554 



PROFESSOR KNOTT ON THE STRAINS PRODUCED IN 



Appendix (added March 21st, 1896). 



While this paper was passing through the press, certain aspects of the phenomenon 

 suggested questions which only experiment could answer. I was accordingly led to 

 make a new series of experiments with Steel No. VII. 



The extraordinary manner in which the tube differed from the other and earlier 

 borings has been noted above (§ 9 ; — see also the curves on Plates III. and IV.). 

 There is not the least doubt that the early experiments of January 2 were correctly 

 interpreted. At the very first observation made I was struck with the fact that the 

 movement of the meniscus in the capillary was in the direction opposite to what the 

 behaviour of the other tubes led me to expect. But the subsequent experiments of 

 January 7 th and 8 th fully corroborated the early results. It was after that date that 

 I measured the volume of Steel Tube VII. by weighing the filled-in mercury in the 

 usual way. 



Steel Tube VII. 



Volume Change in 10 " 5 c.c. 



Field. 



First condition, 



Second condition, 



Third condition 





January 2. 



March 4. 



(after annealing). 



25 



+ -1 



- 2-6 



-1-45 



50 



+ "6 



- 7-1 



-2-5 



75 



+ 2-5 



-11-4 



-2-1 



100 



+ 4-8 



-14-5 



- -5 



125 



+ 7-16 



-13-0 



+ -75 



150 



+ 8-2 



- 9-75 



+ 1-6 



200 



+ 6-3 



- 4-65 



+ 2-5 



250 



+ 3-4 



- 1-2 



+ 2-75 



300 



- 1-4 



+ 1 



+ 2-7 



400 



-11-4 



+ 3-9 



+ 1-9 



500 



-20-4 



+ 5-8 



+ -9 



As the early experiment on Steel VII. in different distributions of field had not 

 been so complete as was desirable, I set up the tube again on March 4th. To my 

 amazement the behaviour of the tube was quite altered. Nothing had been done to it 

 within that two months' interval except what was involved in the measurement of its 

 volume by means of filled-in mercury. Yet, whereas formerly there was diminution of 

 volume in high fields and increase of volume in low and moderate fields (see Plates III. 

 and IV.), now there was increase of volume in high fields and diminution in moderate 

 and low fields. The behaviour of the tube was, broadly speaking, reversed. Was it 

 possible that in its first condition, immediately after being bored out, the material of 

 the tube was in a critical and approximately unstable condition, out of which it was, so 

 to speak, shaken by the pressure of the mercury which was subsequently filled in ? If 

 so, then it was altogether peculiar to the steel. For Iron Tube No. VII., whose volume 



