The electron, its isolation and measurement and the determination of some of its properties — John Stuart Mill — John Shaqi
The electron, its isolation and measurement and the determination of some of its properties
John Stuart Mill · en
Although the elimination of the assumption of equality of the number of
droplets and the number of ions makes Wilson’s determination of
more reliable as to method than its predecessors, the accuracy actually
attained was not great, as can best be seen from his own final summary
of results. He made eleven different determinations which varied from
to . His eleven
results are:
TABLE I
In 1906, being dissatisfied with the variability of these results,
the author repeated Wilson’s experiment without obtaining any
greater consistency than that which the latter had found. Indeed,
the instability, distortion, and indefiniteness of the top surface
of the cloud were somewhat disappointing, and the results were not
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considered worth publishing. Nevertheless, it was concluded from these
observations that the accuracy might be improved by using radium
instead of X-rays for the ionizing agent, by employing stronger
electrical fields, and thus increasing the difference between
and , which in Wilson’s experiment had been quite small,
and by observing the fall of the cloud through smaller distances and
shorter times in order to reduce the error due to the evaporation of
the cloud during the time of observation. Accordingly, a 4,000-volt
storage battery was built and in the summer of 1908 Mr. Begeman
and the author, using radium as the ionizing agent, again repeated
the experiment and published some results which were somewhat more
consistent than those reported by Wilson.[38] We gave as the mean of
ten observations which varied from 3.66 to 4.37 the value
. We stated at the time that although we had not
eliminated altogether the error due to evaporation, we thought that
we had rendered it relatively harmless, and that our final result,
although considerably larger than either Wilson’s or Thomson’s (3.1 and
3.4, respectively), must be considered an approach at least toward the
correct value.
IV. THE BALANCED-DROP METHOD
Feeling, however, that the amount of evaporation of the cloud was
still a quite unknown quantity, I next endeavored to devise a way of
eliminating it entirely. The plan now was to use an electrical field
which was strong enough, not merely to increase or decrease slightly
the speed of fall under gravity of the top surface of the cloud, as
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had been done in all the preceding experiments, but also sufficiently
strong to hold the top surface of the cloud stationary, so that the
rate of its evaporation could be accurately observed and allowed for in
the computations.