30 



SOLAR DIURNAL VARIATION. 



Diagram (II) exhibits tlic diurnal variation of the total force for summer, winter, 

 and the whole year. 



(H). Solar-Diurnal Variation of the Total Force between 1841 and 1845. 





- 



1 1 1 1 1 



1 



1 1 1 



1 1 1 1 1 



1 



1 1 1 1 



- 





- 







/, 



^ ^ 







. 





- 





^^ 



#^ 



\ '■'■ \ 







- 



Winter 

 Year 



- 



'-f 



A — 





'\ 



v\ 







Summer 



- 



1 1 1 1 1 



1 



1111 



11111 



I 



1 1 I 1 



- 



Winter 

 Year 



+.000500 

 400 

 300 

 200 

 100 

 .000000 

 100 

 200 

 300 

 Summer ^qq 



—.000500 



C 2 4 6 8 10 g 14 16 18 20 22 24i> 

 Philadelphia mean time. 



The diurnal curve is single crested in summer, and on the average during the 

 year, but in winter it assumes a double crested form, having a secondary maximum 

 between 2 and 3 A. M., and a secondary minimum about 6 A. M. The principal 

 maximum in summer occurs about 2 P. M., and in winter about one and a half hours 

 earlier; the principal minimum in summer occurs about 10 P.M., and in winter 

 about two hours earlier. The summer range is about 0.0009, and the winter range 

 about 0.0004 parts of the force. 



The following table contains the computed times of the principal maximum and 

 minimum, together with the elapsed time, amount and range of variation in force 

 for each month and season, also the time and amomit of range of early morning 

 secondary wave as taken from the diagrams. 



Table'X. — Total Force. 



1841— 184S. 



Principal 



Amount 

 0.000 



Principal 



Amount 

 0.000 



EIap.sed 

 time. 



A.M.&P.M. 

 ranf?e 

 0.00 



A. M. 

 secondary 



A. M. 

 secondary 



Secondary 

 range 

 .000 



.January 



February . 



March 



April .... 



May .... 



Juue .... 



July .... 



August 



September . 



October 



November . 



December . 



13" 02-° 

 14 00 



13 07 



14 46 

 14 46 



13 41 



14 04 

 13 23 

 13 64 



11 00 



12 50 

 12 33 



+225 

 +320 

 +237 

 +299 

 +422 

 +521 

 4-560 

 +618 

 +498 

 +190 

 +199 

 +193 



19" 38'" 

 20 19 



20 45 



21 54 



22 57 



22 32 



23 05 

 23 42 

 23 33 

 20 30 

 20 02 

 19 29 



—283 

 —331 

 —204 

 —342 

 —404 

 —486 

 —522 

 -447 

 —360 

 —266 

 —118 

 —231 



6" 36" 



6 19 



7 38 



7 08 



8 11 



8 51 



9 01 

 10 19 



9 39 

 9 30 

 7 12 

 6 56 



0508 

 0651 

 0441 

 0641 

 0826 

 1007 

 1082 

 1065 

 0858 

 0456 

 0317 

 0424 



3" 

 1 

 4 



2.V 



oi 



8 



7i" 



4 



7 



5 

 4i 



7" 



15 



07 

 04 



04 

 04 

 05 



Summer 

 Winter 

 Year .... 



14 02 



12 58 



13 36 



+485 

 +220 

 +344 



22 38 



20 11 



21 28 



—421 

 -229 

 —296 



8 36 

 7 13 

 7 52 



0906 

 0449 

 0640 



2i 



6 



04 



