264 Idr. De Luc on BakewelVs 



point, by turning the screw. The point is placed at a very small 

 distance from the cork ball when tlie latter is in the most di- 

 stant part of its vibration from the disk 1; so that, in proportion 

 as the electricity is more abundant and intense, the disk 19 

 causes it to make a longer vibration, and thus to bring it nearer 

 to the point, which discharges a portion i)roportionate to its 

 proximity. The columns represented in the plate have kept the 

 pendulum thus circumstanced in activity about three weeks. 

 When the temperature of the room is above 53 degrees, it gains 

 about two secorids in five minutes for every advance of one de- 

 gree ; but when it is below this degree it diminishes its velocity 

 gradually, until it no longer vibrates so fast as seconds. 



In this state of the apparatus, the Right Hon. Lord Henneker 

 suggested to me a method of imj)roving it, by coimecting two or 

 more of the columns at both extremities, wliich would produce 

 a greater frequency; and I am taking advantage of this hint, by 

 constructing a colunm much larger in diameter and in the numr 

 t)er of groups. 



I am, sir, 



Your obliged and humble servant, 

 Ilammersuiiti!, ilaich 9, 1315. Fraxcis RonaldS. 



XLVI. Bemarks on Mr. Eakewell's Geology on Nortlmm- 

 ierland and Durham. By G. A. De Luc, Esq. F. R. S. &c. 



To Mr. Tilloch. 



J Windsor, Aprils, 1815. 



Sir, — 1 HAVE found in Art. XVII. of your Number for last 

 January, under the title of " Observations on the Geology of 

 Northumberland and Durham," some propositions on which I 

 .shall communicate to vou my remarks, as thev concern a most 

 important point of geology, namely, wctallic veiv!. 



The author, I\Ir. Robert Bakewell, thus attacks the celebrated 

 M.Werner (p. 1)1 of the Journal): "The almost invariable change 

 in ihe quantity, or in the content of metallic veins as they jjass 

 through different rocks is, 1 conceive, a demonstrative proof of 

 the fallacy of IVerner's theory, which rejir.esents veins as open 

 fissures, filled with metallic solutions from above, either by an 

 opening at the to]) or through openings in the sides. Were 

 ve'in'y filled in this manner, the qiiality of the rock v/ould have 

 little influence on the ore. Werner quotes an instance at Kings- 

 berg in Norway, as if it were unique, of the content of the vein 

 being richer as it passes some of the beds, than in others. It 

 would not have suited his theory to have admitted more j but 



the 



