302, 



On the Crystalline Structure of the 



[April 



Vvater and feveral solutions by its means, while another has produced 

 from it a clear and distinct spark. 



Sufficient has now, I trust, been said, to establish satisfuctorily the 

 development of electricity under circumstances analogous to those of trap 

 dykes. In the latter there is every essential for such an effect, the ori- 

 ginal high temperature of the injected trap, the consequent abstraction 

 of its heat by the including rock, in which the temperature was m.uch 

 lower, are in themselves the elements of thermo-electric currents, and a 

 remark due in common with many others of a like nature, to Dr. Faraday, 

 that when a solid which is not a metal becomes fluid it almost entirely 

 loses its power of conducting heat, while it acquires a capacity for con- 

 ducting electricity in a high degree," proves to us how favourable their 

 original state was, for being traversed by currents thus excited. Indeed 

 from views which have thus gradually, and step by step, developed them- 

 selves during the progress of this enquiry, I caanot but look on trap 

 dykes as being essentially electrical machines, developing continued cur- 

 rents of electric energy during the time that their temperature remains 

 above that of the including rocks — these currents, following the law of 

 intensity formerly announced, being proportii-nal to the difference of 

 temperature between the elements of the circuit. Viewed in this light, 

 trap dykes contain within themselves both the agent, and the substance 

 acted upon, the electricity developed during the process of refrigeration 

 being the one, the constituents of the mass the other. The preceding form 

 another of those many links by which heat and electricity are connected, 

 and though confessedly this bond yet remains enwrapped in mystery, the 

 time seems not far distant when greater light will be thrown upon it, as 

 analogies are becoming stronger and stronger, and materials for the dis- 

 cx)very, we might almost say, of their identity are rapidly accumulating. 

 It would be quite foreign to our subject to digress on this point, I 

 would therefore now offer a few remarks on tlie efficiency of the cause 

 to produce the effects I have attributed to it, and enquire into the con- 

 nection subsisting between electricity and the phenomena of crystalliza- 

 tion; our enquiry must here be exclusively analogical, for it is only thus 

 we are permitted to conduct investigations like the present, where effects 

 remain after the cause to which they are due has ceased to operate. 



Electricity, as known in the natural world, may be considered as of 

 five kinds, to which the names, common, voltaic, magnetic, thermo and 

 animal electricities have respectively been given ; now one of the tri- 

 umphs ©f modern science has been to establish, bej'-ond a doubt, the 

 identity of these varieties, by clear and distinct proofs. Similar effects 

 have been produced by all ; composition and decomposition, deflection 



