May I, 1902] 
proposed by Balmer and others to express them. The 
suggestions of Dr. Johnstone Stoney and the later 
developments of Kayser and Runge will not be forgotten 
in this relation. He also made observations on at- 
mospheric absorption in the spectrum, using photo- 
graphic methods, at his country house at Courtenay, 
where he used to spend most of his vacations. He thus 
was able to fix the inferior limit to the ultra-violet end of 
the spectrum, so far as it is visible at low elevations, and 
found that in the laboratory air is opaque to ultra-violet 
waves of a lesser wave-length than 07185 p. His work 
on meteorological optics has thus been summarised by 
M. Guillaume :—“Such researches, in the course of which 
he was often led to a scrutiny of the sky, could not fail 
to draw his attention to the optical phenomena of the 
atmosphere, the study of which, though energetically pur- 
sued by the French physicists of last century, is to-day 
somewhat neglected. The splendid glows which were 
observed in the sky toward the end of 1883 furnished to 
Cornu an occasion to utilise the profound knowledge 
which he possessed of the phenomena of optics. He 
showed that the twilight glow, which at that time gave 
such marvellous charm to the sunsets, was due to a diffrac- 
tion caused by fine powders, and it became evident that 
the formidable volcanic explosion of Krakatoa was the 
prime cause of it.” 
Cornu published an elegant method for the investi- 
gation of the optical constants of lens systems. He 
devised the optical lever for the measurement of the 
curvatures of lenses, and he perfected the Jellett prism for 
polarimetric work. To him is due the elegant geometrical 
construction in which spirals are applied to express | 
graphically the relative intensities of the light in diffrac- 
tion images. His preference for geometrical demon- 
strations of theorems which might otherwise be hidden 
under a burden of analytical symbols was _ well 
known. He worked at acoustics in conjunction with 
M. Mercadier, and at elasticity, and in conjunction 
with M. Baille redetermined the constant of gravitation. 
He was occupied, too, with the. problems of the syn- 
chronisation of two resonant systems capable of vibration 
under elastic forces, these memoirs being published in 
1888 and 1889, the second of them including the applica- 
tion of his ideas to the synchronisation of clocks for the 
distribution of time. His plan was closely akin to that of 
Wheatstone, depending on the sending, at every second, 
of feeble induction currents generated by the movement 
of a magnet attached to the pendulum of a master clock. 
In 1884 he reported on the electric transmission of power 
by M. Marcel Deprez on the Chemin de Fer du Nord. 
He took part in the first electrical congress at Paris in 
1881. In 1886 he became a member of the Bureau des 
Longitudes, and in 1900 of the International Commission 
on Weights and Measures. He was president of the 
Académie des Sciences; twice, at different periods, 
president of the Société de Physique ; and by general 
consent was elected to preside also over the International 
Congress of Physics in 1900. 
_ He was elected a foreign member of the Royal Society 
in 1884, and was also an honorary member of the 
Physical Society of London. In 1878 he received for his 
work on the velocity of light the Rumford Medal of the 
Royal Society. At least twice he gave Friday evening 
discourses at the Royal Institution ; the last of these in 
1895 on the physical phenomena of the high regions of 
the atmosphere. 
In 1899 he delivered, with delightful eloquence and 
learned ease, the Rede lecture at Cambridge, on the 
wave-theory of light and its influence on modern physics. 
On this occasion, which was at the time of the jubilee 
celebration of Sir George Stokes, he received the 
honorary degree of Doctor of Science. 
In Cornu, France has lost one of her most distinguished 
men of science, and one who, not only as investigator, 
NO. 1696, VOL. 66] 
NATURE 13 
but as teacher and wise counsellor, had won universal, 
esteem and respect. A true follower of the great tradi- 
tions of France inthe pursuit of science, and a passionate 
follower of Arago, Biot, Fresnel and Fizeau, he was in his 
own person much more than this. He was the ideal 
of a well-equipped, well-balanced, intellectual leader in 
scientific thought. SILVANUS P. THOMPSON. 
M. VIGNON’S RESEARCHES AND THE 
“HOLY SHROUD.” 
et the meeting of the Paris Academy of Sciences on 
April 21, some remarkable photographs of brownish 
stains found on the “ Holy Shroud” keptin the Treasure 
Chamber of Turin Cathedral, and traditionally said to 
be the winding-sheet of Christ, were exhibited in connec- 
tion with a paper by Dr. P. Vignon, of which a translation 
from the current number of the Comptes rendus of the 
Academy is given below. Upon reproducing these stains 
by photography, Dr. Vignon found that he obtained a 
realistic picture of a human figure, and the suggestion is 
that the picture is actually a representation of the body 
of Christ, produced by radiographic action from the 
body, which, according to ancient texts, was wrapped in 
a shroud impregnated with a mixture of oil and aloes. 
We give Dr. Vignon’s paper, which it. will be noticed is 
confined to an account of principles relating to radio- 
activity. 
ON THE FORMATION OF NEGATIVE IMAGES BY THE ACTION 
OF CERTAIN VAPOURS. 
Ir is known, from the work of M. Colson, published in the 
Comptes rendus of the Academy of Sciences in 1896, that 
freshly cleaned zinc emits vapours at the ordinary temperature 
which are capable of affecting photographic plates in the dark. 
The researches of Russell have also shown that the striations of 
a plate of zinc reproduce themselves on a photographic plate. 
But it is a long step from this to the realisation of an object in 
relief. I have succeeded in obtaining images either with 
medals powdered with zinc, or with bas-reliefs or objects fully 
embossed, in plaster, and rubbed with zinc powder. These 
images are negatives, not by the inversion of light and shade, 
since they are formed in the dark, but by the fact that the 
reliefs give more energetic impressions than the cavities. To 
interpret these it is necessary then to invert photographically ; 
| positive images are then obtained in which the scale of relief is 
scrupulously respected, which is far from being the case in 
normal photographs of the same objects illuminated from the 
front. Naturally, upon images made at a distance, the repro- 
duction of the most minute details could not be expected, the 
precision of the detail obtained being less as the distance 
increased. The clearness of the image depends upon the 
rapidity with which the action diminishes when the space in- 
creases between the emissive surface and the receiving screen. 
From a point of the active surface let a perpendicular be 
lowered on to the receiving plate ; the foot of this perpendicular 
constitutes the centre of a circle which makes a more energetic 
impression in its central region than on its edges; the clearness 
of the image will thus be greater the smaller the surface of the 
circle acted upon, and this surface varies inversely as the 
rapidity with which the actions decrease when the distance 
increases. It is on this account that the images correspond very 
nearly to those which would be realised if the actions were pro- 
duced only according to the orthogonal projections of the dif- 
ferent points of the active surface. 
It is a curious point that the images converted into positives 
frequently give rise to the impression of having been lit from 
above. 
This will be the case when a plane, such as the forehead, is 
seen from the front and forms at the same time a strong relief, 
whilst a plane near it is rapidly shifting, such as, for example, 
the region which connects the superciliary arch to the eyeball. 
When this plane shifts it appears to sink into a deep shadow. 
The truly specific character of these negative images which 
arise from action at a distance lies in the softness of the contours. 
The limit of the visible portion is the result for the eye of the 
receding of the surface. If this falling back takes place at a 
small distance {rom the receiving plane, the contour is still 
marked, though vaguely ; but if this falling away is produced 
