AT BROUGHTON. 395 



The first of these objections is removed when 

 the parties making the chains are situated near 

 to some pubhc testing machine, as that at 

 Liverpool. The second objection has great 

 plausibihty, and I took the following methods 

 to satisfy myself how far it was really the case. 



It is well known, that if a body be stretched 

 with a force, such as but little to exceed j of 

 its ultimate strength, its elasticity will remain 

 perfect ; but if the force be greater, as i or f 

 of the full strength, the elastic force will be 

 impaired, and the length of the body somewhat 

 increased, as is shown in the following experi- 

 ment. I took a thin wire 20 feet long, and 

 fastening it firmly at one end to an elevated 

 object, let it hang vertically with a small weight 

 attached to the other end to render it straight : 

 then, hanging weights at the bottom, increasing 

 by lOlbs. at a time, and always taking the 

 preceding weights off before others were laid 

 on, I found that the wire constantly returned 

 to the same length, till 90lbs. had been laid 

 on, when it showed an inappreciable increase 

 of length; with 100 lbs. the increase was .03 

 inch, with 1401bs. it was .2 inch, and the 

 wire broke with 2081bs. The ratio of the 

 elastic to the breaking force was therefore 



90 3 , ^ 



208 = y Jf^early. 



3d2 



