156 Prof. Weber on the Application of Magnetic Induction 



millims. It was covered first with wool and then with gutta 

 percha, and so coiled round the cylinder as to form 605 coils 

 arranged in eighteen strata. The circumference of the last en- 

 circling stratum is 1078'6 millims. 



This induction coil is surrounded by a strong wooden frame, 

 bbbb ; at its extremity is a wooden pulley C, with two circular 

 grooves, in which lie the wires connecting the inductor and gal- 

 vanometer. To this frame two strong brass pivots, d, d', are fixed. 

 The two pivots are exactly cylindrical and of equal diameters, and 

 rest on the Y-formed supports e, e', fixed to the beam of the 

 frame B, B'. Fig. 1 shows the induction coil in the position in 

 which it can rotate around a horizontal axis. To test the hori- 

 zontality of the axis of rotation, a level, c, is used ; its setting is 

 provided with two Y-formed feet, by means of which it can be 

 placed on the two pivots d, d' which form the axis of rotation. 

 At the end of one of the pivots, d', is a brass ball, in which 

 a conical-shaped cavity at / is turned. This ball serves to 

 displace the induction coil, so that from being horizontal, its 

 axis of rotation is brought into a vertical position. For in- 

 stance, the level c being removed, the induction coil A can be 

 raised by the pivot d when the sphere on the pivot d' sinks into 

 a spherical cavity cut at ff into the beam B'. When the axis of 

 rotation is thus brought into a vertical position, as shown by the 

 dotted lines in the figure, the raised pivot d&ts into a Y-formed 

 support //, fixed to the beam D of the framework, and is held 

 there by the pressure of a spring ; this pressure can be regulated 

 by a screw. In this position the ])oint of a screw, passing ver- 

 tically through the beam B', fits into the conical-shaped cavity 

 of the ball on the pivot d' ; thus the induction coil can be raised 

 so as to rotate freely on this point by merely turning the screw 

 head at k under the beam. To test the verticality of the axis of 

 rotation, a level is placed upon the level carrier // which fits on 

 to the end of the pivot d. 



Fig. 2 represents the induction coil in its horizontal position, 

 as seen from above. The inductor's axis («'. e. the axis of 

 the cylinder on which the wire is coiled) is here perpendicular 

 to the plane of the figure. Perpendicular to the frame to which 

 the pivots d, d' are fixed, is a second frame mm, surrounding the 

 induction coil, which carries two stout brass pins at n, n. On the 

 rotation of the induction coil these pins strike against screws 

 fixed into the beam of the framework, and thus at the end of 

 each induction stroke the inductor's axis is held vertical. One of 

 these pins ; which during the rotation moves in the upper semi- 

 circle, strikes on these screws from above; the other, which 

 moves in the lower semicu-cle, from below. These screws can 

 be somewhat displaced in a vertical direction, and their position 



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