Intelligence and Miscellaneous Articles. 157 



were so, we could not explain many phenomena which only require 

 to be generalized in order to demonstrate the existence of this 

 property. 



Porous bodies present, in a very small space, a considerable amount 

 of internal surface ; the gases which penetrate into these substances 

 lose their repulsive force, and accumulate in them as though by the 

 influence of an extremely energetic attractive force. The pheno- 

 menon of porous bodies may be compared to that of capillarity ; and 

 just as the elevation of water in a tube may serve to show the exist- 

 ence of attractions between liquids and glass, the absorption of gases 

 by charcoal is a proof of the attraction which a solid, isolated and 

 continuous surface may exert upon gases. 



After ascertaining and measuring the absorption of gases by various 

 porous bodies, De Saussure called the attention of chemists to an 

 important fact, namely, that he had proved that gases condensed in 

 charcoal produced abnormal chemical actions ; since that time Dobe- 

 reiner discovered spongy platinum : these combinations, anticipated 

 by De Saussure, became more evident ; but it was seen that they 

 were preceded by a condensation of the gases, and, in fact, were the 

 consequence of this ; they consequently serve to prove it. 



As soon as the discovery of Dobereiner was announced, Thenard 

 and Dulong repeated his experiments with some variations. They 

 ascertained that the properties of spongy platinum were possessed 

 by all porous bodies ; they found them to exist in thin leaves of all 

 the metals, and even in pounded glass or porcelain. Now if these 

 combinations be the consequence of condensation, it must be admitted 

 that this condensation takes place upon the metallic leaves and on 

 the fragments of glass. 



To these various experiments we must add the leading fact an- 

 nounced by M. Pouillet, — the absorption of oxygen in a platinum 

 thermometer, and the condensation of the vapour of water by glass. 



Moreover, this general idea admitted by geometricians, has often 

 constituted the study of physicists, who, not hoping to prove it 

 directly, have sought to verify it by indirect but very precise expe- 

 riments. M. Arago proposed to cause the interference of two rays 

 of light passing through the air, the one at a certain distance from, 

 the other in contact with, a solid surface ; he has recently returned 

 to the same question, making use of the oscillations of a magnetized 

 needle. 



There exist, therefore, indirect proofs, which however to us appear 

 conclusive, of the condensation of gases by solid surfaces ; thus it 

 was with nearly a certainty of success that we undertook the follow- 

 ing experiments. 



We filled glass vessels, which had been carefully measured, with 

 puiVerized solid substances ; we ascertained the densities of the 

 powders and the quantities contained in the vessels, and we had all 

 the elements necessary for calculating the space left free. 



Thus arranged, the vessels were connected with a good air-pump 

 and with a manometer with two branches ; one of the two branches 

 was open to the air, it allowed the pressures to be ascertained ; the 

 other was closed, and communicated with the vessel by a tube and 



