164 
MAGNETIC OBSERVATIONS. 
MAGNETIC DIP AT CAMBRIDGE. 
1840. 74° 21' 
1844. 14° 18' 
1849. 14° 24' 
DECLINATION. 
1840. 9° 18' W. 
1844. 9° 39' W. 
1852. 10° 08' W. 
1854. 10° 39' W. 
With much esteem, I remain, dear sir, yours truly, 
Lieut. A. W. Wiiipple, 
Topographical Engineers , Washington. 
W. C. BOND. 
The total intensity at Cambridge, May 4, 1842, was reported to be, by Sabine’s unit, 1.7982 ; 
which number is used as the standard of comparison in the following table. 
Supposing the weights that are used, and the magnetism of the needles, both to remain con¬ 
stant, the intensities of the earth’s magnetic force in different localities are inversely as the signs 
of the angles of deflection at those places. 
By the observations made at Cambridge, in 1850 and 1854, it is found that the magnetism of 
the needles suffered a change between those dates, and a correction has been made upon the 
principle that the diminution in intensity progressed at a uniform rate. 
