The coils are wound with copper wire (covered with silk), 10 mils.
Cynthia looped the coils of the telephone cord around her finger.
The current then passes through the coils of an electromagnet, which releases the printing mechanism.
Thus the most efficient vacuum pans of the present day are those which have their coils so arranged that no portion of them exceeds 50 or 60 ft.
Attempts have been made to improve submarine cables in this respect, and in 1906 a short cable " loaded " with Pupin coils was laid across Lake Constance.