122 PHILOSOPHICAL TRANSACTIONS. [aNNO 1/45. 



sented in the same manner ; from an imitation of which they might perhaps be 

 introduced at first, as well for cheapness, as ready convenience, in some of the 

 more remote provinces. And it is very remarkable, that no two impressions on 

 these plates are in all respects exactly alike ; as we do not often meet with tw o 

 Roman coins struck from the same die. 



As to the time when the plates were made, the inscription on the first fixes it 

 to the reign of Diocletian ; and as not only the characters of the other inscription 

 exactly correspond with that, but also the manner of the work on each plate is 

 the same ; it is highly probable they were all made about the same time, which 

 was near the end of the third century. And to this likewise the form of the 

 letters, particularly a and m, very well agrees. Nor ought it to seem strange, if more 

 of them have not been preserved ; since from their nature they appear so liable to 

 be destroyed, either by the injuries of time, or for the sake of the silver. 



Concerning the Poles of Magnets being Variously placed. By Gowim Knight, M. B. 



N»476, p. 361. 



1. Mr. K. cut a piece of natural loadstone into the shape of a parallelopiped, 

 1 inch -iV in length, in breadth -pV of an inch, and -^ in thickness : its weight 

 was 3 drams 10 grains. In this stone he placed the magnetical virtue in such a 

 manner, that both the two opposite ends became south poles ; and the middle 

 was, quite round, a north pole. 



1. Another stone was in length 1 inch -Js-j in breadth ■^, and in thickness 

 about tV at a medium, it being thicker at one end than at the other . its weight 

 1 dram 57 grains. The 2 opposite ends of this stone he made both north poles, 

 and the 2 opposite sides south -^oles. 



3. An irregular stone, that weighed about 54. oz., had 2 broad flat surfaces 

 opposite to each other, at the distance of 1 inch and -^. He made half of 

 each of these surfaces a north pole, and the other half a south pole ; so that the 

 north pole of one surface was opposite to the south pole of the other surface, and 

 vice versa. 



4. He took a stone of a pretty good kind, that had a grain very apparent, 

 running the length ways of it : it was 1 inch ^V in length, 1 inch -^ in breadth, 

 and its thickness at the sides was -^ of an inch ; but in the middle -J-^ ; it being 

 tapered away from the middle to the sides : its weight was 3 ounces wanting 4 

 grains. At one end of it he placed a north pole surrounded by a south ; and 

 at the other end a south surrounded by a north pole ; so that the edges of each 

 surface had a pole of a different denomination from that which occupied the 

 middle. 



A great many varieties of this kind might be easily devised ; but these ex- 



