April 7, 1892] 



NA rURE 



537 



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 realize what this range of 

 temperature really means, for we have but little power of 

 appreciating temperatures beyond those we can con- 

 veniently 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 mflicted by ex- 

 treme 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 resent- 



we came to the conclusion that each molecular simpHfica- 

 tion is marked by a distinctive spectrum, and that there- 

 is also an intimate connection between the facility with 

 which the final stage is reached, the group to which 

 the element belongs, and the place which it occupies in 

 the solar atmosphere. At the highest temperature of the 

 oxyhydrogen flame, molecules of metals are simplified, 

 but their constituent atoms remain unchanged. Mr. 

 Lockyer has, however, since done far more : he has 

 shown that the intense heat of the sun carries the process 

 of molecular simplification much further ; and, if we 

 compare the complicated spectra of the vapours of 

 metals produced by the highest temperatures available 

 here with the very simple spectra of the same metals 

 as they exist in the hottest part of the sun's atmosphere, 

 it is difficult to resist the conclusion that the atom of 

 the chemist has itself been changed. My own belief 

 is that these " atoms " are changed, and that iron, as it 

 exists in the sun, is not the vapour of iron as we'"know it 



ment, 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," ' 

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

 " by the power 

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

 and, I think, deserved a better fate. 



We are now in a position to consider certain other effects 

 of high temperature on metals. Many years ago, my col- 

 league Mr. Lockyer, and I, conducted an investigation 

 on the spectra of the vapours of certain metals - at the 

 highest temperatures we could produce, with the aid of the 

 oxyhydrogen flame. We distilled silver, zinc, cadmium, 

 and volatilized iron and other metals, from a lime crucible, 

 and caused their vapours to pass into a horizontal tube of 

 strongly-heated lime. By these experiments we satisfied 

 ourselves that the molecular structure of metals is gradu- 

 ally simplified as higher temperatures are employed ; and 



' The golden florin of Florence. 



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



NO. I 171, VOL. 45] 



upon earth. We will not dwell in this lecture on the 

 effects of very high temperatures on metals, but rather 

 on the influence of comparatively low temperatures — that 

 is, below whiteness — in changing the number and ar- 

 rangement of the atoms in metallic molecules. A pro- 

 found change must occur when the viscous form of 

 sulphur passes spontaneously at the ordinary tempera- 

 ture into the yellow crystalline variety, but the change is 

 accompanied by but little thermal disturbance. In the 

 case of metals there is also abundant evidence thatmole- 

 cular change may take place at low temperatures. Take 

 the fusible alloy of bismuth, lead, and tin, which bears- 

 Newton's name, and contains — 



Bismuth 



Lead 



Tin 



50-00 

 31 "25 

 1875 



It fuses at 90' ; it may be cast round a thermo-j unction, 

 and plunged in water and cooled thoroughly until the 

 observer is certain that the mass has returned to the 

 atmospheric temperature : take it out of the water, dry it 



