CONCEENED IN PEODUCING THE GEEATEE MAGNETIC DISTUEBANCES. 631 
Table IV. — Comparison in length of the Horizontal-force changes with those of the 
Vertical Force. 
Date. 
Horizontal-force change (vertical-force change = unity in each 
instance). 
1858. March 2— 3 
March 12—16 . 
March 27 — 29 . 
April 9 — 10 
June 23 — 24 .... 
July 5 — 6 
1859. February 9 — 10 . 
February 27 — 28 
May 19 — 21 .... 
June 8 — 9 
July 11 — 13 .... 
August 28 — September 7 . 
October 12 — 18 .. 
December 13 — 15 
I860. March 26 — 29 .. 
April 9 — 15 
July 4 — 6 
2*4, 
1- 9, 
2- 3, 
1- 9, 
2”3, 
2 - 1 
1-9, 
1- 9, 
2 - 0 , 
12% 
12 - 1 , 
2 * 0 , 
ri-8, 
2 - 1 . 
* U) 
2 - 0 , 
L2-0, 
2 - 0 , 
2-3, 
J 2-3, 
l2-2, 
J 2-1, 
1 1-8, 
2-1, 
r2-i, 
August 6 — 12 
1- 9, 
2 * 0 , 
2 - 0 , 
Actual measurements. 
2-1, 2*3, 2-0 
1-9, 2-1, 1*8, 1-9, 2'3, 2-0, 2-1 
1- 9, 2-0 
2 - 1 , 2*0 
2 - 1 , 2*0 
2 * 2 , 2*2 
2-1 
1 - 9 , 2 - 2 , 2*1 
2 - 0 , 2 - 0 , 2 - 2 , 2 - 2 , 2 - 0 , 2*0 
1- 9, 2*1, 1*9, 1-9, 2-0, 2*1 
2 * 1 , 2 - 1 , 1 - 9 , 2 - 0 , 2-2 
2 - 0 , 2 - 0 , 2 - 0 , 1 - 9 , 1 - 6 , 2-0 
2 * 2 , 2 * 2 , 2 " 2 , 2 * 2 , 2 * 0 , 2*2 
1 * 6 , 2 * 0 , 2 * 0 , 2 * 0 , 2 - 1 , 1 * 8 , 1*7 
1*9, 1*9, 2*1, 1*9, 2*2, 1*9, 1*7, 2*1 
2 * 1 , 2 * 0 , 2 * 1 , 2 * 0 , 1 * 9 , 2 * 0 , 2 * 2 , 2*0 
2 * 0 , 2*0 
1*9, 1*8, 2*2, 1*9, 2*3, 1*8, 2*0 .... 
1*9, 1*8 
1 * 9 , 2 * 0 , 1 * 9 , 1 * 6 , 1 * 8 , 1 * 9 , 1*6 .... 
2*0 
2*3, 2*0, 2*1, 1*9, 2*0, 1*8, 2*0 .... 
2*1 
1*9, 2*1, 2*0, 2*0, 2*2, 1*7, 2*3, 2*0 
2*0, 2*1, 1*9, 2*1, 1*9, 1*9, 2*2 .... 
1*9, 2*0, 2*1, 2*0, 2*1, 2*0, 1*9 .... 
2*0, 1*9, 2*2, 2*1, 1*9, 2*0, 1*9 .... 
2*2, 1*9, 2*1, 2*0, 2*0 
Mean. 
2*2 
2*0 
2*1 
2*0 
2*1 
2*1 
2*1 
2*0 
2*0 
2*0 
2*0 
2*0 
2*0 
2*0 
1*9 
2*0 
2*0 
2*0 
In this Table the actual measurements have been exhibited in order to afford an idea 
of the accuracy with which the proportion holds, without attempting to estimate the 
probable error. 
22. In endeavouring to frame a similar Table between the horizontal force and decli- 
nation, a curious fact presented itself. 
Although it is comparatively easy to find changes in the vertical force which are similar 
to corresponding changes in the horizontal force, yet it is much more difficult to find 
similar corresponding changes in the horizontal force and declination. Indeed, for many 
of the cases recorded in the above Table, the declination-change would not be similar to 
that of either force. It thus appears that, even in cases which do not indicate the action 
of a pure elementary disturbance, the horizontal-force change preserves an almost 
invariable relation to that of the vertical force*. 
23. The following would appear to be the explanation of this. 
Whatever be the nature of an elementary disturbing force, its effect upon the hori. 
* This proves, in addition to a physical fact, that these magnetographs are capable of recording with pre- 
cision the slightest change in either element of the earth’s force. 
MDCCCLXIl. 4 R 
