534 



PROFESSOR KNOTT ON THE STRAINS PRODUCED IN 



on a ballistic galvanometer of the induced current in the secondary coil which surrounded 

 the midway section of the tube. For reasons already explained (§ 6), these observations 

 have not been made much use of. 



From time to time a careful study was made of the manner in which the volume 

 went through its cyclic changes as the magnetising force was carried by successive stages 

 through its cycle. Some very remarkable results were obtained, which will be found 

 described in § 12. 



I now proceed to the discussion of the results for Iron, Steel, and Nickel, taken in order. 



§ 8. The Iron Tubes Nos. I. to VII. — As already stated, these are all successive 

 borings of one original bar. The bore of No. I. was a quarter of an inch in diameter, 

 and each new bore was made an eighth of an inch wider than the preceding one, with the 

 single exception of No. VII., whose bore is l^ inch instead of 1 inch in diameter. 



Each tube was experimented with at least twice (generally oftener) — the iron cap 

 being used in the one case and the brass cap in the other. The results are shown 

 graphically in Plates I. and II. Magnetic field is measured horizontally, and the 

 ordinates give the corresponding changes of volume in 10 ~ 6 cubic centimetre., 



It has not been thought necessary to give the numbers obtained directly by observation. 

 From these, however, the curves shown in the Plates are drawn. To facilitate compari- 

 son, changes of volume corresponding to definite fields are here tabulated. The numbers 

 in any column give the volume changes for the corresponding tube. The numbers in any 

 row give the volume changes in the successive tubes corresponding to a definite .field. 



Iron Tubes with Iron Cap. 



Field. 



I. 



II. 



III. 



IV. 



V. 



VI. 



VII. 



25 



+ -3 



+ -3 



+ -4 



+ -1 



+ -6 



- -1 



- -8 



50 



+ 1-0 



+ 1-4 



+ 1-4 



+ -4 



+ 1-3 



- 1-2 



- 4-0 



75 



+ 1-2 



+ 1-6 



+ 1-3 







- -2 



- 1-8 



- 3-7 



100 







+ -2 



-1-4 



-2-1 



- 1-4 



+ 1-6 



+ 4-7 



125 



-1-9 



-1-6 



-3-3 



-2-8 



+ 3-0 



+ 9-5 



+ 12-8 



150 



-3-1 



-2-8 



-4-2 



-1-1 



+ 8-3 



+ 14-2 



+ 18-7 



200 



-3-8 



-2-4 



-1-9 



+ 3-2 



+ 12-5 



+ 17-8 



+ 22-6 



250 



-4-55 



-2-7 



-T4 



+ 4-9 



+ 13-8 



+ 19-3 



+ 24-6 



300 



-5-65 



-3-4 



-1-4 



+ 5-2 



+ 14-0 



+ 19-8 



+ 25-8 



400 



-8-55 



-5-2 



-2-8 



+ 4-4 



+ 13-2 



+ 19-6 



+ 26-6 



500 



-12 



-7-4 



-5-3 



Iron Tubes i 



+ 3-0 

 ;vith Brass C 



+ 11-8 



AP. 



+ 18-6 



+ 27-0 



25 



+ -1 



+ -2 





+ -4 



+ -2 



+ "2 



- 1-4 



50 



+ '4 



+ -6 



+ -6 



+ -7 



+ -2 



- -4 



- 4-5 



75 



+ -8 



+ 1-0 



+ -6 



+ '6 



- 13 



- 1-8 



- 5-5 



100 



4- -4 



+ 1-0 



- -4 



-1-2 



- 2-1 



- -3 



+ 2-8 



125 



-1-2 



- -5 



-2-7 



-2-2 



+ 1-5 



+ 7-0 



+ 115 



150 



-2-5 



-1-8 



-3-4 



+ -2 



+ 6-6 



+ 12-6 



+ 16-5 



200 



-3-0 



-1-7 



-1-7 



+ 4-3 



+ 12-0 



+ 17-0 



+ 21-1 



250 



-3-2 



-1-4 



- -4 



+ 5-7 



+ 14-0 



+ 19-0 



+ 23-4 



300 



-3-4 



-1-5 



+ -1 



+ 6-2 



+ 15-0 



+ 20-0 



+ 24-3 



400 



-4-2 



-2-0 



- -1 



+ 6-3 



+ 15-3 



+ 20-0 



+ 25'1 



500 



-5-5 



-2-4 



- -6 



+ 5-8 



+ 15-3 



+ 21-0 



+ 25-5 



