bowen: significance of glass-making processes 



91 



for fortunately the action can be interrupted and observed at an 

 intermediate stage. When the pot is removed at such a stage 

 and the glass is chilled, sand grains are found suspended in the 

 glass. That they were rising slowly in the liquid and dissolving 

 at the same time is shown by the fact that pointing downward 

 from each grain there is a tail of glass of lower refractive index 

 than the surrounding glass. 



Fifi. 1. Glass containing rising silica grains. Natural si^e. 



In a former paper' I criticized the interpretation that has 

 been offered of the result of a certain experiment by Morozewicz. 

 The glass from his experiment showed a density and composi- 

 tion gradient, with the heavier portion at the bottom of the pot, 

 and this arrangement had been explained as the result of the 

 Gouy-Chaperon action. I offered the suggestion that the ar- 



' The later stages of the ei'oluiion nf the igneous rocks. Journ. Geol., Suppl. 

 to Vol. 23, p. .5. 1915. 



