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XXXIII. Preliminary Experiments on the Effects of Percus- 

 sion in Changing the Magnetic Moments of Steel Magnets. 

 By William Brown, Thomson Experimental Scholar, 

 Physical Laboratory, University of Glasgow*. 



Part I. 



THE experiments described in this paper were made in 

 the Physical Laboratory of Glasgow University. They 

 were first suggested by some casual observations made while I 

 was assisting Mr. T. Gray during his recent determination of 

 the horizontal intensity of the Earth's magnetic force, and I 

 am greatly indebted to him for many hints and much valuable 

 advice during the progress of the experiments. 



This paper is an account of some preliminary observations 

 on a subject which is at present being investigated in this 

 Laboratory, and I hope to give the results of further experi- 

 ments in an early number of this magazine. 



The effects of percussion in changing the magnetic moments 

 of steel magnets have not (so far as I know) been made the 

 subject of special observation. The results hitherto published 

 have, for the most part, formed less important sections of other 

 investigations. 



A number of interesting experiments on magnets were made 

 by Joule at intervals from 1864 to 1882. Among other results, 

 he gives an interesting set on " the effect of mechanical 

 violence on the intensity of magnetic bars," an account of 

 which is published in his Scientific Papers, vol. i. p. 596. 



In 1878, Mr. T. Gray! published a very accurate series of 

 investigations on magnetic moments in absolute measure. 

 One of the objects of his investigation was to obtain informa- 

 tion as to the permanence or non-permanence of magnetism 

 in steel bars when left undisturbed for a length of time. On 

 page 328 of the same paper, however, he gives a short series 

 of observations on the direct effects of percussion, which, so 

 far as they go, agree with my own results. 



There has been published quite recently an excellent series 

 of papers on the " Electrical and Magnetic Properties of the 

 Iron Carburets," by 0. Barus and V. Strouhal, of the U.S.A. 

 Geological Survey J. 



* Communicated by Sir W. Thomson, having been read before the 

 Mathematical and Physical Section of the Philosophical Society of 

 Glasgow, November 30, 1886. 



f "On the Experimental Determination of Magnetic Moments in 

 Absolute Measure," Phil. Mag. November 1878, pp. 321-331. 



\ Bulletin No. 14. 1885, Department of the Interior. 



