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



539 



400. It is easy, however, to follow out their course in imagination to field 500. The 

 curves obtained for the nickel-capped tubes differ so slightly from those shown, that 

 it was not thought necessary to reproduce them here. A comparison of the numbers 

 in the subjoined tables will meet all requirements. 



The brass ring, which was found indispensable in the case of the iron and steel 

 tubes, and the absence of which in Steel Tube T. rendered the observations with it quite 

 untrustworthy, might without serious modification be dispensed with in the case of the 

 nickel tubes. As a matter of fact, Nickel Tubes I. and II. had been investigated and 

 Tube III. bored out before the necessity for the ring was realised. In these cases, 

 however, the differences between the corresponding volume changes in the nickel-capped 

 and brass-capped states are by no means excessive. The effect due to any mechanical 

 motion of the nickel cap because of the attraction between it and the tube must conse- 

 quently be much smaller in proportion to the true effect than in the case of iron and 

 steel. 



Nickel Tubes with Nickel Cap. 



Field. 



I. 



II. 



III. 



IV. 



V. 



VI. 



VII. 



25 



- -5 



+ -5 



+ 1-5 



+ 3 



+ 5 



+ 4-5 



+ 3-5 



50 



- 1 



+ '5 



+ 4-0 



+ 6-8 



+ 10-1 



+ 2-2 



- 7-5 



75 



- 4 



- 3-2 



+ -5 



+ 2 



+ 4 



- 15-5 



- 38-5 



100 



- 9 



-11-2 



- 11-1 



- 11 



- 11'4 



- 46-5 



- 75 



125 



-16.8 



-26 



- 30-5 



- 30-5 



- 33-5 



- 81 



-116-5 



150 



-24-5 



-41 



- 49 



- 49 



- 52 



- 109-5 



-143-2 



200 



-38 



-59-2 



- 82 



- 82 



- 82 



-156 



-179 



250 



-44-5 



-69 



-101 



-103-5 



-101 



-182-5 



- 201-2 . 



300 



-49 



-74-2 



-112 



-116 



-111-7 



-202 



- 208-5 



400 



-55 



-83 



-124 



-127-6 



-121-6 



-222 



-225 



500 



-58 



- 90-5 



-130 



ricKEL Tubes 



-132 

 with Brass 



-127 

 Cap. 



-224 



- 228'5 



25 



+ -5 



+ -1 



+ 2 



+ 5 



+ 6-5 



+ 4 



+ 3 



50 



+ -8 



+ 1-5 



+ 4-5 



+ 7-5 



+ 11 



+ 2-5 



- 4-5 



75 



- -2 



+ 1 



+ 1-5 



+ 4-5 



+ 5 



- 19-3 



- 35 



100 



- 5 



- 6 



- 9 



- 9 



- 10 



- 51 



- 71 



125 



-12 



-15 



- 27 



- 27 



- 30 



- 85 



-106 



150 



-19-5 



-27 



- 44 



- 46 



- 48 



-115 



-135 



200 



-35 



-47-5 



- 76 



- 78 



- 77 



- 158-5 



-175 



250 



-45 



-62 



- 99-5 



-101 



- 98 



-184 



-197 



300 



-49-5 



-64 



-116 



-116 



-110 



-200 



-213 



400 



-53 



-83 



-131 



-132 



-122 



-213 



- 228-5 



500 



-55-5 



-85 



-138 



-140 



-128 



-219 



-233-5 



It will be seen at once that in all fields higher than 100 there is diminution of 

 volume, and that on the whole the volume change increases with the bore. In the 

 majority of cases there is an increase of volume in low fields. The transition from tube 

 to tube does not follow a very regular law. Nos. III., IV., and V. differ so slightly that 

 they might easily have been different observations with one and the same tube. In 

 the case of both the brass cap and nickel cap the same peculiarity is shown. In low 



