AvuGusT 28, 1902] 
NATURE 
415 
SS TT sss 
towards the end of the eighteenth century. The 
historical portion of the work shows the evolution of 
mechanical coal cutting in Great Britain since that date. 
Descriptions are given of every machine that has been 
put to practical use, as well as detailed particulars of 
those that are now in successful operation. The con- 
clusions drawn by the author from his elaborate investi- 
gations are that the whole of the coal of Great Britain 
must be cut by machines, or the industry will find itself 
in much the same condition as the corn-growing industry, 
swamped by American production. The pillar and stall 
method of mining should be replaced by the long wall 
method, and coal-cutting machines would render blast- 
ing unnecessary. The most serious problem to be dealt 
with is that of cutting coal under a weak roof. The 
difficulties are perhaps hardly sufficiently emphasised by 
the author. In a tender coal the roof is crushed down 
on the machines, or supports have to be set near the 
faces. These get in the way of a machine. Moreover, 
machines are so noisy when at work that it is impossible 
to hear the preliminary warning sounds that the roof 
generally gives before it breaks down. Eventually, no 
doubt, it will be ascertained which machine can best be 
adapted to these conditions, or how the conditions can 
be modified to suit the machine that promises best. 
The author's lucidly written and well illustrated volume 
cannot fail to prove of great value in directing the atten- 
tion of mine owners to problems that, at the present 
time, are of the utmost importance. 
Metallography: an Introduction to the Study of the 
Structure of Metals, chiefly by the Aid of the Micro- 
scope. By Arthur H. Hiorns. Pp. xiv + 158; with 
ninety-six illustrations. (London: Macmillan and 
Co., Ltd.; New York: The Macmillan Company, 
1902.) Price 6s. 
THE study of the properties and constitution of metals 
and alloys has made great progress during the last few 
years, and has reached a point when it can no longer be 
neglected by engineers. Steel workers have already 
received some guidance from the labours of metallo- 
graphists, chiefly, perhaps, from investigations on what 
Osmond called the “ pathology of metals,” and the time 
may not be far distant when the microscope and the 
pyrometer will form part of the outfit required in the 
ordinary testing of materials. Metallography has been 
regularly taught for some time at many of the technical 
schools both in this country and in America, and it is 
remarkable that no text-book on the subject existed in 
the English language before the publication of the work 
under review. The researches on which Mr. Hiorns has 
based his book are scattered and highly specialised, and 
the acquirement of a general elementary knowledge of 
the subject has been a difficult matter for the student. 
The appearance of this book is, therefore, particularly 
well timed, and it will be eagerly read by many, who will 
not be disappointed by what they find. 
The author has carefully collected most of the important 
results which have recently been obtained, and has given 
a terse and lucid summary of them which is surprisingly 
complete, considering the modest dimensions of the book. 
He has not devoted much effort to the philosophic aspect 
of the subject, but that is, perhaps, just as well, inasmuch 
as the science is in its infancy. With regard to the illus- 
trations, éxception may be taken to many of the photo- 
micrographs, which appear to have been taken from a set 
of poor negatives. On the other hand, they have been 
beautifully reproduced on special paper. In the study of 
steel, the author has handicapped himself unnecessarily 
by using such low powers of magnification that some of 
the structures of which he speaks cannot be seen at all. 
Nevertheless, taking the book as a whole, Mr. Hiorns 
deserves the thanks of his fellow workers and teachers 
for the useful aid he has given them, 
NO. 1713, VOL. 66] 
LETTERS TO THE EDITOR. 
[The Editor does not hold himself responsible for opinions ex- 
pressed by his correspondents. Neither can he undertake 
fo return, or to correspond with the writers of, rejected 
manuscripts intended for this or any other part of NATURE. 
No notice ts taken of anonymous communications. | 
Notes on Young Gulls. 
In northern Bohemia there is a large pond or artificial lake— 
the Hirschberger Grossteich—with a small, rocky island. This 
is a favourite breeding-place of gulls. Most of these are Larus 
ridibundus, but some Sterna hirundo also breed on the rock. 
For the purpose of studying its plankton I have repeatedly 
visited this pond, and have thus had occasion also to make some 
observations on the gulls which may perhaps be of interest to 
readers of NATURE. 
The rock island which forms the breeding-place is some 
400 square metres in extent, and rises in ledges to a height of 
15 metres. It is composed of the Cretaceous ‘‘ Quadersandstein ” 
of those parts, partly bare and partly covered with patches of 
tough, greenish-brown grass and brighter green thistles. The 
Larus ridibumdus nests on this rock are pretty carefully built 
and entirely composed of dry leaves of bulrushes. There are 
generally three eggs in each nest. At the height of the 
breeding season there are about 200 such nests on the rock, 
besides the much less numerous Sterna nests. The nests 
usually lie on the bare rock close to the margin of a patch of 
vegetation. The dirty brownish-yellow and black-spotted, 
mimetic colouring of the down-covering of the young is very 
effective. When from two to ten days old these young crouch, on 
being disturbed, against the half-dry grass-tufts and thistles close 
to their-nest, and are then by no means easy to detect. It seems 
to me that the colouring of these young gulls is not quite the 
same as that in young of the same species breeding in different 
environments. It is quite likely that we have here a case of 
adaptation of the colour of the young to different surroundings, 
unaccompanied by any difference in the colouring of the adult 
into which they develop. Older ones, which are already begin- 
ning to replace the down with feathers, but in which the head 
is still entirely covered by the primitive yellowish-brown and 
black down, do not, as a rule, try to hide themselves in this 
way, but hurl themselves into the water and swim away rapidly 
when the boat approaches the rock. The old birds scream 
loudly and try, first, to entice the intruder away in the usual 
manner by slowly swimming and flying about near the boat and 
pretending to be wounded and lame. Besides this, however, 
they also swoop down on the swimming young, sometimes 
pushing them right under the water. The first of these actions 
clearly tends to draw the attention of the intruder away from 
the young; the second has the very opposite effect. Perhaps 
it may be accounted for in this way. The young have—this 
can be observed clearly enough—no idea of the nature of the 
movements of a boat, and often try to escape it by swimming 
straight ahead in front of the bow. It gives the impression that 
the old birds try by their screams to convey instructions to 
the young about the direction in which they should swim so as 
better to escape the boat. The young, however, often appear 
not to understand or to heed these ‘‘ words of advice,” where- 
upon the old birds pounce down on them and give them one or 
two good slaps with their wings so as to make them understand 
and obey. These sharp lessons do not seem to be of much 
good, however. -After being thus slapped, the young continue 
to swim straight ahead of the boat as stupidly as before. 
One of the eggs I brought home and hatched artificially. 
The bird began to chirp in the egg a few days after I had placed 
it in the oven, upon which I cut away the blunt end of the 
eggshell and found, as was natural after hearing the bird give 
voice, the beak protruding into the air-chamber. On the fourth 
day after this the young gull left the egg-shell. It then weighed 
22'7 gr. We weighed it daily for a fortnight. The ‘average 
daily gain of weight during this time was 8°5 gr. 
The daily increments were quite irregular, varying between 
1°6 and 3:2 gr. the first four days, and between 5 and 27°5 gr. 
the latter ten days. These irregularities were, of course, due 
to differences in the quantity of the contents of the intestine. 
One day—not three, as has been stated by Prof. Thomson 
(NaTuRE, vol: lxiv. p. 588)—after birth the young bird swam 
about when placed in water just as well as a young duck. For 
