L. A. Bauer— Variation of Terrestrial Magnetism. 319 
It will be observed that both poles have undoubtedly been 
moving westwardly during the interval from 1780 to 1885. It 
would appear, moreover, as though they are not moving along 
the equator but along a line inclined to it, from the northern 
to the southern side. How much reliance is to be put upon 
this latter result I cannot, at present, say. 
Average Annual Motion 1780-1885, 
In Latitude. In Longitude. 
Secondary Mag’c N. P._.-- 0°092 0°146 
ik op Sit eee ane 0°146 0°242 
Ia ee ees. nic 07119 0°194 
These figures would appear to indicate that the two poles 
are moving westwardly and southwardly at different rates. 
Whether this is really the case must be the subject of a more 
detailed examination. It is sufficient to know, at this stage of 
our inquiry, the general direction and the average rate of 
motion. 
Since the intersections of the agonic lines*—the lines mark- 
ing out the places where the magnetic declination is zero— 
with the equator fall so nearly together with the secondary 
magnetic poles, it may be interesting to see how the agonic 
lines have been moving along the equator for the last 34 cen- 
turies. This opportunity is furnished by the table on the fol- 
lowing page. 
In the third and sixth columns are given the positions as 
obtained from charts giving the lines of equal magnetic decli- 
nation. Thefourth and seventh columns contain the computed 
quantities supposing the motion to have been linear. The 
formula, obtained by a least square adjustment of the observa- 
tions properly weighted, is for the west agonic: 
; A, = +50°°6 +0°°228 (€—1850) 
for the east agonic, 
A,=—83°-0+0°139 (¢—1850) 
A being the longitude and ¢ the date to which 2 refers. 
By casting the eye over the differences between the observed 
and computed quantities, it will be noticed that the accord is 
satisfactory. Plotting the observed quantities, it will readily 
be seen that the motion for 350 years has been nearly linear 
for both agonics. A very slight curvature is noticeable in the 
secular motion of the west agonic. In the case of the east 
agonic, the errors of observation (or fluctuations) are so large 
as to mask any slight curvature that might be present. 
We have before us a most interesting result. For 33 cen- 
turies the lines of no declination have been moving apparently 
* Shown on the diagrams by the broken lines. 
