474 



SCIENCE. 



[N. S. Vol. VII. No. 171. 



The reviewer is aware that with all en- 

 deavor he has given but an imperfect ac- 

 count of this remarkable book. That 

 Klein's researches constitute a splendid 

 advance in the dynamics of the rotation of 

 a rigid body there can be no question. 

 One cannot but hope that the outline given 

 in these Princeton lectures may soon be 

 expanded and put in shape more easily 

 assimilable by persons moderately versed 

 in the theory of elliptic functions. The 

 boon of an appropriate lemma is ideal gen- 

 erosity, and not even a mathematician can 

 scorn its almost mathematical elegance. A 

 man may be a thoroughgoing soldier 

 enough on land ; but put him in the foot 

 ropes of the flying jibboom in a storm, and 

 he is apt to cut a most ludicrous figure. 

 Shift a physicist's foothold of Cartesian dif- 

 ferential coefficients, suspend him over an 

 abyss of non-Euclidian space, and he will 

 kick sturdily. Poor policy this, for a mis- 

 sionary ! 



Carl Baeus. 



Beown Univeesity, Providence, E. I. 



THE TRANSMISSION OF RADIANT HEAT BY 

 GASES AT VARYING PRESSURES."* 



Before describing my own investigations 

 on the transmission of heat by gases, I shall 

 refer briefly to the classical work of a some- 

 what similar nature by MM. Dulong and 

 Petit early in the present centurj^, ' Re- 

 searches on the Measure of Temperatures, 

 and on the Laws of Communication of 

 Heat,' Ann. of Phil., 1819. 



In their researches on the ' Communica- 

 tion of Heat,' Dulong and Petit used as the 

 cooling body a very large thermometer bulb 

 filled with mercury, and as the recipient of 

 the heat a large copper bulb or ' Balloon ' 

 about three decimeters in diameter, in the 

 center of which the thermometer bulb was 



* Abstract of a paper read before the American As- 

 sociation for the Advancement of Science, August 10, 

 1897. 



placed. The copper balloon was coated 

 with lamp-black on the inside, and kept at 

 any desired constant temperature by means 

 of a water-bath or melting ice. The ther- 

 mometer tube was of such length as to 

 bring the zero of the scale outside the bal- 

 loon ; and the thermometer was adapted to 

 be removed, heated and quickly replaced, 

 air-tight. The balloon was connected with 

 an air-pump capable of rapidly exhausting 

 it down to about two millimeters pressure, 

 and also with a gas-holder from which it 

 could be quickly filled with the gas whose 

 cooling properties were to be determined. 

 The rate or ' Velocity' of cooling of the ther- 

 mometer bulb was deduced from obser- 

 vations of the falling temperature at equal 

 intervals of time. 



With this apparatus Dulong and Petit 

 made many carefully conducted experi- 

 ments at differences of temperature be- 

 tween the thermometer and balloon rang- 

 ing as high as 300 degrees ; and with sev- 

 eral different gases besides air, ranging in 

 pressure from atmospheric to two milli- 

 meters. From the results of these experi- 

 ments they deduced several laws of cooling 

 which they held to be general in their 

 application. They sharply divided the 

 cooling into two parts : that due to convec- 

 tion — the actual contact of the surrounding 

 cooler gas renewed by its own currents, and 

 that due purely to radiation — the same as 

 would occur in an 'absolute vacuum.' 

 They derived a constant value for the lat- 

 ter, and values for the former varying with 

 different gases and different pressures. 

 They generally used the thermometer bulb 

 naked, with its natural vitreous surface, 

 but sometimes they silvered it. While 

 this radical change in the character of sur- 

 face greatly changed the loss of heat due to 

 radiation, it apparently had no effect on 

 that due to convection. 



MM. Dulong and Petit fell into the grave 

 error of deducing the behavior of the last 



