a journey in other worlds-第7部分

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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　superstructural　deck　by　ankle…jointed　pipes；　through　which；
when　necessary；　a　pressure　of　air　can　be　forced　down　upon　the
enclosed　surface　of　water。　　Ordinarily；　however；　they　go　at　great
speed　without　this；　the　weight　of　the　water　displaced　by　the　bell
feet　being　as　great　as　that　resting　upon　them。　　Thus　they　swing
along　like　a　pacing　horse；　except　that　there　are　four　rows　of
feet　instead　of　two；　each　foot　being　taken　out　of　the　water　as　it
is　swung　forward；　the　first　and　fourth　and　second　and　third　rows
being　worked　together。　　Although；　on　account　of　their　size；　which
covers　several　acres；　they　can　go　in　any　water；　they　give　the
best　results　on　Mediterraneans　and　lakes　that　are　free　from　ocean
rollers；　and；　under　favourable　conditions；　make　better　speed　than
the　nineteenth…century　express　trains；　and；　of　course；　going
straight　as　the　crow　flies；　and　without　stopping；　they　reach　a
destination　in　considerably　shorter　time。
　　　
Some　passengers　and　express　packages　still　cross　the　Atlantic　on
'spiders；'　but　most　of　these　light　cargoes　go　in　a　far　pleasanter
and　more　rapid　way。　　The　deep…displacement　vessels；　for　heavy
freight；　make　little　better　speed　than　was　made　by　the　same　class
a　hundred　years　ago。　　But　they　are　also　run　entirely　by
electricity；　largely　supplied　by　wind；　and　by　the　tide　turning
their　motors；　which　become　dynamos　while　at　anchor　in　any　stream。　
They　therefore　need　no　bulky　boilers；　engines；　sails；　or
coal…bunkers；　and　consequently　can　carry　unprecedentedly　large
cargoes　with　comparatively　small　crews。　　The　officers　on　the
bridge　and　the　men　in　the　crow's　nestthe　way　to　which　is　by　a
ladder　INSIDE　the　mast；　to　protect　the　climber　from　the
weatherare　about　all　that　is　needed；　while　disablement　is　made
practically　impossible；　by　having　four　screws；　each　with　its　own
set　of　automatically　lubricating　motors。
　　　
〃This　change；　like　other　labour…saving　appliances；　at　first
resulted　in　laying　off　a　good　many　men；　the　least　satisfactory
being　the　first　to　go；　but　the　increase　in　business　was　so　great
that　the　intelligent　men　were　soon　reemployed　as　officers　at
higher　rates　of　pay　and　more　interesting　work　than　before；　while
they　as　consumers　were　benefited　as　much　as　any　one　else　by　the
decreased　cost　of　production　and　transportation。
　　　
〃With　a　view　to　facilitating　interchange　still　further；　our
Government　has　gradually　completed　the　double　coast…line　that
Nature　gave　us　in　part。　　This　was　done　by　connecting　islands
separated　from　shore　by　navigable　water；　and　leaving　openings　for
ingress　and　exit　but　a　few　hundred　yards　wide。　　The　breakwaters
required　to　do　this　were　built　with　cribbing　of　incorrodible
metal；　affixed　to　deeply　driven　metallic　piles；　and　filled　with
stones　along　coasts　where　they　were　found　in　abundance　or　excess。　
This；　while　clearing　many　fields　and　improving　them　for
cultivation；　provided　just　the　needed　material；　since　irregular
stones　bind　together　firmly；　and；　while　also　insoluble；　combine
considerable　bulk　with　weight。　　South　of　Hatteras；　where　stones
are　scarce；　the　sand　dredged　from　parts　of　the　channel　was　filled
into　the　crib；　the　surface　of　which　has　a　concave　metallic　cover；
a　trough　of　still　water　being　often　the　best　barrier　against　the
passage　of　waves。　　This　double　coast…line　has　been　a　great
benefit；　and　propelled　vessels　of　moderate　draught　can　range　in
smooth　water；　carrying　very　full　loads；　from　Labrador　to　the
Orinoco。　　The　exits　are；　of　course；　protected　by　a　line　of
cribbing　a　few　hundred　feet　to　seaward。
　　　
〃The　rocks　have　been　removed　from　all　channels　about　New　York　and
other　commercial　centres；　while　the　shallow　places　have　been
dredged　to　a　uniform　depth。　　This　diminishes　the　dangers　of
navigation　and　considerably　decreases　the　speed　with　which　the
tides　rush　through。　　Where　the　obstructions　consisted　of　reefs
surrounded　by　deep　water；　their　removal　with　explosives　was　easy；
the　shattered　fragments　being　allowed　to　sink　to　the　bottom　and
remain　there　beneath　the　danger　line。
　　　
〃Many　other　great　works　have　also　been　completed。　　The　canals　at
Nicaragua　have　been　in　operation　many　years；　it　having　been　found
best　to　have　several　sizes　of　locks；　and　to　use　the　large　ones
only　for　the　passage　of　large　vessels。　　The　improved　Erie　and
Champlain　Canals　also　enable　ships　four　hundred　feet　long　to
reach　New　York　from　the　Great　Lakes　via　the　Hudson　River。
　　　
〃For　flying；　we　have　an　aeroplane　that　came　in　when　we　devised　a
suitable　motor　power。　　This　is　obtained　from　very　light
paper…cell　batteries　that　combine　some　qualities　of　the　primary
and　secondary　type；　since　they　must　first　be　charged　from　a
dynamo；　after　which　they　can　supply　full　currents　for　one　hundred
hoursenough　to　take　them　around　the　globewhile　partly
consuming　the　elements　in　the　cells。　　The　power　is　applied
through　turbine　screws；　half　of　which　are　capable　of　propelling
the　flat　deck　in　its　inclined　position　at　sufficient　speed　to
prevent　its　falling。　　The　moving　parts　have　ball　bearings　and
friction　rollers；　lubrication　being　secured　automatically；　when
required；　by　a　supply　of　vaseline　that　melts　if　any　part　becomes
hot。　　All　the　framing　is　of　thin　but　very　durable　galvanized
aluminum；　which　has　superseded　steel　for　every　purpose　in　which
weight　is　not　an　advantage；　as　in　the　permanent　way　on　railways。　
The　air　ships；　whose　length　varies　from　fifty　to　five　hundred
feet；　have　rudders　for　giving　a　vertical　or　a　horizontal　motion；
and　several　strengthening　keels　that　prevent　leeway　when　turning。　
They　are　entirely　on　the　principle　of　birds；　maintaining
themselves　mechanically；　and　differing　thus　from　the　unwieldy
balloon。　　Starting　as　if　on　a　circular　railway；　against　the　wind；
they　rise　to　a　considerable　height；　and　then；　shutting　off　the
batteries；　coast　down　the　aerial　slope　at　a　rate　that　sometimes
touches　five　hundred　miles　an　hour。　　When　near　the　ground　the
helmsman　directs　the　prow　upward；　and；　again　turning　on　full
current；　rushes　up　the　slope　at　a　speed　that　far　exceeds　the
eagle's；　each　drop　of　two　miles　serving　to　take　the　machine
twenty　or　thirty；　though；　if　the　pilot　does　not　wish　to　soar；　or
if　there　is　a　fair　wind　at　a　given　height；　he　can　remain　in　that
stratum　of　the　atmosphere　by　moving　horizontally。　　He　can　also
maintain　his　elevation　when　moving　very　slowly；　and　though　the
headway　be　entirely　stopped；　the　descent　is　gradual　on　account　of
the　aeroplane's　great　spread；　the　batteries　and　motors　being
secured　to　the　under　side　of　the　deck。
　　　
〃The　motors　are　so　light　that　they　develop　two　horse　power　for
every　pound　of　their　weight；　while；　to　keep　the　frames　thin；　the
necessary　power　is　obtained　by　terrific　speed　of　the　moving
parts；　as　though　a　steam　engine；　to　avoid　great　pressure　in　its
cylinders；　had　a　long　stroke　and　ran　at　great　piston　speed；
which；　however；　is　no　disadvantage　to　the　rotary　motion　of　the
electric　motor；　there　being　no　reciprocating　cranks；　etc。；　that
must　be　started　and　stopped　at　each　revolution。
　　　
〃To　obviate　the　necessity　of　gearing　to　reduce　th