20 Mr. 11. W. Fox's RemarliS on Mhicrul Fcins^ <§r. 



and W. veins intersecting the cross veins without sufftjring 

 interruption. 



The great veins or dykes of poiphyry, or Elvan courses as 

 the miners term them, ma}^ also be connected with electrical 

 action. They are nearly in an E. and W. direction, and are 

 not aftected by the veins which cross them. 



I need not say that the above is a very summary and im- 

 perfect statement ofsome of the phsenomena of veins; and I can- 

 not but believe, that a more minute investigation and complete 

 classification of tacts than has yet been attempted, relative to 

 this important branch of geology, would be interesting to the 

 philosopher, and perhaps valuable to the miner. This object 

 might, I think, be best attained by scientific individuals, or so- 

 cieties, employing a suitable person who would devote his 

 time and attention to the subject. He might also try various 

 experiments, especially with the magnetic needle, near the 

 junction of clifFerent rocks, and in the vicinity of veins havhig 

 different directions, to ascertain if the variation or the mag- 

 netic intensity is affected thereby. 



With the view of making some experiments hereon, when 

 I can find sufficient leisure for the purpose, I have had some 

 magnetic needles prepared with one polarity only in action ; 

 the other being neutralized, or nearly so, by altering the centre 

 of suspension to within the neutralized pole itself, and extend- 

 ing it with brass as a counterpoise to the acting pole*. 



If it should prove that veins differently circumstanced have 

 different effects on these needles; may it not tend to explain 

 the cause of the periodical variation of the compass, if we sup- 

 pose electrical action to vary in its relative intensity at differ- 

 ent periods of time? And may not electricity, the intensity 

 of which varies so continually in the atmosphere, affect the 

 oscillation of the pendulum and cause the discrepancies ob- 

 servable, especially when the pendulums are insulatetl, or only 

 partially so, on agate edges ? 



• To make the above descrip'tion more intelligible : Suppose N S to be 

 the magnetic steel; S6 



an addition to the steel, b S c d N 



made of brass or some «g7.^ ^-w^/X - vx >y-<. -^ j ^rT^?:/ £fc rsrrT?T^ , 77 ^ f,v^;i, - ;^;^j ; 4(^ 

 other metal not affected 

 by magnetism, to act as 



a counterpoise to the opposite arm ; d the centre of the steel part of the 

 needle where magnetic neutralization takes place. It is evident that c, the 

 centre of suspension, can be so placed that the two arms c S, erf havnig 

 south polarity, may counteract each other, and leave the north polarity r/N 

 to its full action ; or the case may be reversed, by substituting the S pole 

 for the N. Would it not be interesting to make experiments with these 

 needles on the magnetic intensity at different places, and in different lati- 

 tudes ? 



I may 



