Biess on Electric Currents of the First and Higher Orders. 18 J 



The dependence of the principal current on the shape of the 

 wire through which it passes, or in other words, the action of 

 the current upon itself, has been already demonstrated. This 

 action is exhibited in a more striking degree by the secondary 

 current. A small induction-disc was introduced into the pri- 

 mary circuit, and a corresponding one into the secondary circuit ; 

 the remaining portion of the secondary circuit consisted of 44*7 

 feet of copper wire ^ths of a line in thickness, and the wire of 

 the thermometer. The 44" 7 feet of copper wire were first so 

 stretched out, that when a secondary current passed through it 

 the action of one portion of it upon another was null, and the 

 strength of the secondary current under these circumstances was 

 measured. The same wire was then wound into a spiral shape, 

 the form alone of the circuit being thus altered, its length re- 

 maining as before, and the strength of the secondary current in 

 this case was also measured. The following are the results ob- 

 tained : — 



Thus we see that by a mere alteration of the form of the cir- 

 cuit, without any diminution whatever of its length, the secondary 

 current is weakened in the proportion of 100 : 11. In this case 

 the direction of the secondary current was the same in both the 

 spirals through which it passed, the shape of the circuit being 

 therefore that which has already been illustrated by the letter N ; 

 we observe that the effect of this shape is exactly similar to that 

 which occurs in the primary circuit under the same circumstances. 



The large proportion of the entire circuit which, in the above 

 experiment, received the spiral form, accounts for the magnitude 

 of the diminution ; in the following experiments another arrange- 

 ment was adopted. From a copper wire ^ths of a line in thick- 

 ness, three portions, each 53 feet long, were cut; the first was 

 stretched out so that no action could occur between its parts ; 

 the second was wound into a plane spiral, similar to the induc- 

 tion-discs so often alluded to; and the third was carried back 

 and forward, m B Qgzag manner, from side to side of an oblong 

 frame about a foot in width; twenty-five CJa were thus formed, 

 the legs of which were 1*2 line apart. In order to limit the 



