100 



l. XII 



464. /iV/o////v//r.sv; timi / / i/st.eresis. It is found tha.t after the magnetising 



force i removed from a sample of iron, I, lie iron s!,ill retains home of its 

 -h in. Here We ha.Ve :i. phenomenon similar In the electrostatic 

 phenomenon of residual eliar^'- a.lrea.dy descri hed in ,'J!)7. 



I-V-. I I I i taken from ;i. paper hy 1'rof. Kwin^ ( Tkil. Trait*. /!</. Nor. 

 Tin-. ahseissae represent values of //, ;md ordin;i!,cs v;ilucs of 



//, t,h- indu<:t ion. Th<- magnetic fi<-ld w;is increased from // o i<> // = iJ2, 



;ind ;is // Increased UK- v.-ilm- of />' in<-n-; l; s<-d in I, IK- in.-uincr shewn l>y Un; 

 curve O/' of i.ln- ;M:IJ'|I. On ;i;.';:iin diininisliin^ // from // = 22 to 11 = 0, the 

 <.M;IJ>|I for />' w;is found to he tlutt ^iven liy I, lie curve I*! 1 !. f riius during tliis 



|)-r;ition tli-i-c WJLS al\v;i) : :, mon- magnetisation th.-ui ,-it the corresponding 



of I, he nri'.MM.-d o|M-r;i.l.ion, ;ind lin:dly when the inducing field was 

 entirely r-ni(, V e<l, tln-n- w;is ni;i^nefis;ition left, of intensity i'e})i-esenf(!(l by 

 O/'J. The field w;is tln-n further <|eere;ised from // to // = 20, and 

 tlii-n inei' mi from 11 = 20 to Jl - 'I'l. The changes in />' are shewn 



in tin- iM.-i.h. 



Ki<. Ml. 



465. hrfx'inlciicc of ft on lent /x'rof n re. As has aJrea.dy heen sa,id, the 

 \'a.lu- of //, de|icnds to a |;I.I-M- extent <>n the teni|ier;i! u re of the metal. As 

 the temperature is men-ased the vaJue of //, eontinually inerea.ses, slowly a! 

 first hut afterwards more i a pidl y, u ntd a, tempera,ture known a.s ihe'fem- 

 pera.ture ..f ive;dese,.|ice ' is reached. This femperafui-e ha,s value: ra.n^in^ 

 I'rom liOO I,, 700 for steel and from 700 !o ,SOO f,,r iron. This temperature 

 takes ils na.me from the cireumstanee |,h ;i t a piece of metal cooling ihroindi 

 this lemperatiire will sink to a dull ^low helore rrarliin^ it, a,nd will then 



become brighter again <>n passing tlmm^li it. 



After passing the temperature of I ee;de: eelire, the \allle of //. falls with 



Die rapidity, and at a temperature only a. few decrees ahove this (em 

 pera.tui-e iron appeal's to |>e almost, completely non magnetic. 



