Viscosity encountered on passing from Fluid to Solid. 341 



meniscus, while the lower end of the capillary is submerged 

 in glycerine. 



6. By applying equation (3) I obtained the r) expressed in 

 the following Table : — 



Table I. — Transpiration of Marine Glue. 

 P = 10 6 dynes ; r = *0406 centim. ; temperature (say) = 25°. 



Date. 



t. 



I. 



v xicr 6 - 



May 7, 1889. 12 h 



Dec. 7, 1889, 12 h 



sec. 

 



18-5 xlO 6 



cm. 

 3-7 



7-2 



cfgs. 

 200 





This is a striking result, remembering that a sphere of the 

 cement, if placed on a plane surface, will run out to a flat 

 cake in a few months. Nevertheless this type of viscous fluid 

 is 20 billion times as viscous as water at the same temperature. 



After long continued transpiration the thread of marine 

 glue shows two strata. The advance portion is amber-coloured 

 and less viscous, the rear portion brown, clearly containing 

 most of the shellac. Hence the observed rj is probably some- 

 what low. (Cf. § 10.) 



7. Paraffine (melting-point 55°) treated in the same way 

 showed no transpiration. The tube (2p = "082 centim.) was 

 nearly of the same bore as above, and the length of thread in 

 the most favourable case 2*2 centim. The motion, if any, 

 must have been below *01 centim. Hence the viscosity of 

 the paraffine must be greater than 2 x 10 11 g/cs at about 25°. 

 It is nearly impossible to insert a capillary paraffine thread in 

 a tube, free from the vacuum- bubbles due to contraction on 

 cooling. 



Solids. 



8. Having obtained the result in § 6, I proceeded to use it 

 for obtaining the viscosity of hard steel by the method of 

 comparison indicated in § 1. The apparatus was essentially 

 like that of my earlier experiments*. To secure additional 

 safety f I introduced the principle of substitution, whereby 

 the steel wire and the rod of marine glue were consecutively 

 subjected to known torsion-couples, in ways otherwise iden- 

 tical. From the enormous viscosity of steel, as compared 



* From the context it appears that the method of substitution is pro- 

 bably necessary. 



f American Journal, xxxiv. p. 2 (1887). 

 Phil. Mag. S. 5. Vol. 29. No. 179. April 1890. 2 D 



