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
Again, when we compare the experimental uncertainties in Townsend’s and
Thomson’s methods, it is at once obvious that the assumption that the
clouds are not evaporating while the rate of fall is being determined
is even more serious in Thomson’s experiment than in Townsend’s, for
the reason that in the former case the clouds are formed by a sudden
expansion and a consequent fall in temperature, and it is certain
that during the process of the return of the temperature to initial
conditions the droplets must be evaporating. Furthermore, this sudden
expansion makes the likelihood of the existence of convection currents,
which would falsify the computations of the radius of the drop from
the observed rate of fall, more serious in Thomson’s work than in
Townsend’s. The results which Thomson attained in different experiments
gave values ranging from to .
He published as his final value .
In 1903, however,[36] he published some new work on in which
he had repeated the determination, using the radiation from radium
in place of that from X-rays as his ionizing agent and obtained the
result . He explained the difference by the
assumption that in his preceding work the more active negative ions
had monopolized the aqueous vapor available and that the positive ions
had not been brought down with the cloud as he had before assumed was
the case. He now used more sudden expansions than he had used before,
and concluded that the assumption made in the earlier experiments that
the number of ions was equal to the number of particles, although
shown to be incorrect for the former case, was correct for these
[Pg 54]
second experiments. As a matter of fact, if he had obtained only half
the ions in the first experiments and all of them in the second, his
second result should have come out approximately one-half as great as
the first, which it actually did. Although Thomson’s experiment was an
interesting and important modification of Townsend’s, it can scarcely
be said to have added greatly to the accuracy of our knowledge of .
The next step in advance in the attempt at the determination of
was made in 1903 by H. A. Wilson,[37] also in the Cavendish Laboratory.
III. H. A. WILSON’S METHOD