Intelligence and Miscellaneous Articles. 75 



north as Dunstanborough Castle, showing tho varying positions at 

 which it occurs in the Limestone scries, and noting points of 

 interost in somo of tho sections. Tho Whin shifts its position 

 amongst tho strata to the extent of 1000 feet or more. It fre- 

 quently comes up in bosses through tho bedded rocks, and bakes the 

 beds above it quite as much as those below, especially when thoso 

 beds consist of shale. 



As to the ago of the Whin Sill, nothing definite can bo said. It 

 is frequently thrown by faults and lodes. Thore is no certain case 

 of its being unaffected by faults which throw the neighbouring 

 rocks, although there are a few doubtful cases which seem to point in 

 this direction. As the Whin Sill docs not approach the Permian 

 area of Durham, the fact that some of the faults there are believed 

 to be pre-Permian cannot be applied as a test of age in this case. 



In other districts in Britain in which intrusive basaltic sheets 

 occur amongst the Carboniferous rocks, there is good reason to 

 believe that in most cases they are pre-Permian, or at least pre- 

 Triassic. Whether or not this be the case with the Whin Sill 

 cannot be determined. No light is thrown on this question by the 

 composition of the rock. Mr. Allport has shown that it resembles, 

 in all essential characters, the basalts of other Carboniferous districts, 

 some of which are possibly contemporaneous, some certainly in- 

 trusive. 



XI. Intelligence and Miscellaneous Articles. 



ON THE POKTATIVE FORCE OF HORSE-SHOE MAGNETS. 

 BY V.-S.-M. VAN DER WILLIGEN. 

 ^0 saturate horse-shoe magnets, I place them vertically with 

 -*- their poles upon the poles of a Buhrnkorff coil, the circuit of 

 which I open and close three or four times successively ; the 

 magnetism of my magnets, of the usual dimensions, has then at- 

 tained its maximum, even of super-saturation. After the last 

 opening I slide the magnet, carefully and without lifting it, toward 

 the edges of the polar planes of the electromagnet. Arrived at 

 the margin I place the armature, well cleaned, before the magnet, 

 slowly inclining the latter, while its poles still remain in contact 

 with those of the electromagnet. As soon as the armature has 

 closed the magnet, this can be raised without the slightest effort ; 

 its carrying force is then nearly one third greater than the 

 usual permanent portative force of the best magnets of M. van 

 Wetteren *. 



* The manufacturers of magnets, at the time when touching with per- 

 manent magnets was the only method known, had already noticed this 

 state of supersaturation of horse-shoe magnets, which is dissipated at the 

 first pulling off of the armature. Haecker even says that the portative 

 force in this state is double the permanent force — which agrees with my 

 observations, since the permanent portative force of these magnets is only 

 two thirds of that of the magnets of M. van Wetteren. 



