﻿Barus and SProuhal — Viscosity of Steel. 



447 



The ends*of this twist- 

 ed system are now to be 

 secured to the blocks of 

 brass ABC and DEGF. 

 One method of fastening 

 is given (J- actual size) 

 in figure 2, the parts of 

 which are lettered simi- 

 larly to figure 1. The 

 two wires, w and cc, are 

 pressed firmly against a 

 little rectangular piece 

 of steel, o by aid of the 

 bolt pp' and the nut qq'. 

 The bolt is provided 

 with a square hole near 

 its head, through which 

 o and the steel wires 

 may easily be passed. 

 A little pin prevents o 

 from rotating around 

 the axis of the screw, 

 thus diminishing liabil- 

 ity to breakage. In the 

 apparatus figured it is 

 necessary to slide the 

 bolts pp' over the wires 

 w. x, before the torsion 

 is applied by fastening a. 



In a more convenient 

 form of apparatus, per- 

 haps, we replace the 

 brass blocks ABC and 

 DEGF by little hand 

 vises, the axle of the 

 lower one of which has 

 been perforated and fit- 

 ted with a screw subserv- 

 ing the purposes' of r 

 in the figure. By aid of 

 a disc of lead vertical 

 symmetry of the whole 

 apparatus is here also 

 maintained. 



The advantages of this 

 form of apparatus, apart 

 from our own special 

 purposes, is this, that 



1, 2. 



Fig. 1. — Differential apparatus for torsional 

 viscosity (scale £). 



Fig. 2. — Device for suspension (scale -J). 



