EARLIEST ISOCLINICS AND FORCE OBSERVATIONS. 409 
To Whiston, then, is due the credit for the following three 
achievements: 
1. He drew the first isoclinics and invented the name 
“ magnetic parallels ” for them. 
2. He made, in 1720, the first relative intensity observa¬ 
tions. 
3. He invented the vibration method for determining 
the dip. 
Friedenau, bei Berlin, August 4, 1894. 
Note. 
The following extracts kindly communicated to me since 
writing the above paper are deemed of sufficient importance 
in connection with this paper to warrant their insertion here. 
They are extracted from a book entitled 
“ Memoirs of the Life and Writings of Mr. William Whiston, containing 
memoirs of several of his friends also.” Written by himself. London, 
1749. 
Volume I, page 292: About this Time, 1720, I printed and gave away, 
to some of my mathematical Friends, a few Copies of a small imperfect 
Essay on a Discovery of the Longitude by the Dipping Needle. But because 
I afterward made many and great Improvements in that Matter, and pub¬ 
lished the whole in a much larger Treatise, a Year or two afterward, 
upon that Subject; of which presently; I drop this first Essay intirely. 
Volume I, pages 296- 7: In the Year 1721, I published The Longitude 
and Latitude found by the Lnclinatory or Dipping Needle ; Wherein the laws 
of Magnetism are also discovered. To which is prefixed an Historical 
Preface ; and to which is subjoined Mr. Robert Norman’s New Attractive, 
or Account of the first Invention of the Dipping Needle, price 2s. 6d. 
N. B.—After the Publication of this Treatise, I found so much Encour¬ 
agement from many Benefactors, that I was enabled to procure some 
New Observations of the Angle of Dip in several Parts of the World, in 
order to perfect this Discovery; the Substance of w r hich is printed at the 
End of my Calculation of Eclipses, without Parallaxes ; of which presently. 
Which upon the whole cost me a very great deal of Pains, to contrive 
the Instruments and hang them in Ships so as to take the Dip, with an 
Exactness sufficient for my Purpose ; but found the Power of Magnetism 
so very weak, and the Concussion of a Ship so very troublesome, that I 
had little Hopes of succeeding. And when I knew of Mr. George Gra¬ 
ham’s new Discovery of an Horary uncertain Inequality , as I may call it, 
