184 



MESSRS. A. M. WORTIIIXiiTON AND K s. COI,K 



Series XVII. 

 Fig. 3. Fig. 4. 



J 



19 millims. in diameter falling 30 centims. into Alexandra oil, a height at which 

 ordinary observation in continuous light had shown that a little air was already 

 taken down. In Series XVIII. the height was 40 centims., and in Series XIX. it was 

 50 centims. 



Series XVIII. 



Fig. 1. 



Fig. 4. 



