t>ROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 669 



face, and shining with all kinds of reflection, and a luster like that 

 of the diamond. When exposed to the sun's vajs, they became 

 almost instantly garnet red ; retaining, however, all their luster, 

 they resembled small rubies. In this condition it was found to 

 have the peculiar properties of the amorphous red phosphorus. 



Thallium Glass. 

 Thallium has been used by M. Lamy, of France, in the manu- 

 facture of glass for special uses. Having observed that ethyl- 

 thalic alcohol is more highly refringent Jhan any other known 

 liquid, and that great refractive and dispersive powers belong to 

 other compounds containing thallium, he commenced a series of 

 experiments in which he used that metal in various proportions in 

 making glass. A mixture consisting of 300 parts of sand, 335 

 parts of carbonate of thallium, and 200 parts of oxide of lead, pro- 

 duced a glass perfectly homogeneous throughout, transmitting 

 light of extreme brilliancy, although of yellowish tint. Its den- 

 sity was 4.235, and the refractive index of the yellow ray was 1.71, 

 which is higher than that of any other glass not containing borates. 

 He subsecjuently made glass having a density of 5.625, and a refec- 

 tive index of 1.9G5. His general conclusions are : 



1. That thallium replaces potassium better than it replaces lead, 

 and that thallium glass is denser and more refringent than potas- 

 sium glass. 



2. That thallium glass always gives a yellowish tint, as sodium 

 glass gives a greenish color* 



3. That thallium glass will be useful in making certain optical 

 instruments and artihcial irems. 



&' 



Spectra of Heavenly Bodies. 

 A lecture before the British Association on the results of spec- 

 trum analysis, as applied to the heavenly bodies, by William Hug- 

 gins, F. R. S., lately published, concludes as follows : 



1. All the brighter stars, at least, have a structure analogous 

 to that of the sun. 



2. The stars contain material elements common to the sun and 

 earth. 



3. The colors of the stars have their orio-in in the chemical con- 

 stitution of the atmosphere which surrounds them. 



4. The changes in brightness of some of the variable stars are 

 attended with changes in the lines of absorption of their spectra. 



