On the Composition of Vegetable Membrane and Fibre, 42 1 



the vith volume of the Transactions of the Cambridge Phi- 

 losophical Society, p. 85. 



This equation to the wave-surface is 



(.r 2 +j/ 2 + * 2 ) (« 2 x* + b*f +c 2 z*) - a 2 (b* + c 2 ) & 

 -^(a 2 + c 2 ) < y 2 -c 9 (a 2 + i 2 )2 2 + a 2 6 2 c 2 = 0. 



The coordinate axes being those of elasticity. 



M. Cauchy has arrived at a similar equation, which is given 

 at the foot of page 63, vol. v. of the Exercises. M. Cauchy 

 seems to consider this equation identical with that of Fresnel. 

 See Memoir es del 'Institut, torn. x. p. 312. See also Mr. 

 Lloyd's excellent Report on Physical Optics, Fourth Report 

 of the British Association, p. 391. In order that this may be 

 the case I apprehend that it would be necessary to have 

 P in M. Cauchv's notation identical with a 2 in that of Fresnel. 

 Q b* 



R c* 



which I confess does not seem to me to have been proved. 

 Moreover FresneFs wave-surface depends upon the situation 

 of certain fixed axes (of elasticity), while M. Cauchy's wave- 

 surface does not appear to depend upon them in the same 

 manner, and therefore I suspect that the conclusions of that 

 eminent mathematician are so far in discordance with those 

 of Fresnel. I submit this opinion with great deference to 

 those more conversant than myself with physical optics and 

 with M. Cauchy's works, but at all events I think it will be 

 admitted that the question is of sufficient importance to de- 

 serve further elucidation by showing, if it be possible, that 

 M. Cauchy's quantities P, Q, R have the same signification as 

 Fresnel's a\ b\ c\ 



LV. On the Chemical Composition of Vegetable Membrane 

 and Fibre*; with a Reply to the Objections of Professor Hen- 

 slow and Professor Lindley. By the Rev. J. B. Reade, 

 M.A. 

 FT is stated by Professor Henslow in his" Descriptive and 

 ■■■ Physiological Botany f" that all that is known of the che- 

 mical composition of the two elementary textures of plants, 

 viz. membrane and fibre, has been derived from experiments 

 made upon the gross material imperfectly separated from the 

 various matters which the cells and tubes contain ; that in 

 this state the gross material is found to be composed of the 



* Read before Section D, Zoology and Botany, of the Seventh Meeting 

 of the British Association held at Liverpool ; and now communicated by 

 the Author. 



f Cabinet Cyclopaedia. Henslow's Principles of Botany, p. 13. 



