men of invention and industry-第16章

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of　his　clock　to　a　spring　wound　up；　so　that　the　regularity　of　the

motion　might　be　derived　from　the　vibrations　of　balances；　instead

of　those　of　a　pendulum　as　in　a　standing　clock。　　Mr。　Folkes；

President　of　the　Royal　Society；　when　presenting　the　gold　medal　to

Harrison　in　1749；　thus　describes　the　arrangement　of　his　new

machine。　　The　details　were　obtained　from　Harrison　himself；　who

was　present。　　He　had　made　use　of　two　balances　situated　in　the

same　plane；　but　vibrating　in　contrary　directions；　so　that　the　one

of　these　being　either　way　assisted　by　the　tossing　of　the　ship；

the　other　might　constantly　be　just　so　much　impeded　by　it　at　the

same　time。　　As　the　equality　of　the　times　of　the　vibrations　of　the

balance　of　a　pocket…watch　is　in　a　great　measure　owing　to　the

spiral　spring　that　lies　under　it；　so　the　same　was　here　performed

by　the　like　elasticity　of　four　cylindrical　springs　or　worms；

applied　near　the　upper　and　lower　extremities　of　the　two　balances

above　described。



Then　came　in　the　question　of　compensation。　　Harrison's　experience

with　the　compensation　pendulum　of　his　clock　now　proved　of　service

to　him。　　He　had　proceeded　to　introduce　a　similar　expedient　in　his

proposed　chronometer。　　As　is　well　known　to　those　who　are

acquainted　with　the　nature　of　springs　moved　by　balances；　the

stronger　those　springs　are；　the　quicker　the　vibrations　of　the

balances　are　performed；　and　vice　versa；　hence　it　follows　that

those　springs；　when　braced　by　cold；　or　when　relaxed　by　heat；　must

of　necessity　cause　the　timekeeper　to　go　either　faster　or　slower；

unless　some　method　could　be　found　to　remedy　the　inconvenience。



The　method　adopted　by　Harrison　was　his　compensation　balance；

doubtless　the　backbone　of　his　invention。　　His　〃thermometer　kirb；〃

he　himself　says；　〃is　composed　of　two　thin　plates　of　brass　and

steel；　riveted　together　in　several　places；　which；　by　the　greater

expansion　of　brass　than　steel　by　heat　and　contraction　by　cold；

becomes　convex　on　the　brass　side　in　hot　weather　and　convex　on　the

steel　side　in　cold　weather；　whence；　one　end　being　fixed；　the

other　end　obtains　a　motion　corresponding　with　the　changes　of　heat

and　cold；　and　the　two　pins　at　the　end；　between　which　the　balance

spring　passes；　and　which　it　alternately　touches　as　the　spring

bends　and　unbends　itself；　will　shorten　or　lengthen　the　spring；　as

the　change　of　heat　or　cold　would　otherwise　require　to　be　done　by

hand　in　the　manner　used　for　regulating　a　common　watch。〃　　Although

the　method　has　since　been　improved　upon　by　Leroy；　Arnold；　and

Earnshaw；　it　was　the　beginning　of　all　that　has　since　been　done　in

the　perfection　of　marine　chronometers。　　Indeed；　it　is　amazing　to

think　of　the　number　of　clever；　skilful；　and　industrious　men　who

have　been　engaged　for　many　hundred　years　in　the　production　of

that　exquisite　fabricso　useful　to　everybody；　whether　scientific

or　otherwise；　on　land　or　sea　the　modern　watch。



It　is　unnecessary　here　to　mention　in　detail　the　particulars　of

Harrison's　invention。　　These　were　published　by　himself　in　his

'Principles　of　Mr。　Harrison's　Timekeeper。'　It　may；　however；　be

mentioned　that　he　invented　a　method　by　which　the　chronometer

might　be　kept　going　without　losing　any　portion　of　time。　　This　was

during　the　process　of　winding　up；　which　was　done　once　in　a　day。　

While　the　mainspring　was　being　wound　up；　a　secondary　one

preserved　the　motion　of　the　wheels　and　kept　the　machine　going。



After　seven　years'　labour；　during　which　Harrison　encountered　and

overcame　numerous　difficulties；　he　at　last　completed　his　first

marine　chronometer。　　He　placed　it　in　a　sort　of　moveable　frame；

somewhat　resembling　what　the　sailors　call　a　'compass　jumble；'　but

much　more　artificially　and　curiously　made　and　arranged。　　In　this

state　the　chronometer　was　tried　from　time　to　time　in　a　large

barge　on　the　river　Humber；　in　rough　as　well　as　in　smooth　weather；

and　it　was　found　to　go　perfectly；　without　losing　a　moment　of

time。



Such　was　the　condition　of　Harrison's　chronometer　when　he　arrived

with　it　in　London　in　1735；　in　order　to　apply　to　the　commissioners

appointed　for　providing　a　public　reward　for　the　discovery　of　the

longitude　at　sea。　　He　first　showed　it　to　several　members　of　the

Royal　Society；　who　cordially　approved　of　it。　　Five　of　the　most

prominent　membersDr。　Bailey；　Dr。　Smith；　Dr。　Bradley；　Mr。　John

Machin；　and　Mr。　George　Grahamfurnished　Harrison　with　a

certificate；　stating　that　the　principles　of　his　machine　for

measuring　time　promised　a　very　great　and　sufficient　degree　of

exactness。　　In　consequence　of　this　certificate；　the　machine；　at

the　request　of　the　inventor；　and　at　the　recommendation　of　the

Lords　of　the　Admiralty；　was　placed　on　board　a　man…of…war。



Sir　Charles　Wager；　then　first　Lord　of　the　Admiralty；　wrote　to　the

captain　of　the　Centurion；　stating　that　the　instrument　had　been

approved　by　mathematicians　as　the　best　that　had　been　made　for

measuring　time；　and　requesting　his　kind　treatment　of　Mr。

Harrison；　who　was　to　accompany　it　to　Lisbon。　　Captain　Proctor

answered　the　First　Lord　from　Spithead；　dated　May　l7th；　1736；

promising　his　attention　to　Harrison's　comfort；　but　intimating　his

fear　that　he　had　attempted　impossibilities。　　It　is　always　so　with

a　new　thing。　　The　first　steam…engine；　the　first　gaslight；　the

first　locomotive；　the　first　steamboat　to　America；　the　first

electric　telegraph；　were　all　impossibilities！



This　first　chronometer　behaved　very　well　on　the　outward　voyage　in

the　Centurion。　　It　was　not　affected　by　the　roughest　weather；　or

by　the　working　of　the　ship　through　the　rolling　waves　of　the　Bay

of　Biscay。　　It　was　brought　back；　with　Harrison；　in　the　Orford

man…of…war；　when　its　great　utility　was　proved　in　a　remarkable

manner；　although；　from　the　voyage　being　nearly　on　a　meridian；　the

risk　of　losing　the　longitude　was　comparatively　small。　　Yet　the

following　was　the　certificate　of　the　captain　of　the　ship；　dated

the　24th　June；　1737：　　〃When　we　made　the　land；　the　said　land；

according　to　my　reckoning　（and　others）；　ought　to　have　been　the

Start；　but；　before　we　knew　what　land　it　was；　John　Harrison

declared　to　me　and　the　rest　of　the　ship's　company　that；　according

to　his　observations　with　his　machine；　it　ought　to　be　the

Lizardthe　which；　indeed；　it　was　found　to　be；　his　observation

showing　the　ship　to　be　more　west　than　my　reckoning；　above　one

degree　and　twenty…six　miles；〃that　is；　nearly　ninety　miles　out

of　its　course！



Six　days　laterthat　is；　on　the　30th　Junethe　Board　of　Longitude

met；　when　Harrison　was　present；　and　produced　the　chronometer　with

which　he　had　made　the　voyage　to　Lisbon　and　back。　　The　minute

states：　　〃Mr。　John　Harrison　produced　a　new　invented　machine；　in

the　nature　of　clockwork；　whereby　he　proposes　to　keep　time　at　sea

with　more　exactness　than　by　any　other　instrument　or　method

hitherto　contrived；　in　order　to　the　discovery　of　the　longitude　at

sea；　and　proposes　to　make　another　machine　of　smaller　dimensions

within　the　space　of　two　years；　whereby　he　will　endeavour　to

correct　some　defects　which　he　hath　found　in　that　already

prepared；　so　as　to　render　the　same　more　perfect；　which　machine；

when　completed；　he　is　desirous　of　having　tried　in　one　of　His

Majesty's　ships　that　shall　be　bound　to　the　West　Indies；　but　at

the　same　time　represented　that　he　should　not　be　able；　by　reason

of　his　necessitous　circumstances；　to　go　on　and　finish　his　said

machine　without　assistance；　and　requested　that　he　may　be

furnished　with　the　sum　of　500L。；　to　put　him　in　a　capacity　to

perform　the　same；　and　to　make　a　perfect　experiment　thereof。〃



The　result　of　the　meeting　was　that　500L。　was　ordered　to　be　paid

to　Harrison；　one　moiety　as　soon　as　convenient；　and　the　other　when

he　has　produced　a　certificate　from　the　captain　of　one　of　His

Majesty's　ships　that　he　has　put　the　machine　on　board　into　the

captain's　possession。　　Mr。　George　Graham；　who　was　consulted；

urged　that　the　Commissioners　should　grant　Harrison　at　least

1000L。；　but　they　only　awarded　him　half　the　sum；　and　at　first　only

a　moiety　of　the　amount　voted。　　At　the　recommendation　of　Lord

Monson；　who　was　present；　Harrison　accepted　the　250L。　as　a　help

towards　the　heavy　expenses　which　he　had　already　incurred；　and　was

again　about　to　incur；　in　perfecting　the　invention。　　He　was

instructed　to　make　his　new　chronometer　of　less　dimensions；　as　the

one　exhibited　was　cumbersome　and　heavy；　and　occupied　too　much

space　on　board。



He　accordingly　proceeded　to　make　his　second　chronometer。　　It

occupied　a　space　of　only　about　half　the　size　of　the　first。　　He

introduced　several　improvements。　　He　lessened　the　number　of　the

wheels；　and　thereby　diminished　friction。　　But　the　general

arrangement　remained　the　same。　　This　second　machine　was　finished

in　1739。　　It　was　more　simple　in　its　arrangement；　and　less

cumbrous　in　its　dimensions。　　It　answered　even　better　than　the

first；　and　though　it　was　not　tried　at　sea　its　motions　were

sufficiently　exact　for　finding　the　longitude　within　the　nearest

limits　proposed　by　Act　of　Parliament。



Not　satisfied　with　his　two　machines；　Harrison　proceeded　to　make　a

third。　　This　was　of　an　improved　construction；　and　occupied　still

less　space；　the　whole　of　the　machine　and　its　apparatus　standing

upon　an　area　of　only　four　square　feet。　　It　was　in　such

forwardness　in　January；　1741；　that　it　was　exhibited　before　the

Royal　Society；　and　twelve　of　the　most　prominent　members　signed　a

certificate　of　〃its　great　and　excellent　use；　as　well　for

determining　the　longitude　at　sea　as　for　correcting　the　charts　of

the　coasts。〃　　The　testimonial　concluded：　　〃We　do　recommend　Mr。

Harrison　to　the　favour　of　the　Commissioners　appointed　by　Act　of

Parliament　as　a　person　highly　deserving　of　such　further

encouragement　and　assistance　as　they　shall　judge　proper　and

sufficient　to　finish　his　third　machine。〃　　The　Commissioners

granted　him　a　further　sum　of　500L。　　Harrison　was　already　reduced

to　necessitous　circumstances　by　his　continuous　application　to　the

improvement　of　the　timekeepers。　　He　had　also　got　into　debt；　and

required　further　assistance　to　enable　him　to　proceed　with　their

construction；　but　the　Commissioners　would　only　help　him　by

driblets。



Although　Harrison　had　promised　that　the　third　machine　would　be

ready　for　trial　on　August　1；　1743；　it　was　not　finished　for　some

years　later。　　In　June；　1746；　we　find　him　again　appearing　before

the　Board；　asking　for　further　assistance。　　While　proceeding　with

his　work　he　found　it　necessary　to　add　a　new　spring；　〃having　spent

much　time　and　thought　in　tempering　them。〃　　Another　500L。　was

voted　to　enable　him　to　pay　his　debts；　to　maintain　himself　and

family；　and　to　complete　his　chronometer。



Three　years　later　he　exhibited　his　third　machine　to　the　Royal

Society；　and　on　the　30th　of　November；　1749；　he　was　awarded　the

Gold　Medal　for　the　year。　　In　presenting　it；　Mr。　Folkes；　the

President；　said　to　Mr。　Harrison；　〃I　do　here；　by　the　authority　and

in　the　name　of　the　Royal　Society　of　London　for　the　imp