170 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



therefore the co-efficient of friction should be 0.000058 x 

 pressure ; but actual observations give a result very near- 

 ly twice as great. Hence it is concluded that in the strik- 

 ing of the molecules against the walls, their velocities are 

 not completely equalized. The absolute co- efficient of 

 friction for the air is given by these authors at 0.000189, 

 being exactly midway between the four previous deter- 

 minations made by Graham, Maxwell, Meyer, and Pu- 

 ling. The co -efficients of friction for hydrogen and for 

 carbonic-acid gas were determined by them to be respect- 

 ively 0.488 and 0.806 (that of the air being 1), agreeing 

 closely with the values deduced from the observations of 

 Graham. The co-efficient of friction for pure steam at a 

 temperature of 15 Centigrade resulted about one half of 

 that of air. The investigation into the dependence of the 

 co-efficient of friction on the density or barometric pressure 

 of the gas shows that the diminution of friction with press- 

 ure is greater the rarer the layer of gas. Further experi- 

 ments bearing upon the kinetic theory of gases were made 

 by Messrs. Kundt & Warburg in that they attempted to de- 

 termine the co-efficient of conductivity for heat. Their ap- 

 proximate result for the atmosphere is one eleventh less than 

 that deduced a few years ago by Stefan; and from these same 

 observations there resulted also the value of the radiating 

 power of glass, which agreed nearly with that of Lehnebach. 

 The variation of the radiating power with the temperature 

 does not seem to them to have been reliably determined in 

 the classical work of Dulong and Petit. Monatsbericht der 

 K. Akademie von Prenssen, Berlin, 1875, 160. 



THE CONNECTION BETWEEN FLUORESCENCE AND ABSORPTION. 



Dr. Sorby, President of the Royal Microscopic Society, 

 states that he has been surprised to find that some of those 

 who have paid considerable attention to such subjects have 

 so far misunderstood the question as to suppose that the 

 light of fluorescence consists of rays which are, as it were, 

 reflected by this solution, and do not penetrate through it, 

 so that the spectrum of the fluorescence would show a bright 

 band in the same place as some dark bands seen in the spec- 

 trum of the transmitted light. This is certainly an error, 

 and his own observations agree more nearly with Lubarsch, 



