Vol. XXIV. No. 3.] 
POPULAR SCIE^^CE :J^EWS. 
37 
Practical CljorQlstry and tlje ]?Irts. 
ULTRAMARINE. 
A BEAUTIFUL bluc mineral, known as lapis- 
lazuli, occurs rather sparingl3', which has 
been used for many years in the manufacture 
of pigments for artists. . Little preparation is 
needed, beyond finely grinding and separat- 
ing it from the gaiigue, or rock in which it 
is found. Its magnificent blue color is all 
the more remarkable in that it contains 
neither copper, cdbalt, nor any other metal 
forming colored salts, but is simply a silicate 
of aluminium afid other bases, containing 
also a certain amount of sulphur, both as 
sulphates and sulphides, to which the color 
is probably due. 
The great beauty of this ultramarine, as it 
was called, and also its scarcity and conse- 
quent high cost, early led to attempts to 
produce the compound iirtificially. . Its com- 
position was known from analysis, and from 
this an empirical formula was deduced, and 
a mixture of China clay, sodic sulphate and 
carbonate, coal, ancU sulphur w.ns strongly 
heated in a closed crucible, the resulting mass 
proving to be a very good article of artificial 
ultramarine. This is one of the few qases 
where "the rule of thumb" gives results 
wliich would not have been anticipated from 
a theoretical consideration of the principals 
involved. 
Artificial ultramarine was first prc|>nred by 
Cmclin, in 1S23, and in 1S2S it was made at 
Lyons on a commercial scale. Since then 
the. production has greatly -increased, and 
enormous quantities are now annually pro- 
duced, and from its cheapness it has largely 
replaced such pignlents as smalt (cobalt), 
litmus, and Prussian blue. The process of 
manufacture varies in difierent factories, but 
is essentially that given above, where the 
constituents, as shown by analysis, are mixed 
together and ignited in closed crucibles. In 
one process, a green ultramarine is first 
obtained, which is roasted with access . of 
air and additional sulphur to convert it into 
the blue variety ; but the mixture is also 
made so as to form the blue variety at the 
first ignition. Artificial ultramarine is quite 
stable imder ordinary conditions, but it is 
readilv affected bj' even weak acids, which 
destroy the color. Natural lapis-lazuli is not 
affected in this way, showing that there is 
some chemical or molecular difference be- 
tween them. A similar acid-proof variety is 
occasionally produced artificially in the fur- 
naces, but the conditions governing its pro- 
duction are not known. 
The chemical constitution of ultramarine, 
and the cause of its blue color, are not well 
understood. According to the experiments 
of Stein, it consists chiefly of a white mass, 
with which black sulphide of aluminium is 
intimately and molecularly incorporated, the 
blue color being due, not to chemical com 
position, but to the optical relations of the 
component substances. Green ultramarine 
contains less soda and more sulphur than 
the blue. The native ultramarine surpasses 
the artificial in beauty and softness of color, 
and is still used by artists, and for purposes 
where the artificial product is unsuitable. 
A DEVICE FOR WRITING IN 
MOVINC VEHICLES. 
Umder the phonetic name of Wryteezy^ 
the London Industries^ describes an ingenious 
and useful, though rery simple, invention, by 
which one can write in a carriage or on 
the cars without anj- disturbance from the 
motion, even when travelling over the rough- 
est roads. The writing-desk, as shown in 
the engraving, consists of a light piece of 
wood, the lower part of which is attached 
to the arm by an elastic band. The upper 
part is supported by two cords (not elastic) 
V'ir»:4/'i'^-fr7«J^ 
which are attached to a point at some dis- 
tance above the writer's head. By this 
arrangement, all movements of the vehicle, 
paper, and fingers are rendered synchronous, 
or occur at the same time and in the same 
direction. 
Everyone who has tried to write on the 
cars knows what an exasperating and.imsat- 
isfactory operation it is, and this simple little 
devite — which can be made by anyone, and 
carried in an ordinary hand-bag — will be of 
great service to those who have occasion to 
make many railroad joinneys. 
A New Way of Preparing Hydrogen is de- 
scribed' by J. Haderniann as follows : A granulated 
alloy of tin and zinc, containing about 83 per cent, 
of ilie latter metal, is prepared by adding zinc to 
molten tin as longas.it dissolves in tlie liquid metal. 
The product is recommended for the production of 
hydrogen. The pieces retain their shape and size 
after all the zinc is dissolved out by acid. 
[Original in PojmUir Sci*>nce New8.\ 
THE SCIENTIFIC KNOWLEDGE OF THE 
ANCIENT GREEKS AND ROMANS. 
BY JOHN C. ROLKE, PH. D. 
V. — ASTRONOMY. 
So much attention was given to this branch of 
science, and so much progress was made, that only 
a very brief survey of the field can be made in this 
article. 
The Greeks began at very early times to observe 
the heavens, and to distinguish the heavenly bodies 
froin one another. In the poems of Homer mention 
is made of the Pleiades, Hyades, Orion, Sirius, the 
Great Bear, and Arcturus. The morning and even- 
ing stars are spoken of, but their identity is not 
suspected. The earth is conceived to be a disc, 
around which flows the stream of Oceanus. Thales 
of Miletus, one of the " Seven Wise Men of Greece," 
who lived at the end of the seventh century before 
our era, looked on the heavens as a hollow sphere 
divided into five zones. He discovered the true 
causes of the phases of the moon, and of eclipses, 
and is said to have foretold an eclipse of the sun 
which occurred during the reign of Alyattes of 
Lydia, in the year 609. Anaximander, his great 
successor, held that the earth had the form of a 
cylinder, suspended in the middle of the universe, 
and that men dwelt on its base.' It was surrounded 
by water, air, and fire in successive layers. This 
fire, shining through different openings, took the 
form of the sun, the moon, and the stars. The first 
to turn his attention to the planets was Anaxi- 
menes. He looked on them as flat- discs, supported 
by the air between the earth and the arch of hea\^n. 
Heracleitos believed that the. heavenly bodies were 
shaped like cups. When these were turned towards 
the earth, they caught its vapors, which took fire 
and reflected their flame. When they were turned 
from the earth, darkness ensued. Bv the time of 
.Vnaxagoras, who lived in the fifth century before 
our era, the spherical form of the earth was known. 
The first to elaborate a regular cosmic system 
was, apparently, Pythagoras, although it is dilficult 
to distinguish hi§ own personal work from that of 
his successors. This system, as finally elaborated, 
was as follows : In the center was an ever-burning 
fire, not the same as the sun. Around it revolved 
the sun, the moon, the earth, the five planets 
(Saturn, Jupiter, Mars, Venus, and Mercury), and 
the sphere containing the fixed stars. There was 
assumed to be a counter-earth, — probably merely to 
make up the niynber ten, — which was distinct from 
the earth itself, but always moved parallel to it at a 
distance of 180°. Pythagoras defined the inclina- 
tion of the courses of the planets ai?d of the ecliptic. 
Aristarchus of Samos, in the fourth century B. C., 
first made the sun the center of the universe. 
Copernicus mentions three other Greeks as prede- 
cessors of his in this regard. 
Aristotle wrote a work in four books on astronomy. 
He gives various proofs of the spherical shape of the 
earth, among others the circular shape of the edge 
of the earth's shadow in a partial eclipse of the 
moon. He also discusses comets and meteors, and 
the nature of the milky way, which he believed to 
be formed of luyriads of small stars. Aratus, an 
Alexandrine astronomer of the same century, gave 
especial attention to the constellations, whose form 
and location in the heavens he describes in a 
didactic poem. 
Many attempts were made to ascertain the size 
of the earth. The method of Eratosthenes was, 
perhaps, the most ingenious. He was informed 
that at Syene in upper Egypt, near the modern 
town of Assouan, deep wells were lighted to their 
bottoms at the time of the summer solstice, and 
