EARLIEST ISOCLINICS AND FORCE OBSERVATIONS. 399 
publication has come to light. Lines of equal magnetic 
declination are hence frequently called Halleyan lines. 
Halley’s method, though in a certain sense artificial, is yet 
applicable for many purposes, and has been frequently ap¬ 
plied, not only to magnetic, but to many other phenomena. 
The representation of the distribution of the magnetic dip 
or inclination by the Halleyan method— i. e., by isoclinics— 
has hitherto been credited to Wilcke, who issued his isoclinic 
chart in 1768.* 
Isoclinics have, therefore, also received the name of 
Wilckean lines.t In the following it will be shown that 
Wilcke cannot properly be given priority in originating iso¬ 
clinics ; hence the term “ Wilckean ” applied by Hansteen is 
not justifiable and this honor must be given to Whiston. 
By studying the Halleyan lines Whiston found that from 
their irregularity and “ the Quickness of the Mutations of 
those Lines and their different Position in the rest of the 
World” they could not be satisfactorily used for determin¬ 
ing longitude; hence he was led to consider “ Lines of equal 
Dip,” thinking these would serve his purpose better (see p. 
xxvii). To this end he collected all observations of dip made 
up to his time, and by means of them drew upon a Moly- 
neux terrestrial globe the lines of equal dip as far as was 
then possible. He mentions this on page 53, but unfortu¬ 
nately neither gives the collected observations (which were 
those made by Hudson, Noel, Pound, Cunningham, Feuillee, 
and Windham), nor does he reproduce these isoclinics in 
his book. Further proof of his right to be regarded as the 
* Forsok tel en magnetisk inclinations-charta. Vetensk. Akad. Handl., 
Stockholm, 1768, or German translation in K. Schwed. Akad. Abth. 
xxx, p. 209, Leipzig, 1768. Wilcke’s article makes such mention of some 
of the contents of Whiston’s book that it seems to me probable that he 
was familiar with Whiston’s work and got his idea of isoclinics from it. 
While he nowhere mentions Whiston’s isoclinics, he also nowhere lays 
claim to originating lines of equal dip. Still to Wilcke belongs the credit 
of having first published a general isoclinic chart. Hansteen’s isoclinic 
chart for 1700 is chieily made up from Wilcke’s. 
f Called so by Hansteen in his “Magnetismus der Erde,” Christiania, 
1819. Hansteen evidently had not seen Whiston’s book. 
