282: Procccdiiif/f; of Iiidiand Acdihniij of Science. 



to attach themselves to surroitncling crystitls. As the crystals huikl \ip there 

 is a shrinking in the length of the specimen. This shrinking continues until 

 the more easly occupied si)ac('s are filled, the displac-ement gradually be- 

 coming less and less until it is not detectable. Rut there is still strain left 

 for not all metals anneal perfectly at ordinary tcnii)eratiiix's. When more 

 strain is produced by applying stress there is an agitation of the particles 

 of the metal and the shrinking starts again. ;is soon as the stress is re- 

 moved. Since in the drawn wire a large ikm- cent of tlie metal is in the 

 amorjihus phase it is only logical to expect that there would be a greater 

 recovery for a given immediate strain thaii in jiii annealed specimen. 



It is easily seen from this viewpoint how increased stress and increased 

 time of applying stress produce greater recovery. Starting with an annealed 

 specimen, the greater the stress applied the more crystals there are broken 

 down and the more anioi-jihous substance there is to take part in the process 

 of crystal formation, hence the greater contraction. The same argument 

 holds for increased time of applying stress. 



There is no legitimate l>asls of comparison of the rai>i(iity of contraction 

 of two different metals. A susi)ended alumirnuni wire a meter long meets 

 but comi)aratively little opl>osition to contraction due to its own weight. A 

 piece of lead wire a meter long suspended by one end. when freshly annealed 

 flows of its own weight. This indicjites the great force that must be over- 

 come, in the case of lead, by the forces of recrystallization. even to main- 

 tain the original lengtli. Since exiierimental results show that there is actu- 

 ally greater recovery for lead ]ier unit of length per unit of stress applied. 

 other conditions being the .same, in spite of this handicap, than for either 

 copper or aluminium we .see how much gri-ater nuist l)e the forces that 

 cause the shrinkage in lead. l>ut lead anneals ]ierfectly at ordinary tem- 

 peratures, aluminium at higher temperatures and coi)i)cr at still higher 

 temperatures, just the order that must be expected if recovery is to be 

 accounted for by recrystallization The fact that greatest recovei*y takes 

 place where greatest activity of iccrystallizatiou is involved is a strong 

 point in favor of the hypothesis that the one is (U-pendent on the other. 



This idea fits exactly Prof. :MiclK'lson"s ( .". ) picture of elastlco-viscous 

 recovery. The force that causes the shriidvage is an elastic force but pro- 

 duces no instantaneous effect for just the same reason that a rubber band 

 stretched on a block of wood cannot contract to its original length. But 

 cause the block of wood to contract gradually l>y any means whatsoever 

 and the rubber band follows it. In just the same manner the elastic forces 

 which are contained within the remaining crystalar structui-e cannot act 

 because they encompass the amorphous phase of the material. lint let, this 

 phase begin to reform into crystals. It is wedged between the crystals 

 and fills all the spaces between them. As it joins neighboring crystals or 

 forms new ones the original crystalar structure begins to make a readjust- 

 ment because of the strain which it is under. The more active the amor- 

 phous idiase is the more rapidly the whole structure contracts. 



Such a conception of tlu' state of a metal after strain will account for 

 what I'rof. Michelson (o) calls "Lost ^Motion"', the failure of a sti'ained 

 metal to return to its original confignnition when the stress is removed. It 

 is found that the more nearly perfect the process of annealing is, the greater 



