26 



SOLAR DIURNAL VARIATION 



The hours of no semi-annual change are 6 A. M. and 7 P. M. ; the greatest changes 

 take place about 2 A. M. and 4 P. M., with a range of .000370 and .000328 parts 

 of the force respectively. 



The turning epochs are found from the variations at the hours 6 A. M. and 7 

 P. M. The following numbers are the differences from the respective annual means. 



For 20"' the simi has been changed. 







MeaQ 



Mean 





6 A. M. 



IS iind 20. 



6 A. M. 7 P. M. 



.lanuarr .... 



+027 



—122 



—048 



Pebrnary 









—084 



—037 



—060 



Mar<-h . 









—037 



—095 



—066 



April . 









+041J 



+0«0 



+053 



May 









+104 



+080 



+092 



June . 









+030 



+090 



+060 



July . 









+100 



+097 



+098 



August 









—025 



+091 



+033 



September 









—111 



+055 



—028 



October 









—025 



—044 



—034 



November 









—043 



—059 



—051 



December 









+01*4 



—116 



—051 



All expressed in units of the sixth place of decimals. 



The values in the last column are represented by the formida : — 



A,= 0.000075 sin {0 + 280°) + 0.000025 sm {2d + 131°) 

 counting from January 1st. The change of sign occurs about April 4th and about 

 September 12th, on the average, therefore, the change takes place about three days 

 after the equinoxes. 



ANALYSIS OF THE SOLAR-DIURNAL VARIATION OF THE TOTAL FORCE. 



In the following expressions of the solar-diurnal variation of the total force, 6 is 

 counted from midnight at the rate of 15° an hour ; a positive sign indicates increase 

 of total force, a negative sign the reverse. The coefficients are expressed in parts 

 of the force. The formidfe are deduced directly from Table VIII. 



A, = 0.000139 sin (fl + 3180 14') + 0.000157 sin (28+ 37° 57') + 0.000020 sin (36 + 217°) 

 A, = 0.000215 Sin (fl + 276© 00') + 0.000143 sm (2S+ 41° 01') + 0.000060 sni (39+ 96°) 

 A,= 0.000148 sin (6 + 2840 00') + 0.000106 sin (29 + 310 27') + 0.000014 sin (39 + 242°) 

 A, = 0.000283 sm (9+ 270O 27') + 0.000084 sm (29+ 3420 03') + 0.000042 sm (39+ 740) 

 Zi, = 0.000383 sm (9+ 264° 08') + 0.000084 sm (29 + 3250 13') + 0.000062 sm (39 + 108O) 

 A, = 0.000470 sin (9 + 2660 26') + 0.000108 sin (29 + 20 57') + 0.000016 sin (39 + 960) 

 A^ = 0.000513 Sin (9+ 2650 24') + 0.000103 sm (29 + 344o 53') + 0.000036 sm (39 + 1260) 

 A, = 0.000500 sin (9 + 2590 41') -|. 0.000109 sin (29+ 290 29') + 0.000025 sin (39+ 1930) 

 For September a,= 0.000405 sin (9 + 252o 37') + 0.000097 sin (29+ 150 05') + 0.000010 sin (39+ 1630) 

 For October A,= 0.000170 sin (9 + 307O 00') + 0.000084 sin (29 + 450 35') + 0.000033 sin (39 + 440) 

 For November a,= 0.000122 sm (9+ 2660 37') + 0.000074 sm (29+ 680 28') + 0.000010 sm (39 + 1190) 

 For December A, = 0.000136 sm (9+ 317° 52') + 0.000112 sm (29+ 460 38') + 0.000017 sm (39 + 2340) 



The months from April to September are counted as summer months ; those from 

 October to March as winter months. 



For Summer A, = 0.000426 sm (9+ 2620 51') + 0.000095 sin (29 + 3580 00') + 0.000026 sm (.39+1140) 

 Af= 0.000146 sm (9 +2920 00') + 0.000110 sm (2fl^ 430 20') + 0.000007 sm (39+1190) 

 A, = 0.000277 sm (9 + 2700 45') + 0.000095 sin (29+ 220 29') + 0.000018 sin (39+11.50) 



For January 

 For February 

 For March 

 For April 

 For May 

 For June 

 For July 

 For August 



For Winter 

 For Year 



