1892.] on Metals at High Temperatures. 509 



able ; thus iridium will only just melt in tlie flame produced by the 

 combustion of pure and dry hydrogen and oxygen. By the kindness of 

 Mr. Edward Matthey, a thin rod of iridium has been prepared witli 

 much labour, and it can be used as a thermo-junction with a similar rod 

 of iridium alloyed with 10 per cent, of platinum. The junction may be 

 readily melted in the electric arc, and by this means a temperature 

 may be registered which careful laboratory experiments show to be 

 close to 2000°, and this agrees with the estimate of the melting-point 

 of iridium which Violle * deduced from calorimetric experiments. 

 [This experiment was shown, a different scale being employed for 

 the screen, as the thermo-electric constants of the iridium, and 

 iridium-platinum couple, are different from those of the platinum and 

 rhodium one previously used.] 



It is interesting to remember that within a year, in this Institu- 

 tion, temperatures ranging from — 200 to -f- 2000° have been mapped 

 out, the lower temperature by Prof. Dewar in his memorable Faraday 

 Lecture ; the higher point is now measured in public for the first 

 time. 



How difficult it is for us to realise what this range of temperature 

 reall}" means ! for we have but little power of appreciating tempera- 

 tures beyond those we can conveniently bear. We, perhaps, know 

 the meaning of extreme cold better than great heat, but even the 

 vivid imagery of Dante, who might have been expected to afford some 

 guidance, gives us singularly little help. I think in depicting the 

 terror of torture inflicted by extreme cold he succeeds better than 

 when he describes the suffering of those who are exposed to flames. 

 His words (Canto xxxiii.) — 



" Blue, pinched, and shrined in ice the spirits stood " — 



mark the highest suffering drawn in the " Inferno." It is, however, 

 probable that my failure to appreciate the descriptive powers of 

 Dante may be the result of resentment, for I read with regret that 

 he consigns to the tenth chasm of Hell, not only the coiner who 



" falsified 

 The metal with the Baptist's form impressed," f 



but also an honest metallurgist, Cappoqcio of Sienna, who, 



" by the power 

 Of alchemy, . . . aped creative Nature by his subtle art " ; 



and deserved a better fate. 



We are now in a position to consider certain other effects of 

 high temperature on metals. Many years ago, my colleague Mr. 

 Lockyer, and I, conducted an investigation on the spectra of the 

 vapours of certain metals | at the highest temperatures we could 



* Loc. cit. t The golden florin of Floreuce. 



X Proc. Roy. Soc. vol. xxiii. p. 344, 1875. 



