The Democratic press. [volume] (Ravenna, O. [Ohio]) 1868-1901, 1881-01-20
SCIENTIFIC,

DR.. Holub intends, as soon as the
money to cover expenses is raised. to
make journey through Africa, begin
ming at the Cape of Good Hope and
ending in Egypt. Of the $4,000 forins
required he gives 5000 himself.
Mr.. j. w. Swan, of Newcastle-on-
Tyne, has come forward as the inventor
Of system of incandescent electric
lighting, which he claims can be econ
omically applied to domestic purposes.
He thus states in general terms what he
has done: 1t was found after many
troublesome experiments that when the
vacuum within the lamp was good, and
the contact between the carbon and the
conductor which supported it sufficient.
there was no blackening of the globes
and no appreciable wasting away of the
earbons. The main principle of the
Swan system is that upon which Mr..
Edison has lately been working, and
upon which, many years ago, other
| American inventors devoted good deal
Of attention with considerable success.
Mr.. Swan arranges his lamps in series,
and feels warranted in asserting that at
least twice as much light is produced
by certain quantity Of gas used to
! generate an electric current employed
| in his lamps that can be obtained from
this quantity of gas burned in gas-burn-
ers in the usual manner. Putting the
! question of economy in other words, ho
reckons that forty pounds of coal en-
ployed in raising steam to generate
electricity, is capable of producing the
effect in his lamps of one thousand feet
of gas burned in gas-burners.
In speaking of the well-known meth
| DDS of preserving posts and wood which
are partially imbedded in the earth, by
charring and coating with tar, it is said
these methods are only effective when
both are applied. Should tho poles be
charred without the subsequent treat
ment with tar, the charcoal formation
on the surface would only act rs an ab-
sorber of the moisture, and. if anything,
only hasten the decay. BY applying q
coating OF tar without previously char
ring. the tar would only form . casing
about the wood. nor would it penstrate
to the depths which the absorbing prop
critics Of the charcoal surface would in
sure. Wood that il exposed to the ac-
ton of water or let into the ground
should first be charred, and then, be-
fore it has entirely cooled, be treated
with tar until the wood is thoroughly
impregnated. The acetic acid and oils
contained in the tar are evaporated by
the heat, and only the resin left behind,
which penetrates the pores Of the wood |
and forms an air-tight and waterproof !
envelope. 1t is important to impreg- |
nate the poles little above the lines of |
exposure, for here it is that the action |
of decay affects the wood first, and |
where the break always occurs when
removed from tho earth or strained in |
testing.
Prof. Dufour, of Paris, has arranged
a thermometric apparatus which shows
marked way. The mere approach of
the hand to the bulb will throw a needle
over the whole of a graduated arc. The
device consists of bent tube, having a
bulb Mt one end, coated on the outside
with lampblack. The middle of this
tube is filled with mercury, and is sup
ported by arms nicely pivoted. Above
the pivot is fixed an index needle, which
moves across a graduated arc, and be-
meath the pivot hangs rod to which is
attached by friction a small weight,
which serves to balance the needle so
as to make it point to zero on the arc.
When the temperature rises in the
slightest degree, the heat, being readily
absorbed by the lampblack on the air
bulb, drives the mercury forward and
displaces the centre of gravity so that
the needle turns at once towards the
right. When the bulb is exposed to a
decrease of temperature the needle points
toward the left. So sensitive is this ap-
partus to changes of temperature, it has
been necessary, to check its sudden :
tippling over when exposed to rather
high heat very quickly, to place two
fixed pins at convenient points beneath
The tube. i