Fig. 17. 



COMMON THINGS. 



CLOCKS AND WATCHES. 



CHAPTEE I. 



1. General want of time measurers. 2. No natural measures for short 

 intervals. 3. Approximative expedient by shadows. 4. Sun-dials. 

 5. Differently constructed for different places. 6. Earliest sun- 

 dials. 7. Clepsydra, or water-clock. 8. Hour-glass. 9. Mercurial 

 time-gauge. 10. Clocks their chief parts. 11. Regulating power 

 of the pendulum. 12. Uniform rate of vibration. 13. Analysis of a 

 vibration. 14. Experimental verification of isochronism. 15. Moving 

 power sustains the vibration. 16. Vibration not dependent on weight 

 of pendulum. 17. Time of vibration varies with the length. 

 18. Analysis of motion of pendulous mass. 19. How the pendulum 

 governs the hands. 20. Produces intermitting motion. 21. Pen- 

 dulum's motion maintained by moving power. 



1. AFTER the supply of the absolute necessaries of physical 

 existence food, clothing, and lodging one of the first wants of a 

 society, emerging from barbarism, is the means of measuring and 

 registering time. In civilised society, all contracts for labour, 

 and for all kinds of service, are based upon time. Even in the 

 cases of the highest public functionaries, and where the service 

 rendered is purely social and intellectual, still it is regulated, 

 limited, and compensated with relation to time. Time measurers 



LARDNER'S MUSEUM OF SCIENCE. B 1 



No. 66. 



