226 LIFE AND LABORS OF HENRY GUSTAVUS MAGNUS. 



and simultimeously two of the most skillful experimenters of the time 

 took up this important subject. Magnus communicated the results of 

 his experiments to the Academy of Berlin November 25, 1841, and a 

 few days after, December 13, 1841, M. Eegnault gave to the scientific 

 Academy of Paris his researches upon the same subject. These me- 

 moirs are master-pieces. Magnus says, in the opening of his: '•! 

 decided to take up the study of this important question, knowing well 

 that I should gain very little, if any, distinction by the work, however 

 long or laborious it might be, since its object was only to confirm one 

 of two figures already known." This, the dictate of his excessive mod- 

 esty, is the only error of his memoir. Contrary to his opinion, the work 

 was one of his strongest claims to renown. 



Eepeating first the experiments of Gay Lussac, which consist in ob- 

 serving the dilatation under constant pressure of a certain quantity of 

 air contained in a glass globe, by means of a small globule of mercurv, 

 which rises and falls according to the dilatation in the slender neck of 

 this globe, Magnus soon discovered that there were several causes for 

 uncertainty, but found as mean result of his experiments the figure 

 0.3G9 iuvstead of 0.375, probably on account of the greater dryness of the 

 air. He then tested Rudberg's method. His apparatus consisted of a 

 tubular reservoir of glass, communicating with a manometrical appa- 

 ratus, and inclosed in a triple envelope of sheet iron, in the interior of 

 which any constant temperature desired could be maintained. By in- 

 crease of pressure the volume at 100° was reduced to what it had been 

 at 0°. A very simple equation resulting from the law of Mariotte gave 

 the coefiicient of dilatation with the difference of pressure observed. 

 The value of the coefiQcient thus obtainedfortheatmosphere wasa very 

 little greater than that found by Rudberg. !N"ot content with this im- 

 portant numeral, IMagnus experimented with different gases, and found 

 for hydrogen a coefijcient of dilatation less than that of the atmosphere, 

 viz, 0.305(550 ; for carbonic and sulphurous acids, on the contrary, coeffi- 

 cients of dilatation greater than that of the atmosphere; for the former, 

 0.3C90S7 ; for the latter, 0.3S5G18. The law of Gay Lussac was but an 

 jipproximation to the truth. Magnus proved that gases did not dilate 

 equally, as had been until then generally admitted. 



M. Eegnault had made four series of experiments. The first two, in 

 which he changed at the same time both the volume and the pressure, 

 gave him two coefflcients for the atmosphere, both equally sure, 0.3GG23 

 and 0.3GG33. The third and fourth gave, with the volume constant and 

 the pressure varied, 0.3GG70 and 0.3GG50 as coefficients of dilatation for 

 the atmosphere. While operating on different gases, he had arrived at 

 results very nearly identical with those of Magnus. The two experi- 

 menters concluded .to replace the old coefficient 0.375 by the figure 

 0.3GG for the atmosphere, and decided that the different gases dilated 

 unequally. 



The cause of the difference between the figure found by Gay Lussac. 



