Clock and Watch Work [By E. Beckett]. from the 8th Ed. of the Encyclopaedia Britannica, with Improvements (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1855 edition. Excerpt: ... time, more accurately than from railway clocks, or public clocks of ordinary quality. For those who feel any difficulty about using the dipleidoscope, or who wish to be quite independent of the setting by a chronometer in the first instance, Mr Denison recommends, in his treatise on clocks, the following simple and independent construction of a sun-dial on a larger scale for noon only, which is quite sufficient for the occasional correction of a tolerably good clock: --Fix a thin plate of metal (protected against rust in any way you please) with a small hole in it, facing the south as nearly as you can, and inclined to the horizon at about 50 (not that the inclination is material), with the hole about nine inches above a stone slab set quite firm and level. Mark the point on the slab exactly under the hole by means of a pointed plum-bob, and call it C. About 11 o'clock see where the bright spot falls on the slab, and call that A, and with radius C A draw as much of a circle as is likely to be wanted for the bright spot again to reach it about 1 o'clock. Mark the place where it does reach it a, and bisect the arc A a in M suppose, and draw a straight line C M, as long as the slab will hold, from C through M. That line is the meridian, and the spot will always fall upon it at solar noon. Before you mark the line strongly, it will be as well to take several observations of this kind at different times, before and after noon, and on different days, and if their bisections agree in falling on the line C M you may be sure it is right. We have seen one of these dials with the gnomon only six inches high, and the time can be taken from it perhaps as accurately as from a dipleidoscope, and certainly with far less trouble. In order that the bright spot may...