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Page 39
This oil is at present not in the market, but given a demand, it can
be produced in four months, at the latest, in very large quantities,
as the apparatus is very easy and cheap to erect, and the crude
material can be plentifully obtained.
If this oil becomes, as I think it will, an important factor in the
illumination of the future, it will mark as important an era in the
history of our industries as any which the century has seen, as, by
using it, you are giving smoke a commercial value, and this will do
what the Society of Arts and the County Council have failed in--that
is, to give us an improved atmosphere. If I were lecturing on an
imaginary "Hygeia," I should point out that the smoke of London
contains large quantities of these oils, and they, by coating the
drops of mist on which they condense, give the fog that haunts our
streets that peculiar richness which is so irritating and injurious to
the system, and, further, by preventing the water from being again
easily taken up by the air, prolong the duration of the fog. Make this
oil a marketable commodity, and another twenty years will see London
without a chimney; underground shafts will be run alongside the
sewers; into these shafts by means of a down draught all the products
of combustion from our fires will be sucked by local pumping stations,
and the oil condensing in the tubes will serve in turn to illuminate
our streets, instead of performing its former function of turning day
into night and ruining our health; but as I am not at all sure of the
engineering possibilities of such a scheme, I will leave its discovery
to some other abler prophet than myself.
(_To be continued_.)
* * * * *
ELECTRICAL LABORATORY FOR BEGINNERS.
BY GEO. M. HOPKINS.
It is only when theory and practice, study and experiment, go hand in
hand that any true progress is made in the sciences. A head full of
theory is of little value without practice, and although the student
may apply himself with all his energies for years, his time will, to a
great extent, have been spent in vain, unless he by experiment rivets
the ideas he gains by his study.
In the study of electricity, for example, let the student try to
remember the position a magnetic needle will take when placed below or
above a conductor carrying a current which flows in a known direction.
Without experiment there are nine chances of forgetting to one of
remembering; but let the student try the experiment, and he will ever
afterward be able to determine the direction in which the current is
flowing by the position taken by the needle relative to the conductor.
In the matter of ampere turns, as another example, it is quite simple
to assert that a ten ampere current carried once around a soft iron
bar produces the same result as a one ampere current carried ten times
around the bar, but how much more strongly is this fact stamped upon
the memory when its truth is established by experiment?
Reading about a fact, or commiting to memory the literature of a
subject, is desirable and even necessary, but knowledge of this
character partakes more of the nature of faith than that gained by
actual experience.
Let the reader learn first all that can be learned by the aid of this
simple apparatus, then branch out to allied things, making each step
as thorough as possible, and before long he will be congratulating
himself on having gained at least an elementary knowledge of
electricity.
Very little can be done in the way of electrical experiment without an
electrical generator of some sort, and nothing at present known can
excel a battery for this purpose. Although not the most desirable
battery for all purposes, that shown in Fig. 1 is the most desirable
for the amateur who desires a strong current for a short time. It is
formed of two plates, a, of carbon arranged on opposite sides of an
amalgamated plate, b, of zinc, and separated from the zinc by strips
of wood. Bars of wood are placed outside of the carbon plates, and the
four bars are fastened together by two common wood screws, thus
clamping all the bars and the zinc and carbon plates securely in the
position of use.
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