The Baltimore County union. [volume] (Towsontown, Md.) 1865-1909, 1902-04-05
Correspondence Baltimore County Union.
SCIENTIFIC MISCELLANY.

OOITctpOtUtftCc DuttCUtOJc OOU0ey SfteV"s
SCIENTIFIC MIS- CELLANY.
Duration of Twilight-Absolute Vaccina-
tion-Source of One "Blood-Rain"-
The Civilization Coming-Art1fic CT /
Clay-A Trade Secret From India--A
Suggestion in Heat Storage-The Lee
onids.
The prevalent idea that tropical twilight is
very brief-not more than 10 or 20 minutes-is
corrected by Mr.. S. J. Bailey, who states that in
general the light does not fade away until the
sun has sunk about 18o below the horizon. The
time varies with the latitude, and the North
Pole has about six months Of daylight, followed
in turn by more than two months of night. In
summer, places beyond 500 of latitude have
twilight from sunset to sunrise. In the temper
ate zones the duration is from an hour and
half to two hours; and even in the tropics.
where the suns descent is vertical, more than
an hour is necessary for reaching the point
stated. Actual observation shows that tropical
twilight is never less than an hour, usually
much longer. At Arequipa, Peru, whose height
of 5000 feet and clear atmosphere favor very
short twilight, the light of the sky cast faint
shadow 70 minutes after sunset.
81
1t has been urged that doctors at least should
be absolutely vaccinated." To show what is
meant, DR.. Arthur Maude states that after four
effective vaccinations at intervals of to
years, in 1892 he revaccinated himself four times
at intervals of month, the effects decreasing
to no reaction at all and since that time he has
regularly vaccnated himself every few months.
He insists that the physician should have this
protection, which gives no inconvenience after
two applications.
The great dust-cloud of the Krakatoa erup-
ton in 1883 has been reproduced on small scale
by an explosion of $40 pounds of blasting gela-
tine at Perranporth on the Cornwall coast. Rain
and snow falling six days afterward deposited
yellow sediment, even at one point lib miles
away, and this proves to be undoubtedly dust
from the explosion.
Considering 'the discovery of the future in
a recent Royal Institution lecture, Mr.. H. G.
Wells is forced to the conclusion that man is
not the final product of evolution. The rapid
changes in lifeis conditions point to further de-
velopment, and what is to come after man is
''the most persistently fascinating and the most
insoluble question in the whole world" Imagi-
nation supplies no answer. But we may note
that, while man is still man, greater changes
must come than have been known, that our
dense populations are in the opening phase of
process of diffusion and aeration, and that the
white population at least will be forced some
way up the scale of education and personal eff
fciency in the next two or three decades At
ter this, within couple of hundred or thous-
and years or so, will come a great world States
with deliberate improvement of the blood and
character of the race Over the hill on which
this beautiful State stands we cannot peer, but
hot NO md limo nj Ms
and faith for what surpasses the Imagination.
.*s
The artificial clay of NJ. Hecht De Huben, con-
tains sand, carbonate of lime, cement, liquid
glue and petroleum, which are mixed in a GER
tain way, and yield material that can be
moulded and given extraordinary hardness by
heat. 1t is coming into use in Germany for
building stone bricks, tiles, etc. Among the
advantages claimed for it are the great hardness,
freedom from liability to crack, resistance to
atmospheric influences, incumbustibility and
proof against moisture and, as it is inexpen-
sive and easily shaped, it seems to fill a genuine
need of the small builder and decorator.
&*s
The preservation of fruits and vegetables by
cold has been a subject of tests by the makers
of French sulphurous acid freezing machine.
At $40 to 400F., perfectly ripe melons were kept
unchanged for eight days, and the ripening of
plums, pears, bananas, etc., was completely ar
rested.
The youthful appearance of native women of
Swaziland is attributed to secret elixir which,
like all Kaffir remedies, is obtained from an
herb, and which preserves plumpness, ETC., 30 or
40 years.
BY his discovery of the secret of Afridi wax
cloth, Mr.. George Watt has brought to notice
an interesting industry of India. This cloth is
kind of raised colored painting on cotton ia
brics, and it has been made by the Afridis for
many generations, but the medium used has
been mystery. IT. is now shown that the
dunn, known as rOghan, is a peculiar product of
the saffiower seed Roghan is a thick, jelly-like
substance, prepared only at Peshawar, and is
obtained when the oil pressed from the seed is
boiled for twelve hours and then thrown hot
into shallow pans of cold water. Before use it
is mixed with mineral color and drawn out into
fine threads on a pointed style, with which the
pattern is traced by the Afridi artists. The
cloth is heavy for dress, but is adapted to house
hold drapings. Tests have proven that roghan
is a superior waterproofing material, with prob
able advantages over linseed for linoleum man
ufacture.
-.
Some remarkable lakes of the siebenburgen
salt district in Pennsylvania have been found to
have a layer of hot salt water between one of
cold fresh water and one of cold salt water.
A. V. Kalecsinsky reports that in the Medoc
Sea, for example, when the summer tempera-
ture at the surface was ZOE F., at depth of five
feet the temperature 1882 and the specific
gravity LII, thence declining gradually to the
bottom to 66' with specific gravity of 119 cor
responding to % per cent. of salt in solution.
The warm layer may even reach 14Oo in summer,
cooling to minimum of 79o in May. The lakes
are not fed by hot springs, but the salt layer is
heated by the sum- the fresh surface layer pre-
venting rapid radiation.
"a
The next return of the Leonids, of November
meteors will mark the 1,00Oth anniversary of
the first record of this swarm, Last Novem-
Der, on the morning of the 18TH one American
observatory estimated that 1.6O0 meteors per
hour were falling. In England number of
meteors were doubly Observed the mean heights
- l. -