History, theory, and practice of the electric telegraph (1866)
Prescott, George B.(George Bartlett),1830-1894 · Boston, Ticknor and Fields · leaf 121
similar to ordinary needles.Mr. Walker found advantage in substituting for the diamondneedle, a needle formed of several very short needles of thinsteel and strongly magnetized, fixed upon an ivory disc of 1£inches in diameter. A single narrow, coffin-shaped rhomb makesa good needle. The outer… … Fig. 59. THE NEEDLE SYSTEM. 103 nished on the side towards the Case, and supported against itsframe ; or it is made in halves, and slides into grooves at theback of the case, independently of the dial. The -wire of thebobbin is less than a hundredth of an inch in diameter; its twoextremities abut…
Telegraph
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![An illustration from Novo teatro di machine et edificii per uarie et sicure operationi : co[n] le loro figure tagliate in rame é la dichiaratione, e dimostratione di ciascuna : opera necesaria ad architetti, e a quelli, ch[e] di tale studio si dilettano (1607)](https://img.insideoutlibrary.com/img/200/ia-novoteatrodimach00zonc-124-76.webp)
