LIFE AND LABORS OF HENRY GUSTAVUS MAGNUS. 227 



on one liand, and by liudberg', Magnus, and M. Eegnault, on the other, 

 was that upon the interior surface of the vessel in which the dihitation 

 of the air was observed, there was a stratum of humidity whicli passed 

 into the gaseous condition when the reservoir was heated to 100°, and 

 thus increased the dilatation. It was evident that an effect of the same 

 kind might be i)rodnced by the condensation of the gas itself, on the 

 surface of the vessel. To jirove the fact Magnus ascertained two 

 measures of the coefficient of dilatation of a single and the same gas, 

 sulphurous acid, increasing greatly in one case the extent of glass sur- 

 facein jH-oportion to the volume of gas coming in contact with it. This was 

 effected, by introducing a number of globules of glass into the reservoir 

 containing the sulphurous acid. He obtained as coefficient of dilatation 

 a value greater than b^^ the ordinary i^rocess without the globules of 

 glass, and while confirmiug the fact that gases condense at low tem- 

 peratures upon solid bodies, gave at the same time the measure of this 

 condensation. 



After his researches upon the dilatation of the air at high temperatures 

 and upon the tension of steam, finding himself again in competition 

 with M. Regnault, Magnus left the field to be explored by the illustrious 

 French savant, with far greater resources than he could command, re- 

 suming, however, at intervals, his favorite study of gases and vapors. 

 In 1860 and ISGl he published a very important article upon the trans- 

 mission of heat through gases in the double aspect of conductibility 

 and radiation. Placing a thermometer in a. glass vase heated moder- 

 ately and filled successively with different gases or vapors, he found 

 that the thermometer was heated differently in different gases, and 

 indicated a lower temperature in any one of them than in a vacuum. 

 He concluded from this that gases transmit very little if any heat by 

 conductibility, and absorb a considerable portion of radiant heat. Only 

 one gas, hydrogen, he declared an exception to this rule, atleastasregards 

 the first point; the thermometer rises higher in this gas than in a 

 vacuum, notwithstanding, as he also observed, that it absorbs radiant 

 heat in the same proportion as the atmosphere, azote, and oxygen. 

 The thermometer rose higher when the gas was more dense, which 

 seemed to indicate that gases conduct heat like the metals. This was 

 one proof more in confirmation of the theory, making a metal of hydro- 

 gen, which has since been fully established by the beautiful experiments 

 of Graham. This conductibility of hydrogen is well exhibited when it 

 is surrounded by a non-conducting substance such as eider down or 

 cotton, so that the currents produced in it may not be disturbed. 



As we have said, all gases, without exception, absorb radiant heat, and 

 in greater proportion as the pressure is greater. Those which absorb the 

 least are the atmosphere, nitrogen, and oxygen, and, almost to the same 

 degree, hydrogen. Among colorless gases, ammonia first, then olefiant 

 gas, arrests most readily the radiations of heat. The difference in the 

 transmission of radiant heat tlu'ough different gases varies with the 



