The incandescent mantle is more extensively used every year. In Germany 90 per cent. of gas lighting is on the incandescent system, and in England about 40 per cent. We may notice, as an interesting example of the fluctuating fortunes of invention, that the once doomed gas-burner has, thanks to Welsbach's mantle, in many instances replaced the incandescent electric lamps that were to doom it.
[38] If, of course, there is no safety-valve in proper working order included in the installation.
Chapter XX.
VARIOUS MECHANISMS.
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.