1 879.] Spider's Web for Micrometers. 245 
having previously been charged, and standing at an angle of 
112 0 from one another, as at Fig. 5. The water was con- 
nected electrically with “ earth,” and the whole was set aside 
in a cabinet on the 1st of January, 1878. 
At the present time, after having remained in this condi- 
tion for thirteen months, the leaves form exactly the same 
angle with one another which they did when they were first 
put in the cabinet. 
Fig. 5. 
From this experience I think we may consider that at an 
exhaustion of a millionth of an atmosphere, air is an abso- 
lute non-condudtor of statical electricity. It is therefore 
legitimate to conclude that the vacuum of interstellar space 
offers equal obstruction to the discharge of electrified bodies, 
without necessarily interfering with their mutual repulsion if 
similarly electrified. It is possible that in these faCts an 
explanation may be found of some obscure celestial phe- 
nomena. 
VII. SPIDER’S WEB FOR MICROMETERS. 
t HE web used is that of the common garden spider; the 
spinner of those geometric webs is abundant in sum- 
mer and autumn. The reason why this spider is 
selected, rather than the house spider, may easily be seen by 
anybody who watches the proceedings of each when a fly is 
caught. The house spider seizes his victim and spins 
around him a winding-sheet of web, before carrying him 
