272 Dr. Fleming, and Messrs. Ashton and Tomlinson on 



Mean outside diameter of ring .... 13*84 cms. 



Mean inside diameter of ring .... 11*15 „ 



Diameter of mean perimeter of ring . . 12*50 „ 



Mean perimeter 39*26 „ 



Mean depth of cross-section of ring . . . 3*91 „ 



Mean cross-sectional area 5*23 sq. cm. 



The mass of the ring was 1665 grams. 



The volume of the ring 205*6 c. cm. 



The mean densitj r 8*1 



The ring was then insulated with silk tape and wound over 

 with four secondary coils of No. 36 s.w.G. silk-covered 

 copper wire of 100, 50, 25, and 10 turns respectively, put on 

 at quadrantal positions. 



Over these secondary coils was wound a series of six 

 primary coils of No. 18 s.w.G. cotton-covered copper wire 

 laid on uniformly round the ring and having 195, 187, 180, 

 167, 161, and 155 turns respectively. The wire was well 

 insulated with tape and shellac varnish. The ring so prepared 

 was mounted on a board. From some of the turnings a 

 chemical analysis of the metal was made for us by Mr. R. A. 

 Hadfield, M.lnst.C.E., to whom we are greatly indebted. 



The analysis showed that the metal had the following- 

 composition : — 



Cobalt . . . 

 Nickel . . . 

 Iron . . . 

 Manganese . 

 Silicon 

 Carbon 

 Sulphur . 

 Phosphorus . 



The metal cannot therefore be considered as even approxi- 

 mately chemically pure. It contains nearly 1 per cent, of 

 iron and 1 per cent, of nickel. 



The ring thus prepared was submitted to a complete set of 

 magnetic tests by aid of the ballistic galvanometer in the 

 usual manner for the determination of the magnetic flux- 

 density or induction corresponding to certain cyclic values of 

 magnetizing force. It is unnecessary to give the details, 

 excepting to state that the electrical measurements required 

 were all ultimately referred to a standard resistance and 

 Chirk cell by means of a potentiometer. The ballistic galva- 

 nometer us.id was a Crompton-d Arsonval with a movable coil 

 having a periodic time of fourteen seconds, 



)5*95 



per 



cent 



•80 





•j 



•91 





J5 



•25 





?? 



•42 





'" 



1-36 





}) 



trace. 







trace. 







