304 



Gn the Cri/stall'me S'irucfure of the 



[AfriL 



were required for the production of some crystals. I believe this philo- 

 soplier has been the means of forming a Company at Paris, for the purpose 

 of obtaining certain precious stones by the above means, in which I am 

 told by a gentleman who saw them, they have so completely succeeded, 

 that the rubies of the Company could not be distinguished from those of 

 the jeweller. Now I cannot but consider it as strikingly confirmative 

 of the view I am inclined to take of the cause to which the crystalline 

 structure of the trap dykes, &c. is due, that the electric action in them 

 is so precisely similar to that in the above cases. It is even more favour- 

 able in the dyke, for the circulation of the currents is more free, espe- 

 cially at first ; of course as solidification progresses this is diminished, but 

 this process goes on very slowly, as is proved by lava currents regain- 

 ing their heat for such immense lengths of time, when the upper surface 

 becomes solid, so as to oppose the farther abstraction of heat. 



It is further interesting to learn that already have electric currents 

 been detected in metalliferous veins, as by Mr. Fox in those of the 

 Cornwall mines ; and though the electricity generated seems more due to 

 chemical actions between different materials in the vein, than to any 

 variations of temperature, still we know the identity of the two kinds, 

 and therefore if one produces a certain series of effects, it is natural to 

 conclude the other would do so likewise. Of Mr. Fox's experiments by 

 which he was led to the above discovery, Professor Wheatstone remarks 



the value of these interesting researches consists, in the exact analogy 

 they bear to what actually takes place in mineral veins ;" and the re- 

 sult proved how true this remark was. The details of these experiments 

 are now before me, but I do not consider it necessary to enter into fur- 

 ther detail on this point, as I trust analogies sufficiently powerful and 

 numerous, have now been brought forward to demonstrate the efficiency 

 of thermo-electricity to produce the phenomena as observed in the struc- 

 ture of trap, and also in other rocks placed under analogous circum- 

 stances. 



This principle of explanation will readily be applied to all the classes 

 forming the ground work of this enquiry, which here might fairly be 

 brought to a conclusion, since of the peculiar manner in which electri- 

 city acts in producing crystallization, little or nothing is known. That 

 it does do so we have seen, and beyond this all is comparative uncertain- 

 ty ; it is therefore with most unaffected diffidence that 1 ven^are to offer 

 a few remarks grounded on what is known on this subject, as I can 

 scarcely deem my enquiry complete till such an addition has been made 

 to it. I feel my incompetency to do any thing like proper justice to this 

 question, yet as some intereslnig information, though small in quantity. 



