18 Professor Grove oti a Voltaic Process for Etching 

 Similarly, the two following equations become 



dt m^ ^" '' dt vi^ \^ y)^ 



hence adding and integrating, 



S^ + Sj+S, = ^|a- + i2 + c2-?A^ + constant. (41.) 



XXX. Let tangent planes be drawn to the three vertices 

 of a, b, c, the semiaxes of the ellipsoid, cutting off from the 

 axis of the impressed moment, three segments whose recipro- 

 cals are f, u, 5, we shall have ^- + u- + ^ = constant, during 

 the motion, 



for ^ a^ = cos- a; but cos- a = — g- , hence ^'^u^ = —^. 

 Similarly, o^M^-^^ ^^2 ^ „ . hgnce 



g2 + „2 + ^2^ i 



XXXI. The sum of the squares of the dislaiices of the ver~ 

 tices of the three semiaxes of the ellij)soidfrom the plane of the 

 impressed mome7it divided by the correspo7idi7ig moments of in- 

 ertia is constant during the motion. 



Let x^ be the distance of the vertex of a from the j)lane of 

 the impressed moment, then x^ = a^ cos- «, and A = n^ a^; 



cos^ y 

 1 



7V' ' 



V. On a Voltaic Process for Etching Daguerreotype Plates. 

 By W. R. Grove, Esq., M.A., F.R.S., Professor of Ex- 

 perimental Philosophy in the London Instittition^. 



11. BERRES of Vienna was the first, I believe, who pub- 

 lished a process for etching Daguerreotypes : his method 

 was to cover the plates with a solution of gum-arabic, and 

 then to immerse them in nitric acid of a certain strength. 



D 



• From the Proceedings of the London Electrical Society, Part II. >' 

 having been read before the Society on the 1 7th of August, 1841. Re- 

 vised by the Author. 



