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XV. — The Strains produced in Iron, Steel, Nickel, and Cobalt Tubes in the Magnetic 

 Field. Part U. By Professor C. G. Knott, D.Sc, F.R.S.E. (Plates I. and II.) 



(Read 6th June 1898.) 



CONTENTS. 



§ 1. Introduction, ..... 



$ 2. Methods of Experiment, . 



§ 3. The Strain Coefficients, . 



§ 4. The Bored Nickel Tubes, 



§ 5. The Coiled Nickel and Cobalt Tubes, 



PAGE 



457 

 458 

 459 

 461 

 463 



The Bored Iron and Steel Tubes, . 

 Curious Behaviour of Iron Tubes, 

 The Dilatations in Iron and Steel, 

 The Coiled Iron Tubes, 

 General Conclusions, 



PAGE 



. 464 

 . 466 

 . 470 

 . 471 



. 472 



§ 1. Introduction. — The remarkable changes produced by magnetization in the 

 internal volumes of hollow cylinders of iron, steel, and nickel have been described in 

 Part I. (see Trans. R.S.E., vol. xxxviii. pp. 531-555). As pointed out in the 

 closing paragraph, a complete discussion of these changes had to be " deferred until 

 direct measurements of elongation had been obtained with the various tubes under the 

 same magnetic influences." It was not possible, of course, to measure the elongations of 

 all the tubes that had been experimented with ; for of these, eighteen (Nos. I. to VI. 

 of each inclusive) were no longer in existence, having been the successive stages 

 through which No. VII. was brought from the condition of small bore and thick walls 

 to that of wide bore and thin walls. 



As the investigation with the existing tubes proceeded, it became more and more 

 matter for regret that the idea of measuring the elongations as well as the volume 

 changes of the successive tubes had not occurred to me at an earlier stage. I therefore 

 resolved to carry out a complete series of experiments with a new set of iron tubes, all 

 successive stages in the life-history of one and the same bar. These are distinguished 

 below as Nos. V. to VHP. inclusive. The changes of length and the changes of volume 

 of bore of each of these tubes were measured, and from these measurements certain 

 interesting results were obtained. 



But it now became evident that a much clearer insight into the character of the 

 strain accompanying magnetization in iron and nickel tubes would be obtained if the 

 cubical dilatation of the material of these tubes could be measured directly. This, 

 unfortunately, could not be effected with the tubes in use, which nearly filled the core 

 of the magnetizing coil (Part I., § 6). 



Led by these considerations, I proceeded to study the volume and length changes 



of sets of smaller tubes, each of which could be enclosed in a strong brass tube inserted 



in the core of the magnetizing coil. The new nickel tubes, distinguished as the B 



tubes, were formed by successive borings from a nickel bar, 20*2 cm. long and 272 cm. 



vol. xxxix. part II. (no. 15). 3 z 



