130 Mr. Willoughhy Smith on Electric Induction. [June 6, 



the metals copper and iron is that iron gives the higher current of the 

 two, as it has done in all my experiments. 



I have no doubt that we should be able to get approximately 

 near for all practical purposes to the relative conductivity of metals 

 by revolving discs of the metal under test in a magnetic field, and 

 measuring the amount of current between the poles or the amount of 

 •'drag." The results given on diagram 5 show how suitable the 

 method also is for obtaining the saturation point of the cores of electro- 

 magnets, whether of ditferent qualities of iron or different metals. 



Plate 5. 



IRON 



NICKEL 



3-5 



Very recently an Electrical Congress, held in Paris, agreed to an 

 universal system of electrical units. I believe the value of some of 

 the units to be adopted was determined by passing masses of metal at 

 varying velocity through a magnetic field of uniform intensity, and 

 noting the amount of current so produced. I understand that the 

 results obtained by different experimentalists did not agree, and from 

 what I have shown you this evening, you will readily understand the 

 reason of the discrepancy. To obtain accurate results the influence 

 of what I have called " drag " must certainly be taken into the calcu- 

 lations as an important factor. There are other matters to which I 

 attach importance connected with the experiments I have endeavoured 

 to make clear to you, especially with those on magneto-electric induc- 

 tion, which I publish for the first time this evening ; but of the many 

 good rules of this Institution, there is one which does not allow me 

 to tax your patience for more than one hour, and, as I have already 

 exhausted that time, I must not detain you longer, except to thank 

 you, which I do most sincerely, for the kind attention you have given 

 to my humble endeavours to advance our knowledge of volta-electric 

 and magneto-electric induction. 



[W. S.] 



