434 



SCIENCE. 



[N. S. Vol. II. No. 40. 



metallic guard tube. This guard tube was 

 alwaj's metallically connected to the other 

 pair of quadrants of the electrometer and 

 to its case, and to a metallic screen sur- 

 rounding it. This prevented any external 

 influences from sensiblj^ affecting the 

 electrometer, such as the working of the 

 electric machine which stood on a shelf 5 

 metres above it. 



some minutes, so as to electrify the air in 

 the can. As soon as the machine is stop- 

 ped the electrifying wire is lifted clear out 

 of the can. The can and the quadrants in 

 metallic connection with it are disconnected 

 from the case of the electrometer, and the 

 electrified air is very rapidly drawn away 

 from the can by a blowpipe bellows ar- 

 ranged to suck. This releases the opposite 



■^PARAFFINE 



Fig. I.- 



paraffine: 

 -Connected with guard screen (not shown in diagram) . 



§ 2. The experiment is condiicted as fol- 

 lows : One terminal of an electric ma- 

 chine is connected with the guard tube and 

 the other with the electrifj'iug wire, which 

 is let down so that the needle is in the 

 centre of the can. The can is temporarily 

 ■connected to the case of the electrometer. 

 The electric machine is then worlced for 



kind of electricitj' from the inside of the 

 can, and allows it to place itself in equili- 

 brium on the outside of the can and on the 

 insulated quadrants of the electrometer in 

 metallic connection with it. 



§ 3. "We tried different lengths of time of 

 >electrifieation and different numbers of nee- 

 dles and tinsel, but we found that one nee- 



