8S "W. Sturgeon, Esq., on the 



would give the sum-total of all the magnetic action that any- 

 individual coinage would display. Suppose, for instance, the 

 magnetism displayed by a half-crown piece were to be taken 

 as the unit of quantity equal q, then the number of the pieces 

 being w, the sum-total of magnetism which the whole of that 

 coinage would display would be w q nearly ; and similarly 

 for any other coinage of silver. 



31. The difference of magnetic action displayed in the silver 

 coinage and domestic articles of that metal (29, 30), led to the 

 supposition that minute portions of iron might accidentally 

 have got introduced to the alloys whilst in a state of fusion, 

 which had some probability in its favour, from the fact that 

 the metal for silver coinage is fused in cast-iron pots,* and, 

 therefore, liable to take up a portion of those vessels. But, 

 on the other hand, if that were always the practice, it would 

 lead to the inference that in all the silver coins the iron would 

 be nearly in the same proportion, and the extent of magnetic 

 action almost the same in all ; whereas, by the tests already 

 described, this is not the case. 



32. The current silver coinage of "William and Mary be- 

 came so base, that in the year 1694 it was all called in, and 

 a new coinage issued. From this fact, it occurred to me that 

 there was a possibility, at least, that the high degree of mag- 

 netic action displayed by the half-crown of 1691 (29), was 

 owing to an undue proportion of copper, or of some other in- 

 ferior metal. This idea led to the selection of a shilling, in 

 which scarcely a trace of magnetism could be detected, for 

 fusion with an additional portion of copper, also non-magnetic, 

 having been obtained by the electrotype process. These, 

 together with a piece of pure silver, were fused in an earthen- 

 ware crucible, and run out upon a sheet of copper. The cop- 

 per in this alloy was about one to five of silver, which is more 

 than twice the proportion of that in the standard coinage. 

 On subjecting this mass to the torsion magnetoscope^ it was 



'^ Ure's Dictionary of Arts and Manufactures. Brande's Chemistry, page 

 1073. 



