262 
NATURE 
[FEBRUARY 24, 1923 
Obituary. 
Pror. W. K. von RontcEN. 
) big is given to few men of science to make a con- 
tribution to knowledge which compels world- 
wide interest from its first announcement. The late 
Prof. Réntgen’s discovery of the X-rays in 1895 was 
not only of the first importance, but also enjoyed the 
distinction of finding an immediate and immense field 
of application in surgery and medicine. Presently 
they were destined to play also a prominent part in 
the extraordinary developments in atomic and mole- 
cular physics which have characterised the last twenty 
years—developments which make it safe to assert that 
at no period in its history has physical science been 
more effective and wide-reaching in its fundamental 
activities. Réntgen was happily spared to be a witness 
of all this, and although his contributions to X-ray 
research ceased some years ago, his satisfaction at 
the growth of the subject can have been in no way 
diminished. 
Wilhelm Konrad von Réntgen was born at Lennep 
in the Rhineland on March 27, 1845. Although a 
German by birth, he was sent to school in Holland, 
and later he took his doctor’s degree in Switzerland at 
Zurich in 1869. Then he was appointed assistant to 
Kundt at Wirzburg in Bavaria, and afterwards at 
Strasbourg, where he carried out a well-known piece 
of work on the ratio of the specific heats of gases. He 
became a privat-dozent of the latter University in 
1874. A brief period followed as professor of mathe- 
matics and physics at the Agricultural Academy at 
Hohenheim, after which he returned to Strasbourg 
in 1876 as extra-ordinary professor of physics. In 
1879 he became professor of physics and director of 
the Physical Institute at Giessen ; and six years later 
followed his appointment to the chair at Wurzburg. 
It was here he made his famous discovery. After- 
wards he was appointed to the chair of experimental 
physics and director of the Physical Institute at 
Munich; he resigned these appointments in 1919. 
Réntgen died at Munich on February ro, 1923, at the 
ripe age of seventy-eight years. He received the 
Nobel Prize for physics in rgor, and with Prof. Lenard 
the Rumford medal of the Royal Society in 1896. 
While Réntgen’s researches extended over a fair 
range of physics, their importance is completely over- 
shadowed by his discovery of the X-rays, the credit 
for which is in no way lessened, but rather is enhanced 
by the curious belatedness of the event. Crookes, 
during his memorable investigations (1879-85), con- 
structed a discharge tube with a concave cathode and 
a platinum target to display the heating effects of 
focussed cathode rays. Thus all the essential features 
of a modern gas X-ray tube were there, and X-rays 
must have been generated in abundance, but, although 
much of value within the tube was noted and recorded, 
the X-rays remained unnoticed. 
Later Lenard, in 1894, demonstrated conclusively 
that cathode rays could pass through a thin window 
of aluminium, and were able to excite phosphorescence 
a few millimetres away in air. This was a correct 
observation, despite the fact that we now know that 
part of the phosphorescence was due to X-rays excited 
NO. 2782, VOL. 111] 
by the aluminium. About this time the inexplicable 
fogging of unopened packets of photographic plates 
in the neighbourhood of excited Crookes tubes was 
engaging the attention of more than one English 
physicist, but not until the autumn of the following 
year was the major discovery made by Rontgen, the 
manner of it being somewhat accidental. It so 
happened that in a search for invisible light rays he 
had enclosed a discharge tube in light-proof paper, 
and, to his surprise, noticed that, when the tube was 
excited, a barium platinocyanide screen lying on a 
table a few metres distant shone out brightly. If 
obstacles were interposed between the tube and the 
screen they cast shadows, and very quickly a unique 
and fascinating feature was revealed—the new or 
“X-rays could penetrate many substances quite 
opaque to light. The degree of penetration depended 
on the density ; for example, bone was more absorb- 
ent than flesh, When Réntgen communicated his 
results to the Physico-Medical Society of Wirzburg 
in November 1895, the immense significance of his 
discovery received universal appreciation. A trans- 
lation of his paper appeared in the issue of NATURE 
for January 23, 1896 (vol. 53, p. 274). 
An army of workers sprang up and a torrential 
output of observations and speculation followed, as a 
glance at the scientific journals of those days will 
verify. The Réntgen Society came into being in 
London in 1897, largely at the instance of the late 
Silvanus Thompson, and similar societies were in- 
augurated later in other countries. Réntgen himself 
contributed three memoirs to the subject during these 
years, but later returned to his earlier interests in 
physics. He had, with others, established the fact 
of the ionising properties of the X-rays. 
Much controversy and a wealth of speculation 
followed as to the nature of the rays. But experiment 
gradually whittled down the various theories, and no 
question now arises that the X-rays are light rays with 
wave-lengths which place them next to, and beyond, 
the ultra-violet. It was their minuteness of wave- 
length that defeated all the earlier attempts to sort 
out the rays, and this uncertainty continued until 
Nature herself was found to have fashioned suitable 
diffraction gratings in the form of crystals, the regular 
atomic spacings in which were of the right order of 
magnitude. We can now claim a knowledge of the 
existence of more than thirteen octaves of X-rays. 
Of these, three octaves or so are used by the radiologist, 
these having wave-lengths of the order of 10~® cm. 
We can only refer briefly to the enormous application 
of the X-rays in medicine. It is probable that no 
more potent weapon has been put into the hands of 
the medical man. The late war brought this home 
in unexampled fashion, and while human endeavour 
reached its pinnacle in almost every phase of life, it 
is difficult to overestimate the services which Rént- 
gen’s discovery rendered to humanity. An extensive 
industry in X-ray equipment has sprung up in this 
country and abroad. 
The new knowledge was not without its menace, as 
many of the pioneers discovered to their cost. Pro- 
longed and frequent exposure was found to produce 

