May 6, 1886] 
NATURE 
3 
The shape of the orbit at once suggests the reflecting cone of 
a thermopile, with the eyeball centred on its axis in the position 
of the pile, but of course much less deeply placed. The cone 
is, in this case, oblique, the maximum slant side being internal, 
Zc. towards the nose, and the minimum slant side external. A 
plane through the outer orbital angle, and perpendicular to the 
axis, will be pretty nearly coincident with the tangential plane 
of the eyeball at the anterior end of its antero-posterior diame- | 
ter, and there will be a considerable part of the nasal surface 
of the cone in front of that plane. This part will act as a 
reflecting surface, and concentrate the rays upon the eyeball. 
Probably variations of complexion will not much affect the re- 
flecting power of this surface, seeing that the difference in the 
skin of black and of white races is mainly a difference in the 
amount of pigment in the rete mucosum, and not in the super- 
ficial parts of the epidermis. 
It is evident that rays reflected from the ground, and from 
objects of no great altitude, are the rays which will have the 
greatest chance of striking the eye after reflection from the sides 
of the orbital cone. The direct rays of the sun in tropical 
countries will, during the hottest part of the day, be too nearly 
vertical to take this course. Now it would seem that it is in the 
case of intense light reflected from rocks, snow, &c., that the 
blackening has been found useful. 
Whether to any appreciable extent the amount of light enter- 
ing the eye is increased by the shape and projection of the orbit 
is a different question. 
should be concentrated upon the eyeball. They must enter the 
pupil. Nevertheless, it would seem from observations made for 
another purpose upon the pupil-reflex, that the diameter of the 
aperture is increased by blackening the skin round the orbit, say 
by means of a piece of black cloth with an elliptical hole in it 
for the eye, the light of course being ke] t of constant intensity. 
April 19 G. N.S. 
On the Form of Mole-Hills Thrown up under Snow 
Motes must have an opportunity of getting to the surface here 
and there to dispose of the results of their excavations. When 
they meet with a deep-laid hard road they come out and cross it. 
When frost has bound the soil into an impenetrable cake they 
sometimes come out of the ground, and, travelling away to seek 
a place more suitable for their operations, are unable to find 
their way back or to burrow into the frozen soil in another place, 
and’so they get killed in considerable numbers. When there is 
a little snow on the ground, protecting it from the frost, the 
moles come to the surface as usual, and throw up mounds of 
earth under or through the snow. But, when deep-drifted snow 
has covered the ground, the mole-hills under it are found to be 
arranged in more or less symmetrical ridges of uniform height 
and breadth, as represented in the sketch. It would appear that 
the moles in these circumstances make galleries about the size 
of their own bodies on the surface of the turf in the bottom of 
the snow, into which they push the earth to be disposed of, find- 
ing it easier to make these small tunnels than to raise the usual 
mound of earth under the superincumbent snow-drift. The 
severe winter just over has caused the snow-drifts to lie long in 
For here it is not enough that the rays_ 
the north of England, where examples of this peculiar form of 
mole-hill may be commonly seen on the Fells. 
Cambridge Tuos. McKenny HuGHEs 
Protective Imitation 
I HAVE been watching for hours with great interest what I 
believe to be a very curious instance of protective imitation. A 
large old thrush has been, all that time, trying to make itself 
look like a serpent, and succeeding remarkably well. The 
object appears to be to frighten away a smaller and more active 
thrush—no doubt younger and with sharper ears—which seems 
to be getting all the worms. It appears afraid to attack its 
young rival, but runs towards it as if it meant to do so, and 
when the young one turns round and faces it, the old one 
crouches down so that nothing of it is seen but a crest-like back, 
two glaring eyes, the spotted throat, and a dark line formed by 
the front view of the beak and the lines at the corners of the 
mouth, which look very much like a serpent’s mouth. If I saw 
the creature protruding from a bush or from the grass, I should 
certainly take it forasnake of some kind. The young bird 
looks alarmed and retreats, though just before it was ready to 
attack the other. No sooner has it recovered its courage and 
advanced to attack than the old one retreats, and resumes its 
serpent-like mask. There has been a little sparring in the air 
occasionally, just enough to show the nature of the feeling, but 
if allowed to do so the young one evidently would be content to 
feed quietly. The old thrush (I know it by asmall white feather 
on one wing) is very much at home on this lawn, and seems to 
consider it as its own private domain, at all events as far as 
thrushes are concerned. A short time ago, when the ground 
was for a long time hard from frost and drought, this thrush 
moped about and seemed nearly starved, and at last fell upon 
two great clumps of yellow crocuses, and not only tore them to 
pieces, as if in a rage, but devoured them entirely, returning 
again and again to them, and gobbling up the yellow petals as a 
rabbit does a lettuce. At that time many birds that are usually 
too shy came down from the hills and strolled about the fields 
and lawns—snipes, plovers, &c. Two exquisite crested plovers 
(I think they are called) stalked about with graceful dignity for 
some days in a garden close by, and roosted in an old hen- 
house. The thrush touched no crocuses but the yellow ones, 
and no other bird did so. I should be glad to know if the 
resemblance to a serpent has been observed 
by any one else. Ve Mie 1s 
Sidmouth, April 19 
P.S.—It may be thought that the crouching 
is only a preparation for a spring, but it does 
not suggest that to the eye, and it is not fol- 
lowed by aspring. If it really is a fact and 
not a fancy, the instincts of imitation and of 
fear in this case must be a very ancient in- 
heritance indeed. 
Iridescent Clouds 
Tus evening at sunset there was here a 
fine instance of iridescent clouds. About 7 
I drew the attention of my companion to some 
remarkable clouds ; three long arms of stratus 
of peculiar texture, like pulled-out cotton-wool, 
and of striking colour, blue-black and silver, 
stretched nearly to where the sun had gone 
down behind a hill. At 5 minutes past 7 a 
detached portion of this cloud assumed lovely 
iridescent colours like bright mother-of-pearl. 
This gradually died away, but other portions assumed the same 
tints. At 7.30 the tints vanished. Wind, south to south-west. 
Glencar, Kerry, April 26 J. G. GRENFELL 
MADRAS MAGNETICAL OBSERVATIONS * 
V E are indebted for the present volume to Mr. 
Pogson, the Government Astronomer at Madras, 
from whose introductory remarks we learn that he is not 
yet at the end of his editorial labours. 
= « Magnetical Observations made at Madras in the Vears 1851-1855, under 
the Superintendence of Mr. W. S. Jacob.” Edited by Mr. N. R. Pogson, 
Government Astronomer. (Madras: Lawrence Asylum Press, 1884.) 
