MEAN AND APPARENT TIME. 



December, the sun is fast by an interval which varies from to 

 16 m 18'51 8 . 



After 25th December the real sun once more falls to the eastward 

 of the mean sun, and consequently it does not arrive at the 

 meridian until after the mean sun has passed it, that is until 

 some time after the mean noon. On the 26th December it passes 

 the meridian at 40 -45 s ; on the 27th at l m 10- 15 s ; on the 28th 

 at l m 39- 71 s after noon, and so on, the lateness of its transit 

 increasing until the llth February, 1856, when it passes the 

 meridian at 14 m 32*36 S after noon. After this its transit is less 

 and less late until the 15th April, when it again coincides with 

 the mean sun. 



It appears, therefore, that from the 25th December to the 15th 

 April the sun is always slow, its deviation from the time of the 

 clock being greatest on the llth February, when it amounts to 

 14 m 32 '36 s . The distance of the true sun from the mean corre- 

 sponding to this interval, computed as before, is 3 38' 5 '4". On 

 the llth February, therefore, the true sun is at this distance east 

 of the mean sun. This distance is not quite seven times the 

 diameter of the sun's disc, 



39. The real interval between two successive transits of the 

 sun being variable, it is evident that no piece of mechanism could 

 be constructed which, without adjustment, would point daily to 

 12 o'clock at the moment of apparent noon. So long, therefore, 

 as the mean time was not adopted as the chronometric measure 

 for civil purposes, it was necessary daily, or at least weekly, to 

 regulate all the clocks, public and private, according to the vary- 

 ing time of apparent noon. This was the practice even in a 

 country so enlightened as France until an epoch so recent as 1816. 

 Before this time the most remarkable disagreement constantly 

 prevailed among the public clocks of Paris, few of which were 

 regulated sufficiently often by observations of the sun. M. Arago 

 relates, that Delambre, the celebrated French astronomer, told 

 him that he frequently heard the public clocks, one after another, 

 striking the same hour during half an hour. 



At the time of introducing the change in the regulation of the 

 clocks of Paris from apparent to mean time, the prefect of the 

 Seine (which is the title of the chief of the municipality, or mayor 

 of Paris,) entertained such serious fears that an insurrectional 

 movement might be excited among the working classes, who, it 

 was supposed, would revolt against a noon which did not corres- 

 pond with the noon of the sun, or mid-day, and which conse- 

 quently would divide the day, from sunrise to sunset, into two 

 unequal parts, that he refused to sign the ordonnance for the 

 change unless it was accompanied by a formal report of the Board 



135 



