ee, eT 
moet Oh. Rood on the discharge of a Leyden jar. 
the manner above indicated, these coatings are during both acts 
in metallic connection, a circumstance which alone might be 
supposed to modify the duration of the discharge and its nature; 
besides this, it is known that the electricity from the coil con- 
tinues to flow for a considerable fraction of a second along the 
terminal wires into the jar, which fact renders it questionable 
bis cap the duration of the discharge of the jar itself may not 
be proportionately lengthened. Hence it is evident that it 
would not be safe to conclude without experiment, that the re- 
sults obtained by Feddersen with jars charged by ordinary fric- 
tio electricity, were applicable to those connected with an 
induction coil. 
_ Historical—tIn the year pe anges published i in the 
"Philosophical Transactions, part age 583, an account of 
his celebrated experiment on the ae of the discharge of a 
den jar charged by a common frictional machine. The light 
: yom the spark was received directly on a plane mirror revolv- 
ing at rates between 30 and 800 times in a second ; the mirror 
was driven by a set of multiplying wheels connected by strings. 
This apparatus was constructed by Mr. Saxton of Washington, 
who at that time was residing in London. The eye of the ob- 
server was placed near the mirror, and as the image of the sp 
was not sensibly drawn out by the rotation of the mir 
Wheatstone concluded that its duration was less than the 0! 
millionth of a second, a result which was accepted by the s¢ 
entific world for about a quarter of a century, passing unques- 
ee till the publication in 1858 of the first of an admira 
es of investigations of this subject by Feddersen ; (P: 
Annalen, Ba. 103, seite 69.) This physicist employed a 
mirror with a radius of half a meter, driven by a train 
foiled otis and obtained as high a ‘rate of rotation as 
ee 
