258 Mr. S. R. Roget. Effects of prolonged 



The efficient cultivation of this field of research depends upon 

 combination and assistance of an exceptional kind ; but in the first 

 instance money must be available, and the members of the Royal 

 Institution deserve my especial gratitude for their handsome dona- 

 tions to the conduct of this research. Unfortunately its prosecution 

 will demand a further large expenditure. The handsome contribution 

 made by the Goldsmiths Company ought also to be mentioned as 

 very materially helping the progress of the work. 



During the whole course of the low temperature work carried out 

 at the Royal Institution, the invaluable aid of Mr. Robert Lennox 

 has been at my disposal ; and it is not too much to say that but for 

 his engineering skill, manipulative ability, and loyal perseverance, 

 the present successful issue might have been indefinitely delayed. 

 My thanks are also due to Mr. J. W. Heath for valuable assistance 

 in the conduct of these experiments. 



" Effects of Prolonged Heating on the Magnetic Properties of 

 Iron." By S. R. RoQET, B.A. Communicated by Professor 

 EwiNG, F.R.S. Received April 4, Read May 12, 1898. 



It has been known for some years that when transformers are 

 kept in use, their open-circuit loss is liable to increase considerably 

 with the lapse of time. This implies a deterioration of the iron core 

 in regard to magnetic hysteresis. The subject began to receive 

 attention in 1894-5, when some curves showing this increase in 

 hysteresis were published by Mr. G. W. Partridge.* The effect 

 was first thought to be due to a species of magnetic fatigue, resulting 

 from repeated reversals of magnetism in the iron, but it was proved by 

 Professor Ewing early in 1895 not to be due to this cause ; f and 

 was further shown by the experiments of Mr. Blathy and Mr. 

 Mordey to be a direct effect of heat and to occur in transformers as a 

 consequence of the iron being maintained for long periods at a com- 

 paratively high temperature. Continued baking of iron was found 

 to produce a similar augmentation of hysteresis. The published 

 results of Mr. Mordey,^ and, later, those of Mr. Parshall, deal 

 with prolonged heating at temperatures which do not exceed 140 C. 

 At the suggestion of Professor Ewing, the author has been carrying 

 out, in the laboratory of the Engineering Department of Cambridge 

 University, some investigations which deal with a more extended 

 range of temperature. The experiments are still in progress, but 



* * The Electrician/ vol. 34, p. 160, December, 1894. 

 t Ibid., p. 297, January, 1895. 

 J ' Proc. Roy. Soc.,' vol. 57, p. 224, June, 1895. 

 ' Min. Proc. Inst. C.E.,' vol. 126, p. 244. 



