MIJ. I- 



OK T11H IJKI-OVKKY OK IKON 0* OVKKSTKAIX. 



he length of 



Tins instnnuent gTO the extend, ring * -JJ* * i 



tll , s,K,imen under test. It enabled elongations to * measured to ^- 00 th of an 



ill( ,, S to be measured to that degree of precision w,th ease ft."**"* . lh .;' 



^tnment was iound especially convenient on account -of the facility with winch it 



,;,,,, a! the ,,id distance-piece) be immediately re-apphed to a specimen winch 



,,,,1 just l*en strained beyond its yield-point ; and also on account of t readme** 



wit h' whirl, the correct adjustment of the instrument itself could be tested 



Th, s,H,i,n,ns e.nployed were, with one or two exceptions, 18 to 20-mch lengths , 

 steel-.-*!. I inch in diameter, of a quality which may be descnbed as semi-mild. 

 detail, of the particular rods employed in the various experiments will be given when 

 these C....U- to be described. Here, us illustrating the general character of 

 naterial the chemical analyses and elastic characteristics of two of the bars made use 

 of will IK- "iven The first is that from which diagram No. IX. has been obtained. 

 \ neeimen imm it showed a well-defined yield-point at a stress of '23 tons to the 

 snuaiv inch, and gave an ultimate strength of 36 tons per square inch of original an-,, 

 with an elongation of 2'4 ler cent, on an 8-inch length. The second bar is that from 

 which diagrams Nos. IV. and VII. have been obtained ; it was characterised 

 small Haw running up the centre through the whole length of the bar. A well- 

 d.-tined yield-ix.int was not obtained with specimens from this bar; there was si 

 distinct departure from obedience to HOOKE'S law, at a stress of about 22 tons per 

 squaw inch, but the yield-point should, perhaps, be placed as much as 6 or 7 tons higher 

 than this stress, at which elastic behaviour broke down* The ultimate strength of 

 the material as obtained from a short specimen was 39 tons per square inch, the 

 elongation being only about 20 $ per cent, on a 3-inch length. The chemical analyses 

 of these two bars were kindly supplied by Messrs. EDGAK ALLEN and Co., Sheffield, 

 from whom the material was obtained ; they are as follows : 



- tlic tii^t mlnnm nf tht ta'ili; on ji. 15. 



