176 G. Bcums — Effect of Magnetization on the 



of Wiedemann* insufficiently emphasize. I refer to the effect 

 of magnetization on the rigidity of iron and steel, as modified 

 by the dimensions of the metal temporarily strained. I shall 

 show that the increment of rigidity due to magnetization in- 

 creases at an accelerated rate as the soft, temporarily twisted 

 wire becomes more nearly Alimentary. Now, since the said 

 increment is independent of the sign of the current in the helix, 

 and moreover increases with the current intensity in a way 

 which I have found not seriously irregular, it seems profitable 

 to attempt to utilize this principle for the construction of elec- 

 tric dynamometers. f This is the point of view from which 

 much of the present paper has been written. It also contains 

 a series of results on the rigidity of magnetized steel temporarily 

 strained and varying in temper from extreme hard to extreme 

 soft. 



Viscosity of Magnetized Steel and Iron. 



Apparatus and method. — To make the present measurements 

 it is merely necessary to replace the heating apparatus de- 

 scribed in the former paper by an appropriate helix. The two 

 wires to be examined are in the same vertical line, separated 

 by a rigid piece of brass which carries the index mirror. Any 

 desirable rate of twist may be imparted by rotating and then 

 fastening either the upper or the lower end of the system. If 

 both ends be rotated symmetrically in opposite directions, the 

 mirror remains stationary. In this way any reasonable amount 

 of twist may be stored without moving the,j image of the scale 

 out of the field of the telescope. 



The wires of the system were identical as regards length, 

 diameter, and composition ; and the arrangement adopted was 

 such that at any time the upper wire might be under the influence 

 of a powerful magnetic field. The helix used for this purpose 

 consisted of ten layers of 230 turns each, doubly wound in 

 such a way as to form two independent partial helices of 115 

 turns of wire for each laj^er. For the same current 'the fields 

 of these partial helices were identical ; by connecting them, 

 either differentially or in series, the field obtained was either 

 zero or the maximum for the given conditions. The length of 

 the helix being 20 cm , its internal radius l-25 cm , its external 

 radius 2*0Y cm , the magnetizing force at the center proves to be 

 1425 e.g. s. units of intensity per c. g. s. unit of current or 142*5 



* Wiedemann : Pogg. Ann., ciii, p. 571, 1858; ibid., cvi, p. 161, 1859; Galvan- 

 ismus, 3d ed., 1883, III, p. 683-69S. Less closely allied researches on the effect 

 of magnetization on torsion, etc., are due to Matteuci: C. R., p. 301, 1847, and to 

 "Wertheim: C. R., xxxv, p. 702, 1852, as well as to Wiedemann (1. c), and more 

 lately to Ewing (Proc. Roy. Soc, No. 228, p. 117, 1883). 



f Cf. page 177. 



