56 MM. A. Kundt and E. Warburg on Friction 



I. Absolute coefficient of friction /L6 of air, determined from 

 three series of experiments. 



Thickness of the stratum of air. 



^ = 01104 centim. 

 d 2 =0-1967 „ 

 d 3 = 0*2802 „ 



/xforl5°Cels. 



0-000193 centim. sec. 

 186 „ 

 189 



Mean . 0-000189 



We attach the least importance to the value obtained from d 19 

 since the distance of d i was determined less accurately than those 

 of d% and d 3 . 



Maxwell finds for 15° C 0-000198 



Meyer, from his last experiments by Maxwell's"! ~ ™^q 7 

 method J 



Meyer, from transpiration experiments . . . 0*000182 



Puluj *, from transpiration experiments . . . 0*000185 



Our value therefore approaches nearer than the older ones to 

 that deduced from transpiration experiments. 



II. Putting fju for air = 1, the following values of this quan- 

 tity were obtained : — 



For 



From experiments with the 

 distances 



Mean. 



From Graham's 

 transpiration 

 experiments. 



d v 



d 2 . 



d 3 . 



Hydrogen 



0-495 

 0-811 



0-485 

 0-805 



0-484 

 0801 



0-488 

 0-806 



0-4855 

 0-807 



Carbonic acid ... 



Maxwell explains the divergent results obtained by him for 

 hydrogen and carbonic acid by impurity of the gases employed. 



III. The coefficient of friction of pure aqueous vapour for 15° 

 Gels., measured at 21° Cels., and with a tension of about 16 

 millims., amounted to 0*526 of that of air at 15°. 



Passing now to the experiments which were made for testing 

 the above theory, we remark that the chief difficulty in them 

 consisted in placing in a given space gases of small density as 

 pure as possible. It was soon found that here nothing could be 

 effected with caoutchouc connexions ; and hence all the junc- 

 tions used were made of glass ; while, in order to secure the ap- 

 paratus against fracture by expansion of the glass, at suitable 

 places thick, wide, elastic, glass tubes bent in three directions at 

 right angles to one another were inserted, which gave to the 



* Sitzungsberichte der Wiener Akademie, 1874, vol. lxix. p. 289. 



