370 Dr. P. E. Shaw. The Magnetic [Ma}' -L', 



(7. The patient's serum, 3 vols. ; staphylococcus suspension, 1 vol. ; 



A. E. W.'s washed corpuscles, 3 vols. 



Tufa i. Phagocytic power (bacteria in 15 P.W.B.C. 



counted and averaged) 30 



Tube 2. Do. do. 26 



'* The Magnetic Expansion of some of the less Magnetic Metals." 

 By P. E. SHAW, B.A., D.Sc. Communicated by Professor 

 J. H. POYNTING, F.E.S. Eeceived May 22, Eead June 18, 

 1903. 



1. Abundant research has been made on the magnetic expansion of 

 iron, nickel, and cobalt, notably as regards the exact relation between 

 field (H) and expansion per unit length (S///), by S. Bidwell* and 

 H. Nagaoka.f Bismuth also has been investigated by Bidwell, 

 C. G. Knott, Van Aubel, and A. P. Wills. But there seems to be 

 no recorded research on any materials other than the four mentioned. 



Outside the ferro-magnetic group bismuth has the largest suscepti- 

 bility (k) of any substance ; and the tacit assumption seems to have 

 been made that if bismuth shows no change in length as the field 

 varies, it is vain to look for it in less susceptible metals. 



But in the case of the ferro-magnetics there is no direct relation 

 between k and 81/1. Thus, iron has maximum susceptibility six times 

 as much as nickel, and yet expands* far less for any known field. 



Again, cobalt has maximum susceptibility one-eighth of that of iron, 

 yet expands about as much. 



There being, therefore, no close relation between susceptibility and 

 magnetic expansion, it seems possible that there may be appreciable 

 movement for large fields in the case of metals outside the ferro-magnetic 

 group. This paper gives an account of tests applied to bismuth, 

 silver, aluminium, copper, zinc, brass, bronze, lead, and tin. (Not 

 much importance should be attached to the results for lead and tin 

 owing to the softness of these metals ; they tend to work loose in their 

 fittings at each end.) The work has taken from first to last nearly two 

 years : the specimens have been repeatedly changed and the 'magnetic 

 and measuring parts of the apparatus modified in various ways. In 

 this way searching tests have been applied to the investigation. 



For a long time it appeared (1) that all these metals contracted, the 

 contraction being roughly proportional to the field, (2) that all the 

 metals showed permanent magnetisation, on the hysteresis principle, 



* ' Phil. Trans.,' A, 1888. 

 f ' Phil. Mag.,' Jan., 18B4. 



