638 Proceedings of the Royal Society of Edinburgh. [Sess. 
produced is strongly curved, and forms a sensitive detecter of heat. The 
shearing force between the two glasses composing the thread may be so 
Fig. 4. 
great that the halves sometimes come asunder, and thus produce fine fibres 
with a semicircular cross-section. 
Fluorescence, Density, and the Action of Radium Rays. 
The glass glows faintly, a pale blue colour, under the impact of cathode 
rays. It is worth noticing that in spite of the large amount of sodium 
