use； so that only the frames are visible。 Sometimes these also
fold and are housed； or wholly disappear within the mast。
Steam…boilers are also placed at the foci of huge concave
mirrors； often a hundred feet in diameter； the required heat
being supplied by the sun； without smoke； instead of by bulky and
dirty coal。 This discovery gave commercial value to Sahara and
other tropical deserts； which are now desirable for mill…sites
and for generating power； on account of the directness with which
they receive the sun's rays and their freedom from clouds。 Mile
after mile Africa has been won for the uses of civilization； till
great stretches that were considered impassible are as productive
as gardens。 Our condensers； which compress； cool； and rarefy
air； enabling travellers to obtain water and even ice from the
atmosphere； are great aids in desert exploration； removing
absolutely the principal distress of the ancient caravan。 The
erstwhile 'Dark Continent' has a larger white population now than
North America had a hundred years ago； and has this advantage for
the future； that it contains 11；600；000 square miles； while North
America has less than 9；000；000。 Every part of the globe will
soon sustain about as large and prosperous a population as the
amount of energy it receives from the sun and other sources will
warrant； public debts and the efficiency of the governments being
the variable elements。
〃The rabbits in Australia； and the far more objectionable
poisonous snakes in South America and India； have been
exterminated by the capture of a few dozen of the creatures in
the infested districts； their inoculation with the virus similar
to the murus tiphi； tuberculosis or any other contagious…germ
complaint to which the species treated was particularly
susceptible； and the release of these individuals when the
disease was seen to be taking hold。 The rabbits and serpents
released at once returned to their old haunts； carrying the
plague far and wide。 The unfortunate rabbits were greatly
commiserated even by the medicos that wielded the death…dealing
syringe； but； fortunately for themselves； they died easily。 The
reptiles； perhaps on account of the wider distribution of the
nerve centres； had more lingering but not painful deaths； often；
while in articulo mortis； leaving the holes with which they
seemed to connect their discomfort； and making a final struggle
along the ground； only to die more quickly as a result of their
exertions。 We have applied this also to the potato…bug； locust；
and other insect pests； no victim being too small for the
ubiquitous； subtle germ； which； properly cultivated and utilized；
has become one of man's best friends。
〃We have microbe tests that show us as unmistakably whether the
germs of any particular diseaselike malaria； typhoid； or
scarlet feverare present in the air； as litmus…paper shows
alkalinity of a solution。 We also inoculate as a preventive
against these and almost all other germ diseases； with the same
success that we vaccinate for smallpox。
〃The medicinal properties of all articles of food are so well
understood also； that most cures are brought about simply by
dieting。 This； reminds me of the mistakes perpetrated on a
friend of mine who called in Dr。 Grave…Powders； one of the
old…school physicians； to be treated for insomnia and dyspepsia。
This old numskull restricted his diet； gave him huge doses of
medicine； and decided most learnedly that he was daily growing
worse。 Concluding that he had but a short time to live； my
friend threw away the nauseating medicines； ate whatever he had a
natural desire for； and was soon as well as everthe obvious
moral of which is； that we can get whatever treatment we need
most beneficially from our food。 Our physicians are most serious
and thoughtful men。 They never claim to be infallible； but study
scientifically to increase their knowledge and improve the
methods of treatment。 As a result of this； fresh air； regular
exercise for both sexes； with better conditions； and the
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