OFTHETOTALFORCE. ^ 



"-^-^_ 31 



The amount and range are expressed in parts of the force. The time of the~ 

 principal maximum and minimum is computed to the nearest one or two minutes. 

 The diurnal range is greatest during summer, and least during winter. The small 

 secondary inflexion obtains only during the winter months ; its range is only about 

 the seventieth part of the larger annual range. 



Table XI contains the principal morning and afternoon epoch of the normal 

 value of the total force. 



The morning epoch is taken from the diagrams ; the afternoon epoch is computed. 



Table XI. — Epochs of Normal Total Force. 



1841— 1S4S. 



A. M. 



p. M. 



January 

 February 

 March. 

 April . 

 May . 

 June . 

 July . 

 August 

 September 

 October 

 November 

 December 





9" 



7 



8J- 



5i 



H 



H 



5i 



7i 



8 

 not reached 



7f 

 not reached 



4ho2m 



5 16 

 4 51 



6 15 

 6 22 

 6 07 

 6 13 

 6 03 

 6 35 

 4 18 

 4 48 

 3 42 



Summer ...... 



Winter ...... 



Year ....... 



6.5 

 7.4 

 6.6 



6 15 



4 35 



5 38 



Amiiial Inequality of the Dip and Total Force. — The differences of the monthly 

 normals, expressed in parts of the horizontal force, have been taken from Table XII 

 of Part V. The mean of the October and December values, however, has been sub- 

 stituted for the November value, which produced a correction of +0.00004 to each 

 monthly value to balance the annual sum. The approximate values of the aimual 

 inequality of the vertical force are extracted from Part VIII, after converting the 

 scale divisions into parts of the vertical force. 



Table XII contains the values of the annual inequality for the horizontal and 

 vertical components, and, by combination, that of the dip and total force. 



Table XII. 





aX 



aY 



Afl 



A<f 





X 



Y 





* 



January 



—0.00045 



—0.00003 



+0.'4 



—0.00008 



February 









—0.00015 



—0.00053 



—0.4 



—0.00050 



March . 









+0.00023 



0.00000 



—0.2 



+0.00002 



April 









—0.00003 



—0.00003 



0.0 



—0.00003 



May 









—0.00039 



+0.00036 ' 



0.0 



+0.00036 



June 









- -0.00006 



+0.00053 



+0.5 



-f- 0.00049 



July . 









- -0.00043 



-f-0.00017 



—0.3 



+0.00019 



August . 









- -0.00005 



+0.00020 



-f-0.2 



+0.00019 



September 









—0.00020 



—0.00020 



0.0 



—0.00020 



October . 









—0.00013 



—0.00013 



0.0 



—0.00013 



November 









—0.00012 



—0.00040 



—0.3 



—0.00037 



December 









—0.00011 



—0.00003 



+0.1 



—0.00004 



