﻿454 



Barus and Strouhal — Viscosity of Steel. 



Experiments proper. — In tables 1 to 26, R denotes the dis- 

 tance between mirror and scale, L the efficient length of the 

 steel (bifilar) wires, I the distance apart of the upper and lower 

 points of suspension. <p (in degrees) is the stored torsion, 

 imparted to the whole length (30 cm ) of wire, positively or neg- 

 atively as specified, whereas <p (in radians) is the amount of 

 angular motion (differential detorsion) of the bifilar system due 

 to viscosity per centimeter of length of the sj^stem of two steel 

 wires. Positive values of <p and <p refer to the same angular 

 direction, and <p is arbitrarily put zero (to fix the coordinates) 

 at the time one hour after the twist <p has been imparted. This 

 is the best conveniently available method for comparing the 

 divers data. Other methods would have compelled us to wait 

 for the subsidence of motion, certainly several months in each 

 oase. Moreover, to obtain extreme degrees of accuracy, it is 

 necessary to study viscosity under circumstances of constant 

 temperature, and in a place where the viscous yielding may 

 proceed unaccompanied by tremor or vibratory motion of the 

 apparatus. For these nice experiments we are not now 

 prepared. 



The tables furthermore contain the date, the number of 

 hours (h ) elapsed since the beginning of the experiment and 

 the arbitrary deflection, <p (radians per centimeter of bifilar 

 length),"* for each of the times specified. The radius of the 

 wires is given under p. Finally the sense of the couples actu- 

 ating the bifilar body is indicated by r (torsion), b (bifilar),/ 

 (flexure). 



Table 1.— Apparatus I. 



fc21^»; Z=27 cm ; /<0-2< 

 48, glass-hard, V=+ 180°. 2p= 



n . Rods: 

 :0-082 cm . 



No. 47, 



hard, i/>= — 180°; No. 



Date. 



0xlO 3 



h 



<p x 10 3 



Date. 



0xlO 3 



h 



</>o x 10 3 



21/8, 6 h 08 m 

 6 21 



(*) 



0438 

 0-468 



o-oo 



0-22 

 1-00 



(*) 

 — 0-030 



+ 0-000 



25/8, 



9 h 05 m 

 7 01 



0615 

 0-632 



91 92 



0156 



7 08 



26/8, 



9 h 10 m 

 4 08 



0-653 

 0-670 



114-52 



0-194 



22/8, 9 h 57 m 



0*543 

 0*552 



0-555 



15-82 

 23-83 



24-77 



0-075 

 0-084 

 0-087 





5 58 



6 54 



27/8, 



9 h ll m 

 7 36 



0-695 

 0-714 



140-26 



0-237 



23/8, 9 h 08 m 

 12 31 

 5 37 



0-568 

 0-572 

 0-577 



39-00 

 42-38 



47-48 



o-ioo 



0-104 

 0-109 



28/8, 



9 h 21 m 

 6 55 



0-734 

 0-755 



164-00 



0-276 



29/8, 



10 t 12 m 

 6 17 



0-780 



0-792 



188-11 



0-318 



24/8, 9 h I7 m 

 5 13 



0-588 

 0-600 



67-12 



0-126 





* Adjusted r—b—f. 



* In practice (p is the angle between the normals of the upper and lower mirror 

 divided by the efficient length of wire. 



