. 
i ee eee. ti foe 
ders, in reading this book, what 
NATURE 
549 
THURSDAY, JANUARY 15, 1914. 
APPLICATIONS OF POSITIVE RAYS. 
Rays of Positive Electricity and their Application 
to Chemical Analysis. By Sir J. J. Thomson, 
O-M. uaeResree ep: Vii+132+5 plates. (Long- 
mans Green and Co., 1913.) Price 5s. net. 
LL physicists and chemists will welcome this 
account by the author of his wonderful 
series of researches, begun seven years ago, on 
positive rays. This name, “positive rays,” is 
preferable to “canal-rays,” originally applied to 
the stream of positively-charged particles which 
passes through a hole in a flat cathode: and the 
author’s choice of the word “particle” to denote 
an atom carrying a positive charge, and the word 
“corpuscle ” for what is generally now termed an 
electron, will not be challenged. 
After a description of Goldstein's experiments, 
an account is given of Wien’s discovery that 
these rays are deflectable by powerful magnetic 
fields. The theory of the deflection is shortly and 
clearly stated; and also the theory of the electro- 
static deflection of a particle. Then follows an 
account of the author's first experiments, made 
in 1906, for which he devised an apparatus allow- 
ing of the simultaneous application te a bundle of 
positive particles both an electrostatic and a mag- 
netic force, The arrangement is so devised as to 
apply these forces at right-angles to each other: 
and the result, as Sir Joseph Thomson has 
‘described in numerous papers and lectures, is to 
convert the luminous point (if a Willemite screen 
be used) into a parabola. The position of the 
parabola on the screen is conditioned by the in- 
tensity of the forces applied; but if these be kept 
uniform, it depends, inter alia, on the masses of 
the particles. Now the mass is simply related to 
the atomic or molecular weight, and hence the 
nature of the particles can be identified. 
It is found, however, that the same mass may 
hold one or more charges; hence in deducing the 
atomic weights, this has to be borne in mind. 
Descriptions are given, with figures, of the in- 
struments employed; but from a practical point 
of view the figures might have been improved. 
In Fig. 6, for example, connections for maintaining 
an electrostatic field are not shown, and neither 
in that figure nor in Fig. 13 is any arrangement 
shown for introducing gas. Indeed, one won- 
gases were 
present to cause the kathode rays to pass, for they 
cease in a high vacuum. Sir Joseph Thomson 
points out the necessity for removing air very 
thoroughly with a pump before applying absorp- 
tion with cooled charcoal; are the’ residual gases 
NO. 2307, VOL. 92] 
traces of neon and helium? or are they minute 
traces of oxygen and nitrogen, corresponding to 
the vapour-pressures of the gases condensed on 
the charcoal? or do the conducting gases come off 
the electrodes, or off the walls of the tube? It 
would have been useful if information on this 
point had been given. In this connection, on 
Pp. 25, we are told that the gas to be used is kept 
in 41, Fig. 13; but there is no means of introduc- 
ing a gas into .1; the gas is said to be stored 
ever a column of mercury; how then is mercury 
vapour excluded? The same want of precision 
applies to the description of the photographs. It 
is exceedingly difficult, if not impossible; to follow 
on the plates the peculiarities described in the 
text; for example, Fig. 28 is described on pp. 48 
and 49. Eight parabolas are mentioned in the 
text, but only five appear in the photograph. Pos- 
sibly the negatives may show more than the 
prints; but if so, it should have been stated, and 
a diagrammatic reproduction of the photographs 
should have been given. In this connection, too, 
it may be mentioned that there is a considerable 
number of misprints; the well-known “effect” is 
due to Doppler, not Déppler; and commas are 
frequently substituted for semi-colons. 
The ingenuity with which various effects are 
analysed and alternative hypotheses tested is 
extraordinary; Sir Joseph Thomson possesses 
scientific imagination in the highest degree, com- 
bined with the power of mathematical presenta- 
tion and wonderful experimental skill. Take the 
following passage :— 
“We can form an estimate of the magnitude 
of the attraction between a neutral atom and a 
corpuscle. From the measurement of the plates 
we find that there are negatively electrified atoms 
of hydrogen with a velocity as large as 2x 108 
em./sec. This means that a neutral atom cf 
hydrogen is able to capture a corpuscle ¢ven 
though it is moving past it with this velocity. 
This capture, however, would not take place unless 
the work required to remove a corpuscle from the 
surface of a neutral atom cf hydrogen were 
greater than the kinetic energy of a corpuscle 
moving with the velocity of 2x 108 cm./sec. This 
kinetic energy is equivalent to the fall of the 
atomic charge through 11 volts; hence we see 
that it must require an ionising potential of more 
than 11 voits to liberate the corpuscle from a 
negatively electrified atom of hydrogen. The same 
considerations show that to liberate the corpuscle 
from a negatively electrified atom of carbon 
would require at least o'9 volt, while for oxygen 
the corresponding ratio would be o°7 volt. It 
must be remembered that these are merely inferior 
limits ; the actual values may be much larger.” 
It is interesting to note that evidence has been 
obtained of the transitory existence of such 
groupings as CH,, CH, and CH, as well as of 
Xx 
