24 



SOLA 11 DIURNAL A' A R I A T I O N 



Table VI. 













Elapsed 









Range of 





Principal 



AmoaDt 



A. U. 



Amonnt 



time 



A U. 



Afternoon 



Early night 



alternoun 





maximum 



in 



miuiiuum 



in 





rauj,'e. 



minimum 



minimum 



minimum 



1841 to 1S45. 



at 



miuutes. 



at 



minutes. 



max. and 





about 



about 



&. principal 



January . . 



IP 59" 



+0.'69 



6'' 39'° 



— 0.'32 



5''20»> 



l.'Ol 



6i> 



' h 



l.'O 



February . . 



12 15 



+0.67 



6 04 



—0.48 



6 11 



1.15 



8 



— 



0.9 



March . . . 



11 67 



+0.72 



5 54 



—0.43 



6 03 



1.15 



— 



11 



— 



April. . . . 



11 11 



+0.92 



5 11 



—0.48 



6 00 



1.40 



— 



10 



— 



May .... 



10 24 



+0.81 



4 07 



—0.46 



6 17 



1.27 







11 







June .... 



11 01 



+0.91 



5 16 



—0.36 



5 45 



1.27 



5 



10 



1.0 



July .... 



10 57 



+1.00 



31 15 



—0.43 



7 42 



1.43 



5 



11 



1.1 



August . . . 



10 49 



+ 1.21 



4 45 



—0.53 



6 04 



1.74 



4 



11 



1.3 



September . . 



10 56 



+ 1.10 



4 57 



—0.69 



5 59 



1.79 



— 



10 



— 



October . . . 



11 25 



+0.73 



5 17 



—0.49 



6 08 



1.22 



— 



10 



— 



November . . 



11 29 



+0.60 



6 28 



—0.40 



6 01 



1.00 



6 



— 



0.7 



December . . 



12 24 



+0.69 



6 45 



—0.41 



5 39 



1.10 



6 



— 



1.0 



Summer . . 



10 55 



+1.00 



4 45 



—0.48 



6 10 



1.48 









Winter . . . 



11 65 



+0.67 



6 00 



—0.39 



5 65 



1.06 









Year .... 



11 22 



+0.81 



5 18 



—0.40 



6 04 



1.21 









The diurnal range is greater about tlie time of tlie equinoxes than at any otlier 

 time, and in general less in winter and greater in summer. The afternoon minimum 

 disappears about the time of the equinoxes, and is best marked about the solstices ; 

 the early night minimum only disappears about the time of the winter solstice. 



Table VII. — Principal Epochs op Normal Dip. 



The morning epoch is computed to the nearest minute or two, the 



afternoon epoch is taken from the diagrams. 



1841— 1S45. 



Januaiy . 



February . 



March 



April 



May .... 



June .... 



July .... 



August 



September 



October 



November 



December 



Summer . 



Winter 



Year .... 



A. M. 



8''38"" 

 8 49 

 8 35 

 7 46 



6 52 



7 11 



6 55 



7 16 



7 37 



8 03 



8 10 



9 14 



7 22 



8 33 

 7 50 



Solar-Diurnal Variation of the Total Force. — The combination of the component 

 values of -— and -—- to form the corresponding values of the total force is ejected 



Y 



by the formula 



A^ 



, A r , ,„ AX 



the result being expressed in parts of the force. A -|- sign indicates an augmenta- 

 tion of the force, a — sign a diminution. 



' About 3| A. M. ; minimum not distinctly marked. 



