Absolute Viscosity of Solids and Liquids. 



337 



The sharp doublet (to = 2) is nearly coincident with the two 

 lines which hitherto have been measured. The wave-lengths 

 of these lines are, viz : — 



After Lecoq de Boisbaudran. 



4170] 



> v. 



4031 J 



: 826-9 



After Deville and Mermet. 

 4171 



4033 



;}- 



820-3 



The accordance is even better than could well be expected. 



Finally, I will remark that the hypotheses of Mr. Lockyer 

 on dissociation of the elements are quite incompatible with 

 the results of my researches. The observations of Lockyer 

 within the spectra of Na and K prove only that, with lumi- 

 nous atoms as with sounding bodies, the relative intensity of 

 the partial tones may vary under different circumstances. 

 For the lines in question belong, without doubt, to the same 

 system of vibrations. . 



Lund, February 1890. 



XXXY. The Change of the Order of Absolute Viscosity encoun- 

 tered on passing from Fluid to Solid. By Carl Barus. 



1. fT^O my knowledge nobody has thus far defined the dif- 

 -1- ference between the solid state and the fluid states 

 quantitatively. In the case of liquids and gases viscosity can be 

 absolutely expressed with facility, and the data have therefore 

 to be stated with considerable rigour. This is not true for 

 solids, where the results are relative throughout. 



The present paper submits two methods for the coordination 

 of the viscous behaviour of solids and of liquids. In descri- 

 bing the differential method applied by Dr. Strouhal and 

 myself f, we incidentally pointed out the way in which the 

 relative viscosity of two solids may be stated in terms of the 

 respective sectional areas, by which the motion at the junction 

 of the two counter-twisted wires or rods is annulled. Suppose 

 that one of the wires is a solid, whereas the other is a very 

 viscous liquid. Then if the viscosity of the latter can just be 

 measured by transpiration-methods (§§4, 5), it follows that 

 the viscosity of the true solid with which it was counter- 

 twisted may also be absolutely expressed. This indicates the 

 first method of the present paper (§§ 8, 9). 



* Communicated by the Author. 



t Barus and Strouhal, American Journal, xxxiii. p. 29 (1887). 



