IRON, STEEL, AND NICKEL TUBES IN THE MAGNETIC FIELD. 



541 



however, differ in a very marked manner from Nos. V. and VII. It is only through a 

 comparatively small range of field that there is diminution of volume in the two last 

 named ; while in high fields both are characterised by comparatively large increase of 

 volume. A glance at the corresponding columns in the two tables will show how 

 different may be the behaviour of tubes cut from the same bar and almost identical in 

 form and dimensions. 



It will be noticed that No. 7 differs from No. 5 in much the same way as Nos. VII. 

 and V. differ. The tube with the higher numerical designation has either a greater 

 positive or a smaller negative change of volume than the tube with the lower distinguish- 

 ing number. If we subtract the volume changes of each No. Five from those of the 

 corresponding No. Seven in the same fields, we get two series of numbers remarkably 

 alike, as in the following table. The first row gives the fields, the second row the 

 differences of the corresponding volume changes of Tubes VII. and V., the third row 

 the same numbers for Tubes 7 and 5. 



Field. 



25 



50 



75 



100 



150 



200 



300 



400 



500 



(VII.) -(V.) 



-1-4 



-5-3 



-3-5 



+ 6-1 



+ 10-4 



+ 10-1 



+ 11-8 



+ 13'4 



+ 15-2 



(7) -(5) 



+ -4 



-3-1 



-55 



+ 2-9 



+ 11-1 



+ 9-1 



+ 11-4 



+ 13-8 



+ 15-1 



The conclusion to be derived from this comparison is, that although Nos. 5 and 7 

 are different tubes cut from the same bar, they differ from each other in precisely the 

 same way and to almost exactly the same extent as do Nos. V. and VII, which are 

 different stages in the boring out of a third tube cut also from the same bar. The very 

 marked manner in which No. 3 differs from No. III., No. 5 from No. V., and No. 7 from 

 No. VII., shows that different parts of one long bar may undergo appreciably different 

 kinds of strain when subjected to the same magnetising force. 



Passing now to the steel tubes, and comparing the results for Nos. 3, 5, and 7 with 

 those for Nos. III., V., VII. in § 9, we see at a glance how wholly different they are. 

 This is hardly surprising when we bear in mind the extraordinary diversity of behaviour 

 in the Tubes I. to VII. themselves. A detailed comparison leads to nothing definite. 



Passing, finally, to the nickel tubes, we find much greater similarity between the 

 two groups than in either of the previous cases. Nos. 1 and I., indeed, .might easily be 

 different experiments with one and the same tube, the differences in their behaviour 

 being no greater than could be produced by having the cap screwed up a little tighter 

 in the one case. No. 4 differs in detail from No. IV., but they are similar in type ; and 

 similarly with Nos. 7 and VII. The general resemblance between the groups is the 

 more striking, inasmuch as Nos. I. to VII. are successive borings of a tube which was 

 not part of the same bar that supplied Tubes 1, 4, and 7. Thus there appears to be 

 greater uniformity in the behaviour of nickel than in the behaviour of either iron or steel. 



