The Conductors of tlie London and Edinburgh Philosophical Magazine 

 have to acknowledge the editorial assistance rendered them by their friend 

 Mr. Edward W, Bravley, F.L.S., F.G.S., Assoc. Inst. C. E., Correspond- 

 ing Member of the Royal Geological Society of Cornwall and of the Philoso- 

 phical Society of Basle, Hon. Mem. S. Afric. Inst.; Librarian to the Lon- 

 don Institution, and Secretary to the Electrical Socikty. 



