﻿452 Barns and StrouTial — Viscosity of Steel. 



Now in order to make sharp comparisons on the viscosity of 

 solids, in order to investigate its dependence both on time and 

 on stress, the apparatus is so to be adjusted that like stresses 

 produce like strains in the substances compared. Hence put 

 (/>=</>„ whence 



d* G X L L 



w^r^Lr^^L, (2) 



This applies to the bifilar apparatus for ^=0. The equation 

 (2) shows at once how to study viscosity under conditions in 

 which like stresses produce like strains upon like sectional 

 areas of the viscous solids compared. 



Notation. — In Bulletin 14 we used the word " retentiveness"' 

 in the restricted German sense to designate magnetic stability,. 

 or the property in virtue of which a magnet resists such influ- 

 ences as temperature, percussion, time. The common English 

 use of the term is much broader than this and refers to residual 

 induction* in a general way. Fortunately the context of our 

 paper is sufficiently clear and does not admit of serious misap- 

 prehension. Inasmuch as measurement of total induction has 

 not yet fallen properly within the scope of our work, we pur- 

 posely withhold many obvious allusions to magnetic permea- 

 bility. We moreover retain the term permanent magnetization 

 to denote the magnetic moment per unit of mass of a perma- 

 nently saturated rod, for the sake of uniformity with our earlier 

 notation. Its ratio to magnetic intensity is therefore the density 

 of steel. 



To avoid troublesome circumlocution we use the adjective 

 "viscous" with the very broad meaning of "pertaining to vis- 

 cosity." Such expressions as "viscous phenomena" though 

 not elegant are convenient. Similarly we often speak without 

 confusion of "linear magnetization" where "magnetization of 

 a linear rod " is meant. 



EXPEEIMENTAL DATA. 



Introductory explanations. — The following tables, Nos. 1 to 

 26, contain results for the viscosity of steel in different states of 

 temper. To these are appended other tables of a miscellaneous 

 kind. For convenience of comparison we insert a little index.. 

 The apparatus used in obtaining the data are designated by 

 the Roman numerals in the first column. Nos. I to IV are 



* Mr. Bwing proposes a new aud very elegant extension of the current use of 

 "retentiveness." He defines it as "resistance to any change of magnetic state- 

 which (magnets) exhibit whenever the magnetic field in which they are placed 

 suffers any change."- -Phil. Trans., ii, 1885, p. 526. 



