432 The Rev. J. A. Coombe on the form of 



presents no other idea to the mind than the fact itself presents, 

 it furnishes no link by which we may extend the phsenomena. 

 I therefore, until a better theory be found, should be inclined 

 to adopt the former view, and to regard mixed gas as in a 

 state of feeble chemical union, the more especially as through- 

 out nature we find no absolute lines of demarcation, though 

 for conventional reasons we are obliged to adopt them ; there 

 must be many cases in which it is difficult, if not impossible, 

 to draw the line between mechanical mixture and chemical 

 combination. 



In conclusion, I would say with regard to the whole of the 

 experiments contained in this paper, that a longer time and 

 more experience may give positive results in cases where I 

 have only obtained negative ones; it is far from impossible 

 that since curious solid combinations are formed by slow elec- 

 trical currents, as in the experiments of Crosse and Becquerel, 

 so novel gaseous or liquid products may be obtained by the 

 long-continued voltaic action of gases and liquids. This time 

 alone can show. 



For previous experiments and theories on the combination 

 of gases by platinum, I may refer to Dobereiner's paper, Phil. 

 Mag. Oct. 1823, in which I find he expresses an opinion that 

 it is a voltaic effect; to the papers of Dulong and Thenard, 

 Annates de Chimie, torn. 23 and 24 ; and to Faraday's Expe- 

 rimental Researches, Series 6. The various experiments on 

 polarized electrodes of Ritter, Faraday, De la Rive, Becquerel, 

 Matteucci, and Schcenbein, are also in point. 



LXII. On the Form of Equilibrium of an Inextensible String 

 laid on a surface and acted on by any forces. By the Rev. 

 J. A. Coombe, M.A., Fellow of St. John's College, Cam- 

 bridge *. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



THE following method of investigating the form of equi- 

 librium of an inextensible string laid on a surface and 

 acted on by any forces, has the advantage of presenting a re- 

 sult extremely neat and symmetrical. I adhere to the suffix 

 notation in expressing a differential coefficient, never having 

 yet seen any arguments, of much value, brought against this 

 elegant and convenient method. 



Let u = be the equation to the surface. 

 xy z the rectangular coordinates of any point of the string, 

 and therefore of a point in the surface. 



* Communicated by the Author. 



