Magnetometer for showing the Influence of Temperature. 5 



that the apparent increase of the magnetisation of iron, 

 magnetite, and nickel is anomalous, and masks the 

 principal phenomena of the decrease of magnetic power 

 with ascending temperatures. M. Curie has extended his 

 observations to the magnetic behaviour of gaseous oxygen, 

 and has found with Professor Dewar, when experimenting 

 with this element in a liquid state, a decrease of power 

 with increase of temperature. 



The general law of the diminution of the magnetisation 

 of all known magnetic substances with increasing tempera- 

 tures is now completely established. 



In connexion with this brief summary of experiments 

 on the influence of temperature on magnetic substances, I 

 would direct attention to the close analogy, if not an actual 

 relation, which subsists between the anomalous surface 

 resistance of cold iron to magnetisation and its anomalous 

 property of resisting chemical action. Schonbein and 

 Faraday have shown that bright iron wire, slightly oxidised 

 by heat, is quite insensible to the action of strong nitric 

 acid.* Not only is there no reaction under these conditions, 

 but the oxidised wire has the property of inducing voltaic 

 passivity in a number of pieces of bright iron wire by simple 

 contact with them when immersed in the acid. Further, a 

 passive bright wire has the property of inducing the passive 

 condition in other pieces of ordinary bright iron wire. 



It is admitted on all hands that this anomalous voltaic 

 condition of iron is a surface resistance, as it disappears (1) 

 by abrasion ; (2) by the action of dilute nitric acid ; and 

 (3) by the application of heat to the wire. 



To affirm, therefore, as a general property of iron, that 

 its magnetic power increases with the temperature, is as 

 irrational as to maintain that iron throughout its substance 

 is, like gold and platinum, insensible to the action of strong 

 nitric acid. 



* Phil. Mag., 1836, Vol. IX., pp. 53-65. 



