Publications, Newspaper Cuttings, Photographs and Correspondence about Persia and the Persian Gulf [‎191r] (382/879)

(8
JOURNAL OF THE ROYAL SOCIETY OF ARTS.
May 27, 1910.
It is produced in a variety of modifications by the
■union of foimaldehyde and carbolic acid, in connec
tion with certain metallic salts. In one form it has
the appearance of ordinary resin, but in another form
it can be poured as liquid into moulds. After
coagulation it is transparent, with a ruby tint, infu
sible, and unaffected by ordinary chemical reagents.
It is well adapted for making ornaments, such as hat
pin heads, imitation jewellery, &c., and for most
purposes where enamel, or enamel varnish is em-
iployed. As compared with celluloid, it has the
great advantage of being non-combustible.
CORRESPONDENCE.
A THEORY OF COMETS.
The nucleus of a comet is a globe O1 gas of extreme
tenuity, probably not more than one hundred
thousandth of the density of our atmosphere at the
earth’s surface. Still, however small the density of
the nucleus, it must be more dense than the sur
rounding space. Therefore, it must form a lens, i.e.,
a burning glass which will cause the sun’s rays
which pass through it to set on fire the cosmic
matter, which is of course chiefly found in its own
path, which is curved.
In thinking of a comet as a lens we should com
pare it with a globe of natural crystal of very varying
density, which contains also a considerable amount of
non-transparent mineral matter.
The gases of which the nucleus of a comet is com
posed will often be of very varying density, and in
consequence it will produce the numerous distinct
tails with which some comets seem to be furnished.
So large a lens as the nucleus of a comet will also
produce extraordinary phenomena of reflection, as
well as refraction, such as we see comets do, in fact,
present to our vision.
The nucleus of a comet being transparent is of
necessity quite invisible when passing between the
■earth and the sun. This is the reason why in so
many instances a comet has been erroneously sup
posed, even by skilled observers, to have passed
behind instead of in front of the sun.
This simple theory seems to explain satisfactorily
-all the observations, whether spectroscopic or other
wise, that have hitherto been recorded respecting
comets. Edwin Durning-Lawrence.
NOTES ON BOOKS.
Brazil in 1910. By J. C. Oakenfull. Published
by the Author at 21, Clifford Terrace, St. Bor
deaux, Devonport.
In this, the second revised edition of his excellent
little handbook of Brazil, the author has brought the
669
work up to date, furnishing many useful statistical
details of a country which offers tempting openings to
European energy and capital. The book is well illus
trated with photographs and maps. The frontispiece
is a striking picture of the “ Minas Geraes,” the
world’s largest and most heavily-armed battleship,
while three of the maps will be familiar to readers of
the Journal, where they appeared to illustrate Mr.
Hugh Pearson’s paper on the diamond fields of
Brazil. Mr. Oakenfull writes with much enthusiasm
of the resources of this vast country. In an appendix
he gives some valuable information as to salaries and
cost of living in Rio Janeiro, &c.
Metallography. By Cecil H. Desch, D.Sc.,
Ph.D. London: Longmans, Green and Co.
According to the author, the use of the word
“metallography” in its old sense of a general de
scription of metals, is now obsolete. Nevertheless
the term metallography in the old sense has a use
extending over a century and a half to its credit, and
what Dr. Desch terms the “ reintroduction ” of the
word to designate the microscopic structure of metals
and alloys, ranks only 1rom 1892; but he tells us
that since that time the term has received an ex
tension of meaning, so that in this work the ex
pression, metallography, is used as having relation
to the internal structure of metals, or mixtures
of metals, and also to their physical properties
generally.
Considering that the book consists of over 400
pages, and the wording is almost epigrammatic in
conciseness, it is by no means surprising to find a
rich fund of various and detailed information. For
example, on page 390 there are interesting notes on
the methods employed by the Chinese and Japanese
for the production of black or purple patina on the
surface of metal objects, and on the same page there
is a short reference to the speculum metal that was
formerly so much used in the construction of reflect
ing telescopes; we are also told that it is " now
commonly replaced for that purpose by glass, coated
electrolytically with silver or palladium.” This may
be so, but the well-known method of silvering glass,
which is due to Liebig, cannot reasonably be called
electrolytic. On page no the production of alloys
by cementation and analogous processes is touched
upon, and we are told that iron and copper may be
coated with zinc by being heated in zinc dust of 200
deg., a true alloy being formed ; but we are not told
whether the temperature referred to is Fahrenheit or
Centigrade.
The chief and more real value of Dr. Desch’s book
rests in the remarkably full account of the various
uses of the microscope, and of the photographic
camera in combination with the microscope, as means
of revealing the inner nature of alloys, or ot metals
associated with a non-metal as carbon. It must not,
however, be supposed that this chief feature of the
book is confined to details of microscopic or photo-

Publications, Newspaper Cuttings, Photographs and Correspondence about Persia and the Persian Gulf [‎191r] (382/879)

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Publications, Newspaper Cuttings, Photographs and Correspondence about Persia and the Persian Gulf [‎191r] (382/879)

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