310 F. E.. Nipher—Magnetic Survey of Missourr. 
Art. XXXVII.—The Magnetic Survey of Missouri ; by FRANCIS 
EK. NIPHER. 
Ix the summer of 1878, the writer began a magnetic survey 
of the State of Missouri. The work of the first summer was 
confined to the northeastern part of the State, and no points of 
interest were brought out. During the summer of 1879 the 
work was extended over the western half of the State, and it 
was made apparent that diversity of surface exerted a much 
more important influence than had been suspected. The lines 
of equal declination were found to bend very sharply upon en- 
tering the large valleys, and the needle showed a tendency to 
set at right angles to the valleys. This tendency seemed to 
be greatest when the general direction of the valley made an 
angle of 45° with the normal position of the needle, or roughly, 
when the valley runs northeast and southwest or northwest 
and southeast. This tendency seemed to be inappreciable, 
when the valleys ran north and south or east and west. In 
the report of 1878,* it was suggested that this might result 
from the bending of the stream lines of the earth-current sheet, 
due to the greater conducting power of the moist valleys. In 
order to settle this point, further examination is necessary, and 
it is proposed to make determinations of earth currents ata 
number of properly selected stations. 
During the summer of 1880 the work extended over the 
stations. In order to bring out the effect of contour, a relief 
map of the State was constructed in wax, and was finally 
reproduced in plaster. In this work use was made of the pro- 
files of all the railroads in the State, together with a list of 
over 300 elevations in the State collected by Henry Gannett. 
The isogonic lines which were first drawn upon an ordinary 
map in the usual manner to represent the observations thus far 
made, were then copied upon the relief map. ‘ 
In doing this, it became apparent at once, that the 45 sta- 
tions were wholly inadequate, and that the isogonic lines thus 
drawn are probably deserving of about the same weight that a 
topographical map would deserve if constructed from eleva- 
tions at these stations. 
e wood-cut is made after an artotype which will accom: 
pany the third annual report in vol. iv, no. 2, of the Transac- 
* Transactions of the St. Louis Academy of Science, vol. iv, No. 1, P- 143. 
