The Conductors of the London and Edinburgh Philosophical Magazine 

 have to acknowledge the editorial assistance rendered them by their friend 

 Mr. Edward W. Brayley, F.L.S., F.G.S., Assoc, Inst. C. E., Corr. Mem. 

 Roy. Geol. Soc. of Cornwall, Hon. Mem. S. Afric. Inst.; Librarian to the 

 London Institdtion, and Secretary to the Electrical Society. 





