Front Page Titles (by Subject) APPENDIX G.: LEVELLING APPLIANCES. - An Autobiography, vol. 1
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APPENDIX G.: LEVELLING APPLIANCES. - Herbert Spencer, An Autobiography, vol. 1 
An Autobiography by Herbert Spencer. Illustrated in Two Volumes. Vol. I (New York: D. Appleton and Company 1904).
Part of: An Autobiography
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Figs. 1 and 2 show the old and the new modes of dividing levelling staves. When by great distance, or waning light, or fog, or rain, the hundredths are rendered invisible, the new form renders the tenths visible; and they can be divided by the eye with approximate correctness. Further, the correspondence between longer lines and higher decimals, excludes certain errors in reading.
Fig. 3 shows an appliance for plotting sections. ab is a straight-edge, placed parallel to the datum line cd, at the appropriate distance. e is a set-square, made thick to admit of the bevelled edge shown in section at f, Fig. 4. On to this, and under the clips, hh, is thrust the scale g, to which the particular section is to be plotted. The zero mark having been adjusted to the datum line, and the distance points having been marked, it requires only that the scale should be brought to each of them, and the corresponding height in the level-book pricked off: the ground surface, ki, being then drawn through the marks.
A new form of level is shown in elevation by Fig. 5, and in plan by Fig. 6. ab is the telescope (on which is the compass, c) fixed on an elongated brass plate, ddd. ee is the longitudinal bubble, and f is a circular bubble for rough adjustment. On the underside of the plate, dd, is a circular rim, g, shown in section at Fig. 7, which works upon a corresponding rim on the upper parallel plate. At i is the conical head of a screw, on which, as its centre, the plate, dd, rotates.
This screw is sufficiently tightened to give firm but easy rotation, passes through the upper parallel plate into the axis of the parallel plates; and, the screw being prevented from rotating, the central axis of the parallel plates is then tightened upon it, so that thereafter it cannot turn. The advantages are (1) that a much smaller area is exposed to the wind; (2) that this area, being nearer to the point of support, the wind has less leverage, the result being decreased vibration; and (3) that the bubble and the telescope being independent of one another, the line of collimation can be easily adjusted.