216 Dr. D. K. Morris on the Magnetic Properties 



formed of a length of ordinary soft iron wire) were more 

 successful ; but the results, though interesting, have not been 

 thought worth including in this paper. The experience gained 

 in the construction and use of the first two ring-magnets was 

 turned to account in the two later ones. 



Platinum wires were exclusively employed for the windings 

 of the ring-magnets, as no substance either magnetic or fusible 

 below 1200° was admissible. These wires, after use in one 

 ring, were used again, with fresh insulation, in the next. 



Iron cores. — The cores of the third and fourth ring-magnets 

 (referred to in this paper as specimens A and B respectively), 

 were formed from strips, one chosen from each of two groups 

 of iron samples kindly procured for the author by Mr. R. 

 Jenkins from Messrs. Jos. Sankey and Sons, of Bilston. The 

 sample strips were 1 cm. in width ; they were described as 

 follows : — 



Specimen A. — tl Charcoal Iron, No. 4 Quality ; thick- 

 ness *02 in." 

 „ B. — " Best Transformer Quality -*§>£- ; thick- 

 ness *014 in." * 



These specimens proved, after careful annealing, to be 

 exceptionally good both as regards high permeability and low 

 hysteresis. 



Platinum Thermometer Wire. Method of deducing Tem- 

 peratures. — The specimen of pure annealed platinum wire 

 used in the measurement of temperature was from the firm 

 of W. C. Heraus, of Hanau, near Frankfurt-a.-M. The 

 same piece of wire was used in both the later ring-magnets. 

 Its diameter was # 0453 cm., its specific resistance at 0° was 

 10,110 C.Gr.S. units, and its temperature-coefficient, which 

 was remarkably high, was a o_ 100 o = '00386. 



The resistance-temperature curve was taken by mounting 

 the platinum wire (carefully re-annealed by heating to bright 

 redness in a mass of asbestos) on a small cylindrical mica 

 frame, and measuring its resistance at intervals of about 30° 

 up to 200° C. in a balh of linseed oil. The temperature was 

 measured by a standard thermometer which was carefully 

 checked at 0° and 100°. The oil was vigorously stirred, and 

 observations of resistance were only made when the tem- 

 perature was very nearly constant. 



The experiments of Callendar and Griffiths have established 



* This iron, according to the above firm, gives on analysis 99 - 925 

 per cent, of iron by difference, the impurities ( - 075 per cent.) being 

 distributed between carbon, phosphorus, and silicon, with a trace of 

 manganese. It is as pure Swsdish iron as can be produced commercially. 



