DECEMBER 3, 1903] 
NATURE 
103 
A Simple Lecture Experiment with Radium Rays. 
Wuitst preparing some experiments for a lecture on this 
matter, I found a very simple device to demonstrate the 
important fact that radium rays are very easily transmitted 
through a high vacuum; and I am not aware that it has 
been published before in this way. I had at my disposal 
the strongly acting compound of radium bromide which 
is prepared at Brunswick, in Germany; 10 mgr. were en- 
closed in a small box of ebonite with a mica cover having 
a diameter of 20 mm. This was put down in a 
Dewar’s tube with vacuum jacket, as is commonly used in 
experiments with liquid air, and held in place by a stopper 
of cotton wool. The tube was then turned upside down 
in a little dish with some mercury, so as to obtain a perfectly 
enclosed space, and the radium rays could only get out 
by the vacuum walls or through a thick layer of mercury ; 
by taking enough of this dense liquid the escape may be 
stopped altogether, Putting now a charged sensitive gold 
leaf electroscope at a distance of 5 cm. from the tube, a 
leakage instantly sets in, so as to cause the instrument to be 
wholly discharged in fifteen seconds. I also tried a vacuum 
jacketed tube with silvered walls, but though this affords 
much better protection against the heat rays, I did not 
detect any considerable difference with regard to the former 
experiment; the discharge was almost as quick, demon- 
strating that radium rays are not reflected to an appreciable 
amount. Even when the radium bromide was put into a 
large Dewar’s silvered balloon of 5 litres capacity, wrapped 
in cotton wool, and enclosed in a wooden case, in which 
liquid air would be preserved during more than a fortnight, 
the charged electroscope came to zero in half a minute when 
it was placed very near to it. The experiments are effective 
and easily arranged. L. BLEEKRODE. 
The Hague, November 20. 
Nuclei and Ions 
It is perhaps ungracious to reply to a review. I appre- 
ciate very fully that in cases of papers like mine, which 
take an isolated position and are written by a man who 
is not infallible, the task of the reviewer is burdensome 
enough. But Mr. C. T. R. Wilson’s summary of several 
years of my work (October 8, p. 548) seems to me un- 
necessarily captious, and I am obliged to answer in self- 
defence. 
I will not quarrel with Mr. Wilson about the titles of 
my papers, or about references to my first paper (‘‘ Experi- 
ments with Ionised Air ’’). I have had occasion to come 
back to it myself since (Amer. Jour. Sci., xv., 105; ibid., 
217), and shall presumably do so again. 
Turning to the second paper (‘‘ Structure of the 
Nucleus ’’), the impression given is that my first chapter 
is superfluous. The particular direction in which Mr. 
Wilson thinks it superfluous, i.e. the determination of re- 
ciprocal relations in the number of ions and nuclei arising 
in any process, I consider of special importance, as I shall 
explain beiow. Apart from this, the gist of the chapter 
is the (to me) very interesting result that phosphorus as 
a nucleator suddenly bursts forth into maximum activity 
at about 13°. The smoke at higher temperatures is a de- 
gradation. If I had made these experiments earlier I 
should not have drawn the comparison between the number 
of nuclei and the number of ions which Mr. Wilson im- 
pales. Recently (Amer. Jour. Sci., xv., 217) I have de- 
parted widely from this early result. 
With regard to my work on coronas, I had hoped that 
any rational attempt at systematisation would at least be 
tolerated. It was something, I thought, to plough through 
so bewildering a display and to get the general lay of the 
land in that deceptive colour territory, to distinguish sharply 
between the axial and the coronal colours, to ascertain 
that even in the former case the particles are large in com- 
parison with the wave-length of light. So far as I know 
a discrimination of the evidence obtainable from the steam 
jet and the condensation chamber has thus for the first 
time been given. Mr. Wilson, however, has no encourage- 
ment. He gravely doubts ‘t whether the method can be 
made a trustworthy one.’’ Unfortunately I did not know 
this, for I have since ventured to repeat the whole work 
(Amer. Jour. Sci., xvi., 325, and a forthcoming paper in 
Boltzmann’s ‘“‘ Jubelband”’), with corrections of 
NO. 1779, VOL. 69| 
method | 
and calculations, obtaining suggestive periodic variations 
of the coronal apertures for a given colour and the sizes of 
the cloud particles. I have recently succeeded in catching, 
holding, and approximately measuring under the micro- 
scope the particles of the finest fog (beyond the largest 
green-blue-purple corona). Again, in a year’s continuous 
observation by my coronal method of the atmospheric 
“cc 
nucleation of Providence (lest this lead to ‘‘ misconception,” 
let me say that no theological bearing is implied), | have 
found the data useful (Physical Review, xvi., 193; Xvil., 
233). 
ay interpretation of the experiments on the diffusion of 
the nucleus is in error, but I have long since corrected it 
(fully in Amer. Jour. Sci., June, p. 472, briefly in Drude’s 
Annalen, August, p. 1144). Hence I do not find Mr. 
Wilson’s belated comments particularly helpful. I was so 
fully convinced that the excessively slow diffusions observed 
could only be due to the motion of nuclei that I failed to 
see that the small coefficients of the hydrocarbon vapours 
would be virtually accentuated in large degree by the 
occurrence of diffusion from saturated to somewhat less 
saturated vapour. But this bad break is not of primary 
significance in its bearing on my work; the original pur- 
pose of these experiments with hydrocarbon vapours, which 
Mr. Wilson overlooks, was this :—If the ionisation accom- 
panying nucleation is favourable to condensation, it should 
be particularly so, presumably, in the case of the vapour 
of an ionising solvent like water. Hence if non-ionising 
solvents like the hydrocarbons be substituted for water, 
the absence of effects attributable to ionisation might be 
discernible. No essential difference was detected. 
In the following remarks relative to nuclei produced by 
shaking liquids, it is astonishing to find a faint note of 
approval, but Mr. Wilson does not intend that it shall be 
taken too seriously. ‘‘ There is nothing new,’ he hastens 
to add, ‘‘ that nuclei of this kind exist.’? Verbally, this 
may be true, but the implication of the whole paragraph 
is much broader. He does not point out, however, where 
I may find a prior succinct statement, identical with the 
view which I give for the persistence of the solutional 
nucieus. 
My ‘‘ extraordinary hypothesis,’’ as Mr. Wilson calls it, 
is a critical alternative, put forward to ascertain whether it 
has been proved that ionisation has an immediate effect 
on condensation, or whether such condensation is not even 
now to be regarded as a mere question of the size of the 
nuclei. The hypothesis should, in the first place, be fairly 
stated. In any region of intense ionisation there must be 
a correspondingly marked tendency to synthesis. The 
nucleus is the stable result of this synthesis. What its 
structure is to be depends, therefore, primarily on the 
chemical ingredients of the medium out of which the nucleus 
is made. Given a definite medium, simple or complex, and 
one may anticipate a nucleus of definite size and a corre- 
sponding supersaturation needed for condensation. My 
contention is, then, that if nuclei are formed by the X-rays 
at the anode and the kathode, they are liable to be different, 
because the ingredients out of which the nuclei are to be 
compounded are different. If they do not vary in size but 
merely in number with the intensity of the radiation, this 
need be no more surprising than that the products of com- 
bustion remain the same within a wide range of tempera- 
ture. 
My reasons for this view may best be developed in con- 
nection with the case of phosphorus. Mr. Wilson dis- 
misses it by stating, ‘‘ The answer is simply that the nuclei 
causing the phosphorus clouds are not free ions like those 
produced by the X-rays.’’? Let me explain why I fail to 
grasp the term ‘‘ free ion.’’? The phosphorus nucleus, as 
experiment shows, is always a relatively persistent body, 
while the initial ionisation is to an equal degree character- 
istically fleeting. Usually before the emanation has been 
made available for condensation, only a few per cent. of 
the initial ionisation is left. Meanwhile, the nucleation or 
condensational activity has suffered no commensurate de- 
cline (Physical Review, xvi., 288). It is probable that the 
whole series of condensations subsequently to be evoked 
follow in the absence of ionisation. 
The case of water nuclei is in this respect almost the 
same, except that the initial ionisation (I shall venture to 
call it so, since it discharges both positive and negative 
