Evening star., 1937-04-24

culturists showed especial interest Is
that irrigation can be undertaken at
any convenient time, whereas electric
power cannot wait upon shifting
clouds or the whim Of the weather
man, while people remain in dark
ness. Power that can be utilized to
irigate the fields can be turned TO ac-
count whenever old Sol decides to
shine
From Hawaii and Jamaica came re-
quests with regard in irrigation by
means of solar engines; from Mexico,
Peru, Chile, Italy. Spain. North
Africa, Greece and India letters came
flooding in. Some wanted to know
how they could use solar power for
charging storage batteries; others for
cooking their meals; still others for
heating water or warming their
homes. And Dr. Abbot was able to
reply that actual experiments had
been conducted with great measure
Of success along each of these lines.
There was, for example, this matter
Of cooking by the heat Of the sun. In
connection with Smithsonian expedi-
tons to Mount Wilson, California, .
solar cooker has been employed,
which not only served all purposes
of daily cooking. but could be utilized
at night as well.
I'VE cooked all our meals by means
of the suns rays" DR.. Abbot ex-
planned, "and the contrivance was
such that enough heat was stored up
so that we could cook continuously
night and day for weeks at time"
About so years ago solar device
was used in India for cooking pur-
poses, but this instrument had no
reservoir for storing the heat coll
lected and thus could only operate
when the sun was shining. When
DR.. Abbot began his experiments in
Mount Wilson in 1916 he desired to
devise some menas of storing solar
heat in a suitable reservoir, at a
temperature that would permit all
cooking operations, such as stewing.
preserving, boiling and baking meats
and bread. He also wished to devise
an instrument that would permit use
after sundown.
This meant combining solar heat
collector with high-temperature
reservoir, into the back of which two
ovens were to be let. In the words Of
Dr. Abbot, 1T seemed best to con-
centrate the solar rays upon a metal
tube communicating to reservoir at
some distance above the collector. The
scheme is exactly that of common
bath water heater, merely substituting
concentrated sun rays for fire as the
source of heat.
In this way the hot fluid, expand
ing, rises into the top OF the reservoir,
while the cooler fluid at the bottom
flows downward to the heat source IN
replacement. A continuous circulation
Of hot fluid would thus maintain the
temperature of the reservoir. We
used engine cylinder oil, as this fluid
can be heated to temperatures some
what above 200 degrees centigrade
without boiling, flashing or strongly
evaporating"
The cost, beyond the initial cost Of
the contrivance and the negligible
cost Of the oil is nothing at all for
operation. The same oil has been used
for 10 years in the Mount Wilson
solar cooker and will doubtless 90
on being used for many years to come.
that it circulate.
The problems in connection with
catching the suns rays and utilizing
them are interesting Cylindrical mir
rors were used and these had to be
made to rotate from east toward the
west at the same rate as the earth's
daily rotation from west to east, in
order for them to follow the sun.
These cylindrical mirrors were mount
ed upon an axis parallel to the earth's
axis. The mirror had to be made
rather long from north to south, to
minimize the seasonal loss Of sunlight.
The mirror was made then, 1917
feet long and 712 feet wide, and
mounted with its long dimension
parallel to an axis pointing to the
North Star. 1t was framed on sections
of structural steel to make 1t rigid.
To make the mirror brightly rejecting
was another problem that faced DR..
Abbot. At first he tried out strips Of
tinfoil, foot wide, with which he
covered the steel with the aid of shell
lac. The result was very unsattsfac.
tory.
"As the mirror warmed" explained
DR.. Abbot, "the shellac evaporated
and puf1ed up the tinfoil, spelling the
shape of the rejecting surface. We
pricked many Of the blisters and
rolled the surface down, but, though
we used this at first, in 1915, the
shape Of the mirror surface was not
satisfactory. Moreover the tinfoil tar.
nished, losing It's high rejecting power.
This defect was cured when the
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