The Barre daily times. (Barre, Vt.) 1897-1959, 1918-01-31
MAGNETIC TABLES.
Booklet Contains Results Of Observations
in United States.

in United States.
Terrestrial Magnetism, United States
Magnetic Tables and Charts for 1919 II
the title Of publication prepared by
Daniel l.. Hazard, chief of the division
Of terrestrial magnetism of the coast
and geodetic survey, department of com
merce, and made public to-day.
This publication contains the results
of observations made in the prosecution
of the magnetic survey of the United
States TO the end Of 1915, with CORE
spending values for Jan. |. 1918, the col
| lcctcd results of observations at repeat
stations used in determining the change
OF the magnetic elements with lapse Of
time, the secular change tables used in
reducing the observed values to the com.
mon epoch Jan. l, 1915, and five magnetic
charts showing graphically the distribu-
tion of the magnetic declination, dip,
horizontal intensity, vertical intensity
and total intensity in the United States
on Jan. |, 1915. On the declination, dip,
and horizontal intensity charts there are
also lines showing the annual change of
those elements in 1915. In addition TO
the results obtained by the coast and
geodetic survey the collection includes
all available results of high grade from
observations made by Others in the
United States and adjacent land and
water areas, including those at stations
in Mexico, Central and South America
used in the construction of the isogonic
chart of the West Indies published in
1914.
The first edition of the declination
chart, with accompanying secular change
tables, was published in 1915 as special
publication No. 80.
The plan for the magnetic survey of
the United States as laid down in 1890
provided for first general survey, with
stations 80 TO 40 miles apart, to be fol-
lowed by a more detailed investigation of
magnetically disturbed areas. Follow
ing this general plan, the distribution of
stations has been based largely upon the
county subdivision of states, the idea be-
ing to have at least one magnetic station
in each county, so that the necessary
data may be available for the use of
surveyors in testing their com
passes Observations have now been made |
at all but a few OF the county seats
and a number of areas of marked local
have been examined in de-
tail.
In view of the necessarily long period
occupied in the execution of the survey,
It has been deemed desirable to publish
he accumulated results in TIE form OF
magnetic tables and magnetic charts at
various times before its completion. The
asst complete publication prior to this
me was for 1905 and contained the re-
suits of observations to the end of June,
1907. Since that publication was pre-
Jared, the number of available results
las increased about so per cent. In the
construction of the 1918 charts there
rave been used about $500 deelination
esults, $500 dip results and 500 hori-
ontal intensity results. The density of
of the stations corresponds
n a general way with the density of
population, being greatest in the eastern
,art of the country and least in the
Rocky mountain section.
The graphical method was used in the
obstruction of the charts. In the case of
for instance, the reduced
alues were plotted in a large base map
I the United States, and the lines of N
quail declination were drawn free hand, |
or intervals of one degree, to conform
18th the plotted values, the aim being to
rake minimum the average difference
etween the plotted values and the cor
values obtained by interpolat
~ between the lines.
After the lines of equal declination,
ip, and horizontal intensity had been
rawn, values of these three elements
ere scaled off for each degree of lati
ide and longitude for the whole area
,vered by the lines. Corresponding val
IS of vertical intensity and total in
nsity were then computed, and these -
values were used in the con-
ruction of the vertical intensity and to-
4 intensity charts.
Copies of Terrestrial Magnetism,
nited States Magnetic Tables and
larts for 1915, Special Publication No.
!" can be purchased at a nominal cost
IS cents per copy from the superin-
ndent of documents, government print
G Office, Washington, d. c.
i