Modern practice of the electric telegraph : a handbook for electricians and operators (1874)
Pope, Frank L., 1840-1895 · New York : D. Van Nostrand · leaf 152
The object of this arrangement is to pre-vent the mirror and its attached needle from being dis-turbed by currents of air. A narrow pencil of luminous rays from the lamp, E,passes through the opening, F, which is capable of ad-justment by the slide Gr. This pencil of light, passing MODERN PRACTICE… … right and left of the centre of the instrument, the zeropoint being exactly opposite the lens. The luminouspencil is brought to a sharp focus upon the scale by a 140 APPENDIX AND NOTES. sliding adjustment of the lens M, in the tube N. Whenthe needle is at rest in its normal position, and uo…
Telegraph
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