Now because where the greater continents are joyned, the action and effluence is also greater; therefore those Needles do suffer the greatest variation which are in Countries which most do feel that action. And therefore hath _Rome_ far less variation then _London_; for on the West side of _Rome_ are seated the great continents of _France_, _Spain_, _Germany_, which take off the exuperance, and in some way ballance the vigor of the Eastern parts. But unto _England_ there is almost no Earth West, but the whole extent of _Europe_ and _Asia_ lieth Eastward; and therefore at _London_ it varieth eleven degrees, that is almost one _Rhomb_. Thus also by reason of the great continent of _Brasilia_, _Peru_, and _Chili_, the Needle deflecteth toward the Land twelve degrees; but at the straits of _Magellan_ where the Land is narrowed, and the Sea on the other side, it varieth but five or six. And so likewise, because the Cape _de las Agullas_ hath Sea on both sides near it, and other Land remote, and as it were æquidistant from it, therefore at that point the Needle conforms unto the true Meridian, and is not distracted by the vicinity of Adjacencies. This is the general and great cause of variation. But if in certain Creeks and Vallies the Needle prove irregular, and vary beyond expectation, it may be imputed unto some vigorous part of the Earth, or Magnetical eminence not far distant. And this was the invention of _D. Gilbert_, not many years past, a Physician in _London_. And therefore although some assume the invention of its direction, and other have had the glory of the Card; yet in the experiments, grounds, and causes thereof, _England_ produced the Father Philosopher, and discovered more in it then _Columbus_ or _Americus_ did ever by it. Unto this in great part true the reason of _Kircherus_ may be added: That this variation proceedeth not only from terrestrious eminencies, and magnetical veins of the Earth, laterally respecting the Needle, but the different coagmentation of the Earth disposed unto the Poles, lying under the Sea and Waters, which affect the Needle with great or lesser variation, according to the vigour or imbecility of these subterraneous lines, or the entire or broken compagination of the magnetical fabrick under it. As is observable from several Loadstones placed at the bottom of any water, for a Loadstone or Needle upon the surface, will variously conform it self, according to the vigour or faintness of the Loadstones under it. Thus also a reason may be alledged for the variation of the variation, and why, according to observation, the variation of the Needle hath after some years been found to vary in some places. For this may proceed from mutations of the earth, by subterraneous fires, fumes, mineral spirits, or otherwise; which altering the constitution of the magnetical parts, in process of time, doth vary the variation over the place.