Electric Light. 23 



Any fatal accidents which have occurred have invariably 

 arisen with high tension currents, but it is noteworthy that 

 currents of a certain tension may be practically harmless if 

 continuous or unbroken, whereas the same "pressure" may 

 produce most serious results if intermittent or alternating ; in 

 other words, if there are periods of cessation in the flow of the 

 current, or if it is made to pass in one direction and then in the 

 opposite. The Board of Trade stipulated, in the Act of Parlia- 

 ment passed for permitting companies to supply electricity from 

 central stations for domestic use, that the tension for direct 

 currents inside the house should not exceed 300 volts (the volt 

 is a term applied to the unit of tension), whereas, with alternating 

 currents, the limit should not exceed 100 volts. One advantage 

 gained in the use of high pressure is that the sectional area 

 of the copper wires for conducting the electricity may be 

 much less than what would be necessary for low tension, thus 

 reducing the first cost of the installation ; and, up to certain 

 limits, there is greater economy in the working ; but on the 

 other hand there are certain objections to veiy high tension 

 (besides the danger), as the light produced when arc lights are 

 employed is of an unpleasant blue or violet colour. 



Frictional Electricity, because of its high tension, has not been 

 used to any great extent, except for experimental purposes, or 

 for the explosion of mines ; but latterly a new field has . been 

 opened for its employmeut by a little apparatus for lighting 

 gas. 



It is noteworthy that although the so-called " storage" of 

 electricity has created a great deal of interest of late, yet as a 

 matter of fact the " bottling up" has been known for centuries 

 in respect to Leyden jars, whereas the " storage" of the present 

 day is not a material accumulation of the current, but merely 

 changing the chemical condition of lead plates and the acid in 

 which they are immersed, by the action of a current of electri- 

 city when passed through them, and it is the tendency for the 

 lead plates and acid to return to their original condition, which 

 again gives rise to new electrical currents when a connection is 

 made to permit the currents to flow. The action which takes 



