THE STORAGE OF ELECTRICITY. 
321 
dynamo-electric machine so as to set its coil rotating by a re- 
versal of the generating process, and thus perform work like 
any other engine. Electricity, then, can be produced in large 
quantities, and conveyed to long distances with the speed of 
light ; but there remains another property which it would be 
well to have, if ever it is to become of universal service. It 
should be capable of being stored up, like water in a tank or 
coal-gas in a holder. 
Hitherto electricians have not been quite devoid of appa- 
ratus for storing electricity. They had the contrivance known 
as a ‘ condenser/ in which two or more sheets of tinfoil, A, B, 
are separated by an insulating material, C, such as paper soaked 
in wax-paraffin, or mica. When A is connected to one pole of a 
voltaic battery and B to the other by the wires WW, the metal 
plates take in a charge of electricity, after the manner of the 
Leyden Jar, and will contain it for an indefinite time. To dis- 
charge them it is only necessary to connect A to B by a con- 
ductor ; but this discharge is instantaneous, and therefore 
quite unsuited for electric lighting, or motive purposes, where a 
steady and continuous current is required. Besides the ‘ con- 
denser/ there is however another contrivance known as the 
‘ secondary battery/ which takes in its charge by degrees and 
gives it out again just as gradually ; and under the exigencies 
of modern life, this apparatus has been so far improved within 
the last few months as to become a practical reservoir for elec- 
tricity. 
The ‘ secondary battery/ as it is called, originated, first of 
all, in a discovery made by a French savant named Gautherot as 
far back as 1801, or about a year after Yolta’s pile, the pro- 
genitor of the present voltaic battery, appeared. Grautherot 
connected wires of gold to the poles of the Y olta pile, and when 
he plunged them in water to decompose it into its constituent 
gases, oxygen and hydrogen, he noticed that these wires them- 
selves yielded a brief current after the pile itself had been 
disconnected, and always in a direction opposite to the current 
of the pile. This effect, which is familiar to students of elec- 
tricity under the name ‘polarization of electrodes/ was re- 
marked still later by a German physicist, Bitter, who fertilized 
the observation by his genius and thus created the first ‘second- 
ary battery/ Bitter devised several batteries for the express 
purpose of supplying these secondary currents ; he tried plates 
of platinum, silver, and iron in place of the gold wires of Gau- 
therot, and imm ersed them in solutions of different salts instead 
of water ; but he was wrong in supposing the return current 
to be due to electricity which had soaked into the plates or 
intervening fluid. The true explanation was given by Yolta, 
Marianini, and afterwards by Becquerel, who showed that the 
NEW SERIES, VOL. V. NO. XX. Y 
