按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
preservation of the lives of children that formerly died by
thousands from preventable causes； the physique； especially of
women； is wonderfully improved； and the average longevity is
already over sixty。
〃Our social structure； to be brief； is based on science； or the
conservation of energy； as the Greek philosophers predicted。 It
was known to them that a certain amount of power would produce
only a certain amount of workthat is； the weight of a clock in
descending or a spring in uncoiling returns theoretically the
amount of work expended in raising or coiling it； and in no
possible way can it do more。 In practice； on account of
friction； etc。； we know it does less。 This law； being
invariable； of course limits us； as it did Archimedes and
Pythagoras； we have simply utilized sources of power that their
clumsy workmen allowed to escape。 Of the four principal
sourcesfood； fuel； wind； and tideincluding harnessed
waterfalls； the last two do by far the most work。 Much of the
electrical energy in every thunderstorm is also captured and
condensed in our capacious storage batteries； as natural hygeia
in the form of rain was and is still caught in our country
cisterns。 Every exposed place is crowned by a cluster of huge
windmills that lift water to some pond or reservoir placed as
high as possible。 Every stiff breeze； therefore； raises millions
of tons of water which operate hydraulic turbines as required。
Incidentally these storage reservoirs； by increasing the surface
exposed to evaporation and the consequent rainfall； have a very
beneficial effect on the dry regions in the interior of the
continent； and in some cases have almost superseded irrigation。
The windmill and dynamo thus utilize bleak mountain…tops that；
till their discovery； seemed to be but indifferent successes in
Dame Nature's domain。 The electricity generated by these； in
connection with that obtained by waterfalls； tidal dynamos；
thunderstorms； chemical action； and slow…moving
quadruple…expansion steam engines； provides the power required to
run our electric ships and water…spiders； railways； and
stationary and portable motors； for heating the cables laid along
the bottom of our canals to prevent their freezing in winter； and
for almost every conceivable purpose。 Sometimes a man has a
windmill on his roof for light and heat； then； the harder the
wintry blasts may blow the brighter and warmer becomes the house；
the current passing through a storage battery to make it more
steady。 The operation of our ordinary electric railways is very
simple： the current is taken from an overhead； side； or
underneath wire； directly through the air； without the
intervention of a trolley； and the fast cars； for they are no
longer run in trains； make five miles a minute。 The entire
weight of each car being used for its own traction； it can ascend
very steep grades； and can attain high speed or stop very
quickly。
〃Another form is the magnetic railway； on which the cars are
wedge…shaped at both ends； and moved by huge magnets weighing
four thousand tons each； placed fifty miles apart。 On passing a
magnet； the nature of the electricity charging a car is
automatically changed from positive to negative； or vice versa；
to that of the magnet just passed； so that it repels while the
next attracts。 The successive magnets are charged oppositely；
the sections being divided halfway between by insulators； the
nature of the electricity in each section being governed by the
charge in the magnet。 To prevent one kind of electricity from
uniting with and neutralizing that in the next section by passing
through the car at the moment of transit； there is a 〃dead
stretch〃 of fifty yards with rails not charged at all between the
sections。 This change in the nature of the electricity is
repeated automatically every fifty miles； and obviates the
necessity of revolving machinery； the rails aiding communication。
〃Magnetism being practically as instantaneous as gravitation； the
only limitations to speed are the electrical pressure at the
magnets； the resistance of the air； and the danger of the wheels
bursting from centrifugal force。 The first can seemingly be
increased without limit； the atmospheric resistance is about to
be reduced by running the cars hermetically sealed through a
partial vacuum in a steel and toughened glass tube； while the
third has been removed indefinitely by the use of galvanized
aluminum； which bears about the same relation to ordinary
aluminum that steel does to iron； and which has twice the tensile
strength and but one third the weight of steel。 In some cases
the rails are made turned in； so that it would be impossible for
a car to leave the track without the road…bed's being totally
demolished； but in most cases this is found to be unnecessary；
for no through line has a curve on its vast stretches with a
radius of less than half a mile。 Rails； one hundred and sixty
pounds to the yard； are set in grooved steel ties； which in turn
are held by a concrete road…bed consisting of broken stone and
cement； making spreading rails and loose ballast impossible。 A
large increase in capital was necessary for these improvements；
the elimination of curves being the most laborious part；
requiring bridges； cuttings； and embankments that dwarf the
Pyramids and would have made the ancient Pharaohs open their
eyes； but with the low rate of interest on bonds； the slight cost
of power； and great increase in business； the venture was a
success； and we are now in sight of further advances that will
enable a traveller in a high latitude moving west to keep pace
with the sun； and； should he wish it； to have unending day。〃
CHAPTER V。
DR。 CORTLANDT'S HISTORY CONTINUED。
〃In marine transportation we have two methods； one for freight
and another for passengers。 The old…fashioned deeply immersed
ship has not changed radically from the steam and sailing vessels
of the last century； except that electricity has superseded all
other motive powers。 Steamers gradually passed through the five
hundred…； six hundred…； and seven hundred…foot…long class； with
other dimensions in proportion； till their length exceeded one
thousand feet。 These were very fast ships； crossing the Atlantic
in four and a half days； and were almost as steady as houses； in
even the roughest weather。
〃Ships at this period of their development had also passed
through the twin and triple screw stage to the quadruple； all
four together developing one hundred and forty thousand indicated
horse…power； and being driven by steam。 This； of course；
involved sacrificing the best part of the ship to her engines；
and a very heavy idle investment while in port。 Storage
batteries； with plates composed of lead or iron； constantly
increasing in size； had reached a fair state of development by
the close of the nineteenth century。
〃During the second decade of the twentieth century the engineers
decided to try the plan of running half of a transatlantic
liner's screws by electricity generated by the engines for
driving the others while the ship was in port； this having been a
success already on a smaller scale。 For a time this plan gave
great satisfaction； since it diminished the amount of coal to be
carried and the consequent change of displacement at sea； and
enabled the ship to be worked with a smaller number of men。 The
batteries could also； of course； be distributed along the entire
length； and placed where space was least valuable。
〃The construction of such huge vessels called for much
governmental river and harbour dredging； and a ship drawing
thirty…five feet can now enter New York at any state of the tide。
For ocean bars； the old system of taking the material out to sea
and discharging it still survives； though a jet of water from
force…pumps directed against the obstruction is also often
employed with quick results。 For river work we have discovered a
better method。 All the mud is run back； sometimes over a mile
from the river bank； where it is used as a fertilizer； by means
of wire railways strung from poles。 These wire cables combine in
themselves the functions of trolley wire and steel rail； and
carry the suspended cars； which empty themselves and return
around the loop for another load。 Often the removed material
entirely fills small； saucer…shaped valleys or low places； in
which case it cannot wash back。 This improvement has ended the
necessity of building jetties。
〃The next improvement in sea travelling was the 'marine spider。'
As the name shows； this is built on the principle of an insect。
It is well known that a body can be carried over the water much
faster than through it。 With this in mind； builders at first
constructed light framework decks on large water…tight wheels or
drums； having paddles on their circumferences to provide a hold
on the water。 These they caused to revolve by means of machinery
on the deck； but soon found that the resistance offered to the
barrel wheels themselves was too great。 They therefore made them
more like centipeds with large； bell…shaped feet； connected with
a supers