F. Exner, at Vienna, who found an
increase of 60 to 600 volts per meter. The observations were made by
means of an electrometer. In respect of many inconveniences which are
connected with the use of an electrometer, I have tried the measurements
with a very sensitive galvanometer. In this case it is necessary to
apply a separating air exhaust apparatus, for example flame, or a system
of points at the upper end of the conductor, which is elevated in the
atmosphere. In order to get a constant apparatus, I have used 400 of the
finest needles inserted in a metallic ribbon. This system I have raised
in the air by means of a captive balloon, or by a kite, which was
attached to a conductor of twine or to a twisted line of the finest
steel wire. In this way I have attained a height of 100 to 300 meters.
When the lower end of the kite line was communicating with the
galvanometer whose other terminal was in contact with the earth, a
current passed through the galvanometer. For determining the strength of
this current I proposed to called a micro-ampere the 10^{-9} part of an
ampere. At the height of about 100 meters in the average the current
begins to be regular, and increases at the height of 300 meters to 4,000
or 5,000 of these units. The increase is very regular, and seems to be a
linear function of the height.
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