510 Professor W. C. Boherts- Austen [Feb. 5, 



produce, uitli the aid of the oxyhydrogen flame. We distilled 

 silver, zinc, cfidniium, and volatilised iron and other metals, from 

 a lime crucible, and caused their vapours to pass into a hori- 

 zontal 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 we came 

 to the conclusion that each molecular simplification 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 com- 

 plicated 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 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 white- 

 ness — in changing the number and arrangement of the atoms in 

 metallic molecules. A profound change must occur when the viscous 

 form of sulphur passes spontaneously at the ordinary temperature 

 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 that molecular change may take place at low 

 temperatures. Take the fusible alloy of bismuth, lead, and tin, 

 which bears Newton's name, and contains — 



Bismuth 50-00 



Lead 31-25 



Tin 18-75 



100-00 



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 rapidly, and in a few moments it will become 

 too hot to hold. The " fracture " of the metal is totally different 

 before and after the molecular change which is the cause of this 

 evolution of heat has taken place. The cliange, moreover, takes 

 place in the solid metal, and is not due to the release of the latent 

 heat of fusion. The mass, solid as it appears to be, must be the 

 scene of an internal struggle between the molecules in the effort to 



