Barrett —Loss of Magnetic Susceptibility, 8fc. 109 



tion represented by 1 gramme before heating. Upon heating to 

 redness, after cooling, an attraction represented by 2 grammes 

 was obtained ; but no attraction was sensible by a permanent 

 magnet either before or after heating. Precisely similar results 

 were obtained with a bit of thin manganese wire. In all cases 

 the surface was, of course, discoloured by oxidation through heat- 

 ing. Placing some 36 per cent, manganese steel filings in a hard 

 glass tube, an attraction represented by 5 centigrams was obtained 

 before heating ; after heating to redness, in an atmosphere of coal- 

 gas passing through all the time, upon cooling the attraction had 

 increased to 20 centigrams, the electro-magnet being employed. 

 This is a far higher increase than with the wire or foil, as was 

 obvious by the fact that a permanent magnet readily attracted the 

 filings. 



I now wrapped some filings very tightly in platinum foil and 

 heated them to redness, as before ; now the attraction after heat- 

 ing was only double the attraction before heating ; about the same, 

 in fact, as the wire or foil exhibited : no attraction with a per- 

 manent magnet was found after the compressed filings had been 

 heated. 



The difference in behaviour of manganese steel when in loose 

 filings and when in wire, foil, or compressed filings, may furnish 

 a clue leading to an explanation of the curious phenomena de- 

 scribed in the preceding note, but at present I am unable to 

 suggest any explanation. As regards the temperature at which 

 the increased magnetic property is conferred, I find no alteration 

 is produced by the temperature of 100° C. or 250° C. : a slight 

 increase occurs at a black heat ; but the change sets in at a low 

 red heat. 



I hope before long to make another communication on this 

 subject to the Society. 



