On Water and Air , 
1880.] 
119 
and it was emptied, the water carrying with it in suspension 
any contamination that it had obtained from the sides of 
the funnel and bulb. This washing process was repeated 
several times, when, from the very heart of the ice, the 
Fig. 5. 
water was finally taken, and on examination by the concern 
trated beam it was found to be of a most delicate blue colour, 
proving it to be of the greatest purity.j _ 
If we now send a beam from our eledtric lamp across the 
room, we shall illuminate the suspended dust. [An eleftnc 
beam was made to traverse the theatre from the lamp at l, 
and brought to a sharp focus at b, Fig. 6.J Here we have 
our beam ; that dust which you see in its path is nearly all 
combustible matter. The beam is fairly vividly shown upon 
the dust of the room. Now I will take something that will 
enable me to do away with the dust of the air. [A colour- 
