1878.] 



Electrodynamic Qualities of Metals. 



439 



posteriorly ; valves moderately convex ; surface smooth, white ; length 

 10, width 9, depth 5 millims. 



Five examples of this interesting species were dredged in lat. 36° 

 56' S., long. 150° 30' E., off Twofold Bay, South Australia, in 120 

 fathoms. 



The other species of Brachiopoda, dredged in the ' Challenger ' 

 Expedition, have been already named along with the depths at which 

 they were found. It is, however, somewhat remarkable that the 

 ' Challenger ' Expedition did not bring back any of those red-coloured 

 species which are so abundant near New Zealand, Japan, and other 

 southern places. 



IX. " Electrodynamic Qualities of Metals.* Part VII. Effects 

 of Stress on the Magnetization of Iron, Nickel, and Cobalt." 

 By Sir William Thomson, F.R.S., Professor of Natural 

 Philosophy in the University of Glasgow. Received May 22, 

 1878. 



(Abstract.) 



This paper commences with a detailed description of a series of 

 experiments on the effects of stress on the magnetism of soft iron, of 

 which some first results were described in a preliminary notice, com- 

 municated to the Royal Society on the 10th of June, 1875, and pub- 

 lished in the " Proceedings." A few months later, the author found 

 that he had been anticipated by Villarit in the most remarkable of 

 those results — that showing increase or diminution of magnetization 

 by longitudinal pull, according as the magnetizing force is less than, 

 or greater than, a certain critical value. 



In the first series of experiments described in this paper, the amount 

 of the magnetizing force is varied through a range of values from zero 

 to 900, on a scale on which about 12 \ is the value of the vertical com- 

 ponent of the terrestrial magnetic force at Glasgow, and the effects of 

 hanging on and taking off weights of 7 lbs., 14 lbs., and 21 lbs., J in 

 changing the induced magnetism, are observed. The experiments 

 were made at ordinary atmospheric temperatures, and at temperature 

 100° C. The results are shown in curves, of which the abscissas 

 represent the magnetizing forces and other ordinates, the change of 

 magnetism produced by " ons " and " offs " of the weight while the 

 magnetizing force is kept constant. The Yillari critical value was 



* Phil. Trans., 1875. f Poggendorf 's " Armalen," 1868. * 



% The wire was of about 22 Birmingham gauge, weighing therefore about 14 lbs. 

 per nautical mile. It was so soft that it had experienced a considerable permanent 

 stretch by 21 lbs. ; it would probably break with 30 or 40 lbs. Steel pianoforte wire 

 of same gauge bears about 230 lbs. 



