The electron, its isolation and measurement and the determination of some of its properties
John Stuart Mill · en
The process of making this determination is exceedingly simple and very
reliable. For, since electricity is atomic in structure, there are
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only, for example, three possible speeds which a drop can have when it
carries 1, 2, or 3 elementary charges, and it is a perfectly simple
matter to adjust conditions so that these speeds are of such different
values that each one can be recognized unfailingly even without a
stop-watch measurement. Indeed, the fact that electricity is atomic is
in no way more beautifully shown than by the way in which, as reflected
in Table XII, these relatively few possible working speeds recur. After
all the possible speeds have been located it is only necessary to see
whether one of them is ever skipped in the capture of a new ion in
order to know whether or not that ion was a double. Table XII represents
the results of experiments made with very hard X-rays produced by means
of a powerful 12-inch Scheidel coil, a mercury-jet interrupter, and
a Scheidel tube whose equivalent spark-length was about 5 inches. No
attempt was made in these experiments to make precise determinations of
speed, since a high degree of accuracy of measurement was not necessary
for the purpose for which the investigation was undertaken. Table XII is
a good illustration of the character of the observations. The time of
the fall under gravity recorded in the column headed “” varies
slightly, both because of observational errors and because of Brownian
movements. Under the column headed “” are recorded the various
observed values of the times of rise through 10 divisions of the
scale in the eyepiece. A star (*) after an observation in this column
signifies that the drop was moving with gravity instead of against it.
The procedure was in general to start with the drop either altogether
neutral (so that it fell when the field was on with the same speed as
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when the field was off), or having one single positive charge, and then
to throw on positive charges until its speed came to the 6.0 second
value, then to make it neutral again with the aid of radium, and to
begin over again.
TABLE XII
Plate Distance 1.6 cm. Distance of Fall .0975 cm. Volts 1,015.
Temperature 230 C. Radius of Drop .000063 cm.
No. of Charges
on drop
No. of charges on
Ion Caught
No. of Charges
on drop
No. of charges on
Ion Caught
19.0
100.0
1 P
20.0
10.0*
1 N
16.0
2 P
1 P
20.0*
0
1 P
8.0
3 P
1 P
100.0
1 P
1 P
20.0*
0
1 P
20.0
16.0
2 P
1 P
100.0
1 P
1 P
8.0
3 P
16.0
2 P
1 P
100.0
1 P