56 M. A. Colding on the History of the 



with simultaneous decomposition), is necessary to produce true 

 voltaic phenomena. Contact in the wire, or disruptive discharge 

 in the air, or convection in an external decomposition-cell, re- 

 stores the disturbed equilibrium of the chain. The fluid below, 

 being part of the chain, suffers decomposition as a consequence of 

 the discharge above, and, as Davy would allow, the now liberated 

 gases react directly upon the free gases in the tube ; and so a 

 constant supply of active material is furnished for the production 

 of fresh electricity, and hence the appearance of a current and of 

 circulation. The antecedent chemical action and statical spark 

 is now no longer necessary, unless contact be broken, when all 

 reverts to the original state, and the diffused and dissolved gases 

 are again in requisition. Fresh contact, by allowing discharge 

 of static electricity, will again renew the voltaic or galvanic phe- 

 nomena. 



Such I believe to be a true and philosophical account of the 

 facts and consequences concerned in this remarkable instrument ; 

 and I venture to think it is one that will apply also to the water 

 and salt-and-water excited battery, if not to the acid battery 

 itself. Thus the rival theories find their place and application, 

 but not in the order or manner supposed by their first and illus- 

 trious enunciators, Yolta, Wollaston, and Davy. If truth is 

 found in these facts and views, chemists and electricians will 

 readily see that such topics as passive iron, rusting of metals, 

 and decay, and even general chemical action itself, may yet 

 receive further elucidation from viewing them in the manner 

 here attempted in the case of the gas battery. I may at once 

 mention that the anomaly of free hydrogen being found with 

 the nitrogen in some of Mr. Grove's eudiometric experiments 

 becomes perfectly intelligible and regular by the considerations 

 here evolved. 



I am indebted to Mr. Gassiot, whose known kindness needs 

 no comment, for the use of the Grove gas pair, and also to Dr. 

 Wrigley for permission to carry on my experiments in his labora- 

 tory, aided by his instruments. 



The Grammar School, High Street, 

 Clapbam, December 24, 1863. 



XI. On the History of the Principle of the Conservation of Energy. 

 By A. Colding, Member of the Royal Society of Denmark. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, Copenhagen, November 1863. 



AS the libraries of Copenhagen do not contain the Philoso- 

 phical Magazine and Journal of Science, I have hitherto 

 got all my information about various memoirs published in the 



