1 34; Mr. Sturgeon on Electro-pulsations and Electro-momentum. 



momentum not very generally understood ; but which I will 

 endeavour to explain. A coil of copper wire excited by mag- 

 netic action will become a channel for an electric current ; 

 and whilst the whole circuit is metallic, the velocity of that 

 current would be considerably greater than if any, even a 

 small part of the circuit were of worse conducting materials : 

 and if the current were suddenly transferred from a channel 

 of the former character to one of the latter, by any contrivance 

 whatever, it would meet a resistance on entering the new 

 channel, which the momentum it had previously required 

 would have to overcome; and a sudden disturbance of the elec- 

 tric fluid, previously at rest, would take place, and a violent 

 rush of the current would as suddenly follow. 



It is in this manner that shocks and sparks are produced 

 by magnetic electric machines, where the current, previously 

 in rapid motion, is suddenly transferred to a new channel of 

 inferior conducting character; and all the fluid in the revolv- 

 ing coil rushes through a person properly situated for the new 

 route, and who experiences the electric shock, or else through 

 a thin stratum of air at an interruption in the metallic circuit 

 where the spark is produced. 



These, then, are some of the effects of electric currents, or of 

 the momentum of the electric fluid in a state of motion, after 

 the exciting cause is entirely cut off". The shock thus pro- 

 duced may very conveniently be compared to the blow given 

 by Montgolfier's hydraulic ram. Electro-momenta may be 

 produced by any mode of excitation whatever, and the effects 

 •will be proportional to the velocity and quantity of the electric 

 fluid first put into motion ; and the length of the original 

 channel is also to be taken into account. If then electro- 

 momenta, capable of producing violent shocks and vivid 

 sparks, can be produced by a few hundreds of feet of thin 

 copper wire, what is it that might not be expected from the 

 electro-momenta of nature, arising from currents of many 

 miles in extent, kept in motion either by heat, saline solutions, 

 or by other causes, amongst the metalline strata below the 

 surface of the earth ? A sudden disruption in the circuit 

 would insure the blow, and an earthquake might be the re- 

 sult. 



Artillery Place, Woolwich, July 4, 1836. 



