COMMON THINGS TIME. 



expresses an angle or circular arc, the magnitude of which is 

 8 degrees, 30 minutes, 25 seconds, and 6-tenths of a second. 



29. The absolute uniformity and permanency which thus 

 characterise the diurnal rotation of the heavens, combined with 

 the fact that it is observable at all parts of the earth, would 

 render it eminently suitable as a measure of time. It wants, 

 nevertheless, one condition which is quite as essential for the 

 purposes of civil life as uniformity and permanence. It is not 

 marked and limited by any conspicuous phenomena which strike 

 the senses of all mankind. It does not correspond with the 

 periodical returns of light and darkness, nor with the successive 

 returns of the sun to the meridian. It does not even fall into 

 accordance with the conspicuous lunar phenomena; so that, 

 although it be true that it is observable alike in all parts of the 

 earth, the phenomena by which it is marked are such as can only 

 be observed with the aid of astronomical instruments, and such as 

 do not address themselves to mankind in general. 



30. To obtain, therefore, a fit measure of time for civil purposes, 

 some measure must be found which will fall into such accordance 

 with the periodical vicissitudes of light and darkness and the 

 successive meridional transits of the sun, that the chronometric 

 unit may correspond either exactly, or nearly enough, for all 

 practical purposes with those diurnal appearances by which the 

 records of mankind have in all ages and countries been made. 



And why, it may naturally enough be asked, may not the 

 successive returns of the sun to the meridian serve the purpose ? 



It may be stated briefly but distinctly that the solar diurnal 

 phenomena, as they are actually presented in the heavens, do not 

 answer as a measure of time even for civil, to say nothing of 

 scientific purposes. Why they are unsuitable, and what sub- 

 stitute has been contrived for them, will require some words of 

 explanation. 



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