240 THE REV. W. WHEWELL ON THE DETERMINATION OF THE 



Observations similar to those which have been made concerning the correction of 

 the times for parallax, may be repeated with respect to the declination. The theo- 

 retical correction is of the form* 



(sin2 1 — sin2 A) d . s, 2 <p ; 

 \but observation gives 



(sin2 ^ - sin2 A) (c + c? . a-, 2 (p — 2 /3). 



And the quantity c varies with a change of the epoch. 



The following are the results of the Bristol observations. 



For the year 1834, transit A, we find for the declination 7°, a maximum 7" at 4^^; 

 a minimum — 7" at 7f^. We find also for the declination 24°, a minimum — 3"^ 

 at 5^ ; a maximum 9™ at 7^'^ Hence the corrections for declination of this series 

 may be expressed by these formulae : 



for 7°, 0°^ - 7™ . 5, 2 (p - 12^ ; for 24°, 3°^ + 6°^ . *, 2 (p — 12J^ 



Collecting in the same manner the corrections for the other series, we have 



Decl. 7°. Decl. 24°. 



mm h m ra h 



Year 1834. Transit A, — 7 .*, 2^— 12, 3 +6 .3,20-12^ 



B, - i- oi.s,2<p-i2i, 1 + 71.5^2^-13 



C, 5-5 .*, 2^-14, --2| + 5i.*, 2(p- 13| 

 Year 1835. Transit A, 1 1 — 8f . ^, 2 ^ — 12, 2^ + 5| . 5, 2 (p — 12 



B, li- 7i.^,2^-13i, -li + 7J..S2^-13 



C, 7 -11 .A-, 2?)-14, -1 +7 .*, 2^-14 



We here see that the transits A and B make c very small, so that when they are used, 



the declination correction curve approaches very near to the symmetry of theory. 



Also these epochs make the curve cut the axis very nearly at 6^, as the theory gives. 



The observations at Bristol for 1836 and 1837 give for the declination corrections, 



transit B being used, 



Decl. 7°. Decl. 24°. 



mm h mm h ' ' 



1836, li-7§.^, 2(p-13|; i + sj . *, 2 (p - 12 ; 



1837, 3|-7f .*, 2?)- 12f ; - ij + 7^ • *, 2 ^ - 12. 



The Plymouth observations for 1834, 1835, 1836, 1837, referred to transit B, give 

 in like manner for the low declination 6°, a curve which has a maximum 10™ at 5'^, 

 and a minimum — 3™ at 8j^*. Hence its formula would be 



The correction for 24° has a minimum of — 9"^ at 4*', a maximum of 4™ at 8^. Hence 

 its formula is 



— 24" + 6J™ . 5, 2 (p — 12^ 

 V. How does a change of the epoch affect the parallax correction of heights ^ 



* Here I is the declination, and A the mean declination. 



