Royal Society, 129 



careful treading. This ultimately proved to be the case ; for resu- 

 ming 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 prevented 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 assumes the positive state and the sole the ne- 

 gative state ; the former being a tolerable insulator prevents the po- 

 sitive electricity from running away to the earth, while the sole of the 

 foot, being a much better conductor, readily allows the charge of ne- 

 gative 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 communicated to the instrument. 



Even approaching the electrometer by the hand or body, it be- 

 comes 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 electricity becomes free and expands itself in 

 the body. A single stamp on the carpet followed by an immediate 

 removal of the foot causes the index of the electrometer to advance 

 several degrees ; and by a reiteration of such stamps the index ad- 

 vances 30° or 40°. 



The opposite electrical states of the carpet and the sole of the boot 

 were thus shown : after rubbing, I removed the boot from the carpet, 

 and placed on the latter a proof-plate (i. e. a small disk of metal with 

 an insulating handle), and then transferred it to the plate of the 

 electrometer ; strong positive electricity was manifested. Performing 

 the same operation with the sole of the boot, a very small charge was 

 carried, by reason of its ready escape into the body. 



The negative charge assumed by sole-leather when rubbed with 

 animal hair was thus rendered evident. I placed on the plate of the 

 electrometer a disk of sole-leather and brushed it lightly with a thick 

 camel's-hair pencil ; a negative charge was communicated to the elec- 

 trometer, which charge was principally one of conduction, on account 

 of the very imperfect insulating-power of the leather. 



Various materials, as India-rubber, gutta percha, &c, were sub- 

 Phil. Mag. S. 4. Vol. 40. No. 265. Aug. 1870. K 



