﻿854 Prof. W. A. Douglas Rudge on the Electrification 



A long light rod of wood was balanced upon a pivot. To 

 the end of the wooden rod an ebonite one was attached, and 

 from this there was suspended an aluminium plate about 

 \ sq. metre in area, and from this a tine wire was taken to 



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the electroscope. By tilting the counterpoised end of the 

 rod, the plate could be put in contact with the earth, then 

 quickly raised to a height of about 4 metres above it, any 

 charge removed from the earth being indicated by the elec- 

 troscope. By this means it was shown that the surface of 

 the ground did possess a positive charge which, although 

 small, was quite definite. 



If a block of insulating material (even dry wood will 

 answer in this climate) was placed so that the plate rested in 

 contact with it, but did not touch the ground, then no charge 

 was obtained, and only a small charge if a block of dolerite 

 Mas used, but coating the wood with tinfoil allowed of a charge 

 being obtained. 



It must be pointed out that these experiments were 

 carried out in dry weather when tie earth's surface v»as 

 very poorly conducting. It is quite conceivable that in wet 

 weather a different result might have been shown; but under 

 the conditions of the experiment there certainly was a 

 definite charge of positive electricity. In order to prevent 

 the possibility of there being any electrification due to 

 friction between the plate and the earth, a small spiral spring 

 was attached to the plate, so that it coidd make contact with 

 the earth without rubbing against it. 



(2) The charge upon the Dust carried up by the Wind. — 

 In order to collect the charge in the air, a plate coated with 

 radium was attached to the electrometer. Various means 

 were adopted by which a cloud of dust could be raised, such 

 as throwing a handful of dust into the air ; by directing a 

 stream of air from a pair of bellows against a heap of fine 

 dust; by shaking from the end of a pole a fine muslin bag- 

 filled with fine dry sandy earth; and lastly, and most effica- 

 ciously, by setting a team of mules to plough up the dry 



