412 
NAT ORE 
[Marcu 3, 1904 
LETTERS TO THE EDITOR. 
[The Editor does not hold himself responsible for opinions 
expressed by his correspondents. Neither can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts intended for this or any other part of NATURE. 
No notice is taken of anonymous communications.] 
The Blondlot -Rays. 
Since the date of my last letter on this subject, published 
in your columns on January 21, I have made further 
numerous endeavours to confirm M. Blondlot’s experiments. 
It is by no means difficult to obtain some of the effects 
that M. Blondlot describes, but, so far as my observations 
go, these effects, when obtained, are in every case due 
simply to heat. 
As mentioned by a previous correspondent, the luminosity 
of calcium sulphide is considerably affected by minute 
differences in temperature. For instance, a coin taken 
from one’s pocket and held at the back of a calcium 
sulphide screen will, in a few seconds, show through the 
screen as a disc of increased luminosity, the effect being 
due to the warmth of the coin; or again, when two small 
calcium sulphide screens are placed upon two pieces of 
similar metal differing in temperature by only about 2° F., 
it is easy to discover which of the two pieces of metal is 
the warmer by the superior Juminosity of the screen placed 
upon it. 
This, I think, is the explanation of the experiment de- 
‘scribed in 
February 18, where it is stated that ‘‘ if one of these screens 
be laid on the floor when it is very feebly fluorescing it 
will be invisible, but its light will increase when it is placed 
on the top of the foot and the muscles put into action.” 
I have repeated this experiment with home-made screens 
with entire success, my method being to use two screens 
each about 16 mm. by 2 mm. in size, of normally equal 
Juminosity. When one is placed on the foot it brightens 
up considerably as compared with the other. This experi- 
ment is at first sight most convincing, but unfortunately 
for the n-ray theory I find no necessity for the presence 
of the foot at all. A boot newly taken off and still retain- 
ing some warmth, or any other warm object, acts equally 
well, while if one screen be placed on the foot and the other 
upon a can of water heated to the same temperature as the 
foot, no difference between the luminosity of the two screens 
can be detected. Again, the foot experiment does not 
succeed if a good thickness of paper or cardboard is placed 
between the foot and the screen so as to prevent the trans- 
ference of warmth to the latter. 
Prior to the date of my last letter, I had tried a similar 
experiment to that described by Mr. J. B. Burke in your 
issue of February 18. In my case a large calcium sulphide 
screen was exposed to a high power Nernst lamp, one half be- 
ing shaded with lead and the other with several thicknesses 
of black paper, so that only half was exposed to the n-rays. 
Visually no difference could be detected in the brightness 
of the two halves of the screen, but on exposing a gelatino 
bromide photographic film in contact with the screen for 
some three minutes it was found on development that the 
portion of the photographic film that was in contact with 
the half of the screen that was shaded by the paper only 
was considerably more fogged than the other half. Here 
again, however, the result was clearly due to heat, the 
black paper being perceptibly warm to the touch, as when, 
in place of paper, a thin aluminium sheet was employed 
and the experiment repeated, no difference at all could be 
pores between the two halves of the developed photographic 
m. 
Since making this experiment I have, when using two 
very small separate screens, one shaded only by very thin 
aluminium and the other by thick lead, succeeded in observ- 
ing some slight excess in brightness in the former over 
the latter, but this has been discernible only when the 
aluminium had become appreciably warmed by the heat 
radiated from the lamp, so that the difference in tempera- 
ture would, in the light of my other experiments, entirely 
account for the effect. 
It is, indeed, very difficult altogether to eliminate the 
heat coming either from a Nernst lamp or an Auer burner 
except by using materials such as, for instance, water, 
NO. 1792, VOL. 69] 
the advertisement columns of your issue of | 
which, according to M. Blondlot, is opaque to the n-rays. 
This in itself is instructive, as is also the point noted by 
M. Blondlot that the brightening of the screen under the 
influence of the n-rays is not instantaneous but is gradual, 
as also are most thermic effects. 
During the past fortnight there have been published 
details of some new investigations made by M. Gutton and 
communicated by Prof. Poincaré to the French Academy of 
Sciences, according to which the luminosity of calcium 
sulphide screens is increased by their being placed in a 
non-uniform magnetic field. It is stated by M. Gutton that 
only a weak field is necessary, and that the effect is very 
sensitive. 
Having spent considerable time in endeavouring to con- 
firm this observation without the slightest success, it would 
interest me to know whether anyone else has tried it and 
with what result. 
As everyone who has experimented on similar lines is 
aware, investigations of these descriptions are full of pitfalls, 
and it is very easy to see what one expects. For instance, 
if two or more faintly but equally luminous calcium 
sulphide screens of small dimensions, placed two or three 
inches apart, are observed, one will occasionally appear to 
become dim, and it is quite easy with a little practice, while 
looking directly at the screens, to make any one of them 
actually disappear at will, this being due to certain portions 
of the retina being much less sensitive to these weak radi- 
ations than other portions. However, one can scarcely 
suppose that a man of science of M. Blondlot’s antecedents 
and experiences can have deceived himself or have been 
deceived by others in regard to the numerous positive 
results that he has obtained, and those who have unsuccess- 
fully tried the experiments can only imagine that, assuming 
that the phenomena observed are really objective, they are 
only visible to certain individuals. Whether the persons 
who can or those who cannot see these effects have abnormal 
sight further investigations alone can show. 
66 Victoria Street, London, S.W., February 23. 
A. A. CAMPBELL SWINTON. 
Chalk-stuff Gas. 
In his notice of my ‘‘ Papers on Education,”’ in taking 
exception to my nomenclature, Prof. Smithells has touched 
on a question of much importance to teachers. ‘‘ Chalk 
gas seems unnecessary,’’ he says, ‘‘ even as a temporary 
name for carbon dioxide. Why not * Fixed air,’ which 
is both descriptive and historical?’’ A young student 
(about eighteen years old) who went through my course 
two or three years ago, who has read the article, writes 
to me unsolicited a letter on the subject, from which I may 
be allowed to quote the following passage :—‘‘ One remark 
struck me. The reviewer wants to know the advantage of 
calling CO, chalk-stuff-gas and suggests that the classic 
old ‘ Fixed air’ would be better. He does not seem to 
appreciate that by calling the gas ‘Fixed air’ you must pre- 
suppose that it is fixed and hence all that the word ‘ Fixed ” 
entails of a knowledge of the gas; whereas, your name is 
eminently descriptive and entails no knowledge of the gas 
at all but simply describes the source from which it was 
first obtained.” 
I could not state my case more happily. I regard the 
use of names which are obviously appropriate at the time 
when the work is done, which do not involve giving the 
case away, as of extreme importance. In these days we 
are somewhat spoilt by the use of names which are signi- 
ficant of composition if not of structure; we are too prone 
to introduce them without consideration when teaching 
beginners; it is often desirable to give names temporarily. 
It must not be forgotten that the Germans, even at the 
present day, openly speak of acid-stuff and water-stuff ; we 
do likewise in using the names oxygen and hydrogen, 
although our devotion to classics leads us perhaps to dis- 
guise the fact. In teaching beginners I advisedly speak of 
the gas from chalk (or limestone) stuff, because chalk has 
a definite geological connotation: we deal only with the 
substance of which it chiefly consists. 
Henry E. ARMSTRONG. 
In alluding to the subject of names in the notice of Prof. 
Armstrong's book, my chief object was to deprecate the 
excessive violence of the objections which I have so often 
