414 Prof. A. de la Rive's Memoir of 



1818) an investigation of the passage of gases through narrow 

 tubes, from which it appeared that the velocity of the flow of 

 elastic fluids does not depend upon their density alone, but also 

 upon their individual nature. Various other points of chemistry 

 and physics, besides those which had electricity and magnetism 

 for their object, attracted his attention from time to time through- 

 out the whole of his scientific career. Now we have a note upon 

 the combustion of the diamond; then an investigation of the 

 sounds produced by the combustion of gases, or by the super- 

 position of a strongly heated iron rod upon a mass of copper at 

 the ordinary temperature (Trevelyan's experiment) ; and then, 

 again, researches upon the limit of vaporization, or upon the 

 evaporation of mercury at low temperatures. We may notice 

 two important memoirs — one upon the explanation of certain 

 optical illusions produced by bodies in motion, the other de- 

 scribing some new acoustic figures proceeding from the vibra- 

 tions of the stratum of air in contact with the surface of vibra- 

 ting plates. His elegant discovery of vegetation (that is to say, 

 of the power possessed by two fragments of ice when brought 

 together to become amalgamated by the fact of their simple con- 

 tact at a temperature above 32° F.), followed into its consequences 

 as it has been by Tyndall, has had a much greater influence 

 than perhaps he ever expected. In all these notices, even the 

 least important of them, we find an original idea, a new and 

 striking point of view, which enables us at once to recognize 

 Faraday. And, in connexion with this, how can we omit to 

 mention his simple and clear explanation of table-turning, and 

 the ingenious experiment by which he so clearly shows the mus- 

 cular efforts made unconsciously by the persons who, by laying 

 their hands upon the table, cause its movement ? 



Let us now dwell for a few moments upon some researches of 

 longer duration, the publication of which preceded, and also in 

 great part accompanied, his great works on electricity. 



In 1820 Faraday described two new compounds of chlorine 

 and carbon. One of them is solid, transparent, and colourless ; 

 it crystallizes in little prisms and in lamina?, and is obtained by 

 exposing to the direct action of the sun bicarbonated hydrogen 

 gas with a large proportion of chlorine. The other contains less 

 chlorine; it is liquid and colourless, possesses great density, and 

 is prepared by passing the former through an incandescent tube, 

 from which chlorine is set free. The discovery of these two 

 compounds filled up an important gap in the history of chemistry. 



Subsequently (in 1825), by the compression of the gas ob- 

 tained from coal, Faraday obtained a new compound, which, no 

 less interesting than the preceding from a scientific point of view, 

 had besides a great industrial importance. This was a bicarburet 



