XU The I N T R 0 D U C T I 0 N. 
Needle's , becaufe there they found no fertftble Variation ; and yet, in 1691, a very curious Obferva- 
tion being made there, the Needle was found to vary 1 1° Weft, At the Iflaod of St. Helena , in the 
Year 1600, the Variation was found 8° to the Eaft, which gradually declined to the Year 1667, when 
Dr. Halley himfelf obferved it there, and found the Eaft Variation no more than 40' ; and in 1692, 
it varied 1° Weft. 
Having thus given the Reader as clear and hiftorical sn Account of this Matter as we could, we fhal! 
next give him the fame Gentleman’s Reafonings thereupon in his own Words, becaufe it is impoffible 
to fay any Thing better, or more agreeable to Truth, than what he has delivered upon the Subject, as 
there is very great Reafon to doubt whether we (hall foon fee a more fatisfadory Theory raifed for 
the Service of Mankind, than that which this able and ingenious Perfon has given us. After there- 
fore laying down at large thefe feveral Obfervations, and many more which we have omitted, as tend- 
ing only to prove what we apprehend is Efficiently proved by the Obfervations already fet down, and 
the fubfequent Experience we have had of the fame Thing; he proceeds thus : 
££ Thefe Phenomena being well underftood, and duly confide.ed, fufficiently evince, that the whole 
cc magnetical Syftem is by one, or perhaps more Motions, tranflated whither Eaft wards or Weftwards, I 
££ fhall foon difcufs, that this moving Thing is very great, as extending its Effects from Pole to Pole, 
** and that the Motion thereof is not -per jaltvm , but a gr.dual and regular Motion, 
44 Now, coniidering the Structure of our terraqueous Globe, it cannot be well fuppofed, that a very 
s; great Part thereof can move within it, without notably changing its Centre of Gravity, and the Equi- 
44 librium of its Parts, which would produce very wonderful Effeds in changing the Axis of diurnal Rota- 
44 tioo, and occsfion ftrange Alterations in the Seas Surface, by Inundations and Receffes thereof, fuch 
as Hiftorv never yet mentioned; befides, the folid Parts of the Earth are not to be granted permeable 
£c by anv other than fluid Subftances, of which we know none that are any Way magnetical; fo that 
“ the only Way to render this Motion intelligible, and pofiible, is to fuppofe it to turn about the Centre 
£C of the Earth. And there is yet required, that this moving internal Subftance be loofe, and detached 
“ from the external Parts of the Earth wherein we live; for otherwife; were it fixed thereto, the whole 
<£ mull neceffarily move together. 
“ So then, thefe external Parts of the Globe will be reckoned as the Shell, and the internal Nucleus, or 
€£ inner Globe, included within ours with a fluid Medium between, which, having the common Co- 
<c centre and Axis of diurnal Rotation, may turn about with our Earth, each twenty- four Hours only, 
<c the outer Sphere having its turbinating Motion, fome final! Matter, either fwifter or flower, than the 
<c internal Ball, and every Minute’s Difference in Length of Time, and in many Repetitions, will become 
<£ ienftble; the internal Parts will by Degrees recede from the external, and not keeping Pace with one 
“ another, will appear gradually to move either Eaft ward or Weftward, by the Difference of their 
cf Motions. 
« Now, fuppofing fuch an internal Sphere to have fuch a Motion, we fhall folve the two great DifB- 
<c cullies we encountered in my former Hypothefis ; for if this exernal Shell of Earth be a Magnet, 
<c having its Poles at a Diftance from the Poles of the diurnal Rotation, and if the internal Nucleus be 
“ likewife a Magnet, having its Poles in two other Places, diftant alfo from the Axis, and thefe latter, 
by a gradual and flow Motion, change their Place in refped of the external, we may give a reafona- 
££ hie Account of the four magnetical Poles, I prefume to have demonftrated before, as likewife the 
££ Cha nges of the Needles Variations, which till now have been unattempted. 
“ The Period of this Motion being wonderfully great, and there being hardly an hundred Years fince 
« thefe Variations have been duly obferved, it will be very hard to bring this Hypothefis to a Calculus, 
<« especially, fince tho’ the Variation do decreafe and increafe regularly, in the fame Place ; yet in dif- 
« ferent Places, and at no great Diftance, there are found fuch cafual Changes thereof, as can no Ways 
<< he accounted for by a regular Hypothefis, as depending on the unequal and irregular Diftribution of 
44 the magnetical Matter, within the Subftance, within the external Shell, or Coat of the Earth, which 
« Defed the Needle fupplies from the Petition it would acquire from the Effed of the general Magnetifm 
« of the whole. Of this, the Variations at London and Paris , give a notable Inftance ; for the Needle 
<e hath been conftantly about i° 30' more Eafterly a Paris than at London, tho’ it be certain, that ac- 
«« cording to the general Effed, the Difference ought to be the contrary Way, notwithstanding which, 
the Variations in both Places do change alike. 
«< Hence, and from fome other Things of the like Nature, I conclude, that the two Poles of the ex- 
tc ternal Globe, are fixed in the Earth, and that if the Needle were wholly governed by them, the Va- 
t: nations thereof would be always the fame, with fome little Irregularities on the Account I but juft 
^ above-mentioned; but the internal Sphere having fuch a gradual Tranflation of its Poles, does influ- 
ft ence the Needle, and diredt it varioufly, according to the Refult of the attradive, or diredtive Power 
<c of each Pole, and confequently there muff be a Period of the Revolution of this internal Ball, after 
<c which the Variation will return again as before ; but if it fnould in future Ages be obferved otherwife, we 
t£ muff then conclude, that there are more of thefe internal Spheres, and more magnetic Poles than four, 
44 which at prefen t we have not a fufficient Number of Obfervations to determine, and particularly in that 
vaft Mare del Zur , or South-Sea , which occupies fo great a Part of the Surface of the Earth. 
If then two of the Poles he fixed, and two moveable, it remains to afcertain, which they are that 
keep their Place; and though I cduld wifh we had Experience of another Century of Years to found 
«c our Conclufions upon, yet I think we may fafely determine, that our European Pole (which in the 
« precedent Difcourfe I fuppofed near the Lands-end of E?igla?id , and about 7 0 therefrom) is, that, which 
<C is moveable of the two northern Poles, and that, which has chiefly influenced theVariation in thefe Parts 
c< of the World ; for in Pludfons Bay, which is under the Diredion of the American Pole, the Change 
« is not obferved to be near fo faft as in thofc Parts of Europe , tho’ the Pole be much farther removed 
a from the Axis. 
