2 
ME. J. MUIR ON THE TEMPERING OF IRON 
slightly modified from that of the larger extensometer folly described by Professor 
Ewing in a paper “ On iNIeasurements of Small Strains in the Testing of Materials 
and Structures.”"^ 
For the purposes of tempering and annealing a gas furnace was employed, 2 feet in 
length. This furnace (manufactured by Fletcher, PtUSSELL, and C.'o., Warrington) 
is heated by means of a series of inclined bunsens entirely detached from the fire-clay 
portion of the furnace, so that regulation can be effected not only by altering the gas 
supply, but also by moving the bunsens nearer to or further from the orifices into 
4-iiich Extensometer. 
which they play. The specimens were protected from direct contact with the flame 
by enclosing them in a thick porcelain tube. The temperature inside this tidie was 
measured by means of a Callkndar’s direct-reading platinum-resistance pyrometer, t 
To ensure that the temperature recorded b}" the pyrometer was as accurately as 
})ossihle that assumed by the specimen, readings were taken for both ends of the 
furnace, the specimen being moved from one end to the other to allow of the insertion 
of the pyrometer tube. In this reversal of positions the pyrometer tube in passing- 
through the air was slightly cooled, so that the temjieratures recorded immediaely 
after a change of ])ositions were somewhat low. The following series of pyrometer 
readings is given by way of illustration :— 
* ‘Roy. Soc. Proc.,’ vol. 58, April, 1895. 
t “On the Construction of Rlatinum Thermometers,” ‘Phil. M<ag.,’ Jufv, 1891 ; “On Platinum Ther¬ 
mometry,” ‘Phil. xMag.,’ February, 1899. The instrument referred to above ^vas made by the Cambridge 
Scientific Instrument Company, Limited. 
