NATURAL PHILOSOPHY. 169 



Ducliemin, they suffer infinitely more than at sea. Nothing, he 

 says, is necessary for the preservation of the armor plates but to 

 ensure communication between every part of the cuirass and the 

 neg-ative pole of a powerful pile placed in each basin. 



The other applications to which the marine pile may possibly 

 be adapted are : The explosion of submarine mines and torpe- 

 does, experiments with both having been made by the marine ad- 

 ministration ; the cleaning of sliips' bottoms, which M. Duchemin 

 j)r()posed to effect by connecting one pole of a Ruhmkorft' coil 

 with the iron plating of a vessel and the other with the sea, which 

 causes the molluscs to quit their hold ; the transmission of instruc- 

 tions on board ship ; the signalling the depth of water in ports 

 and other places, such as beneath the keels of vessels; the trans- 

 mission of electric telegrams from ship to ship during naval en- 

 gagements; for night signals, with the aid of the coil, together 

 with Geissler's tubes ; for engraving plates in sea-water by the 

 means of cutting out as with acids ; and, lastly, the possibility of 

 using the marine pile not only for illumination of light-houses and 

 beacons, but also on board ship. — The Engineer. 



LIGHTNING AND ITS EFFECTS. 



At the Chicago (1868) meeting of the American Association for 

 the Advancement of Science, Prof. Stoddard read a paper on the 

 •* Nature of Electric Discharge." 



That theory seems very unwieldy which conceives of electricity 

 as two fluids imponderable and indefinitely rare, quiet when united 

 but intensely active when separated, and that all the violent effects 

 are due to the transfer of the fluids through bodies, and this con- 

 ception constantly manifests itself in the statements of the laws 

 and phenomena of electricity. 



Few, it is believed, will object at present to the view that the 

 electric force is molecular; that, whatever doubt may exist as to 

 its precise nature and mode of operation, it is connected with and 

 acts by and through those particles which chemistry contemplates 

 as atomic ; that whatever changes or disruptions are wrought by 

 it are operations going on among these atoms ; and that electric 

 discharge is not the transfer of matter, but of some change along 

 the line of discharge, producing other correlated forces. All elec- 

 trical excitement preceding discharge is the state of induction, 

 transferred according to Faraday, along lines of particles to other 

 bodies. This condition is one of tension, and the tendency of the 

 particles is to undergo some change antagonistic to cohesion, and 

 consequently resisted by this force. As long as cohesion can re- 

 sist the electrical force the condition is statical.- If the tension 

 rises to a sufficient degree, the particles yield and undergo the 

 change which the force requires. This is discliarge. 



The change, in which consists discharge, will be violent in pro- 

 portion to the degree of tension, and the character of the change 

 will depend upon the nature of the body. The substance may be 

 split, torn asunder, as in trees ; ground to powder or fractured, as 



15 



