INTRODUCTION. lin 
500 micrometer divisions are added to the readings of the balance magneto- 
meter in September 1841; 400 in October and November 1841 ; and 700 in all the 
other months. 
81. In the term-day and extra observations of the bifilar and balance magneto- 
meters, the corrections for temperature are interpolated for the observations in the 
periods between the thermometer readings. 
82. The meteorological observations are made in the period from 2” before till 
7™ after the minute of declination observation. 
83. In forming the abstract of the observations, the sums were taken, acciden- 
tally, according to the astronomical reckoning. 
84. With the exception of Tables VIII. and XV., the other tables of abstracts 
for the bifilar and balance magnetometer are corrected by the quantities given. 
(No. 51.) 
85. Owing to the fewness of the daily observations, the results are to some 
extent limited. The remarks on the tables have been confined to pointing out their 
more prominent features, 
86. When the observations for 1844 and 1845, which are made hourly, are 
reduced, factors may be obtained generally for the approximate conversion of the 
monthly means of four observations to the monthly means from the twenty-four 
observations. 
87. It should be remembered, in considering the tables of abstracts, that the 
means for July 1841, are from only 11 days, and for January 1842 from 15 days. 
88. On account of adjustments at different periods, several months of the ob- 
servations of the Force Magnetometers are not comparable with each other. These 
circumstances are given in the preceding pages; and in the tables of abstracts, the 
means which are not comparable with each other are separated by lines. 
89. All the computations have been made by myself, or with the aid of my 
present assistants, Messrs WELsH and Hoae, and each computation has been per- 
formed twice by the same or by different individuals. 
JOHN A. BROUN. 
MAG. AND MET. OBS. VOL. I. 0 
