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



*3 mm. in diameter. Mica insulation separated the several 

 windings from each other and from the core. 



Fig. 4. — Section of completed Ring. Scale £ full size. 



■Secondary 



/°rmctr, 



I A P rmo»\ tear 

 Wtre 



layers 

 °f fttica insulation 



Haztlng coil 



Fig. 5. — Showing Ring in Glass Vessel. 



Coil /or 

 aitoriing tucyaen 



Mercury 

 gouge. -* 



The heating wire, wound back on itself to avoid magnetizing 

 effect, was passed once or twice round the lower part of the 

 stem to prevent that local abstraction of heat to which the 

 stem would otherwise have given rise. 



The secondary winding was wound last of all ; it being 

 possible in this way to secure better insulation, particularly 

 from the primary, from which even a small leakage into the 

 secondary was much more serious than any leakage from the 

 heating coil ; for in the former case every ballistic throw due 

 to a change in the primary current would be associated with 

 a change of zero, while in the latter case no such change 

 would occur. 



The ring was afterwards successively covered with a layer 

 of mica, a layer of asbestos, a covering of iron-wire gauze, 

 and, finally, with a jacket consisting of three coverings of soft 

 asbestos millboard. The iron gauze, which became red hot 

 when the ring was being used at high temperatures, was 

 placed there to intercept oxygen on its way in. 



