. American telephone practice . ad INDUCTION COILS. 77 of silk wound alongside and parallel with the wire, as shown inFig. 61. This method of winding coils is old, having been inventedby Dr. Leverett Bradley and patented by him in 1865 \ but it hasrecently been introduced by the Varley Company in the variousbranches of telephone work with much success. A layer of paperis introduced between each layer of wire, and in this way the insula-tion is made complete. The machines for winding in this mannerhave been perfected with such nicety that several coils are simul-taneously wound, the layers of p
. American telephone practice . ad INDUCTION COILS. 77 of silk wound alongside and parallel with the wire, as shown inFig. 61. This method of winding coils is old, having been inventedby Dr. Leverett Bradley and patented by him in 1865 \ but it hasrecently been introduced by the Varley Company in the variousbranches of telephone work with much success. A layer of paperis introduced between each layer of wire, and in this way the insula-tion is made complete. The machines for winding in this mannerhave been perfected with such nicety that several coils are simul-taneously wound, the layers of paper being automatically introducedbetween each layer of winding without stopping the machinery,which is run at a very high speed. Considerably more wire can beplaced on a coil in a given space than with the ordinary method ofwinding; and the fact that bare wire is used tends to render thecoil cheaper. This same company has carried the idea of sectional windingsthroughout the entire field of telephone work, They construct their. THREADFIG. OF WINDING VARLEY COIL. spools in such manner that the heads may be readily removedand a coil replaced without the necessity of rewinding. It is now quite common to mount the induction coil in the baseof the arm on which the transmitter itself is mounted, such con-struction being shown in Figs. 62 and 63. The base and arm hereshown are made of cast iron joined in such manner as to allow aconsiderable vertical movement of the transmitter, in order to ac-commodate it to the heights of different users. The coil has some-times been mounted upon the back board of the telephone, so as tobe covered by the base of the arm when secured in place, but a moredesirable method is to mount it in the arm-base, as shown, the vari-ous terminals being brought out to binding posts on the front of thebase. This construction, however, is bad, unless well carried out,and great pains should be taken in insulating the various posts andwires from the conduc
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