Evening star. [volume] (Washington, D.C.) 1854-1972, 1855-07-30
PROPERTIES OF THE ELECTRIC SPARK

The following is the condensed n stract Of
rec nj lecture by Faratay. before jae Royai
Society in London. 1t VIII be lou..I I'M, rest
ing III facts, not geHer.lly known, while at the
anne time 1t Is clear on very important SUBJ
jet, lightning conductors:
The heat of the electric spark is intense.
though the nomeRtary duration of its effects
prevents IT'S heat-slvlng power from being felt
TO is full extent The Inflammation of ether
and the explosion of gunpOwder were shown as
illustrative OF the heat contained in the electric
spark, and the effect of momentary action in
diminishing the heating power was exempiied
by sending an uninterrupted charge through
some loose 9unpOWder, and then repeating the
experiment with a wet string introduced as
part Of the conducting circuit In the first ar
rangement, when the spark passed instantane-
ousiy, the gunpOwder was scattered and not
exploded, but when the resistance of the wet
string prolonged the discharge, the gunpowder
was ignited. The electric spark is sometimes
applied in blasting rOcks as well as yoltaic
electrlcity, and voltaic agency is for general
blasting purposes, very convenient. The ef
tectS of the electric discharge are only per-
celved wnen resistance Is offered to the passage
Of electricity, and several experiments were ex-
hlblted In which 1t was shown that a charge
which passed without producing any apparent
effect when thick wire formed the circuit
was sufficient TO defagrate intcrpoSed pieces of
thin wire and gold Leaf, that were not adequate
to conduct the same quantity freely. The in
geniOus cOntriyance of Professor Wheatstone
for measuring the duration of an electric
spark was exemplified by lighting disk, col.
ored in stripes, and revolving rapidly in the
dark, with a succession Os electric sparks
Though the cOIOrs were mingled together, and
invisible when seen by ordinary light. the
momentary light Of the elecri; spark exhib-
ed cHch colcr 'diStin, tiy, and the disk for the
instant appeared stationary. bJ in"r.-.Il.s
the velocity ~ til ~, Ts became confuaed
even when seen by the sDaIl an approx ina
ton is attained u In. duration Il lhe light;
and N this manner Mr.. Swaine, of .EiinbTr..
proved that the electric spark lasts only the
hundred thousandth part OF a second Aifiash
Of lightning is Of equally short duration, and
every object IN motion. when seen AT night by
the glare of lightning, appears to be stationary
The apparent duration of an electric spark is
about one tenth Of a second, because an i'm
preston once made on the retina is retained
Tor that time, though the object that produced
it, as in the ease Of lightning, is no longer
present.
Another remarkable property in the electric
spark Is the action it eXerts the light storing
power of phosphate of lime. That substance,
together with some others, possesses the power
OF absorbing light in a latent state, which is
given out on the application of heat in the
dark. This light, when once taken from the
phosphate of lime. can be restored to it by the
electric spark, and by that means alone. Pro-
fessor Faraday concluded by explaining and
illustrating the influence OF. the non-conduct.
ing property of the air on the, length of the
spark. By partially exhaustlng glass tube
a spark passed through n much greater space,
and when the exhaustion of the air was more
complete, and the resistance thus removed.
the electricity from the prime conductor Of the
machine passed IN continuous flashes, im;.
tating the effects Of the aurora berealis.