1823.] Proceedings of Philosophical Societies. 461 



vanic wire and the compass, and not that of one galvanic wire 

 on another. What modification the hypothesis may require to 

 explain the latter class of phenomena, will be examined here- 

 after. I have hitherto supposed only one species of action in 

 the galvanic wire, but it is highly probable that it is compound, 

 and that while the north end of the needle is carried in one 

 direction by the action we have supposed, the south end is car- 

 ried in an opposite direction ; not merely as a consequence of 

 the first force, but by a distinct power. This will not, however, 

 in any respect, affect our investigation ; because both forces 



lead to similar results I am well aware of the difficulty of 



conceiving the mechanical principles by which such a tangen- 

 tial force, as is here assumed, can operate ; but, on the other 

 hand, it must, I think, be conceded, that the simple power of 

 attraction is equally difficult to conceive, and that we admit it, 

 not from having any idea of the modus operandi, but because we 

 find that it leads to results that are consistent with actual obser- 

 vations ; and I have endeavoured to show, in the preceding 

 pages, that the force we have assumed is admissible upon pre- 

 cisely the same ground." 



The third section of this part contains a course of electromag- 

 netic experiments, " due to the several ingenious philosophers 

 who have interested themselves in this pursuit;" and in which 

 Mr. Barlow endeavours " to show their mutual dependencies 

 on each other, and their general agreement and particular con- 

 nection with the mathematical theory advanced in the second 



section " 



These are succeeded by addenda to Sect. 12 and 13, Part I. 

 " On the Magnetic Effects of Iron Masts on the Compass," 

 which terminate this valuable work, and from which it appears, 

 that the contemplated employment of hollow iron masts in ships 

 of war, in lieu of those at present in the service, will be product- 

 ive of no disturbance on the compass, under any circumstances, 

 but what may readily be corrected by the method Mr. Barlow 

 has proposed. 



Article XII. 

 Proceedings of Philosophical Societies. 



ROYAL SOCIETY. 



April 17. — On the Application of the Liquids produced by the 

 Condensation of Gases as Mechanical Agents. By Sir H. 

 Davy, Bart. PRS. 



It is well known that the elasticity of vapours in contact with 

 the liquids from which they are produced at high temperatures, 

 increases in a much higher ratio than the arithmetical progres- 



