296 
NATURE 
[JANUARY 28, 1904 
Phosphorescence of Photographic Plates. 
I Ave frequently observed the phenomenon described in 
your correspondent’s letter published in Nature of January 
14 on treating plates which had been exposed to the action 
of Rontgen rays, with a solution of alum. 
I first noticed it in June, 1898, and the temperature of 
the dark room was 23°. The film being ‘‘ hardened ’’ was 
that on an *‘ Ilford Special Rapid Plate,’’ which had been 
subjected to a somewhat protracted development with 
pyrogaliol ; on pouring a 73 per cent. solution of common 
alum over the plate, the liquid lit up with a pale phosphor- 
escence, not unlike that seen on stick phosphorus on a 
warm night, which continued’ for about ten seconds and 
then faded away. 
Plates developed with ferrous oxalate also glow 
occasionally under similar conditions, and phosphorescence 
seems to take place only when the film has not been ex- 
posed to ordinary light, and when the surrounding air is 
exceptionally warm. James F. Ronca. 
Clapham, S.W., January 
23% 
Wit reference to the letter from Mr. T. A. Vaughton 
in your issue of January 14 regarding the phosphorescence 
of silver bromide, it is worth noticing that this is not a 
function of the silver haloid salt. 
Whilst working here for Dr. W. J. Russell, F.R.S., I 
chanced to empty some spent pyro developer and a dilute 
solution of alum into the sink of the dark room at the same 
time, when the whole liquid at once glowed with a brilliant 
phosphorescence. 
This takes place whenever a dilute aqueous solution con- 
taining pyro, a soluble sulphite, and an excess of alkali is 
made acid. It occurs even when the amount of pyro is 
very small, but it is essential that the solution be alkaline. 
If the pyro be mixed with sodium sulphite alone, although 
the latter be in sufficient quantity to ensure faint alkalinity, 
the solution remains colourless and does not phosphoresce ; 
an oxidation of the pyro seems to be necessary. f 
Either a dilute solution of a mineral acid, of an organic 
acid, or of an acid salt can be used to acidify the pyro. 
This phenomenon is not a new one, but so far as I am 
aware has never been studied. O. F. Brocn. 
The Davy Faraday Research Laboratory, 
Albemarle Street, W., January 20. 5 
M. Blondlot’s 7-Ray Experiments, 
AsouT three months ago I independently discovered that 
a feebly luminous phosphorescent zinc sulphide screen when 
brought near the body increased in brightness. 
I mentioned this fact to Mr. H. A. Taylor, remarking 
that I believed it to be the effect of an undiscovered ray 
given off by the flesh; he suggested, however, that heat 
was the cause of the phenomenon. 
Further trials showed this to be the case; by laying the 
back of the screen against a fluted jar filled with warm 
water the zinc sulphide would brighten up along the edges 
of the fluting and clearly indicate the pattern; on removing 
the screen the light would fade, showing the pattern now 
as dark lines against a lighter background. 
With care screens of sulphide of zinc or of calcium may 
be made highly sensitive to warmth, and by this means it 
might be possible to photograph many dark bodies simply 
by means of the heat rays given off, provided a suitable lens 
was emploved. S. G. Brown. 
4 Great Winchester Street, London, E.C., January 23. 
Curious Shadow Effect. 
I SHOULD feel obliged, if not troubling you, if you could 
tell me where I could obtain information with regard to 
the following :— 
During the Christmas holiday my brother and I were 
in North Wales, and happened to be on the ridge that lies 
north of Llyn Llydaw; the sun was about rh. from time of 
Setting, and was low enough to clear the lower edge of the 
thin clouds which came from a northerly direction. The 
hollow (Cwm Glas) to the north of the ridge was, every 
NO. 1787, VOL. 69] 
now and then, filled up with thin mist on which our shadows 
were projected ; surrounding the shadow was a faint oval- 
shaped rainbow, which, as the sunlight strengthened, 
became brighter, and a second bow outside the one nearest 
to the figures appeared, though very faintly. Although my 
companion was within a few feet of me, we each saw our 
saw, 
own shadows only. We also when the mist was 
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Wy 
further from us, a shadow of the ridge itself with our two 
figures on it, in this case the figures appearing much smaller 
than in the other effect, and without any bow. 
These phenomena are, I believe, not rare on this ridge, 
certain conditions, such as a bright low-down sun behind 
one, and a fairly opaque mist in front, being, of course, 
necessary. : 
The point on which I desire information is why the bows 
JP 
should be of this oval form, and why they should appear 
at all? 
The shadow of one’s figure I can more readily under- 
stand. : 
The little pencil sketch enclosed may perhaps explain my 
description. H. M. Warner. 
44 Highbury Park, N., January 14. 
Destructive Action of Rain upon Animal Life. 
Tue protracted and heavy rains during periods of the 
past year must have imposed a severe strain upon the 
smaller and more fragile forms of animals, such as, for 
instance, plant lice, mites, many of the smaller species of 
insects, spiders, &c. Even if adults are able to withstand 
the destructive effects of torrents of rain, it is difficult to 
understand how very immature examples, or individuals that 
have recently undergone ecdysis, can survive. During pro- 
longed and heavy rain over a mixed tract of country the 
available shelter is relatively very small. Practically the 
whole surface soil becomes sodden, and, in the open at any 
rate, almost the whole vegetation is drenched. In some 
plants, as is well known, the flowers and certain areas of 
the leaves and other parts afford shelter, but even taking 
this into account, it would seem that the injury must be 
very great. In the county of Sussex during ordinary June 
