ELECTRICITY. 



271 



ontly boon delayed by what at first p- 



1 to be very puzzling results. OCCUMOU- 



:ill v In- found that he could uut discharge tho 



..iiu-tiT with liia finger, or only to a cer- 



>, and that it was necessary, before 



iifing another experiment, to put him- 



iii communication with a gas-pipe which 



1 the room. The following chain of ob- 



.;ions and experiments then led to tho 



i-xplauation of tho process by which he 



had become electrically charged : 



I was sitting at a table not fur from tho fl replace, 

 10 electrometer (one of Peltier's construction) 

 mi 1 , and was engaged in experimenting with 

 i! ; >ks of various substances. To insure that the ono 

 I li:ul in luind, which was of tortoise-shell, should be 

 ly dry, I rose and held it for a minute before 

 the fire; returning and placing it on the plate of the 

 electrometer, I was surprised to find that it had ap- 

 ! y acquired a strong charge, deflecting the index 

 of tho electrometer beyond 90. I found that tho 

 same thing took placo with every disk I thus present- 

 ed to the fire, whether of metal or any other sub- 

 stance. My first impression was that the disk had 

 been rendered electrical by heat, though it would 

 have been extraordinary that, if so, such a result 

 had not been observed before ; but, 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 tliat the phenomenon might arise from 

 a difference in the electrical state of tho air in the 

 room and at tho top of tho chimney ; and, to put this 

 to the proof, I adjourned to the adjacent room whero 

 there was no fire, and bringing iny disk to the fire- 

 place I obtained precisely the same result. That 

 this conjecture, however, was not tenable was soon 

 i-vMriit, because I was able to produce the same de- 

 viation of the needle of the electrometer by bringing 

 my disk near any part of the wall of the room. This 

 Beemed to indicate that different parts of the room 

 were in different electrical states ; but this again wna 

 disproved by finding that, when the positions of tho 

 electrometer and the placo where the disk was sup- 

 posed to bo charged were interchanged, tho charge 

 of tho electrometer was still always negative. Tho 

 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 nt will to 

 move the index to its greatest extent. A gold-leaf 

 electrometer shows the phenomena as readily. 



The most essential condition appears to be that the 

 boot or shoe of the experimenter must have a thin 

 solo and be perfectly dry ; a surface polished by wear 

 seems to augment the effect. By rubbing tho sole of 

 the boot against tho carpet or rug, tho electricities are 

 separated, the carpet assumes the positive state and 

 the solo the negative state ; the former, being a toler- 

 able insulator, prevents the positive electricity from 

 running away to the earth, while the sole of tho 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 eacli other by the hands, and the first rubs the 

 carpet with his foot while the third touches tho 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 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 car- 

 pet, it be immediately raised from it. When the two 

 arc in contact, the electricities are in some degree co- 

 erced or dissimulated; but, when they are separated, 

 the whole of the negative electricity beeoms free and 

 expands itself in the body. A single stamp on the 



carpet followed by an immediate removal of the foot 

 cuusot the index of tho electrometer to advance tev- 

 eral degrees, and by a reiteration of such stamp* the 

 index advance! 30* or 40*. The opposite electrical 

 states of the carpet and the aolo of the boot were tbu 

 hown : after rubbing, I removed the boot from the 

 carpet, and placed on the hitter a proof-plate (i. e., a 

 small disk of metal with an insulating handle), and 

 then transferred it to thn plate of the electrometer ; 

 strong positive electricity WM manifested. Per- 

 forming tho same operation with the itole of the boot, 

 a very small charge was carried, by rcaaon of iu 

 ready escape into tho body. The negative charge 

 assumed by solo-leather when rubbed with animal 

 hair was thus rendered evident. I placed on the 

 plate of the electrometer a disk of Bole-leather and 

 brushed it lightly with a thick camcl's-hair pencil ; 

 a negative charge was communicated to tho elec- 

 trometer, which charge was principally ono of con- 

 duction, on account of the very imported insulating 

 power of the leather. Various materials, as India- 

 rubber, gutta-percha, etc., were substituted for the 

 sole of the boot ; metal plates were also tried ; 

 all communicated negative electricity to tho body. 

 Woollen stockings are a great impediment to the 

 transmission of electricity from the boot ; when these 

 experiments were made I wore cotton ones. When I 

 substituted for the electrometer a long wire galva- 

 nometer, such as I usually employed in physiological 

 experiments, the needle was made to advance sev- 

 eral degrees. 



Electrification of an Island. Nature men- 

 tions a curious discovery made by M. Gott, 

 superintendent of the French cable company's 

 telegraph station at the little island of St. 

 Pierre Miquelon. At that place there are two 

 telegraph- stations, one worked in connection 

 with the Anglo-American company's lines, and 

 tho other by tho French Transatlantic com- 

 pany. The former uses a powerful battery 

 and the ordinary Morse signal ; the latter has 

 exceedingly delicate receiving instruments, in- 

 vented by Sir William Thomson. These in- 

 struments were found to be seriously affected 

 by earth-currents, depending on some rapid 

 changes in. the electrical condition of the isl- 

 and, these changes causing currents to flow in. 

 and cut off the French company's cables, in- 

 terfering very much with the currents 'indi- 

 cating true signals. This inconvenience was 

 obviated by laying an insulated wire about 

 three miles long, back from the station to the 

 sea, in which a large metal plate was immersed. 

 After this had been done, it was found that 

 part of the so-called earth-currents had been 

 due to the signals sent by the American com- 

 pany into their own lines, for when the delicate 

 receiving instrument was placed between tho 

 earth at the French station and the earth at the 

 sea, so as to be in circuit with the three miles 

 of insulated wire, the messages sent by the 

 rival company were clearly indicated, so clear- 

 ly, indeed, that they have been automatically 

 recorded by Sir William Thomson's siphon 

 recorder. It must bo clearly understood that 

 the American lines come nowhere into con- 

 tact, or even into tho neighborhood of the 

 French line. The two stations are several 

 hundred yards apart, and yet messages sent at 

 one station are distinctly read at the other 

 station ; tho only connection between the two 



