OF THE EARTH’S MAGNETIC FORCE AT BOMBAY. 
83 
Table XIV. corresponds with Table XIII., except that the mean monthly readings 
deduced from all the hourly observations of the large Horizontal-force Magnetometer 
are given instead of those which correspond to the times of the absolute observations 
only ; and the values of Horizontal Force are corrected for the difference between the 
two sets of mean monthly readings, so as to represent the values of the mean Horizontal 
Force for the several months. The scale-coefficient adopted for the large Horizontal- 
force Magnetometer is '001488, or ^X=-|- , 012 for an increase of unity in the 
scale-reading. 
Table XIV. 
Monthly Mean Absolute Horizontal Force 
reduced to Monthly Mean Headings of 
Month. large Horizontal-force Magnetometer. 
Monthly Mean Heading of large Horizontal- 
force Magnetometer, 
corrected to Temperature 82° 0. 
1S67. 
1868. 1 1869. 
1870. 1871. 1872. 
1873. 
1867. 
1868. 
1869. 
1870. 
1871. 
1872. 
1873. I 
January 
8-0556 8-0584 
8-0581 8-0674 8-0668 
8-0725 
2417 
2403 
2415 
24-79 
25-40 
February 
8-0491 8-0680 
8-0610 8 0681 8 0643 
84)727 
244)7 
2400 
24-22 
24-69 
2512 
9 77 
March ' 
80551 8 0629 
8-0654 8-0673 8-0718 
84)757 
2410 
2407 
24-39 
24-80 
25 13 
9-89 
April ; 
8 0606 8-0552 
8-0627 8-0628 8-0770 
8-0802 
23-88 
23-81 
24-32 
24-39 
25-29 
10-19 
May 1 
8-0578 8-0524 
8 0611 8 0658 8 0793 
84)816 

24 02 
23-90 
2470 
2510 
25 63 
10-40 
June 1 
8-0602) 8-0592 
8-0708) 8-0705 84)791 
8-0809 

23-99 
244)8 
24-70 
25 4)7 
25 35 
1034 
July I 8 0480 
8 0617 8-0613 
8-0702 8 0735 84)746' 
8 0833 
23-41 
2379 
2416 
2476 
24-84 
25 13 
10 46 
August i 8-0593, 
8-0444 8-0580 
8-0672 8 0713 8 0715 
8-0822 
23-25 
23-77 
23 81 
2435 
24 63 
24-82 
10 51 
I September I 8-0473 
8-0568 8-0619 
8-0642 8-0718 84)744 
84)791 
23-08 
23-47 
23-55 
23-87 
24-68 
24-86 
10-52 
J October 8-0547 
8-0573 8 0576 
84)604 8-0752 8-0691 
8-0809 
2314 
2357 
23-87 
23-87 
2472 
24-66 
10-62 
I November 8-0487, 
8 0612 8-0671 
8-0630 8-0657 84)707 
8-0793 
23-79 
2412 
24-32 
24-31 
24-54 
25-13 
10-95 
I December 8-0564 
805541 8-0582 
8 0685 8-0662 8 0752 
8-0814 
2403 
2414 
24-38 
24-74 
2519 
25-02 
11-32 
During part of the month of January 1873 the large Horizontal-force Magnetometer 
was under readjustment, and the correction had to be deduced partly from its readings 
before readjustment, and partly from readings of the Horizontal-force Magnetograph 
taken at the time of the absolute observations. From and after February 1873 the 
monthly mean readings of the large Horizontal-force Magnetometer were obtained by 
subtracting from the monthly mean for the five civil hours 6, 10, 14, 16, and 22, the 
excess, expressed in scale-readings, of the mean force at those hours in the years 1846 
to 1872 above the mean force for the twenty-four hours in the same years. 
16. Annual Mean Values and Secular Change . — The mean value of the Horizontal 
Force for the epoch October 1, 1870, is 8-0718 or 8-0658, according as the observations 
are uncorrected or corrected to the mean of the several months. 
The following Table shows the mean values, uncorrected and corrected, of the Hori- 
zontal Force in each year or half-year from 1867 to 1873, and the corresponding annual 
increments of Horizontal Force : — 
x 
MDCCCLXXVI. 
