THE SECULAR CHANGE IN THE DIRECTION OF 
THE TERRESTRIAL MAGNETIC FIELD 
AT THE EARTH’S SURFACE. 
BY 
G. W. Littlehales. 
The observations and results that I am about to present 
relate to the directional elements of the earth’s magnetism 
at many important stations in remote parts of the world, dur¬ 
ing the seventeenth, eighteenth, and nineteenth centuries. 
In view of the desirability of preserving the collection of ob¬ 
servations upon which the present results depend, and of 
the great variety and general inaccessibility of the works of 
reference from which they are drawn, the observed values 
of both declination and inclination are stated in full, with 
the names of the observers and the sources of information. 
Considerable data are thus made available for other workers 
in the same field, and the books are referred to in which in¬ 
formation may be found that may prove valuable to those 
engaged in kindred lines of investigation. 
My first investigations were confined to the magnetic decli¬ 
nation, or the variation of the compass, with a view of form¬ 
ing empirical equations, by the method of least squares, for 
each station at which the extent of the series of observations 
is sufficient for the purpose, and from them predicting values 
of the declination for use in assigning the best values of the 
direction of the magnetic meridian on the nautical charts 
constructed by the Navy Department for the navigation of 
the navy and the mercantile marine, and also from their 
first differentials the yearly rates of change of direction of 
the compass needle at any time not greatly beyond the limits 
40—Bull. Phil. Soc., Wash., Vol. 13. (269) 
