56 Prof. Nagaoka and K. Honda on Magnetostriction 



Cast Cobalt. 



Magnetization produces dinrinu- Mechanical elongation produces 



tion of length in low fields, which, diminution of magnetization in low 



after reaching a maximum, gra- fields, which, after reaching a maxi- 



dually decreases, and finally in- mum, gradually decreases, and 



crease of length is produced in finally becomes an increase in strong 



strong fields. fields. 



Annealed Cobalt. 



Magnetization produces diminu- Mechanical elongation produces 



tion of length, which gradually in- diminution of magnetization, which 



creases with the strength of the gradually increases with the 



field. strength of the field. 



Nickel- Steel. 



Magnetization produces increase Mechanical elongation produces 



of length. increase of magnetization. 



§ 5. Change of Volume by Magnetization. 



It was suggested by Rhoads that the change of volume by 

 magnetization may, in a great measure, be due to the hetero- 

 geneity in the material under examination, while in some ex- 

 periments the arrangement was not free from errors, which, 

 though very small, are sufficient to disguise the minute effect. 

 One serious drawback in these experiments was the use of a 

 disproportionately large mass of iron, which, had the ratio of 

 dimensions been sufficiently great, would not have been 

 altogether objectionable, but as it mostly happened to be, did 

 not give the expected result. Non-uniformity of the field is 

 another source of error, which unfortunately has too often 

 been neglected ; the result obtained in fields which are not 

 uniform will indeed be difficult of interpretation. If the 

 material under test be not placed axially in the direction of 

 magnetization and the mechanical force urging the magnetic 

 substance in one or other direction comes into existence, the 

 change of shape of the volumenometer will in some cases be 

 of such amount that it not only deteriorates the measured 

 change, but screens the desired effect. These various sources 

 of error may, by proper construction of the volumenometer, 

 be easily eliminated. 



The arrangement of the volumenometer has already been 

 described in our former researches, so that it would be super- 

 fluous to enter anew into the details of the apparatus ; suffice 

 it to say that the axis of the ovoid coincided with that of the 

 magnetizing coil, which was all the while waterjacketed. 



As announced by Quincke *, change of volume in the liquid 



* Quincke, Sitzb. d. Berliner Akad. d. Wiss. xx. p. 391 (1900), 



