1921] 



on Cloudlarid Studies 



435 



current of air first established. On liquid air being poured in, 

 heavy clouds flowed out and immediately rolled down the outside, 

 almost obscuring the vessel. On repeating this with a similar current 

 of hydrogen, the cold clouds were rendered quite buoyant and 

 soared away with only a small amount of aggregation, as seen in the 

 companion Fig. 14. 



Slow surging movements and cirrus-like formations were shown 

 by illuminating the quiet layer of cloud over a vacuum cup of liquid 

 air. For this purpose a slightly convergent beam was passed throu gh 



Fig. 15. 



a diaphragm with a horizontal slit, and glanced along the open 

 mouth of the cup. All stray light was absorbed when the cup, 

 wrapped with black velvet, was placed inside a black box having a 

 horizontal slit in one side at the same height as the mouth of the 

 cup. The illuminated clouds were then projected through an 

 elliptical opening higher up on the side of the box opposite to the 

 incoming light. Fig. 15 shows the arrangement, and Figs. 16-20 

 some of the formations observed. 



On a larger scale several beautiful effects were seen when small 

 quantities of liquid air were distributed over the surface of a blackened 



2 H 2 



