Vacuum Gold-leaf Electroscopes in Rarefied Gases. 757 



leaf took the form shown in fig. 7, very different from any 

 that could be due to electrification. 



The gold leaves of the vacuum electroscope show a distinct 

 deflexion when bright daylight falls upon them, and a large 

 divergence is obtained if the gold leaves are illuminated by 

 direct sunlight. A black card interposed, so as to cut off 

 the light, causes the leaves to collapse at once ; but they again 

 attain their maximum deflexion the instant the card is 

 removed. 



Turning the electroscope round its own vertical axis, so 

 that the rays of light, from the sun or any other source, may 

 fall upon the gold leaves at different angles, increases or 

 diminishes the amount of the repulsion of the leaves. 



Experiment 11. — To put in evidence further the difference 

 between these phenomena, and such as could arise from 

 electrification of the vacuum electroscope, the following 

 arrangements were made, of which fig. 8 is a diagram. 



The gold leaves and the metallic coating of the vacuum 

 electroscope A were connected up to the corresponding gold 

 leaves and the metal plates of an independent electroscope B. 

 A wire p made connexion between the metallic coatings and 

 " earth." The two electroscopes were exactly similar in 

 construction ; the main difference between them was that 

 one had a high vacuum, and the other had no vacuum. 

 The gold leaves of both were of the same length and 

 width, and the glass enclosures were made from the same 

 length of glass tubing ; thus, if a common charge were given 

 to both electroscopes, the lower ends of the gold leaves would 

 stand apart at approximately the same distance in each. A 

 Nernst lamp Q, with its metal cover connected to a water- 

 pipe, was brought near to the electroscope A, the gold leaves 

 at once diverged, and those of the electroscope B also diverged; 

 but the distance apart of the leaves of B was not more than 

 half the distance by which those of A stood apart. If now the 

 wire r connecting together the gold leaves of A and B was 

 touched with the hand, electroscope B was discharged, but 

 electroscope A was only partially discharged. 



When electrified rods of glass and sealing-wax were brought 

 up to the electroscope B, the charge on the leaves was found 

 to be resinous, but the charge left on the gold leaves of A, 

 after the electroscope B had been discharged by touching the 

 wire r, was not electricity at all. To confirm this, both 

 electroscopes were charged vitreously, and when the Nernst 

 lamp was brought up to electroscope A, the [vitreous) charge 

 of electroscope B was neutralized, but the gold leaves of 



