398 
BAUER. 
As appears from the title of Whiston’s book, his chief ob¬ 
ject was to set forth a method of determining the longitude 
and latitude by means of the magnetic dip needle. The 
problem of determining geographical positions (chiefly longi¬ 
tudes) by means of the magnetic declination is an old one 
and began with Columbus.* Like the problem of perpetual 
motion, it was revived and studied from time to time, even 
down to the beginning of the nineteenth century. But 
Whiston (1719-’20) proposed to use the magnetic dip for this 
purpose. He dedicates his attempt to the commissioners 
appointed by act of Parliament for the discovery of the longi¬ 
tude, and among these commissioners are found the names 
of Sir Isaac Newton, then president of the Loyal Society, 
and Dr. Edmund Halley, the Astronomer Royal. 
Whiston was led to his method by examining Halley’s 
isogonic chart of 1700.f As is well known, this is generally 
conceded to be the earliest published chart of the lines of 
equal magnetic declination— i. e ., those lines connecting all 
the places on the earth’s surface at which the magnetic 
needle makes the same angle with the true north-and-south 
line. By reason of this chart, Halley is usually credited 
with originating the general method of representing the dis¬ 
tribution of any phenomenon on the earth’s surface by lines 
drawn through all those places where the phenomenon in 
question has the same numerical value. It appears that 
others before Halley had conceived this idea, but, though 
they may have carried it out privately, thus far no earlier 
* Columbus has not been fully credited in America with the discovery 
of the magnetic declination. In Europe, through the researches of Ber- 
telli, Peschel, and others, he long ago received this distinction. For 
several years the writer has been searching for everything pertaining to 
early magnetic observations. Although he has had access to many rare 
old works, he has thus far found nothing indicating a knowledge of or a 
recognition of the magnetic declination on charts before Columbus’ time. 
f Published separately in London, 1701, and reproduced photo-litho- 
graphically in Greenwich Observations, 1869; now about to be republished 
in “Neudrucke von Schriften und Karten uber Meteorologie und Erd- 
magnetismus.” Herausgegeben von Prof. Dr. G. Hellmann. Berlin, A. 
Ascher & Co. 
