Too Long; Didn't Read

Clocks and Watches:—A short history of timepieces—The construction of timepieces—The driving power—The escapement—Compensating pendulums—The spring balance—The cylinder escapement—The lever escapement—Compensated balance-wheels—Keyless winding mechanism for watches—The hour hand train. Locks:—The Chubb lock—The Yale lock. The Cycle:—The gearing of a cycle—The free wheel—The change-speed gear. Agricultural Machines:—The threshing-machine—Mowing-machines. Some Natural Phenomena:—Why sun-heat varies in intensity—The tides—Why high tide varies daily. CLOCKS AND WATCHES. A SHORT HISTORY OF TIMEPIECES. THE oldest device for measuring time is the sun-dial. That of Ahaz mentioned in the Second Book of Kings is the earliest dial of which we have record. The obelisks of the Egyptians and the curious stone pillars of the Druidic age also probably served as shadow-casters. The clepsydra, or water-clock, also of great antiquity,[Pg 411] was the first contrivance for gauging the passage of the hours independently of the motion of the earth. In its simplest form it was a measure into which water fell drop by drop, hour levels being marked on the inside. Subsequently a very simple mechanism was added to drive a pointer—a float carrying a vertical rack, engaging with a cog on the pointer spindle; or a string from the float passed over a pulley attached to the pointer and rotated it as the float rose, after the manner of the wheel barometer (Fig. 153). In 807 a.d. Charlemagne received from the King of Persia a water-clock which struck the hours. It is thus described in Gifford's "History of France":—"The dial was composed of twelve small doors, which represented the division of the hours. Each door opened at the hour it was intended to represent, and out of it came a small number of little balls, which fell one by one, at equal distances of time, on a brass drum. It might be told by the eye what hour it was by the number of doors that were open, and by the ear by the number of balls that fell. When it was twelve o'clock twelve horsemen in miniature issued forth at the same time and shut all the doors." Sand-glasses were introduced about 330 a.d.[pg 412] Except for special purposes, such as timing sermons and boiling eggs, they have not been of any practical value. The clepsydra naturally suggested to the mechanical mind the idea of driving a mechanism for registering time by the force of gravity acting on some body other than water. The invention of the weight-driven clock is attributed, like a good many other things, to Archimedes, the famous Sicilian mathematician of the third century b.c.; but no record exists of any actual clock composed of wheels operated by a weight prior to 1120 a.d. So we may take that year as opening the era of the clock as we know it. About 1500 Peter Hele of Nuremberg invented the mainspring as a substitute for the weight, and the watch appeared soon afterwards (1525 a.d.). The pendulum was first adopted for controlling the motion of the wheels by Christian Huygens, a distinguished Dutch mechanician, in 1659. To Thomas Tompion, "the father of English watchmaking," is ascribed the honour of first fitting a hairspring to the escapement of a watch, in or about the year 1660. He also introduced the cylinder escapement now so commonly used in[Pg 413] cheap watches. Though many improvements have been made since his time, Tompion manufactured clocks and watches which were excellent timekeepers, and as a reward for the benefits conferred on his fellows during his lifetime, he was, after death, granted the exceptional honour of a resting-place in Westminster Abbey.