable movements. But with a 

 current from two Bunsen or Grove elements it is best to employ- 

 conductors which consist of several insulated copper wires placed 

 side by side in such a manner that the current has the same direction 

 in all those parts of the conductor which adjoin. In an arrange- 

 ment of this kind the effect becomes multiplied, for we have not the 

 action of a single current upon another single current, but that of 

 several upon several. 



Upon a small board, fig. 351 -4, a square is drawn, each side be- 

 ing 15 cm long. Wire tacks are driven in at each of the corners a, 

 1), c, d, and also at the points e and /. A piece of covered copper 

 wire, 3 m< 3 or a little more in length and from 0'6 to l mm thick 

 (without the covering), is fastened by one end to the tack /, and 

 drawn very tight round a to &, c, cZ, and then five times round the 

 square ; the end of the wire is fixed by twisting it several times 



