234 ABSTRACTS OF THE MAKERSTOUN OBSERVATIONS, 1843. 
The mean at 18 in January is rendered comparable with the means at the other hours thus; the daily 
means from January 9-14, being the means of 8 daily observations, were corrected by + 0°15 sc. div., obtained 
as for Table VIII., in order to reduce them to the mean of 9 daily observations, then,— 
Se. Div. 
Mean of Bifilar readings, January 9-31, = 537-36 
Be andocecRenate c.¢ fesetoeteiereers nd OO ls eee OO ees 
Difference, = 0:22 
The mean for 18" deduced from the observations January 16-31, was thuxefore corrected by + 0-22, in 
order to reduce it to the mean from January 9 to 31, as for the other hours. 
TABLE XI.—Diurnal Variations of the Horizontal Component of Magnetic Force in 1843, the whole 
Horizontal Component being Unity. 
Periods. 
Months. 
January 
February 
March 
April 
May 
June 
July 
August 
September 
October 
November 
December 
Quarters. 
Spring 
Summer 
Autumn 
Winter 
Half-Years. 
Winter 
Summer 
The Year 
SECULAR CHANGE OF THE HORIZONTAL COMPONENT OF MAGNETIC FORCE. 
The mean change of the horizontal component from 1842 to 1843 has been determined in the following 
manner. 
By the means for the year 1844, it has been found that the mean of the observations at 22 and 04, is 
greater than the mean at 234 by 0:000162, and that the mean of the observations at 4" and 6" is greater than 
the mean at 5" by 0:000027, whence from the last line of Table XI.,— 
Mean of 22 and 0h = +0°000092, corrected to mean for 23" = —0:000070 
Mean of 44 and 6 = +0:001573, corrected to mean for 55 = +0:001546 
