Vol. XIII.] PHILOSOPHICAL TRANSACTIONS. 631 



distance from this latter is very little varied; and as we recede from the Asian- 

 South-pole, the balance is still preserved by the access towards the North- 

 American-pole. 



Thus I hope I have not lost my pains and study in this difficult subject: 

 believing that I have put it past doubt, that there are in the earth four such 

 magnetical points, or poles, which occasion the great variety and seeming irre- 

 gularity which is observed in the variations of the compass. But to calculate 

 exactly what it is, in any place assigned, is what I dare not yet pretend to ; 

 though I could wish it were my happiness to be able to oblige the world with 

 so useful a piece of knowledge. There are difficulties that occur which render 

 the thing as yet not feasible ; for first, a great many observations are requisite, 

 which ought to be made at the same time; not at sea, but ashore; with greater 

 care and attention than the generality of sailors apply. And besides, it remains 

 undetermined in what proportion the attractive power decreases, as we remove 

 from the pole of a magnet; without which it were a vain attempt to endeavour 

 to calculate. There is yet a further difficulty, which is the change of the va- 

 riation, one of the discoveries of this last century ; which shows, that it will 

 require some hundreds of years to establish a complete doctrine of the magnetical 

 system. From the foregoing table it should seem, that all the magnetical 

 poles had a motion westward: but if it be so, it is evident that it is not a rota- 

 tion about the axis of the earth; for then the variations would continue the 

 same, in the same parallel of latitude, the longitude only changed, as much as 

 is the motion of the magnetical poles. But the contrary is found by experience; 

 for there is no where in the latitude of 5 1-f north, between England and America, 

 a variation of 1 1° east at this time, as it was once here at London. It seems 

 therefore that our European pole is got nearer the north pole, than it was here- 

 tofore ; or else that it has lost part of its virtue. But whether these magnetical 

 poles move altogether with one motion, or with several; whether equally or 

 unequally; whether circular or libratory; if circular, about what centre; if li- 

 bratory, after what manner ; are secrets as yet utterly unknown to mankind ; 

 and are reserved for the industry of future ages. 



An Account of a Booh, viz. JVilhelmi ten Rhyne,* M. D. &c. Transisalano- 

 Daventriensis \ \. Dissertatio de Arthriiide. 2. Mantissa Sckematica. 3. De 

 Acupujictura. 4. Orationes tres ; sc. de Chymice et Botaniae Antiquitate et 

 Dignitate. De Physio gnomia. De Monstris. Lond.8vo.l663. N° 148, p. 222; 



This author asserts that flatus or wind, included between the periosteum and 



• William ten Rhyne, a celebrated naturalist of the I7th century, was physician to the Dutch 

 settlement at Batavia, in the island of Java. Besides the abovementioned dissertation, he wrote other 



