16 



RESULTS OF METEOROLOGICAL OBSERVATIONS 



The resulting daily temperatures observed by Mr. "Wood between 1818 and 1823, 

 at sunrise, 2 o'clock, and sunset, require a correction to refer them to the mean 

 daily value resulting from hourly observations. For this purpose we require to 

 know the time of sunrise and sunset, which may conveniently be found by the 

 following formulae : — 



1. By the fundamental equation 



cos ^ — sin ^ sin 8 



cos t ■■ 



where ^ = 90° -\- r — n -\- s -\- d 



cos <p cos S 

 2. By a differential equation 



cos t = — tan <^ tan S and clt = sec 8 sec ^ cosec t d^ 

 where ^ = geographical latitude 

 S = sun's declination 

 ^ = sun's zenith distance 



t = apparent time when the sun's upper limb is in the horizon, for first 

 method, and when the sun's centre is in the horizon, for second 

 method. 

 r, 7t, s, d = refraction, parallax, semi-diameter, and dip, respectively. 

 For ordinary cases Ave may put r = refraction in horizon ^= 34:' for a tempera- 

 ture of 50° Fahr., and for an atmospheric pressure of 30 inches, 7t= solar parallax 

 may be neglected, s = semi-diameter = 16'. Exclusive of parallax and dip we 

 have for sunrise and sunset, d^= -{- 50'. If we wish to take into account the 

 elevation of the eye above the horizon, we have cZ:= 0.98 ■'/x where a;= eleva- 

 tion in feet and d = dip in minutes, which is to be added to the numerical value 

 of d^. 



The apparent time t is to be changed to mean time by application of the equation 

 of time. 



The mean time of sunrise and sunset^ was made out for every tenth day and for 

 the middle of each month ; the corrections were taken from the Philadelphia table 

 (Smithsonian Collection of Meteorological and Physical Tables); they are as 

 follows : — 





O rise. 



G rise. 



7 A. M, 



6 A. M. 



O rise. 



S A. M. 



7 A. M. 



6 A.M. 



5 A. M. 





2 P. M. 



2 P. M, 



2 P.M. 



2 P. M. 



2 P.M. 



2 P. M. 



3 P. M. 



3 P.M. 



3P M. 





0>.et. 





9 P. M. 



9 P. M. 



9 P. M. 



9 P.M. 



9 P. M. 



9 P. M. 



9 P. M. 



January 



— 1°.33 



— 0°.54 



— 0°.22 



— 0°.33 



— 0°.30 











February 









—1.53 



—0.40 



—0.17 



—0.19 



—0.17 











March . 









—1.40 



—0.38 



—0.15 



+0.02 



—0.01 











April . 









—1.40 



—0.17 



—0.53 



+0.06 



+0.17 











May . 









—0.71 



+0.24 



—0.57 



+ 0.14 



+0.33 











June . 









—0.53 



+0.03 



—0.77 



+ 0.04 



+0.59 



+0°.60 









July . 









—0.51 



+0.18 



—0.61 



+0.17 



+0.32 



+0.58 



— 0°.73 



+0°.03 



+ 0°.44 



August 









—1.00 



—0.23 



—0.44 



+0.16 



+0.30 



+0.35 





+0.10 





September 









—1.63 



—0.60 



—0.35 



+0.20 



+0.21 







+0.16 





October 









—2.02 



—0.63 



—0.33 



+0.08 



+0.06 











November 









—1.75 



—0.73 



—0.28 



—0.27 



—0.28 











December 









-1.38 



—0.60 



—0.29 



—0.23 



—0.33 











Year .... 



—1.27 



—0.32 



—0.39 



—0.02 



+0.07 











' A table of mean time of sunrise and sunset is given in the Annuaire Meteorologique de la 

 France pour 1850 ; but it is limited by the latitudes of 42° and 51°. 



