Methods of A stronomical Ohsei^vation . 191 



When A does not exceed 30 or 40 minutes, which will 

 in general be sufficiently distant from the solstice, the 

 operation by the formula, even in natural numbers, becomes 

 remarkably simple, because in that case, the second and 

 third terms are insensible. 



To render the first term applicable to every case, the 

 sum of parts II and III may be taken from the small table 

 in the margin, and is always to be subtracted. 



Example 2. Let the sun's right ascension be 7^ 16" 36% 

 the obliquity of the ecliptic 23° 27' 32"*8 and, consequently, 

 A = 1^ 16°" 36% h w = 7"-2, required the reduction to the 

 solstice ? 



In this way, the computation assumes the following very 

 simple form : 



Const, logarithm 9-855577 



A = Ih 16m 36s ^ 7601.6, log. x 2 . . . = 3-768458 



lstcor.= + l°10'7"-61og 3-624035 



2d cor. = — 2-2 from this small table, ^ w= — 7''-21og 0-857 

 3d cor. = — 0-4 ^ x from calculation. Const, log. 5-123 



a; = + 1 10 5-0 = red. to solstice. ^ x log. . — 9-604 



Hence, it appears that by this formula, the reduction to 

 either solstice is a very easy operation. From these preli- 

 minary formulae it is now proposed to show their general 

 application to one day's observations, consisting of six sets 

 or three pairs, made on the 5th of July last, at Edinburgh, 

 in latitude 55° 57' 15"-67 N. 



1834, July 5th. Chronometer fast for mean time . 2' 40" 

 Equation of time with a contrary sign . . . . 4 16 



Chronometer fast on apparent time 6 56 



Barometer, 30'°' 17, attached thermometer, 70° P., detached, 

 or that in the open air, 68° F. Or, instead of making the 

 6°" 56' the error to each, it may be applied to 12^^ by subtrac- 

 tion, thus giving 11^ 53" 4' for the time of apparent noon 

 by chronometer, a method rather more convenient. 



