together, ranging along side by side at the first covering. Then a series of three lengths of the strand received the second coat together. The third coat was communicated to a solitary strand. The strand and its triple coating of gutta percha were together designated “the core.” [Illustration: F. Jones, lith from a drawing by R. Dudley London, Day & Sons, Limited, Lith. THE REELS OF GUTTA PERCHA COVERED CONDUCTING WIRE CONVEYED INTO TANKS AT THE WORKS AT GREENWICH.] [Illustration: R. M. Bryson, lith from a drawing by R. Dudley London, Day & Sons, Limited, Lith. VALENCIA IN 1857-1858 AT THE TIME OF THE LAYING OF THE FORMER CABLE.] The copper strand was formed and coated with gutta percha in two mile lengths. Each of these lengths, when completed, was immersed in water, and then carefully tested to prove that its continuity and insulation were both perfect. The continuity was ascertained by passing a voltaic current of low power through the strand from a battery of a single pair of plates, and causing it to record a signal after issuing from the wire. A different and very remarkable plan was adopted to determine the amount of insulation. One pole of a voltaic battery, consisting of 500 pairs of plates, was connected with the earth; the other pole was united to a wire which coiled round the needle of a very sensitive horizontal galvanometer, and then ran on into the insulated strand of the core, the end of which was turned up into the air, and left without any conducting communication. If the insulation was perfect, the earth would form one pole of the battery, and the end of the insulated strand the other pole, and the circuit be quite open and uninterrupted; consequently no current would pass, and the needle of the galvanometer would not be deflected in the slightest degree. If on the other hand there was any imperfection, or permeability in the sheath of gutta percha, a portion of the electricity would force its way from the strand through the faulty places and surrounding water to the earth, a current would be set up, and the needle of the galvanometer deflected; the deflection being in proportion to the current which passed, and therefore its degree would become a measure of the amount of imperfection. When about fifty of the two-mile lengths of core were ready, these were placed in the water of the canal which ran past the gutta percha works, and were joined up by their ends into one continuous strand of 100 miles, the joints being covered with gutta percha. The hundred-mile length was then put through a careful scrutiny in the same way that the smaller portions were tried,--and next it was halved, quartered, and separated into groups of twenty, ten, and finally two miles, and each of these were again separately examined, and tested in comparison with similar lengths previously approved.