APPENDIX F. 
MAGNETIC INTENSITY. 
The following extracts from a letter received from Professor W. C. Bond, Director of Harvard 
College Observatory, contains important data for the determination of our magnetic results : 
Harvard College Observatory, 
Cambridge , January 2, 1855. 
My Dear Sir :********** 
The total intensity at Cambridge, in 1842, was 1.777, and the change from year to year is 
probably very small. 
The details of the observations made with your instrument at Cambridge, in December and 
January, 1844-5, by Colonel Graham and myself, are in the possession of the former. I find 
only the following memoranda: 
MAGNETIC RESULTS. 
December 
30, 
1844.—Temperature, 
39°.5 ; 
needle, 
B; weight, 
o 
CO 
grs. ; 
intensity, 1.2960 
CC 
CC 
39°.5 
C C 
B “ 
3.5 
“ 1.2960 
cc 
CC 
39°.5 
CC 
A “ 
3.0 
“ 1.2900 
cc 
cc 
39°.5 
cc 
A “ 
3.5 
“ 1.2890 
Mean by both deflectors. 
. 1.3014 
January 
2, 
1845.—Temperature, 
36° ; 
needle, 
A ; weight, 3.5 
grs. ; 
intensity, 1.2870 
CC 
CC 
36° 
CC 
C “ 
2.5 
“ 1.2940 
cc 
CC 
36° 
cc 
C “ 
3.0 
“ 1.2980 
January 
o 
o, 
1845. “ 
19° 
cc 
C “ 
2.5 
“ 1.3010 
c c 
CC 
19° 
cc 
C “ 
3.0 
“ 1.3020 
cc 
cc 
26° 
cc 
C “ 
3.5 
“ 1.3120 
The foregoing results are given uncorrected for temperature changes. 
Mr. Fox obtained at Falmouth, England, in September, 1844, with the same needles, at 
temperature of 60° Fahrenheit—Fox, 1.000 ; = 1.374 Sabine. 
It will be necessary, in case of differences occurring in the determination of the intensity at 
different years, between 1844 and 1854, to suppose a uniform change in the needles. 
To convert Mr. Fox’s unit to Colonel Sabine’s, multiply the former by 1.374. Thus, total 
intensity at Cambridge : Fox, 1.293 x 1.374 — 1.777 Sabine. 
