CONTENTS. T 



PAGE 



height of an elastic atmosphere. 15. Air less and less dense in 

 ascending. 16. Effects of atmospheric pressure. 17. Boy's 

 plaything of a sucker. 18. Flies walking on ceiling. 19. Res- 

 piration. 20. Action of bellows. 21. Ventpeg lid of tea-pot. 

 22. Pneumatic ink-bottle. 23. Syringes. 24. Exhausting 

 syringe. 25. Eate of rarefaction. 26. Absolute vacuum cannot 

 be obtained. 27. But may be indefinitely approached. 28. Air- 

 pump. 29. Condensing syringe. 30. Condenser . . .97 



COMMON THINGS. TIME. 



CHAP. I. 1. Simple notions difiicult to define. 2. Conception of 

 Time, how obtained. 3. By succession of sensible impressions. 

 4. Proof that such succession is necessary. 5. Time passes faster 

 with some than with others. 6. Is measured only by a regular 

 and uniform succession. 7. Periodic phenomena which may 

 measure time. 8. Natural appearances intended for that purpose. 

 9. Significations of the word "day." 10. Hours. 11. Their 

 length in certain cases variable. 12. Vulgar and equinoctial 

 hours. 13. Commencement of the day with different nations. 

 14. Italian time. 15. Inconvenience of such a mode of 

 reckoning. 16. Modern method. 17. Civil and astronomical 

 time. 18. The day the standard unit. 19. Necessary to deter- 

 mine it rigorously. 20. What is a day ? 21. Diurnal rotation 

 of the heavens. 22. Its constancy and uniformity. 23. Never- 

 theless not fitted to be the unit of civil time. 24. The meridian. 

 25. Diurnal motion of the sun means of observing it. 26. 

 Transit instrument. 27. Method of observing with it. 28. 

 Sidereal day its subdivisions. 29. Its permanency and uni- 

 formity unfit, nevertheless, for a measure of time. 30. Why 

 the sun is not fit 113 



CHAP. II. 81. How to observe the sun's transits. 32. Interval 

 between them variable. 33. Mean and apparent time. 34. 

 Relative changes of mean and apparent time. 35. The days r on 

 which they coincide. 36. The Equation of time. 37. Further 

 explained. 38. Its extreme error. 39. Mean time adopted in 

 France. 40. Unfitness of apparent time. 41. Local time varies 

 with longitude. 42. Equalisation of local time proposed. 43. 

 How time-pieces are regulated. 44. Mean solar hours, minutes, 

 and seconds. 45. Length of sidereal day. 46. The week. 47. 

 Opinions as to its origin.- 48. Both opinions erroneous. 49. 

 Origin of the names of the days. 50. First day of the week. 

 51. The month 129 



CHAP. III. The month (continued). 52. Not conformable with lunar 

 periods. 53. Difficulty of subdividing the year. 54. Division 

 unequal. 55. Egyptian months. 56. Greek. 57. Solon's 

 months. 58. Roman months. Romulus. 59. Origin of names 

 of months. 60. Additional months of Numa. 61. Origin of 

 their names. 62. Their lengths. 63. Superstition in favour of 



