338 Mr. C. Barus on the Change of the Order of Absolute 



My second method for measuring the viscosity of solids 

 absolutely is direct. It is capable of yielding results of any 

 desirable accuracy, supposing the necessary facilities for an 

 adjustment free from vibratory disturbances are given 

 (§§ 12, 13). 



Gases and Vapours. 



2. Results for the viscosity of gases and vapours are given 

 by many observers *. The data present some curious aspects ; 

 thus, for instance, the viscosity of vapours f is frequently 

 smaller than the viscosity of gases. The order of viscosity 

 (77) is about 10~ 4 g/cs (cf. § 18.). Results for the viscosity of 

 substances in the neighbourhood of Andrews's critical tempe- 

 rature are not available. Such an investigation would be 

 highly desirable (§ 18). 



Liquids, 



3. The literature contains extensive researches and is 

 systematized in Landolt and Boernstein's Physical Tables J. 

 The data are easily expressed absolutely, by aid of Slotte's § 

 values of the viscosity of water between 0° and 100°. If 

 water at 20° be taken as a type liquid, rj = '01(g/cs) (cf. § 18). 



Viscous Liquids. 



4. Data are wanting. 



My experiments were made with marine glue || . The 

 method is simple. A fairly wide capillary tube, a be, pro- 

 vided with a cylindrical open reservoir, a, at one end, was 

 half filled with marine glue, the thread extending from the 

 reservoir, a, as far down as the middle, b, of the tube. The 

 other (open) end of the tube was inserted into the flask, dddd, 

 from which the air was then exhausted. Thus a pressure of 

 about 1 atm. is continually brought to bear on the reservoir a 

 of the tube, the other end, c, being in vacuo. A lateral arm, 

 e, closed by fusion, facilitates the exhaustion. A small vacuum- 



* Summarized in 0. E. Meyer's Die kinetiscJie Theorie der Gase, 

 Breslau, 1877, pp. 138 et seq. 



t The most complete set of data are those of Puluj, Phil. Mag. [5] vi. 

 p. 157 (1878). Lothar Meyer, E. Wiedemann, and others have contri- 

 buted to the subject. 



X Physikalisch-chemische Tabellen : Berlin, J. Springer, 1883, p. 153. 



§ Slotte, Wied. Ann. xx. p. 267 (1888). References to other researches 

 (O. E. Meyer, Poiseuille, Rosencranz) are there given. 



|| A valuable cement being (nominally) a specially prepared mixture of 

 rubber and shellac. It has a pitchy consistency, and can be thickened 

 by adding shellac. 



