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Electrical Insulation in High Vacua . [March, 
when the tube got cold it rose to nearly its former position. 
This was repeated several times with uniform results. When 
the leaf was repelled down the vertical leaf also moved away, 
so as to keep the same angle between them. It is therefore 
evident that the leaves themselves were also charged. 
Fig. 4. 
Fig. 4, c, shows the two positions of the leaves, a a before 
applying heat to the side c of the tube, and b b after heating 
the glass at c. 
The tube was now heated on both sides, causing the leaves 
to come nearer together, as shown at Fig. 4, d. While the 
glass was warm the cylinder was raised so that it surrounded 
the leaves : this caused them to get a little closer together, 
and they kept in this position, shown at E, after the whole 
apparatus was quite cold. 
After remaining thus for some time the cylinder was 
lowered, and the leaves widened out and took up the position 
shown at b b , Fig. 4, c. They did not return to the position 
a a, showing that their divergence was now owing to their 
own mutual repulsion, and not to an attraction of one or 
other to the electrified glass. 
In December, 1877, I totally immersed one of these ex- 
hausted glass bulbs in a vessel of water, the gold leaves 
