PROGRESS IN SCIENCE IN TERRESTRIAL MAGNETISM. 331 
variation-chart and nearly two centuries after the discovery 
of the dip, Wilcke issued the earliest world-chart in which 
the first crude attempt was made to represent the distribu¬ 
tion of the terrestrial magnetic inclination, in a manner 
similar to that employed by Halley in setting forth and de¬ 
picting the features of the magnetic declination, although 
Whiston, a professor of mathematics in the University of 
Cambridge, published a work in 1721 giving an account of 
investigations which led him to collect together all the avail¬ 
able observations of dip and by means of them to draw upon 
a Molyneux terrestrial globe the lines of equal dip as far 
as was then possible. Whiston’s work contains small maps 
showing the lines of equal dip for southern England and 
northern France, but neither the collected observations for 
extended parts of the world nor the isoclinics, which are 
described as having been drawn upon the globe, are included 
in the book. 
In an essay, entitled “Magnetismus der Erde,” composed 
to meet a prize-question propounded in 1811 by the Royal 
Society of Science at Copenhagen, Hansteen took occasion 
to collect, in addition to those observations that had been 
brought together by his predecessors, the observations of 
magnetic declination and inclination which had been pre¬ 
viously scattered in books of voyages and travels and formed 
from them maps of the lines of equal declination corre¬ 
sponding to successive epochs from the year 1600 to the year 
1800, and also similar maps of the lines of equal magnetic 
inclination; and between the years 1847 and 1875, in a 
series of fourteen communications to the Royal Society of 
England, entitled Contributions to Terrestial Magnetism, 
Sabine collected and discussed the observations that were 
made after Hansteen’s essay, and framed a series of charts 
of the lines of equal magnetic declination, inclination, and 
intensity covering every part of the world, and related to the 
epoch 1840. 
Perhaps a much closer approach than was made by Sabine 
to the true distribution of the elements of terrestrial mag- 
