JUNE 5, 1902 | 
NATORE 
127 
invoked to account for the white underparts and white quills of 
the pied forms, which would be well concealed if the bird lay 
flat on the ground. 
Yet in this case of a bird which has been protected by man 
for a few centuries only, we see these beautifully arranged mark- 
ings appearing suddenly and almost in full perfection, by simple 
variation happening to take, in this species, these definite forms. 
Last winter I procured in the Bazaar here a pintail snipe 
(Gallinago stenura), marked much like a pied guinea-fowl, with 
white outer primaries, some white down the breast, and orange 
toes. This is the kind of resemblance which is put down to 
mimicry when occurring between two wild sfeczes of similar size 
inhabiting the same country. 
And thus the view of Darwin, that mimicry has always com- 
menced between forms with a considerable resemblance to start 
with, receives confirmation ; as also from the fact that, in birds 
at any rate, so many cases of ‘‘ false mimicry” between species 
inhabiting distant countries can be shown to occur. 
At any rate, whether we are dealing with recognition-marks, 
sexual selection or mimicry, it seems to me that the study of 
variation constantly tends to show that natural selection has 
always at hand far greater material in the shape of colour- 
variation than is commonly supposed. F. FINN. 
Indian Museum, Calcutta, May 1. 
A Cubic and Submerged Cubes. 
THE following is a curious puzzle. Given a square box 
having an area of 27 square inches on its floor and having 
vertical sides, and filled with water to a depth of 2 inches, 
it is required to find the size of a heavy cube which, when 
resting on the bottom of the box, will have its upper 
surface high and dry above the surface of the water. The 
curious thing is that there is no such cube. <A very small cube 
will have its top nearly 2 inches below the surface; the 
largest cube that can go into the box, its edge being 5 inches 
and a fraction, forces all the water above it except a film and, 
again, has its top nearly 2 inches below the surface. There 
is one cube, that with its edge 3 inches, which has its top 
just on a level with the surface of the water; its top may be 
dry, but is not both high and dry. All other cubes are more or 
less submerged. This is a numerical example of a unique case. 
For an example of the general case, let the area of the 
floor of the box be 28 square inches and let it contain 
48 cubic inches of water. Now it will be found that 
there are two cubes which, when placed on the bottom, have 
their tops on a level with the surface of the water. They are 
‘the cubes with edges 2 inches and 4 inches respectively. 
All cubes between those two have their tops high and dry above 
the surface, while all other cubes are more or less submerged. 
It may be interesting to know that these cubes give a physical 
interpretation to the roots of the cubic obtained by equating the 
trinomial «3—a@x+v to zero. The equation has two positive 
roots, # and 2, and a negative root, (w+). Ifa be the area 
of the bottom of the box and wv the volume of the water, then + 
is the edge of the cube which has its top flush with the surface 
of the water. There are, therefore, in general two such cubes, 
m* and n’, the negative root being inadmissible. Since 
a=m+mn+n and v=mn(m+n), by giving values as m=4 
and x=2 we obtain a=28 and w=48, as in the second numerical 
example above. Again, if we suppose the two positive roots 
equal, as #=n=3, we have a=27 and v=54, as in the first 
example. 
If a value be assigned to x lying between # and x, it is 
readily shown that the trinomial is no longer zero, but is 
negative, which is the condition that the top of the cube shall 
stand above the surface, while for values of x on either side of 
mand x the trinomial becomes positive, so that these cubes are 
submerged. TuHos, ALEXANDER. 
Trinity College, Dublin, May 22. 
The Electrical Resistance of the Blood. 
In a letter published in NarureE of July 13, 1899, the 
author communicated some of the results he had obtained in 
measuring the electrical resistance of the blood. These results 
showed that the average resistance of normal blood at 60° F. 
measured by Kohlrausch’s method in the apparatus used 
amounted to 550 ohms, while the specific resistance was 93°5 
NO. 1701, VOL. 66] 
ohms. Further, a marked change was observed in pernicious 
anzemia, the resistance in this disease falling to about one-half 
(300 ohms) that of normal blood. The author has shown 
(Proceedings of the Royal Society of Edinburgh, December 21, 
1891) that the electrical resistance of the urine in this disease 
is greatly increased (about 100 ohms specific resistance instead 
of the normal 45 ohms) ; hence we have the striking fact that, 
while the urine contains too few salts, the blood contains an 
abnormal amount. The kidneys, then, must obviously be in 
fault. In a patient, aged fifty-one, suffering from pernicious 
anzmia, under the care of Dr. A. James, in the Edinburgh 
Royal Infirmary, the blood resistance, measured on February 
25, 1902, amounted to 300 instead of to the normal 550 ohms. 
The resistance of the urine, measured at the same time, 
amounted to 88 ohms instead of to the normal 45 ohms. The 
blood corpuscles numbered 900,000. The blood resistance in 
diabetes mellitus is high, like that of the urine. A number of 
experiments have been made by me to ascertain the time occu- 
pied by ingested sodium chloride to reach the blood. The blood 
resistance in five cases was measured before taking 30 grains of 
the salt and at five-minute intervals afterwards. The average 
time taken for the first lowering of the resistance of the blood 
was 154 minutes, and the maximum effect was produced in 214 
minutes. 
Further observations on these lines 
promise interesting 
results. 
Dawson TURNER. 
Chickens Hatched in a Tree. 
You may, perhaps, think the following account of an incident 
which happened here last week in our poultry-run worth 
printing. 
About May I, one of our hens, which was known to be laying, 
totally disappeared. For some ten days she baffled all our 
efforts to discover any traces of her. At last she was found 
sitting on the eggs she had laid in a squirrel’s nest, in a Scotch 
fir-tree, at a height of 16 feet from the ground. 
For the remaining eleven days of her incubation the hen was 
watched descending, and ascending from bough to bough to her 
high perch, at first every day once, but latterly once every other 
day, as far as could be observed. 
On Thursday, May 22, the hen was found with six live 
chickens and two dead ones at the foot of the tree. Unluckily 
no one witnessed the actual descent. She could not, however, 
be persuaded to enter an ordinary hen-coop. 
With some trouble, the hen and her six chickens were got 
eventually on to some straw in an old railway-carriage, which I 
had erected some years ago on the edge of the hen-run, which 
is sheltered from the north wind bya fir-plantation, where many 
squirrels build their nests. 
In order to convey her chickens from the railway-carriage to 
the ground, the hen was seen to spread out her tail and descend 
with all six young chickens at once on her back. Doubtless 
she had conveyed them down the 16 feet from the fir-tree in the 
same fashion, but probably only one or two at a time. 
Six-Mile-Bottom, Cambs., May 25. W. H. HALL. 
A Curious Optical Effect. 
A FORTNIGHT ago, while standing with my back to the sun, 
which for a few minutes happened to be shining brightly, and with 
my face within a few inches of some darkly painted boards, which 
were covered with minute sparkling particles, presumably from 
an adjacent coke-grinding machine, I noticed that on 
approaching my face a little closer, the particles became 
iridescent and apparently magnified to a size of about one-eighth 
of aninch. On closing one eye and looking closer, concentric 
circles appeared, with a cross x over them, and in some cases 
there was a smaller circle just touching the inner margin of the 
larger one; in others the small circle seemed to be nearer the 
centre of the larger one. Ona subsequent examination, when 
the sun was not so bright, the concentric circles seemed to be 
wavy and indistinct, as was also the case with the cross. 
The whole thing reminded me of illustrations I have seen of 
effects produced by tourmalines under certain conditions. 
If this is a commonly observed phenomenon, I should feel 
obliged for any references to literature on the subject. 
E. Moor. 
49 Arbitration Street, Doncaster, Yorks., May 26. 
