CHAPTER I. 



1. Simple notions difficult 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 soine 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. Incon- 

 venience of such a mode of reckoning. 16. Modern method. 

 17. Civil and astronomical time. 18. The day the standard unit. 

 19. Necessary to determine it rigorously. 20. What is a day ? 

 21. Diurnal rotation of the heavens. 22. Its constancy an<l 

 uniformity. 23. Nevertheless 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 uniformity unfit, nevertheless, for a measure of time. 30. Why 

 the sun is not fit. 



I. TIME IN GENERAL. 



t. THE most simple of our notions are those which it is most 

 difficult to describe or define. It is fortunate that they are pre- 

 cisely those which least need definition. Geometers have failed 

 in defining a straight line, or a plane surface, but no persons 

 differ in their conceptions of the meaning of these terms. Locke 

 observes, with his usual felicity and clearness, that a word which 

 expresses a simple idea, does not admit of definition, inasmuch as 

 a definition being a sentence composed of two or more words 

 having different significations, cannot collectively express one 

 idea which has no composition at all. The only way to convey 

 to the mind of another, the meaning of such a word, is by pre- 

 senting to his senses the object or the quality which it expresses. 

 In that case, if he possess the necessary organ of sense, he will 

 immediately obtain the perception ; if he do not all the words in 

 the world will not convey it to him. A person blind or deaf from 

 infancy can never acquire any perception of colours or sounds. 

 A. blind man after listening attentively to an elaborate description 

 of the colour scarlet, declared that he had a very clear and satis- 

 factory notion of it, and that he considered it like the sound 

 of a trumpet ! 



2. Time is a word about the meaning of which it would seem 

 that there could be no disagreement; yet we cannot as in the 

 case of words expressing sensible ideas refer to any external 

 object from which we can immediately receive the perception 

 which that word expresses. Although we cannot define by words 

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