416 
NATURE 
{Aucust 28, 1902 
the first six or seven days it preferred to stand on its ee/s, and 
usually rose to its toes, that is, the normal position of the adult, 
only when walking. 
The bird often ate indigestible things, little stones, &c., not, 
as it appeared to me, altogether accidentally, but chiefly and 
purposely, after it had made a good meal off some living 
food—Tenebrio larvee, Limnzeus, or the like. Smaller edible 
things like ants’ chrysalids it picked off the ground itself 
very early, but larger morsels, bits of fish, mice, &c., it 
only takes when held in the hand and presented to it even 
now, when it is eight weeks old. The stones, &c., it oc- 
casionally eats, and the hair and larger bones it has swallowed 
it brings up and vomits in a mass. It lost the thorn of the beak 
on the fourth day and began to fly a little after four weeks ; when 
seven weeks old it began to make longer excursions, and flew— 
without precept or example—very well. It has, however, not 
yet attained to anything like the elegant flight of full-grown 
gulls, and occasionally makes an involuntary somersault in the 
air when trying to soar or rest on the wind without flapping its 
wings. R. v. LENDENFELD. 
Prague. 
The Effect of Light on Cyanin, 
WHILE working on the reflective power of cyanin mirrors I 
have noticed some very interesting effects of light on that sub- 
stance. Freshly fused cyanin is of a deep metallic bronze colour, 
but exposure to light turns it plum colour and finally a steely 
blue-black. In the moderate light of a cloudy day the change 
is perceptible in half an hour, in direct sunlight in less than a 
minute. The complete change to blue-black requires an ex- 
posure of about twenty hours to diffuse daylight or half an hour 
to direct sunlight. It has long been known that cyanin is un- 
suitable for use as a cloth dye on account of its rapid fading, in 
sunlight, but recent investigators of the optical properties of this 
substance appear to have overlooked this light effect. That the 
effect is purely photographic and not due to any rise in tem- 
perature is shown by the fact that long-continued heating in the 
dark produces no trace of discoloration, On the contrary, the 
effect of heating is to reverse the effect produced by the light, 
for a thin coating of cyanin, exposed until blue-black throughout, 
returns nearly to its original bronze colour on fusion or long- 
continued heating in the dark. By an exposure of thirty hours 
I have obtained on cyanin easily recognisable photographs of 
small, well-illuminated objects. A cyanin mirror, or better yet 
a piece of ground glass washed over with fused cyanin, exposed 
for ten hours to the spectrum of a Nernst lamp shows the effect 
to be very strong in the yellow, just perceptible in the adjacent 
red and green, and imperceptible in the blue and ultra-violet. 
It appears to correspond with the absorptive index as determined 
by Pfliiger in various parts of the spectrum, At the same time, 
the exposure to light greatly decreases the absorbing power 
where it was originally large, as may be easily seen on looking at 
a sodium flame or a spectrum through an exposed coating of 
cyanin. It is as though the absorption were due to molecular 
resonance and the light produced a fatigue or destruction of this 
resonating power. 
A most noteworthy change in the refractive index accom- 
panies this change in the absorptive index, and is shown by the 
alteration in the reflecting power. The reflecting power of 
fresh cyanin is roughly 20 per cent. in the yellow, 2 per cent. 
in the blue-green and 6°5 per cent. in the ultra-violet. After 
exposure to light the reflecting power is nearly constant, 6°5 
per cent., from the red out to 250uu in the ultra-violet. Now 
in the blue-green the absorptive index is so small as not to 
affect the reflecting power sensibly, so that the refractive index 
varies from about 1'1 to 1°6. Evidently work on the optical 
constants of cyanin is of little value unless carried on without 
exposure of the cyanin to daylight. A decrease in the absorp- 
tive index from 0°75 to nearly zero is indicated by the decrease 
in the reflecting power in the middle of the yellow, where 
exposure to light does not greatly affect the refractive index. 
The general effect of exposure to light is, then, to remove the 
absorption band and to destroy the characteristic anomalous 
dispersion. 
The cyanin used was furnished by Kahlbaum, in Berlin, and 
is the ordinary diamyl iodide, C,,H,,N,I, easily soluble in 
alcohol and ether, but only very slightly soluble in water. 
Gottingen, August. P. G. NUTTING, 
NO. 1713. VOL. 66] 
Fog Bow at Oxford. 
A SOMEWHAT curious phenomenon, presumably an effect 
caused by the searchlights at Spithead, was visible here in 
Oxford on the night of Saturday last. 
About 11.15 p.m., the night being fine and warm and the sky 
somewhat overcast, my attention was arrested by the appearance 
of an arc of whitish light, about 15° above the south horizon, 
within which the sky appeared of an intense black. The arc 
rapidly increased in elevation until, in six or seven minutes’ 
time, it had reached the zenith, forming an arch extending, 
apparently, to the horizon on the east and west; it then 
declined northwards, and in another four or five minutes had 
vanished, 
_ In appearance it suggested a brilliant lunar fog bow, but the 
light was of a more bluish tint, the interior circumference being 
far brighter than the outer ; the brilliancy did not diminish to 
any great extent until the bow attained its highest altitude, after 
which it rapidly become fainter. The distance from Spithead 
is rather more than seventy miles. J. Rose. 
Rawlinson Road, Oxford, August 20. 
{ 
Simple Means of Producing Diffraction Effects. 
IN the interesting article on ‘‘ Photography of Diffraction and 
Polarisation” published in the issue of NaTURE for August 7, 
the writer describes various means of producing diffraction 
effects. It may possibly interest some readers of NATURE to 
know that beautiful fringes may be seen with even simpler ap- 
paratus than that described in the article referred to. All that 
Is required is an ordinary folding foot-rule, preferably of ivory. 
To see diffraction bands by its means, it is only necessary to 
close the two halves of the rule until they are almost in contact 
and then to fold them over. On looking at the sun or other 
bright source of light through both slits, a series of brilliant 
diffraction bands will be seen. WILFRED HALL. 
Tynemouth, August 20.7 
ry 
Time-Signals by Wireless Telegraphy. 
May I suggest that the wireless telegraph offers a means of 
enabling Greenwich or other astronomical time being sent 
to ships at sea for the correction of their chronometers and the 
finding of their longitude? Distinct signals have already been 
transmitted from England to America, and these are all that is 
necessary for communicating time. At certain hours of the day 
or night, for example 1 p.m., a series of wireless signals, per- 
haps ten or twenty, at intervals of one second, might be sent 
from Greenwich far and wide as an extension of the time-ball 
signal which now serves for ships in the Thames and the Downs. 
By international regulation these time-signals could be protected 
from other wireless signals. I need scarcely add that such time- 
signals would also be useful inland. JoHn Munro, 
Croydon, August 25. 
THE BELFAST MEETING OF THE BRITISH 
ASSOCIATION. 
SCE the publication of our last article on the ap- 
proaching meeting, the following additional arrange- 
ments have been made :— 
The local executive committee (chairman, Sir Otto 
Jaffe) invites members, associates and holders of ladies’ 
tickets to a garden party in Botanic Gardens Park, near 
Queen’s College, on September 15, at 3 to 5.30 p.m. 
In connection with this reception, the new fernery re- 
cently arranged by Mr. Charles McKim, curator of the 
Botanic Gardens, will be opened for the first time, and 
will be found well worth seeing by those. interested in 
ferns and tropical plants. 
On September 16, Lord O'Neill gives a garden party 
at Shane’s Castle, picturesquely situated on the shore of 
Lough Neagh. 
The Belfast Harbour Commissioners invite members, 
associates and holders of ladies’ tickets to a reception in 
the Harbour Office on September 16, at 8 p.m. 
