240 Mr. W. M. Mordey. On Sloiv Changes [Jan. 17, 



Added February 9, 1895. 

 APPENDIX I. 



Effect of Pressure without Heat. The following test on the effect 

 of pressure has been made without the application of heat. A trans- 

 former constructed in the manner of Fig. 1 was taken and tightened 

 up by hand in the usual way, sufficient for ordinary purposes of con- 

 struction. The loss, on magnetising to 2180 B at 100 <^ was found to 

 be 59-8 watts. 



It was then submitted to a pressure of 100 tons, or about 1500 Ibs. 

 per sq. in. (10'57 kilos, per sq. cm.), in a direction to force the 

 laminae closer together, the tightening bolts then being screwed up 

 with the pressure on. On magnetising again to 2180 B the loss was 

 found to be 72*5 watts, or an increase of 21 per cent. 



It was kept bolted up in this way for 30 days, and readings 

 taken occasionally as shown in Table IV, the loss remaining practi- 

 cally unchanged under this continued application of pressure. 



The bolts were then slackened and the loss, on being again 

 measured, was found to be the same as before the pressure was 

 applied. 



Thus, without heat, pressure (up to the limits of the test) pro- 

 duces no permanent effect. But that even a very small pressure will 

 increase the permanent effect of heat is shown by the results given 

 in Table VI. 



It should, however, be remembered that Table VI is the record of 

 only a single set of tests, and that it is not known what the effect 

 would have been if the iron had been heated without any application 

 of pressure. It is, therefore, safe only to say that under considerable 

 pressure, without the application of heat, there is a change of a 

 definite amount which remains constant under constant pressure, and 

 which disappears immediately on the removal of the pressure.* 

 It is, however, clear that the slow decrease in permeability under 

 continued moderate heating is not to be accounted for by hardening 

 produced by pressure. 



The hardening, which takes place very slowly at these low tempera- 

 tures, is similar, apparently, to the hardening which takes place 

 when iron is heated to a high temperature and then suddenly 

 cooled. 



* Experiments on a solid bar under pressure hare been made by Ewing and Lo\r. 

 " On the Influence of a Plane of Transverse Section on the Magnetic Permeability 

 of an Iron Bar," ' Phil. Mag.,' September, 1888. 



