1870.] 



in Electroscopic Experiments. 



331 



on placing it in contact with a vessel of boiling water, or heating it by a 

 gas-lamp, no such effect was produced. I next conjectured that the phe- 

 nomenon might arise from a difference in the electrical state of the air in 

 the room and that at the top of the chimney ; and to put this to the proof, 

 I adjourned to the adjacent room where there was no fire, and bringing my 

 disk to the fireplace I obtained precisely the same result. That this con- 

 jecture, however, was not tenable was soon evident, because I was able to pro- 

 duce the same deviation of the needle of the electrometer by bringing my disk 

 near any part of the wall of the room. This seemed to indicate that different 

 parts of the room were in different electrical states ; but this again was dis- 

 proved by finding that when the position of the electrometer and the place 

 where the disk was supposed to be charged were interchanged, the charge of 

 the electrometer was still always negative. The last resource was to assume 

 that my body had become charged by walking across the carpeted room, 

 though the effect was produced even by the most careful treading. This 

 ultimately proved to be the case ; for resuming my seat at the table and 

 scraping my foot on the rug, I was able at will to move the index to its 

 greatest extent. 



Before I proceed further I may state that a gold-leaf electrometer shows 

 the phenomena as readily. 



When I first observed these effects the weather was frosty ; but they 

 present themselves, as I have subsequently found, almost equally well in 

 all states of the weather, provided the room be perfectly dry. 



I will now proceed to state the conditions which are necessary for the 

 complete success of the experiments, and the absence of which has pre- 

 vented them from being hitherto observed in the striking manner in which 

 they have appeared to me. 



The most essential condition appears to be that the boot or shoe of the 

 experimenter must have a thin sole and be perfectly dry ; a surface polished 

 by wear seems to augment the effect. By rubbing the sole of the boot 

 against the carpet or rug, the electricities are separated, the carpet as- 

 sumes the positive state and the sole the negative state ; the former being 

 a tolerable insulator, prevents the positive electricity from running away to 

 the earth, while the sole of the foot, being a much better conductor, readily 

 allows the charge of negative electricity to pass into the body. 



So effective is the excitation, that if three persons hold each other by 

 the hands, and the first rubs the carpet with his foot while the third touches 

 the plate of the electrometer with his finger, a strong charge is communi- 

 cated to the instrument. 



Even approaching the electrometer by the hand or body, it becomes 

 charged by induction at some distance. 



A stronger effect is produced on the index of the instrument if, after 

 rubbing the foot against the carpet, it be immediately raised from it. 

 When the two are in contact, the electricities are in some degree coerced 

 or dissimulated ; but when they are separated, the whole of the negative 



