1000000030

H Y D R

S T A

e s.

ill

moulh, and fo caufes il to empty all ilS water ioto

!he

trough.

SJmetimes this wheel is made to raife water no higher

Ihan its axis; and lhcn, in(lead of buckels hung upoo it,

its fpokes

',f,

are made of a

b.nl

furm, and

hollowwilhin; thefe hollows openiog ioto lhe holes·

c..

D, E, F.

io the outfiJe of lhe wheel, aod alfo iOIO lhofe

iD the bOl(

upon theaxis. So lhat, as lhe holes

e, o,

&c.

dipioto lhe water, it ruosioto lhem; aod as

Ihe wheel turos,

t~e

wattr rifes io the h.llow fpokes,

"d.

&c. aod ruos out in a Uream

fromthe holes al

0 ,

aod f. lls ioto the trough

from whence it is cooveyec\

by pipes. Aod this is a very e. fy way of raiGng waler,

becaufe the eogioe requires oeitber men DOr hQrfel tO

turD it.

th,¡P"ijc gr.?itiu

bodiu.

TH! art of weighing different bodies io water, aod

thereby 6odiog thcir fpecific gravities, or weights, bulk

for bulk, was invented by Archimedes.

The fpeci6c gravities of bodies are as thei r weights,

bulk for bulk : thus a body is fairl to have two or three

time,¡ thé fpeci6e gravi ty of aoolher, when it

eootain~

two or three times as much mmer io the fame fp. ee.

body immerfed io a fluid will 6nk to tbe bottom, if

it be heavier thao il! bulk of the Buid. If it be rufpeod·

ed thereio, it willlofe

mueh of what il weigbed ioair,

its bulk of Ihe Huid weighs. Heoee, all bodies of equal

bulk, which would 60k in fluids, lofe equal weights when

fufpeoded IhereiD. ADd uoequal bodies lofe iDproportiOD

tbeir bulb .

Th, hJdroj/alic ha/anu.

TH!

h]droJlatic ba/anc,

differs very liule from a como

mon balance thal is oieely made : only il has a hook at

Ihe bouom ofeach fcale. 00 which fmall weighls may be

huog by horfe hairs, or by úlk threads.

that a

body, fufpeoded by the hai r or thread, may be immer·

red io water without wwiog the fcale fromwhich il hangs.

Ihe body Ihus fufpended under Ihereale, at onecod

of the balance, he

firll

counlerpo.fedin air by weights in

lbe oppofile fcale, and thtoimOlerfed iDwater, the equi.

libriumwill be immedimly dellroyed. Theo, jf as much

",eighl be put ioto Ihe fcale froOl whieh the body haogs

as will rellore Ihe equilibrium (wilt.out allering tbe

weights io Ihe oppofite fcale) Ihat

wei~bl

whieh reflores

Ihe equilibrium will be equal 10 Ihe weight of

quanlity

of Water as big as theimmerfed hody. AnJ if Ihe weight

of the body iD air be dividcd bywhat it lofes in water,

Ihe quotient will Ihewhow much Ihat body is he"vier

Ihao in bulk of water. T hus, if a

guin~a

fu fpended in

air be eounterbalanced by 129 grains in the oppofi te (cale

of the balance ; and theo upoo ilS be ng immerfed io

waler, it becoo'es fo mueh lighter as

require

graios put ioto Ihe feale over it, tOrefl ore the

c~ uilibri

um ; it Ihews tbal a qUlnti'y of water of cq,,,1 bnlk

with the guioea, wtighs

í'"

grain! , or

7.'S ;

I'Y

wl:ieh

¿¡vide t"9 (the weighl of the guioea inair) anrl the

~uo·

UtOI " ill \>e 17.793 ; wltith

Ihews

that lhe. ¡:uioca is

VOL. l! . No.61 .

17·193

timesas heavyasil! bu!k of bulk of water, Aod

~hu~

. ny pieee ?f gold may be tried, by ,,·.igh·ng it firr.

.,.r, aod titen tn .waler ; and if, upoo dividiogtite

IV,

ight

tn alf by Ihe lofs

water, the q40tienl comes OUI to be

17.793, Ihegold is good ; if Ihe quotient be t8. or ile·

Iweeo 18 aod t9, Ihc gold is vety fine ; but if il be lefs

Ih.an

thegold is too mueh allayed, by beiog mixed

wuh fome other melal.

fi lver be tried io this manner. aod found to be

t~mes

as heav)' as water, it is very fi ne; if it be

10':'

ttmesasheavy. it is Uaodard ; butifit beof any lefs weigh t

complred wilhwater, il is mixedwith fomelighter metal,

(uch as tio.

By Ihis method the fpecine gravities of all bodies that

will Gok io water may be found . BUI as to tho(e which

are lighter tban water, as moll fons of wood are, thq

following method may be I/ken, 10 Ihew ho\V mue"

lighler they are Ihan their refpeélive bulks of water.

Let an uprighl Ilud be fixed ioto a thick Bat piece of

brafs, aod iD this Ilud let a fm. lllever, whofe arms

ar9

equally, long . lurn upon a nne pin as ao axis. Let th;

thread which hangs from Ihe fcale of the balaoce be tic4

to OIJeend of the lever, and a tbread fromIhe bocly 10 b;

weighed lied to Ihe other end. This done, put

th~

brafs and lever into a verTe!: then pour water iOlo lh,

verTe!, and Ihe body will rife and fioat upoo it, aod draw

dowo Ihe CDd Df

th~

balance from which it h.ogs: Ihen,

put aS'mqeh weigbl

the oppoGte fcale as will raifethat

cnd of Ihe balance, (o as 10 pull the body dowo into Ihe

walerbymeansof¡he lever ; and this weight in Ihe fealewill

Ihew how much lhe body is lighter Ihao ils bulk of water,

Thereare fome thiogs \Vhich canoot be weighed iotbis

manner, fuehas quiekfilver, fragmeotsofdiamonds,

&c.

beeaufe they eapnot be fufpended in threads ; and mufl

therefore be pUl into a glafs buckel, haoging by a thread

fromthehook of one fcale, and counterpoifed by weights

put into the oppofite fcale. Thus, fuppofe you waot to

know the fpeeifie gravity of quickfilver, with refpeél to

that of water ; let theemptybucket be firll counterpoifed

iD air, and then Ihe quickfilver pUl into it and weighed.

Wt ite dowo the weighl of the bucker, and al(o of Ihe

quiekfilver; whieh done, empty the buckel, and let il be

immerfed io waler as it haogs by Ihe,hread, and coun–

lerpoifed therein by weighls io the oppofite feale: then,

pour

I~e

quickfilver ioto Ihe bucket io the water, whieh

will caufe it to prepooderale; and put asmuchwcighl into

the oppofite fcale as wdl rellore the balance to an equi–

poife; and this weight will be the \\ eight of a quantilY

ofwater eq ual inbulk toth. quickfilver. LaOl y, divide

the wcight of thequirkfilver io air, hy the weight of its

bu lk of water, and the quotieot will lhcw howmueh the

quickfil vcr is hmier thao ils bulk of

"'",er.

If a piecc of Infs. glafs Icad, or fi lm be immerfecl

aod rufpeod,d ío diff.,ent fOTls of flUlds, its difl'ercnt

loll'ts of we eht Iherein will O'fW how OIurh it is he.vicr

thao its

~uH.

,,( the fl llid ;

t~e

fl uid

iug

li~h'cn,

inwhich

thf immerfcd b(dylof. s leaHof its

' e",1

\Vl it!.t

folid

buhLle of gl,rs is geoerally uf,d for linJing the fpe(ifie

gr.ll·

ilí,

of fluids.

oce

II'r

ha ve an e.fymethod cf fincling the fl'ccifie

gravuics both uf fu!.ds

amI

fluids, Wilh

r~¡;ard

10lhc re·

8 U

fpeai".