2 1 Mr. Cooper on Mean Solar Time. 



ditional remarks on this subject that may have come within 

 their notice, for the satisfaction of Mr. Squire. 



I am, Gentlemen, your obedient servant, 

 Gosport, Sept. 16, 1884. WlLLlAM BuRNEY. 



XXXVII. On folding the exact Mean Solar Time. By Mr. 

 Samuel Cooper. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 A SI have for some time been in the habit of making celes- 

 -^ tial observations for the purpose of ascertaining the rate 

 of an excellent astronomical clock which shows mean solar 

 time ; for this purpose I have usually calculated the time from 

 altitudes of the sun taken a few hours before or after noon, 

 having the latitude and sun's declination given. Now my 

 motive for troubling you on this subject is for the purpose of 

 finding the exact mean solar time, that is, to the fraction of a 

 second. In the first place I have my doubts whether I should 

 use the apparent latitude, or that found by meridian altitudes 

 of the sun taken with the reflecting circle on an artificial ho- 

 rizon corrected for semidiameter, refraction and parallax, or 

 the same when reduced to that at the earth's centre. I shall 

 here give an example for the purpose of more fully illustrating 

 my meaning. 



On August 25, 1824, at 28 minutes after 3 p.m. mean solar 

 time according to the clock, and which I know to be near the 

 true time, I found the visible altitude of the sun's lower limb 

 to be 31° 7' 34" - 7. Required the mean solar time, supposing 

 the visible latitude of the place = 52° 13' 30", or the reduced 

 latitude 52° 2' 37"? 



Solution. 

 First, for the visible latitude 52° 1 3' 30" 



175 44 31 



87 52 15-5 



-58 37 58 



29 14 17-5 



25° 46' 51 "-8 cos. = 9-954:4:655 



2 



51 3S 43-6 = 3 h 26 m 14'-9 



Visible 



