202 



M. R. Thalen on the Determination of 



standing that the load was not increased. For it may in general 

 be noticed that in this kind of investigation, time, as Wertheim 

 has already showed*, exercises an important influence, which 

 Hodgkinson, indeed, endeavoured to determine quantitatively. In 

 my experiments I have continually noted the influence of time, 

 although the apparatus, on account of a leak in the hydraulic 

 press, did not allow any measurements. 



If the load be taken smaller than that which the bar has 

 already borne, no permanent elongation is perceived before the 

 load in magnitude is nearest the greatest which has already been 

 applied. If the latter load is exceeded, increments occur in the 

 permanent elongations, and increase in the same measure the 

 more rapidly the more the bar had been previously stretched. 

 (See Table I. and fig. 1.) 



If this be applied to a metal wire which has been conside- 

 rably stretched in drawing, the permanent elongations, accord- 

 ing to the above, must at first be but slightly perceptible. But 

 when the magnitude of the load approaches that at which it was 

 drawn, permanent elongations must arise, which with greater 

 loads are very perceptiblef. It is thus easy to see that the limit 

 of elasticity in wires must be capable of sharp definition. 



If now the loads are taken several times successively just as 

 large as or less than those which the bar has already borne, 

 and they are then gradually increased, a peculiar phenomenon is 

 observed, which deserves a closer attention. It is illustrated by 

 fig. 5, to which the Table below belongs, and by fig. 1 with 

 Table I. 



Table V. 

 Hard Steel. A=17'13. 



No. 



P. 



AL. 



No. 



P. 



AL. 



No. 



P. 



AL. 



1 



280 



00 



12 



719 



0-8 



23 



980 



35-2 



2 



339 



00 



13 



748 



1-2 



24 



980 



35-7 



3 



397 



.00 



14 



777 



17 



25 



980 



36 



4 



456 



00 



15 



806 



25 



26 



980 



36-4 



5 



514 



01 



16 



835 



46 



27 



980 



366 



6 



543 



01 



17 



865 



83 



28 



980 



36-9 



7 



573 



0-1 



18 



923 



181 



29 



1040 



44-3 



8 



602 



0-2 



19 



980 



307 



30 



1098 



59-5 



9 



631 



0-3 



20 



980 



32-9 



31 



1156 



76-9 



10 



660 



0-4 



21 



980 



340 









11 



689 



0-5 



22 



980 



34-7 









According to this Table ten stretchings had successively taken 



* Loc. cit. p. 55. 

 t Morin, Resistance des materiaux, pp. 8 & 9, 



