I 
The INTRODUCTION , . ix 
how future Difcoveries may be made by a farther Improvement of tbofe Helps, and thofe Inftru- 
ments, which have rendered the modern Navigation fo much fuperior, in Accuracy, as well as Extent 
to the Navigation of the Ancients. 
This leads us to fpeak more particularly of the Properties of the Magnet, or Load-ftone*the Difcovery 
of which, if we may believe the learned Kircher , was originally owing to the Sagacity of an Etffrlijhmdkj 
but which have moft certainly been better explained, and thereby rendered more and more ufeful, by fe- 
veral of our induftrious Countrymen. There have, indeed, been Attempts made to fhew, that the Ancients 
were acquainted with that wonderful and Angular Property of this Stone, which our learned Countryman 
Dr. Gilbert , calls, its Verticity, or Power of pointing to the North ; and it has been likewife aliened, 
that it was commonly known in the Eajl, before it came to be pradifed in thefe Parts of the World ; 
both which Opinions, in the Body of this Work, we have (hewn to be but indifferently founded. The 
Treatifj upon this Subjed, of any great Confequence, was written by a Perfon who ftiled bimfelf 
Petrus peregrinus , who, if Kircher be not miftaken, and Sturmius likewife, was no other than cur 
learned Friar Roger Bacon ; but be this as it will, it is in a Manner agreed, that this Property of the 
Magnet, was reduced to pradice about the Year 1300, that is about fix or eight Years after Friar Ba- 
cons Death, by one John Goia of the Kingdom of Naples . 
After this great and moft ufeful Difcovery was known to Europe , there were foon many inquifitive 
Heads, that employed their Thoughts about making further Enquiries into the Nature of this celebrated 
Stone 5 fothatinfome time its Variation, or Defkdion from the true Meridian, was difcovered by Se- 
hajiian Cabot. The Declination (as it was at firft called, whereas now the Variation often paffes by 
that Name ) or rather, the Inclination of the Needle, was firft difcovered by our Countryman Robert 
Norman , which is a furprizing Property, whereby it always dips under the Horizon, when placed 
upon a Pin like a Compafs, except in fuch Places as are juft under the Equator, and there it keeps al- 
ways parallel to the Horizon exadly ; and he found the greateft Inclination at London to be y i° $o ! . 
Dr. Wallis in the Philofophical Pranfadhons , N°. 276, thinks that the Difcovery of this Dipping of the 
Needle is owing to Mr. Bla grave, or fome other Grejhamite ; and he describes this Property to 
be a Diredion of Altitude above the Horizon ; fo that if it be duly poifed on an Horizontal Axis, 
it will point to a determinate Degree, of Altitude, or Elevation above the Horizon; and he fays truly 
that of this Difcovery, though made fo long ago, there hath not yet been any conliderable Ufe 
made. 
The Variation of the Variation is another confiderable and very furprizing Property of 
the Load-ftone ; that is, that the Magnetick Needle in its Horizontal Pofition, doth not always 
retain the fame Variation or Declination from the true Meridian, in the fame Place ? and at all Times, 
but doth fuccefiively vary in its Declination or Variation from Time to Time. This was firft dif- 
covered by Mr. Gi lit brand, about the Year 1635 ; tho’ Sturmius faith, that this was taken Notice of 
alfo by Hehetius , Auzout , Petit , V olckamer and others, much about the fame Time : So that our En- 
glijh Nation has had a very confiderable Share in the Difcoveries which have been made about the 
Magnet, and its wonderful and ufeful Properties. To make this Matter the clearer, and to reduce 
the Fads neceffary to be known, within a narrow Compafs, we will prefent them to the Eye of the 
Reader in the Form of a Table. 
{ Ihe Properties and Phenomena of the Magnet or Load-ftone, from the beft Authors. 
L That in every Magnet or Load-ftone, there are two Poles, one pointing North, the other South y 
and if a Stone be cut, or broke into never fo many Pieces, there are thefe two Poles in each Piece. 
II. That thefe Poles, in divers Parts of the Globe, are diverfly inclined towards the Earth’s Centre. 
III. That thefe Poles, though contrary one to another, do help mutually towards the Magnet’s 
Attradion and Sufpenfion of Iron. 
IV. If two Magnets are Spherical, one will turn or conform itfelf to the other, fo as either of them 
would do to the Earth ; and that after they have fo conformed, or turned themfelves, they endeavour to 
approach to join each other ; but, if placed in a contrary Pofition, they avoid each other. 
V. If a Magnet be cut through the Axis, the Parts or Segment of the Stone, which before were 
joined, will now avoid and fly each other. 
VI. If the Magnet be cut by a Sedion perpendicular to its Axis, the two Points, which before were 
conjoined, will become contrary Poles, one in one, the other in the other Segments. 
VIE Iron receives Virtue firm the Magnet by Application to it, or barely from an Approch near it, 
tho’ it do not touch it; and Iron receives this Virtue varioufly, according to the Parts of the Stone it is 
made to touch, or approach to. 
VIII. If an oblong Piece of Iron be any how applied to the Stone, it receives a Virtue fiom it only 
as to its L ngth. 
IX. The Magnet lofts none of its own Virtue by communicating any to Iron ; and this Virtue it 
can communicate to Iron very fpeedily, though the longer the Iron touches or joins the Stone, the 
longer will its communicated Virtue hold, and a better Magnet will communicate more of it than one 
that is not fo good. 
X. That Steel receives Virtue from the Magnet fooner than Iron. 
XI. A Needle touched by a Magnet will turn its Ends the fame Way towards the Poles of the 
World as the Magnet will do. 
XII That neither Lead, Stone, nor Needles touched by it do conform their Poles exadly to thofe 
of the World, but have ufually fome Variation from them ; and this Variation is different in different 
Places, and at different Times in the fame Place. 
Numb. LXIX 
d 
XIII 
