APPARATUS FOR MEASURING STRAIN AND APPLYING STRESS. 



269 



weights used for applying the torque were made by Oertling, or were copies therefrom, 

 and the twelve 200-pound weights for applying the tension were standard weights 

 forming part of the equipment of the 100-ton Buckton testing machine in the laboratory. 

 The method of suspension ensures that all the tension load is evenly distributed in the 

 section of the specimen, and there is no correction for friction, 

 as the load is a dead-weight one. 



In applying the torque a small correction must be made 

 for the friction of the pulleys. This was determined as 

 follows : — 



The pulley was first balanced by winding lead strips round 

 its arms until it would stand in any position, or when rotated 

 by a smart pull, continue to revolve several minutes. Next, 

 equal weights, A B, were attached to the spring steel tape 

 passing over the pulley with the ends vertical, and the additional 



mass required to just start the pulley in one direction was determined. The weights 

 were then reversed, and the additional mass required was again determined, the mean 

 value of the two being taken. 



Let Tj be the tension on one side. 



T, 



the other side. 



We have 



T 3 = tension horizontally. 

 T ... 



T, 

 T, 



e*2 



very approximately ; from which we get by a simple transformation, 



This value was calculated throughout the range. As an example the following 

 numbers may be quoted for the left-hand pulley : — 



Table II. 



T : pounds. 



T 3 = VT 1 T 2 



T, pounds. 



T 3 =VT!T 2 



2 



2-0078 



12 



12-0118 



4 



4-008 



14 



14-012 



6 



6-0088 



16 



16-013 



8 



8-0095 



18 



18-014 



10 



10-0113 



20 



20-015 



The correction for the other pulley was slightly less. 



