18 P. M. on certain Experiments in Magneto- electricity 



isting between the intensity of electrical action and the quan- 

 tity of the ores in the vein. 



But a series of electro-galvanic experiments on metalliferous 

 veins is greatly to be desired; and to show my willingness to 

 contribute, I beg leave to annex the following Experiment: — 



At Wheal Vyvyan Mine near Helston in this county, in the 

 present month, I applied one wire of the galvanometer to a 

 productive part of the vein 20 fathoms below the adit; the 

 other wire to the same vein 10 fathoms below this level, — thus 

 leaving 60 feet in depth between the plates connecting the 

 wires with the vein. The action on the magnetic needle was 

 considerable; it passed over an arc of 15 degrees, the lower 

 part of the vein being negative to the upper part. 



There are some peculiarities in the formation of this lode 

 or vein which are not unworthy of the attention of the geolo- 

 gist. It is in some places 20 feet wide in granite strata. A 

 great part of the vein is also composed of granite mixed with 

 quartz and fluor. The more productive part of the vein is from 

 3 to G feet in width, and composed of arsenical pyrites, fluor, 

 yellow sulphuret of copper, and tin ; the tin and copper being 

 so intimately mixed in the same stone, as not to be separated 

 without being first pulverized, roasted, and washed ; the pro- 

 portion of copper to tin in the vein stones being as 5 to 1 in 

 weight. The lode underlies north, about 4 feet in a fathom, 

 and its direction is east and west. 



Perranarwothall, near Truro, John BENNETTS. 



April 10, 1833. 



V. On certain Experiments in Magneto-electricity andElectro- 

 magnetism. By P. M. 



To the Editors of the Philosophical Magazine and Journal, 

 Gentlemen, 

 IT is within these few days that I read by accident in your 

 *■■ Journal the letter I sent to Mr. Faraday ; and I feel much 

 obliged to him for the kind manner in which he noticed it*. 

 The same experiment has with equal success been performed 

 in France by a single powerful magnet: those that I made use 

 of were of the smallest description, yet the wire was of con- 

 siderable length. Shortly after I sent that letter, I made a con- 

 siderable improvement in the apparatus, by connecting a soft 

 iron ring to the wire, which became momentarily a magnet, and 

 in its turn reacted on the wire, and caused a very considerable 

 increase of power. The wire when coiled round the first lifter, 

 before proceeding to the second was wound a considerable 



* Sec Lond. and Edinb. Phil. Mag. and Journal, vol. i. p. 161.— Edit. 



