252 Intelligence and Miscellaneous Articles. 



These experiments, made under conditions of pressure, tempera- 

 ture, and hygrometric condition which cannot have been identical, 

 are nevertheless sufficiently concordant with those of Graham, and 

 permit me to conclude that the natural colloid surfaces of vege- 

 tables have for carbonic acid an admissive poiver which is from 13 

 to 15 times as great as that which corresponds to nitrogen, and six 

 or seven times as great as that which refers to oxygen. 



A few days afterwards I operated with perfectly dry carbonic 

 acid, and only found, as the velocity relative to nitrogen, numbers 

 varying between 9 and 11. It appears, therefore, that carbonic 

 anhydride passes less quickly than hydrated carbonic acid. 



On replacing the vegetable membrane by caoutchouc, I obtained 

 a 'similar result. The difference produced by dried oxygen and 

 nitrogen is less pronounced. 



I mil remark, in conclusion, that these experiments prove the 

 dialysis of carbonic acid through the cuticle of leaves, just as much 

 as the experiments of Dutrochet on membranes and aqueous solu- 

 tions prove endosmose by cellules, or the experiments on absorp- 

 tion made by M. Deherain with porous vessels, to which the 

 Academy accorded one of its highest rewards. In a word, cuticular 

 respiration appears to me sufficiently proved by the presence of 

 this membrane on all the organs, by the analogies of constitution, 

 physical and chemical, with caoutchouc, by Graham's experiments 

 and the measurements of the passage of gases through colloid 

 membranes, and, lastly, by the experiments of M. Boussingault, 

 who attributes to the upper surface of leaves, destitute of stomata, 

 a greater decomposing faculty than that of the lower surface riddled 

 with these minute apertures. — Convptes Rendus de TAcademie des 

 Sciences, Aug. 11, 1873. 



ON THE REFLECTION OF LIGHT INVESTIGATED BY M. POTIER. 

 BY G. QUINCKE. 



The Coniptes Rendus of the Paris Academy, Sept. 9th and 16th, 

 1872 (vol. lxxv. pp. 617 & 674), contain two communications from 

 M. Potier on the reflection and refraction of light at the boundary 

 between two media. 



He has, with the sodium-flame, observed Newton's coloured 

 rings in a thin plate of glass the hinder surface of which was at the 

 same time bounded by air or sulphide of carbon, or in thin lamellae 

 between a glass lens and a metallic mirror. He moreover investi- 

 gated the interference of two pencils of rays, one of which has 

 undergone a metallic, and the other ordinary or total reflection at 

 the base of a glass prism, in its interior. In some experiments the 

 metallic mirror was replaced by a plane glass mirror beneath the 

 surface of the lens, or by a liquid at the outer face of the prism. 



M. Potier is of opinion that the aether in the two media was 

 divided by a transition-layer, and that the process of reflection or 

 refraction may be conceived to take place within the transition- 

 layer of two transparent media, in a plane parallel to their common 

 boundary. This plane, he thinks, which formed the optical 

 boundary of the two media for light polarized parallel to the plane 



