EXPERIMENTS ON AMPERE'S LAWS. 



695 



round the tack e. There will now be four turns of wire in the side 

 ad of the square, and five turns in every other side of it. Thread 

 a needle with a long thread and pass it exactly at the middle of a d 

 under the four turns of wire, and also under the piece of wire be- 

 tween d and e (not under that between a and /), make a loop at 

 the end of the thread, draw it tightly round the wires, and tie the 

 whole together with a double knot. One-half of the piece of wire 

 from d to e, viz., that on the right, will in this way be drawn close 

 to -the other four wires, as represented in fig. 351 A. The thread is 

 then wrapped spirally round all the wires, proceeding along the 

 sides of the square, pushing the needle at each turn underneath the 

 wires, taking care at the corners not to tie tacks and wires together, 



A 



FIG. 351 (A an. proj., | real size ; B % real size). 



but to carry the thread only underneath the wires and round them, 

 leaving the tacks quite free. The figure shows the square when the 

 thread has been wrapped round one-fourth of the whole. When 

 arrived at a the thread is drawn also round the piece of wire af, so 

 that this is made to join the four turns between a and d, and the 

 whole is ended about 6 mm before reaching the middle of a d, where 

 the work commenced. The thread is firmly tied at that point, the 

 ends of the wires are cut close to e and / with the nippers, and the 

 tacks a, 6, and c are drawn out of the board to set the square free. 

 The ends of the wire are held for a short time in a flame to burn 

 away the covering ; they are then neatly polished with emery. 

 paper, and after straightening the sides of the square where neces- 

 sary, so that it may form a correct square with straight sides and 

 right angles, the free ends are bent so as to be parallel to the sides 



