114 Mr. H. Wilde. On the Influence of Temperature [June 11, 



(a.) A small cylinder of iron wire, 0'2 inch long and O5 inch 

 in diameter, was mounted in a twisted loop formed at the end 

 of a piece of thin copper wire. The copper wire was fixed to an arm 

 moving horizontally, in such manner that, when the cylinder of iron 

 was brought into close proximity to one pole of the needle, the iron 

 drew the needle from the magnetic meridian to a point where 

 equilibrium was established between the attractive force of the iron 

 and the earth's magnetism. The needle was then blocked a small 

 fraction of an inch in advance and also behind this position ; so that 

 any increase or diminution of the magnetic power of the iron would 

 limit the range of the needle to a fraction of an inch in either 

 direction. 



When a small gas-flame, or a lighted taper, was brought under the 

 cylinder of iron wire till it became visibly red hot, the needle receded 

 from the iron towards the magnetic meridian, thereby indicating a 

 diminution of the magnetic power of the iron by the magnetometer 

 which had previously shown an increase in the magnetic action of 

 the large bar. On removing the source of heat from the iron, the 

 needle again advanced towards it. On reheating the iron, the needle 

 again receded, and the operation could be repeated at pleasure. 



[That the recession of the needle from the heated iron was not due 

 to the temperature being sufficiently high to render the iron virtually 

 non-magnetic was shown by the needle again advancing towards the 

 heated iron when brought into closer proximity to it without change 

 of temperature, but no increase was observable in the magnetic power 

 of the iron with any increase of temperature above 13 C. June 3, 

 1891.] 



(6.) A small cylinder of steel was prepared from the same piece as 

 that from which the magnetometer needle was cut, and of the same 

 dimensions as the one used in the previous experiment. All trace of 

 permanent magnetism was removed from the steel by heating it to 

 bright redness in a blowpipe flame, so that either end of the cylinder 

 when cold was attracted indifferently by the same pole of the needle. 

 When the steel was submitted to the process of heating and cooling 

 in proximity to the magnetometer, as in experiment (a), its magnetic 

 behaviour was the same as that observed with the iron. 



The increase of magnetic power in the iron and steel, during the 

 period of cooling, appeared to come on gradually, in the same manner 

 as the magnetic power of the bar in relation to the large electro- 

 magnet; and both experiments show decisively that the magnetic 

 power of iron diminishes with increase of temperature for small, as 

 well as for large, magnetising forces. 



(c.) A fragment of the natural magnet (magnetite), weighing 2 

 grains, was detached from a compact and well crystallised mass of this 

 mineral. The magnetite was heated to bright redness to remove all 



