508 Professor W. Chandler Roberts- Austen [March 15, 



the green-blue hue of the sunset, the central band of the arc changing 

 rapidly from peach-blossom to lavender and purple. The arc can 

 then be lengthened, and as the poles are drawn further and further 

 asunder, the irregular masses of chromium fuse in silver droplets 

 below an intense blue field of light, passing into green of lustrous 

 emerald ; theu the last fragments of chromium melt into a shining 

 lake, which reflects the glowing poles in a glory of green and gold, 

 shot with orange hues. Still a few minutes later, as the chromium 

 burns, a shower of brilliant sparks of metal are projected from the 

 furnace, amid the clouds of russet or brown vapours which wreath the 

 little crater ; whilst if the current is broken, and the light dies out, 

 you wish that Turner had painted the limpid tints, and that Ruskin 

 might describe their loveliness. 



The effect when either tungsten or silver (Fig. 4) replaces chromium 

 is much the same, but, in the latter case, the glowing lake is more 

 brilliant in its turbulent boiling, and blue vapours rise to be con- 

 densed in the iridescent beads of distilled silver which stud the crater 

 walls. 



Such experiments will probably lend a new interest to the use of 

 the arc in connection with astronomical metallurgy, for, as George 

 Herbert said long ago — 



" Stars have their fetorms even in a high degree, 

 As well as we ; " 



and Lockyer has shown how important it is, in relation to such storms, 

 to be able to study the disturbances in the various strata of the stellar 

 or solar atmosphere. Layers of metallic vapour which differ widely 

 in temperature can be more readily obtained by the use of the electrical 

 furDace, than when a fragment of metal is melted and volatilised by 

 placing it in the arc on the lower carbon. 



It must not be foi gotten that the use of the electric arc between 

 carbon poles renders it practically impossible to prepare the rare 

 metals without associating them with carbon, often forming true 

 carbides ; but it is possible in many cases to separate the carbon by 

 subsequent treatment. Moissan has, however, opened up a vast field 

 of industrial work by placing at our disposal practically all the rarer 

 infusible metals which may be reduced from oxides, and it is necessary 

 for us now to consider how we may best enter upon our inheritance. 

 Those members of the group which we have known long enough to 

 appreciate are chromium and manganese, and these we have only 

 known free from carbon for a few months. In their carburised state 

 they have done excellent service in connection with the metallurgy of 

 steel ; and may we not hope that vanadium, molybdenum, titanium, 

 and uranium w r ill render still greater services ? My object in this 

 lecture is mainly to introduce you to these metals, which hitherto few 

 of us have ever seen except as minute cabinet specimens, and we are 

 greatly indebted to M. Moissan for sending us beautiful specimens of 



