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FAEM IMPLEMENTS,

PRINCIPLES OF THEIR CONSTRUCTION AND USE;

ELE^IENTARY AND FAMILIAR TREATISE

ON MECHANICS,

AND ON NATURAL PHILOSOPHY GENERALLY, AS APPLIED

TO THE ORDINARY PRACTICES OF

AGRICULTURE.

WITH 200 ENGRAVED ILLUSTRATIONS.

BY JOHN J. THOMAS.

" We should like to see this work printed, bound, and hung up in every work-
shop, tool-room, and farmer's book-shelf in the country. It gives the reason and
explains the action of mechanical powers, and the forces of nature generally, with
illustrations so directly drawn from the farmer's daOy routine, that it gives a direct
meaning and value to every point, rarely found in text-books." — Downing's Review
of the First Edition.

NEW YORK:

HARPER & BROTHERS, PUBLISHERS,
82 BEEKMAN STREET.

1854.

Entered, accoi-ding to Act of Congress, in the year 1854, by

HARPER & BROTHERS,

In the Clerk's Office for the Southern District of New York.

PREFACE.

This work, in its original form, was published in the
Transactions of the New York State Agricultural So-
ciety for 1850, under the title of " Agricultural Dy-
namics," or the Science of Farm Forces. The present
edition is prepared on the basis of the original essay,
and is thoroughly revised and greatly enlarged, with
the addition of more than double the former number
of illustrations.

It comprehends those branches of Natural Philoso-
phy known as Mechanics, Hydrodynamics, Pneumat-
ics, and Heat, in their more common application to the
practices of modern improved farming ; and, so far as
practicable, technical words and phrases have been
avoided, and the whole rendered simple and intelhgi-
ble to ordinary readers.

The leading principles have been derived from the
existing stock of knowledge ; but no treatise on these
subjects, as specially applied to agriculture, having be-
fore appeared, the various examples of the application
of those principles to the structure and use of farm im-
plements, and to the farmer's daily routine, are mostly
original.

For the purpose of adapting the work to schools,
wherever it may be desirable, it is divided into sec-
tions, each of sufficient length for a single recitation.

CONTENTS.

PART I.

MECHANICS.

CHAPTER I.

INTKODUCTION.

Page

Benefits of Mechanical Knowledge 13

CHAPTER n.

GENERAL PKINCIPLES OF MECHANICS.

SECTION I.

General Properties of Matter 18

Divisibility 18

Impenetrability 20

Indestructibility 20

Inertia 21

SECTION II.

Momentum, or Inertia of moving Bodies 24

The Fly-wheel 27

Application of Fly-wheel in churning and cutting Straw 28

Estimating the Quantity of Momentum 30

SECTION III.

Compound Motion 31

Centrifugal Force 34

CHAPTER HI.

ATTRACTION.
SECTION I.

Gravitation 35

Measuring Velocity of falling Bodies — Atwood's Machine 38

CONTENTS.

SECTION II.

Page

Cohesion 42

Strength of Materials 43

Capillary Attraction 47

Ascent of Sap 49

SECTION III.

Centre of Gravity 50

Line of Direction 52

CHAPTER IV.

SIMPLE MACHINES, OR MECHANICAL POWEES.
SECTION I.

Advantages of Machines 60

Law^ of Virtual Velocities 61

SECTION II.

The Lever 63

SECTION III.

Estimating the Power of Levers 67

Combination of Levers 70

Weighing Machine 71

Machines for extracting Stumps 72

SECTION IV.

Wheel and Axle 75

Mole-plow 78

Band and Cog Wheels 79

Form of Teeth or Cogs 80

SECTION V.

The Pulley 83

SECTION VI.

The Inchned Plane 86

Ascent in Roads 87

Form and Materials for Roads 90

Importance of good Road.s 92

SECTION VII.

The Wedge 93

The Screw 94

CONTENTS. IX

CHAPTER V.

APPLICATION OF MECHANICAL PRINCIPLES IN THE STRUCTURE OF THE
PARTS OF IMPLEMENTS AND MACHINES Page 96

CHAPTER VI.

FRICTION.

SECTION L

Rolling Friction 103

Nature of Friction 104

Estimating the Amount of Friction 104

SECTION II.

Results with the Dynamometer 107

Width of WTieels 109

Velocity as affecting Friction 110

Friction at the Axle Ill

Friction Wheels 112

SECTION III.

Lubricating Substances 113

Advantages of Friction 115

SECTION IV.

Principles of Draught 117

Combined Draught of Animals 120

SECTION V.

Construction and use of the Dynamometer 122

Self-recording Dynamometer 125

Dynamometer for Rotary Motion 126

CHAPTER Vn.

CONSTRUCTION AND USE OF FARM IMPLEMENTS AND MACHINES.

SECTION I.

Plows and Plowing 130

Trench and Subsoil Plowing 134

The double Mould-board Trench Plow 135

The Subsoil Plow 136

Fowler's Draining Plow 136

The Paring Plow— The Gang Plow 140

A2

X CONTENTS.

SECTION II.

Pulverizers 141

The Harrow 141

Cultivators 143

Clod-crushers 146

SECTION III.

Sowing-machines 148

Horse Rakes 152

Mowing and Reaping Machines 156

SECTION IV.

Knee-joint Power 159

Endless-chain Powers 164

SECTION V.
Application of Labor 167

SECTION VI.
Models of Machines 173

PART II.

HYDRODYNAMICS.
CHAPTER I.

HYDROSTATICS.

SECTION I.

Upward Pressure 176

Measurement of Pressure at different Heights 178

Detennining the Strength of Pipes 179

Springs and Artesian Wells 179

SECTION II.

Determining Pressure on Surfaces 180

Hydrostatic Bellows 183

Hydrostatic Press 184

SECTION III.
Specific Gravities 187

CHAPTER n.

HYDRAULICS.

SECTION I.

Velocity of falling Water 189

Discharge of Water through Orifices and Pipes 1 90

CONTENTS. XI

SECTION II.

Page

Velocity of Water in Ditches 192

Leveling Instruments 194

SECTION III.

HYDRAULIC MACHINES.

Archimedean Screw 196

Archimedean Root-washer 197

Pumps 198

Water-ram 200

Water-engines 202

Flash-wheel 203

SECTION IV.

WAVES.

Nature of Waves 204

The Water not progressive 205

Breadth and Velocity of Waves 206

Preventing the Inroads of Waves 208

SECTION V.

Contents of Cisterns 210

Rule for determining the Contents 211

Determining their Size 212

PART III.

PNEUMATIC
CHAPTER I.

PRESSURE OF AIR.

Height and Weight of the Atmosphere 213

The Barometer 216

The Syphon 218

CHAPTER II.

MOTION OF AIK.
SECTION I.

Winds— Force of Wind 221

Wind-mills for Farms 223

Causes of Wind 227

SECTION II.

Page

Chimney Currents 227

Construction of Chimneys 228

Chimney-caps 229

Ventilation 232

PART IV.

HEAT.
CHAPTER I.

CONDUCTION OF HEAT.

SECTION I.

Conducting Power of Bodies 235

UtiUty of this Principle 236

Conducting Power of Liquids 237

SECTION II.

Expansion by Heat 238

The Steam-engine 241

Exception to Expansion by Heat 246

SECTION III.

Latent Heat 248

Advantages of Latent Heat — Latent Heat of Steam 249

Green and dry Wood for Fuel 250

CHAPTER n.

Radiation of Heat 253

Dew and Frost 255

Frost in Valleys — Remarkable Efl'ects of Heat on Water 256

APPENDIX.

Apparatus for Experiments 259

Tables of Specific Gravities 263

AVeight of a cubic Foot of various Substances 264

Discharge of Water through Pipes 264

Velocity of Water in Pipes 265

Rule for the Discharge of Water 266

FARM IMPLEMENTS,

PUmCIPLES OF THEIE. CONSTEUCTION
AND USE.

PART I.

MECHANICS.

CHAPTER I.

INTRODUCTION.

No farm, even of moderate size, can be well fur-
nished without a large number of machines and im-
plements. Scarcely any labor is performed without
their assistance, from the simple operations of hoeing
and spading, to the more complex work of turning the
sod and driving the thrasliing-machine. It becomes,
therefore, a matter of vital importance to the farmer
to be able to construct the best, or to select the best
aheady constructed, and to apply the forces required
for the use of such machines to the best possible ad-
vantage.

A great loss occurs frequently from the want of a
correct knowledge of mechanical principles. The
strength of laborers is often badly applied by the use
of unsuitable tools, and that of teams is partly lost by
being ill adjusted for the best hue of draught ; as, for

14 MECHANICS.

example, by a bad attachment to the plow for forcing
its wedge-like form most effectively through the soil.
"We may perhaps see but few instances of so great a
blunder as the man committed who fastened his
smaller horse to the shorter end of the whipple-tree,
to balance the large horse at the longer end ; or of the
other man, who, when riding on horseback to mill,
atop of his bag of grain, concluded to reheve the ani-
mal by dismounting, shouldering the bag himself, and
then remounting ; yet cases are not uncommon where
other operations are performed to almost as great a
disadvantage, and which, to a person well versed in
the science of mechanics, would appear nearly as
strange and absurd.

The improvement of farm machines and tools with-
in the last fifty years has probably enabled the farmer
to effect twice as much work with the same force of
horses and men. Plows turn up the soil deeper, more
evenly and perfectly, and with greater ease of draught ;
hoes and spades have become lighter and more efficient ;
grain, instead of being beaten out by the slow and la-
borious work of the flail, is now showered in torrents
from the tlirashing-machinc ; horse-rakes accomplish
singly the work of many men using the old hand-rake ;
twelve to twenty acres of ripe grain are neatly cut in
one day with a two-horse reaper ; wheat drills, avoid-
ing the tiresome drudgery of sowing by hand, are ma-
terially increasing the amount of the wheat crop ;
while a few farmers are making a large yearly saving
by the application of horse-power to sawing wood,
churning, driving washing-machines, and even to ditch-
ing. A celebrated Enghsh farmer has lately accom-

INTRODUCTION. 15

plished even more ; for, by means of a steam-engine
of six-horse power, he drives a pair of mill-stones for
grinding feed, thrashes and cleans grain, elevates and
bags it, pumps water for cattle, cuts straw, turns the
grindstone, and drives liquid manure through pipes
for irrigatmg his fields ; and the waste steam cooks
the food for his cattle and swine — all this work being
performed in a first-rate manner.

Now these improvements were mainly effected
through the knowledge of mechanical principles, and
many of them would doubtless have been sooner
achieved and better perfected if these principles had
been well understood by farmers ; for, constantly using
the machines themselves, they could have perceived
just what defects existed, and, by understanding the
reasons of those defects, have been able to suggest the
remedies in a better manner than the mere manufac-
turer. Moreover, as the introduction of what is new
and valuable depends greatly upon the call for them,
farmers would have been prepared to decide with more
confidence and certainty upon their real merits, and
thus to increase and cheapen the supply of the best,
and to reject the worthless.

One great reason that farm implements are still so
imperfect, is, that the farmers themselves do not fully
understand what is needed, and how much may be yet
accomphshed. They have not enough knowledge of
the principles of mechanics to qualify them for judgmg
of the merits of new machines ; and, being afraid of
imposition, often reject what is really valuable, or else,
being pleased with a fine appearance, are easily de-
ceived with empty pretensions.

16 MECHANICS.

The implements and machines which every farmer
must have who does his work well are numerous and
often costly. A farm of one hundred acres requires
the aid of nearly all the following : two good plows, a
small plow, a subsoiler, a single and two-horse culti^
vator, a drill-barrow, a roller, a harrow, a fannmg-mill
a straw-cutter, a root-slicer, a farm wagon with hay
rack, an ox-cart, a horse-cart, wheel-barrow, sled, shov
els, spades, hoes, hay-forks and manure-forks, hand
rakes and revolving rakes, scythes and gram-cradles
grain-shovel, maul and wedges, pick, axes, wood-saw
turnip-hook, hay-knife, apple-ladders, and many other
smaller conveniences. The capital for thus furnisliing
in the best mamier all the farms m the Union has
been computed to amount to five hundred millions of
dollars, and as much more is estimated to be yearly
paid for the labor of men and horses throughout the
country at large.

To increase the effective force of labor only one fifth
would, therefore, add annually one hundred millions in
the aggi'egate to the profits of farming ; while on the
other hand, if we look back fifty years to the imperfect
implements then in use, we may at once perceive the
vast amount saved by the improvements since made ;
and when, especially, we notice the condition of bar-
barous nations, and contrast that condition with our
own — ^the former tliinly scattered in comfortless hovels
through far-stretching and gloomy forests, subsisting
mainly by hunting and fishing, and often suffering
from hunger and cold ; the latter blessed with smooth,
cultivated fields, green meadows, and golden harvests,
interspersed with comfortable farm-houses; with the

INTRODUCTION. 17

hum of business through populous cities, and along
far-reaching lines of canals and rail-roads, and ships
for foreign commerce, freighted with the productions
of the soil, threading every channel and whitening
every sea — when we observe this contrast, we can
not fail to be struck with the convincing proof that
" knowledge is power," and of the loss sustained on
the one hand from its absence, and the advantages on
the other of availing ourselves of its accumulated
stores.

18 MECHANICS.

CHAPTER IL

GENERAL PRINCIPLES OF MECHANICS.

SECTION I.
GENERAL PROPERTIES OF MATTER.

Having briefly pointed out. some of the advantages
to the farmer of understanding the principles of the
macliines he constantly uses, we now proceed to an
examination of these principles. It will he most con-
venient to begin with the simpler truths of the soiencej
proceeding, as we advance, to their application in the
construction of machines.

The term matter is applied to whatever composes
those substances which we perceive with our external
senses ; and when we speak of a " body," we mean
any thing composed of matter. Thus, wood, stone,
water, and metal are matter ; while the mind and its
quahties are not matter. A stone, a block of wood, a
bag of sand, and any other mass of matter, are termed
bodies.

DIVISIBILITY.

Matter possesses several general properties, the ex-
amination of which is both useful and interesting. One
of these is its divisibility, or capability of being divided
into small parts, and again divided, so far as we know,
without any limit. Many experiments show the great
minuteness to which this division may be carried. For

DIVISIBILITY. 19

example, a gold leaf may be hammered till 55^ of an
inch in tliiclmess, or one thousand times thinner than
a leaf of this hook. A silver wire may he coated with
gold, and then drawn out so fine that the gold coating
shaU become a thousand times less than the gold leaf
itself. So attenuated is one of the threads of a small
spider's web, that half a pound would reach round the
globe. It has been found that tripoh, a mineral used
.in the arts, is made up of shells of exceedingly minute
animals, so small that a single cubic inch contains forty
thousand millions, or fifty times as many individuals
as there are human beings on the face of the earth.
Hundreds of animalcules (or minute animals) have
been seen with a microscope in a single drop of water,
without in the least degree affecting its transparency.
Some of these are so small that thousands could rest,
without crovv^ding, on the point of a pin ; yet these
have blood-vessels, muscles, and other parts, as well as
larger animals. Still more minute appears to be the di-
vision of those substances which are constantly throw-
ing oft' odors or perfumes. A grain of musk wiU scent
the air of a room for years, with particles inconceivably
minute ; and a bed of flowers will fill the air with their
odor, as hundreds of miles of the breeze successively
pass over them, with an insensibly small portion of
their own weight.

But no division, however minute, ever destroys mat-
ter ; every particle still retains its identity ; and the
largQgt mountains, weighing millions of tons, are made
up of these innumerable particles.

20 MECHANICS

IMPENETRABILITY.

Another property of matter is impenetrability , or
the inability of two portions to occupy the same space
at the same time. A nail driven into wood only
crowds the particles of wood asunder. Sugar will
dissolve in water, but the particles of the sugar only
pass in between those of the water. "Wood becomes
soaked with water by its entering the pores of the
wood. These pores are seen by means of a powerful
microscope, and are so small that one million have
been computed to exist m a space not larger than a
five-cent piece.

INDESTRUCTIBILITY.

Another property is indestructibility. Matter is
separated and changed in form from one body to an-
other, but never destroyed. When wood is burned in
the fire, it disappears ; but it is found that the smoke,
vapor, and ashes weigh as much as before, although in
a different form. The flashing of gunpowder appears
to destroy it wholly ; but if all the vapors and gases
are retained within a vessel, they are found to weigh
as much as the original soHd. Growing plants derive
all their weight from the soil and air ; they decay
again, and form the manure for new plants ; but none
of their particles are lost. They furnish food for ani-
mals, or are manufactured into different substances,
and, in all the changes they undergo, still retain their
existence.

21

There is still another and very important quahty of
all material bodies, called inertia. This term express-
es their passive state— that is, that no body (not hav-
ing hfe), when at rest, can move itself, nor, when in
motion, can stop itself. A stone can not commence
rolling of its own accord ; a carriage can not travel on
the road without being drawn ; a train of cars can not
commence gliding upon the rails without the power of
the locomotive.

On the contrary, a body, when once set in motion,
will continue in motion perpetually, unless stopped by
something else. A cannon ball rolled upon the ground
continues rolling till its force is gradually overcome
by the resistance of the rough earth. If a polished
metallic globe were driven swiftly on a level and pol-
ished metallic plane, it would continue in motion a
long time and travel to a great distance ; but still the
extremely minute rougliness of the surfaces, with the
resistance of the air, would continually diminish its
speed until finally stopped. A wheel made to spin on
its axis continues till the friction at the axis and the
impeding force of the air bring it to rest. But if the
air is first removed by means of an air-pump, the mo-
tion will continue much longer. Under a glass re-
ceiver, thus exhausted, a top has been made to spin
for hours, and a pendulum to vibrate for a day. The
resistance of the air may be easily perceived by first
striking the edge and then the broad side of a large
piece of pasteboard against the air of a room. It is
further shown by means of an interesting experiment

22

MECHANICS.

Fig. 1.

with the air-pump. Two fan-wheels, made of sheet
tm, one (a) striking the air with
its edges, and the other (6) with
its broad faces {Fig', l), are set in
motion ahke ; b is soon brought to
rest, wliile a continues revolving a
long time. If now they are placed
under the receiver of an au*-pump,
the air exliausted, and motion given
to them alike by the rack-work d,

Fans ruolnns^m,, vacuum. l]^Qy will both COUtinue iu motioU

during the same period.

There is no machmery made by man free from the
checking influence of friction and the air ; and for tliis
reason, no artificial means have ever devised a perpet-
ual motion by mechanical force. But we are not with-
out a proof that motion will continue without ceasing
when nothing operates against it. The revolutions of
the planets in their orbits furnish a sublime instance ;
where removed from all obstructions, these vast globes
wheel round in their immense orbits, through success-
ive centuries, and with unerrmg regularity, preserving
undiminished the mighty force given them when first
launched into the regions of space.

To set any body in motion, a force is requisite, and
the heavier the body, the greater must be the force. A
small stone is more easily thrown by the hand than a
cannon ball ; speed is much more easily given to a skiff
than to a large and heavy vessel ; but the same force
which sets a body in motion is required to stop it.
Thus, a wheel or a grindstone, made to revolve rapidly,
would require as great an effort of the arm to stop it

Fig. 2.

suddenly as to give it sudden motion. An unusual
exertion of the team is required in starting a loaded
wagon ; but when once on its way, it would require
the same effort of the horses to stop it as to back it
when at rest.

The force of inertia is finely exhibited by means of a
little instrument called the iner-
tia apparatus {Fig. 2). A mar-
ble or small ball is placed on a
card (c) resting on a concave
stand. A spring snap is then
made to strike the card, tlirowing
it to a distance, but leaving the
ball upon the hollow end of the stand. The same ex-
periment may be easily performed by placing a very

Inertia Apparatu

on a common sand-box, or even the hollow of the hand.
A sudden snap with the finger will throw the card
away, while the apple will drop into the cavity. The
following experiment is still more striking: Procure
a thread just strong enough to bear three
pounds, and hang upon it a weight of
two pounds and a half Another half
pomid would break it. Now tie an-
other thread, strong enough to bear one
pound, to the lower hook of the weight.
If the lower thread bo pulled grad-
ually^ the upper thread will of course
break ; but if it be pulled with a jerk.,
the loiver thread will break. If the
jerk be very sudden, the lower string
will break, even if it be considerably

24 MECHANICS.

stronger than the upper, the inertia of the weight re-
quiring a great force to overcome it suddenly. The
threads used in this experiment may be easily had of
any desired strength hy taking the finest sewing cot-
ton, and doubling to any required extent.

This experiment shows the reason why a horse, when
he suddenly starts with a loaded wagon, is in danger
of breaking the harness ; and why a heavier weight
may be lifted with a windlass or pulley having a weak
rope, if the strain is gradual and not sudden. For the
same reason, glass vessels full of water are sometimes
broken when hastily lifted by the handle. When a
bullet is fired through a pane of glass, the inertia re-
tains the surrounding glass in its place during the mo-
ment the ball is passing, and a round hole only is
made ; while a body moving more slowly, and pressing
the glass for a longer space of time, fractures the whole
pane.

SECTION II.
MOMENTUM.

The force which a moving body has to continue on-
ward is called its momentum ; it is, in fact, the inertia
of a moving- body. When a force is first applied to
any heavy body, it moves slowly ; but the little mo-
mentum it thus acquires, added to the continued force,
increases the velocity. This increase of velocity is
of course attended with increased momentum, which
again, added to the acting force, still further quickens
the speed. For this reason, when a steam-boat leaves
the pier, and its paddle-wheels commence tearing

MOMENTUM.

25

through the water, the motion, at first slow, is con-
stantly accelerated tiU the increasing resistance of the
water to the moving mass becomes equal to the strength
of the engine and the momentum.* Were it not for
the momentum of moving bodies (inertia existing),
no speed ever could be given to any heavy body, as a
carriage, boat, or train of cars.

The chief danger in fast riding, or fast travehng of
any kind, is from the momentum given to the trav-
eler. If a rail-way passenger should step from a car
when in full motion, he would strike the earth with
the same velocity as that of the train ; or if the train
at thirty miles an horn* should be instantly stopped,
the passengers would be pitched forward with a swift-
ness equal to thirty miles an hour. When a horse
suddenly stops, the momentum of the rider tends to
throw him over the horse's head. Wlien a wagon
strikes an obstruction, the driver falls forward. A
case in court was once decided against the plaintiff,
who claimed that the defendant had driven against his
wagon with such force as to throw the plaintiff to a
great distance ; but the fact was shown that by such
momentum he himself must have been driving furi-
ously, and not the defendant, and he lost his suit.

An African traveler once succeeded in saving his
life by a ready knowledge of this principle. He was
closely pursued by a tiger, and when near a precipice,
watchmg his opportunity, he threw his coat and hat

* In ordinary practice, this is not strictly correct, as friction will
make some difference. This influence will be more particularly
considered on a subsequent page. Its omission here does not at all
alter the principle under consideration.

B

26

MECHANICS.

Fig. 4.

on a bush, and jumped one side, when the animal,
leaping swiftly on the concealed bush, was carried by
momentum over the precipice.

As a large or heavy body possesses greater moment-
um than a small or light one, so any body moving with
great speed possesses more than one moving slowly ;
for instance, the momentum of a
rifle ball is so great as to carry it
through a thick plank, wliile, if
thrown slowly, it would scarcely
indent it.

This property of bodies is ap-
plied with great advantage to
many practical purposes. The
momentum of the hammer drives
the nail into the wood; for the
mere pressure of its weight would
not do it, if it were a hundred
times as heavy. Wedges are
driven by employing the same
kind of power.

On a larger scale, the pile-en-
gine operates in a similar man-
ner. The ram or weight, h {Fig.
4), is slowly lifted by means of a
pulley and wheel-work, worked
by the handles or cranks, b b, un-
til the arms of the tongs which
hold the ram are compressed in
the cheeks, i /, when it sudden-
Piie Engine. \y falls with prodigious force on

Ihe pile or post to be driven. In this way long posts of

THE FLY-AVHEEL. 27

great size are forced into the mud of swamps and riv-
er bottoms, where other means would fail. When a
steam-engine is used for lifting the ram, the work is
more rapidly performed.

An interesting example of the use and efficiency of
momentum is furnished by the water-ram, a machine
for raising water, described on a subsequent page.

THE FLY-WHEEL.

Thefli/'iuheel, a large and heavy wheel used to reg-
ulate the motion of machinery, derives its value from
the power of inertia, or momentum, which prevents the
machine from stopping suddenly when it meets with
any unusual obstruction. In the common thrashing-
machine, it has been found that a heavy cyhnder, by
acting as a fly-wheel, renders the motion steadier, and
less liable to become impeded by large sheaves of grain.
An ignorance of this principle has sometimes proved a
serious inconvenience. A farmer, having occasion to
raise a large quantity of water, erected a horse-pump ;
but at every stroke of the pump the animal was sud-
denly tlurown loosely forward, and again jerked back-
ward, as the piston fell lightly and rose heavily. A
fly-wheel attached to the machinery would have pre-
vented this unpleasant jerking, and have enabled the
horse, in consequence, to accomplish more work. In
the pile-driving engine, where a great weight is sud-
denly thrown loose from a height, the horses would be
pitched forward when suddenly relieved of this load,
but for the regulation of a fly-wheel, the motion of
which is not quickly changed, neither from fast to slow
nor from slow to fast.

28

MECHANICS.

Fig. 5.

Where there is a rapid succession of forces required
in practice, the fly-wheel
is usually of great advan-
tage. Hence its use in all
revolving straw - cutters,
where the knives make
quickly-repeated strokes
{Fig. 5). More recently
it has been applied to the

Straw-cutter with fly-wheel. dasher - ohum {Fig. 6),

where the rapid upright strokes
are so well known to be very fa-
tiguing for the amount of force
applied.

By thus regulating motion,
the fly-wheel frequently enables
an irregular force to accomplish
work which otherwise it could
not perform. Thus a man may
exert a force equal to raising a
hundred pounds, yet, when he
turns a crank, there is one part
of the revolution where he
works to great disadvantage, and where his utmost
force will not balance forty pounds. Hence, if the
work is heavy, he may not be able to turn the crank,
nor to do any work at all. If, however, a fly-wheel be
applied, by gathering force at the most favorable part
of the turning, it carries the crank through the other
part.

An error is sometimes committed by supposing the
fly-wheel actually creates power, for as much force is

Chum with a fly-ivheel, far-equal-
izing the motion.

THE FLY--VVHEEL. 29

required to give it momentum as it afterward imparts
to the machine ; it consequently only accumulates and
regulates power.

A curious example of the effect of momentum is
shown in the failure and success of two different modes
of constructing wire fences with very slender wires for
the boundaries of pastures. The unsuccessful mode
consisted of tightly-stretched wires between solid posts
not more than twelve to twenty feet apart. A side
strain of only a few mches was enough to snap the
wires ; consequently, a bullock plunging blindly against
them could not be quickly enough checked in his mo-
mentum, and such fences were therefore nearly useless
without stronger wire. The successful mode was to
stretch the wires well between strong and deeply-set
posts some hundreds of feet apart, the intervening space
being kept even by upright bars, but not posts. When
an animal accidentally struck this fence, the great
length permitted it to yield sidewise far enough to ex-
pend the momentum without rupture, when its elas-
ticity at once threw it back to its former place.

On rough roads, the force of inertia causes a severe
strain to a loaded wagon when it strikes a stone. The
horses are chafed, the wagon and harness endangered,
and the load jarred from its place. This inconvenience
is avoided in part by placing the box upon springs,
which, by yielding to the blow, gradually lessen the
effects of the shock. For carts and slowly - moving
lumber-wagons their advantages are considerable, but
much greater as the velocity and momentum increase.
Even on so smooth a surface as a rail-road, it was
found, by experiments made some years ago, that when

30 MECHANICS,

the machinery of a locomotive was placed upon springs,
it would endure the wear and tear of use four times as
long as without them.

For this reason, a ton of stone, brick, or of sand is
more severe for a team than a ton of wool or hay, wliich
possesses considerable elasticity.

ESTIMATING THE QUANTITY OF MOMENTUM.

The quantity of momentum is estimated by the ve-
locity and weight of the body taken together. Thus
a ball of two pounds' weight moves with twice the force
of a one-pound ball, the speed being equal ; a ten-pound
ball with ten times the force, and so on. A body mov-
ing at the rate of two feet per second possesses twice
the momentum of another of equal size with a velocity
of only one foot per second. A musket ball, weighing
one ounce, flying with fifty times the speed of a cannon
ball, weighing fifty ounces, would strike any object
with equal force ; or, if they should meet each other
from opposite directions, the momentum of both would
be mutually destroyed, and they would drop to the
earth.

Where the mass is very great, even if the motion is
slow, the momentum is enormous, A large ship float-
ing near a pier wall may approach it with so small a
velocity as to be scarcely perceptible, and yet the force
would be enough to crush a small boat. When great
weight and speed are combined, as in a rail-way loco-
motive, the force is almost irresistible. This circum-
stance often insures the safety of the passengers ; for
as nothing is capable of instantly overcoming so pow-
erful a momentum, when accidents occur the speed is

COMPOUND MOTION. 81

more gradually slackened, and the passengers are not
pitched suddenly forward. A light wagon, rapidly
driven, possessing but little comparative force, is more
suddenly arrested, and the danger is greater.

"When two bodies meet from opposite directions, each
sustains a shock equal to the united forces of both.
Two men accidentally striking, even if walking mod-
erately, receive each a severe blow ; that is, if each
were walking three miles an hour, the shock would be
the same as if one at rest were struck by the other
with a velocity of six miles an hour. This principle
accounts for the destructive effects of two ships run-
ning foul of each other at sea, or of the collision of two
opposite trains on a rail-road.

The preceding principles show that a sledge, maul,
or ax will always strike more effective blows when
made heavier, if not rendered unwieldy.

SECTION" III.

COMPOUND MOTION.

It often happens that two or more forces act on the
same body at the same time. If they all act in the
same direction, the effect will be equal to the sum of
the forces taken together ; but if they act in opposite
directions, the forces will tend to destroy each other.
If two equal forces act in contrary directions, they wiU
6e completely neutralized, and no motion will be pro-
duced. Thus, as an example of these forces — a bird
flying at the rate of forty miles an hour, ivith a wind
blowing forty miles an hour, will be driven onward by
these two combmed forces eighty miles an hour ; but

'SZ MECHANICS.

if it undertake to fly against such a wind, it will not
advance at all, but remain stationary, A similar re-
sult will take place if a steam-boat, having a speed of
ten miles an hour, should first run down a river with a
current of equal velocity, and then upward against the
current ; in the first case it would move twenty miles
an hour, and in the latter it would not move at all.
Where forces act neither in the same nor in opposite
Fig. 7. directions, but obliquely, the re-

j suit is found in the following
~7 manner : If a ball, placed at the
/ point a {Fig-. 7), be struck by
■' two different forces at the same
moment, in the direction shown
by the two arrows, and if one
force be just sufficient to carry it from a to c, and the
other to carry it from a to b, then it will move inter-
mediate between the two, in the direction of the diag-
onal of the parallelogram a d, and to a distance just
equal to the length of this diagonal or cross-diameter.
"When the forces act very nearly together, the paral-
lelogram of the forces will be very narrow and quite

long, with a long di-

agonal [Fig: 8) ; but

^^ ^"^"--^^^^^I-! _^ if they act on nearly

opposite sides of the
ball, they will very nearly neutralize each other, and the
Fig. 9. diagonal or result will be

**^ " " ' ""^ very short, showing that

"^ the motion given to the ball
will be very small {Fig: 9.)
These examples show the importance of having

COMPOUND MOTION.

33

teams attached to a plow or to a wagon very nearly
in a straight hne with the draught, or else a part of
the force will be lost; and also the importance, when
several animals are drawing together, of their working
as nearly as possible in the same straight hne. For,
the more such forces deviate from a right line, the
more they will tend to destroy or neutralize each other.
A famihar example of the result of two oblique forces
is furnished when a boat is rowed across a river. If
the river has no current, the boat will pass directly
from bank to bank perpendicularly ; but if there is a

strilvc the opposite bank lower down, according to the
rapidity of the stream and the slowness of the boat.

Another instance is afforded when a ferry-boat is
anchored, by means of a long rope, to a pomt some
distance above {Fig. 10); the boat bemg turned

Fig. 10.

obhquely, will pass from one bank to the other by the
force of the current. Here the water tends to carry
the boat downward, wliile the force of the rope acts
upward ; the boat passes between the two from bank,
to bank. The ascent of a kite is precisely similar, the
wind and the string being counteracting forces. When
a vessel sails under a side-wind, the resistance of the
keel against the water, and the force of the wind
against the sail, act in different directions, and pro-
duce a motion of the vessel between them.
B2

34 MECHANICS.

CENTRIFUGAL FORCE.

All bodies, when in motion, have a tendency to move
forward in a straight line. A stone thrown into the air
is gradually bent from this straight course into a curve
by the attraction of the earth. When a ball is shot
from a gun, the force being greater, it flies in a longer
and straighter curve. A famihar example also occurs,
while driving a wagon rapidly, in attempting to turn
suddenly to the right or left ; the tendency of the load
to move straight on will sometimes cause its overtlu-ow.
An observance of this principle would prevent the error
which some commit by making sharp turns or angles in
ditches and water-courses ; the onward tendency of the
water drives it against the bank, checks its course, and
wears away the earth. By giving the ditch a curve,
the water is but slightly impeded, and a much larger
quantity will escape through a channel of any given size.

When a grindstone is turned rapidly, the water upon
its surface is thrown off by this tendency to move in
straight lines. In the same way, a weight fastened to
a cord, whirled by the hand, wiU keep the cord stretch-
ed during the revolution. The same principle causes
a stone, when it leaves a sHng, to fly off" in a line. This
tendency to fly off from a revolving centre is called
centrifugal force — the word centrifugal meaning fly-
ing from the centre. Large grindstones, driven with
great velocity by machinery, are sometimes split asun-
der by centrifugal force.

The most sublime examples of centrifugal force oc-
cur in the motion of the earth and planets, which will
be more fully explained on a future page.

GRAVITATION. 35

CHAPTER III.

ATTRACTION.

SECTION I.
GRAVITATION.

The earth, as is well known, is a mass of matter in
the form of a globe, the diameter being upward of
7900 miles. From its enormous size and the small
portion seen from one point, the surface appears flat,
except where broken into mountains and valleys.

The tendency which all bodies possess of faUing to-
ward the earth is owing to the attractive force which
this great mass of matter exerts upon them. This kind
of attraction is called gravitation. The force with
which a body is thus drawn is the weight of that body.

When a stone is dropped from the hand, its velocity
is at first slow, but continues to increase till it strikes
the earth ; hence, the further it falls, the harder it will
strike. This accelerated motion is precisely similar to
that of a steam-boat when it first leaves the wharf; the
force of gravity may be compared to the driving power
of the engine, and the quickened velocity of the falhng
stone to the increased headway of the boat.

All bodies, whether large or small, fall equally fast,
unless they are so light as to be borne up in part by
the resistance of the air. In the first second of time
they fall 16 feet ; in the next second, 3 times 16, or
48 feet ; in the third second, 5 times 16, or 80 feet, and
so on. Or, if the whole distance fallen be taken togeth-

36

MECHANICS.

er, they fall 16 feet in one second, 4 times 16 in two
seconds, 9 times 16 in three seconds, and so forth. In
other words, the whole distance is equal to the square
of the time. This is plainly exhibited hy the following
table :*

Seconds, from beginning
to fall.

1

2

3

4

5 6

Whole height fallen in
feet.

16

4X16
or 64.

9X16
or 144.

16X16
or 256.

25X16 36X16
or 400. |or 576.

Space fallen in each see- -j „
end in feet.

3X16
or 48.

6X16
or 80.

7X16
or 112.

9X16 111X16
or 144. lor 176.

A stone or other body wiU fall 1 foot in a fourth of
a second, 3 feet the next fourth, 5 feet the third fourth,
and 7 feet the last fourth ; which is the same as 4 feet
in half a second, 9 feet in three fourths of a second, and
16 feet for the whole second.

The depth of an empty well, or the height of a prec-
ipice, may be nearly ascertained by observing the
time required for the fall of a stone to the bottom.
The time may be measured by a stop-watch, or, in its
absence, a pendulum may be made by fastening a peb-
ble to a cord, which will swing from the hand in reg-
ular vibrations of an exact second each if the cord be
39 1 inches long, or of half a second each if it be about
9§ inches long.

The velocity increases simply as the time — that is,
the speed in falling is twice as gi-eat in two seconds
as in one ; three times as great in three seconds ; four
times as great in four seconds, and so forth. A stone
will. fall four times as far in two as in one second, while

* The distance, accurately stated, is sixteen feet and one inch for
the first second, and hence the numbers in the table fall a very little
short of the distance actually fallen.

GRAVITATION. 37

its velocity will be doubled ; nine times as far in three
seconds, while its velocity will he tripled, &o.

If a stone is thrown upward, its motion continues
gradually to decrease, at the same rate as it increases
in falling; hence the same time is required to reach
its highest point, as to fall from that point back to the
earth. Therefore the velocity with which it is first
projected upward is equal to the velocity wliich it at-
tains at the moment of strildng the ground. There is
an exception, however, to this general rule. In a vac-
uum it would be perfectly correct, but in ordinary prac-
tice the resistance of the air tends to diminish the ve-
locity while as cending, and still further to retard it while
descending. For this reason, it wiU fall with less speed
than it first arose. For heavy bodies and small dis-
tances, this exception would be imperceptible ; but
with small bodies falling from great heights, the difier-
ence will be considerable.

The velocity of a stone after falling one second, or
sixteen feet, is at the rate of thirty -two feet per second ;
hence, if thrown upward at that rate, it will rise just
sixteen feet high. After falling tlnree seconds, the rate
is ninety-six feet; and hence, if projected upward at
ninety-six feet per second, it will rise nine times sixteen
feet, or one hundred and forty-four feet high. And so
of other heights.

Were it not for the resistance of the air, a feather
would fall as swiftly as a leaden baU. Tliis is conclu-
sively shown by an interesting experiment. A tall glass
jar [Fig-. 11), open at the bottom, is covered with a
brass cap, fitting it air-tight. Through this cap passes
an air-tight wire, which, by turning, opens a small pair

38

MECHANICS.

Fig. 11.

I

of pincers. Within these are placed
a feather and a half dollar, and the
air is then thoroughly drawn from the
receiver by means of an air-pump.
The wire is turned, and the feather
and coin both drop at once, and strike
the bottom at the same moment.

measuring the velocity. ^at-

wood's machine.

In consequence of the swiftness of
falling bodies, it is not easy to meas-
ure the exact distance through which
they fall in a given time. There is an
instrument, however, known as At-
woocVs, Machine^ which renders their
motion much slower, at the same time
Feather andcomfaiiing^^^'^ the rate of iucreasc iu velocity is

ame in a vacuum, precisely the samc, and it
therefore admits of an exact measurement of
the descent. The principle of this machine
may be easily understood by Fig. 12, where
two weights, hung on a fine silk cord run-
ning over a wheel, exactly balance each oth-
er. If now a small additional weight be
placed on one of these, it will destroy the bal-
ance, and the weight will begin to move
downward. As this little weight has to impart mo-
mentum to both the other larger weights, they will
move as much slower than ordinary falling as the
smaller weight is less than they. On this principle
Atwood's Machine, represented by Fig. 13, is made.

MEASURING THE VELOCITY.

39

Fig. 13.

The two weights are first made to
balance each other, when one of
them is raised nearly to the wheel
at c, and a small weight in the form
of a short rod is placed across it.
It immediately descends with ac-
celerated or increasing velocity un-
til it reaches the hole in the shelf a,
through which the weight passes,
but the rod is caught and retained.
The motion is now no longer accel-
erated, because the weights have
become equal, and the descending
one continues to fall uniformly ait
the same rate that it passed through
the hole in the shelf, until it strikes
the bottom. Durmg this time its
velocity may be accurately meas-
ured by means of the clock and pen-
dulum attached to the instrument.
By sliding the shelf up or down, the
velocity, after falling through different spaces to reach
the shelf, may be accurately determined. When the
shelf is placed very near the top, so that but little ve-
locity is acquired, the descending weight will move
very slowly all the way down ; but when placed low-
er, the weight continues downward more rapidly. It
is necessary that the wheel turn with extreme ease, to
effect which, friction-wheels, described hereafter, are
usually employed.

There are many instances showing the accelerated
motion and increased force of fallinsr bodies. Wlien a

Atwood's Machine for
measuring the de-
scent of bodies.

40 MECHANICS.

large stone rolls down a mountain, it first moves slow-
ly, but afterward bounds with rapidity, sweeping be-
fore it all smaller obstacles. Hail-stones, although
small, acquire such velocity as to break windows ; and
but for the resistance of the air, they Avould be much
more destructive. The blow of a sledge-hammer is
more severe as it is lifted to a greater height. New-
ton was first led to the examination of the laws of
gravity by observing, when sitting under an apple-tree,
that the fruit struck his hand with greatest severity
when it fell from the top of the tree.

It is not an unusual error to suppose that a large
body will fall more rapidly than a small one. Some
can scarcely believe that a fifty-six pound weight will
not drop with a greater velocity than a small nail, not
remembering that a proportionately greater force is re-
quired to overcome the inertia and set the larger body
in motion. Tliis error existed for many centuries, from
the time of Aristotle until G-alileo first questioned its
correctness. The celebrated experiment which estab-
lished the truth on this subject, and led to the discov-
ery of the laws of falHng bodies just explained, and
which formed an era in modern philosophy, was per-
formed from the top of the leaning tower of Pisa.
Gralileo was a philosophical teacher, and, being a man
who thought for himself, soon discovered, by reasoning,
the errors that had been received without a doubt for
more than twenty centuries. AU the learning of the
age and the wisdom of the universities were against
him, and in favor of this time-honored error, the truth
of which no one had ever thought of submitting to ex-.
periment. The hour of trial arrived, when he, an ob-

MEASURING THE VELOCITY. 41

scure young man, stood nearly alone on one side, while
the multitude, with all the power and confessed knowl-
edge of the age, were on the other.

The balls to be employed were carefully weighed
and scrutinized to detect deception, and the parties
were satisfied. The one baU was exactly twice the
weight of the other. The followers of Aristotle main-
tained that when the baUs were dropped from the top
of the tower, the heavy one would reach the ground in
exactly half the time employed by the lighter ball.
Galileo asserted that the weights of the balls would
not affect their velocities, and that the times of descent
would be equal. The balls were conveyed to the sum-
mit of the lofty tower — the crowd assembled round the
base — ^the signal was given — the balls were dropped at
the same instant, and swiftly descending, at the same
moment struck the earth. Again and again the ex-
periment was repeated with uniform results. Galileo's
triumph was complete' — not a shadow of doubt remain-
ed ; but, instead of receiving the congratulations of
honest conviction, private interest, the loss of place,
and the mortification of confessing false teaching,
proved too strong for the candor of his adversaries.
They clung to their former opinions with the tenacity
of despair, and he was driven from Pisa.*
* J^Iitchell's Lectures.

42 ■MECHANICS,

SECTioiT n.

The attraction of gravitation, as we have just seen,
takes place between bodies at a greater or less distance
from each other. There is another kind of attraction,
acting only when the parts of substances are in actual
contact; this is called cohesion. It is this which
holds the parts of a body together and prevents it from
falling to pieces. It may be shown by taking two
pieces of lead, and, after having made upon them two
smootlily-shaven surfaces with a knife, pressing them
Fig. 14. firmly together with a

twisting motion {Fig. 14).
The asperities of the sur-

Cohesive attraction m two lead balls. facCS arC tllUS pUshcd

down, and the particles are brought into close contact,
so that cohesion immediately takes place between them,
and some force will be required to draw them asunder.*
Two pieces of melted wax adhere together in the same
way. Melted pitch or other similar substance, smeared
thinly over the polished surfaces of metal or glass, also
causes cohesion to take place between them. Smooth
iron plates, two inches in diameter, have been made to
stick together so firmly with hot grease as to require,
when cold, a weight of half a ton to draw them apart.
Plates of brass of the same size, cemented by means
* That this is not atmospheric pressure, like that which holds two
panes of wet glass together, is shown by the fact that it requires
nearly as great a force to separate them when they are placed under
the exhausted receiver of an air-pump. Besides this, atmospheric
pressure is much weaker than this force, with so small a surface.

STRENGTH OF MATERIALS. 43

of pitch, required 1400 pounds. On this principle de-
pends the efficacy of those substances which are used
for cementing broken vessels.

The most perfect artificial polish which can be given
to hard metals is still so rough as to prevent the faces
from coming mto close contact ; hence they must be
either melted, or softened like iron when it is welded.

The diiferent degrees of cohesion which take place
between the particles of various soils, to reunite them
after they have been crumbled asunder, occasion the
main difference between light and heavy soils. When
a light soil becomes soaked with water, the particles
adhere in a very slight degree ; and hence, when it be-
comes dry again, it is easily worked mellow. But if
it be of a clayey nature, too much moisture softens it
like melted wax : the particles are thus brought into
close contact, and strong adhesion takes place ; hence
the hardness and difficulty of working such soils when
again dried. This adhesion is lessened by applying
sand, chip-dirt, straw, yard-manure, or by burning the
earth, but more especially by thorough draining, which,
preventing the clay from becoming so moist and soft,
lessens the adhesion of its parts. .

Different substances are hard, soft, brittle, or elastic,
according to the different degrees or modes of action
in the attraction of cohesion.

STRENGTH OF MATERIALS.

It is a matter of great utility in the arts to determ-
ine the different degrees of cohesion possessed by the
different substances; or, in other words, to ascertam
their strength. This is done by forming them into

44 MECHANICS.

rods of equal size, and applying weights to their lower
extremities sufficient to break them, by drawing them
asunder. The amount of weight shows their relative de-
grees of strength. The following table gives the weights
required to break the different substances, each being
formed into a rod one quarter of an inch square :

Woods.

Ash, toughest 1000 lbs.

Beech 718 "

Box 1250 "

Cedar ' 712 "

Chestnut 656 "

Elm 837 "

Locust 1280 "

Maple 656 "

Oak, white. 718 "

Pine, white 550 "

" pitch 750 "

Poplar 437 "

Walnut 487 "

Metals.

Steel, best 9370 lbs.

" soft 7500 "

Iron, wire 6440 "

" best bar 4690 "

" common bar 3750 "

" inferior bar 1880 "

" cast 1150 to 3100 "

Copper, wire 3800 "

cast 2030 "

Brass 2800 "

Platina wire 3300 "

Silver, cast 2500 "

Gold, east 1250 "

Tin 310 "

Zinc, cast 160 "

" sheet 1000 "

Lead, cast • 55 "

" milled 207 "

STRENGTH OF MATERIALS. 45

From these tatles we may ascertain the strength of
chains, rods, &c., when made of different, metals, and
of timhers, bars, levers, swing-trees, and farm imple-
ments, when made of woods. Wood which will hear
a very heavy weight for a minute or two will break
with two thirds of the weight when left upon it for a
long time. This explains the reason that store-house
and barn timbers sometimes give way under heavy
loads of grain, which have appeared at first to stand
with firmness.

Although the preceding table gives the strength of
wood drawn lengthwise, yet the comparative results
are not greatly different when the force is applied in a
transverse or side direction, so as to break in the usual
way.

The following table shows the results of several ex-
periments with pieces of wood one foot in length, one
inch sqviare, with the weight suspended from one end,
bending them sidewise.

"White oak, seasoned, broke with 240 lbs.

Chestnut, " " 170 "

White pine, " " 135 "

Yellow pine, " " 150 "

Ash, " " 175 "

Hickory, " " 2*70 "

A rod of good iron is about ten times as strong as
the best hemp rope of the same size. The best iron
wire is nearly twenty times as strong as a hemp cord.
Hence the enormous strength of the wire cables, sev-
eral inches in diameter, which are employed for the
support of suspension bridges.

A rope one inch in diameter will bear about 5000
lbs., but in practice should not be subjected to more

46 MECHANICS.

than half this strain, or about one ton. The strength
increases or diminishes according to the size of the
cross-section of the rope ; thus a cord half an inch in
diameter wiU support one quarter as much as an inch,
and a quarter-inch cord a sixteenth as much. A knowl-
edge of the strength of ropes, as used by farmers in
windlasses, pulleys, drawing loads, &c., would some-
times prevent serious accidents by their breaking. The
following table may therefore be useful :

Diameter of rope or Pounds borne Breaking

cord in inches. with safety. weight.

One eighth 31 lbs. 78 lbs.

One fourth 125 " 314 "

One half 500 " 1250 "

One 2000 " 5000 "

One and a quarter 3000 " 7500 "

One and a half 4500 " 12,500 "

These results will vary about one fourth with the
quality of common hemp. Manilla is about one half
as strong as the best hemp. The latter stretches one
fifth to one seventh before breaking.

Wood is about seven to twenty times stronger when
taken lengthwise with the fibres than when a side
force is exerted, so as to split it. The splittmg of tim-
ber or wood for fuel is, however, accomphshed with a
comparatively small power by the use of wedges, the
force of heavy blows, and the leverage of the two parts.

The attraction of cohesion is very weak m liquids ;
it is sufficient, however, to give a round or spherical
shape to very small portions or single drops, and to fur-
nish a beautiful illustration, on a minute scale, of the
same principle which gives a rounded form to the sur-
face of the sea. In one case, cohesion, by drawing to-
ward a common centre, forms the minute globule of

CAPILLARY ATTRACTION.

47

dew upon the blade of grass ; in the other, gravitation,
acting in like manner, but at vast distances, gives the
mighty rotundity to the rolhng waters of the ocean.

CAPILLARY ATTRACTION.

Capillary attraction is a species of cohesion ; it
takes place only between solids and liquids. It is this
which holds the moisture on the surface of a wet body,
and which prevents the water from running instantly
out of a wet cloth or sponge. By touching the lower
extremity of a lump of sugar to the surface of water
in a vessel, capillary attraction will cause the water to
rise among its granules and moisten the whole lump.
It may be very distinctly shown by placing the end of
a fine glass tube into water ; the water wiU rise in it
above the level of the surrounding surface. If the bore
of the tube be the twelfth of an inch in diameter («,
Fig. 15), it wiU rise a quarter of an inch ; if but the

Fig. 15. Fig. 16.

Capillary attraction in tidies.

Capillary attraction between two panes of
glass.

twenty-fifth of an inch in bore, as b, it will rise half an
inch ; but if only a fiftieth of an inch, the water will
rise an inch. This ascent of the liquid is caused by
the attraction of the inner surface of the txibe, until the

48 MECHANICS.

weight of the column hecomes equal to the force of the
attraction. Capillary attraction may be also exhibited
by two small plates of glass, placed with their edges in
water, in contact on one side, and a little open at the
other side, as in Fig. 16, p. 47. As the faces of the
plates approach each other, the water rises liigher,
formmg the curve, a.

Capillary attraction performs many important offices
in nature. The moisture of the soil depends greatly
upon its action. If the soil is composed of coarse sand
or gravel, the interstices are large, and, like the larger
glass tube, wiU not retain the rain which falls upon it.
Such soils are, therefore, easily worked in wet weather,
but become too dry in seasons of drought ; but when
the texture is finer, and especially if a due proportion
of clay be mixed with the sand, the interstices become
exceedingly small, and retain a full sufficiency of moist-
ure. If, however, there is too much clay, the soil is
apt to become close and compact, and the water can
not enter until it is broken up or pulverized. It is for
this reason that sub-soil plowing becomes so eminently
beneficial, by deepening the mellow portion, and thus
affording a larger reservoir, which acts lilce a sponge
in holding the excess of falling rains, till wanted in the
dry season. For the same reason, a well-cultivated
soil is fomid to preserve its moisture much better dm*-
ing the heat of summer than a hardened and neglect-
ed surface.

If capillary attraction should cease to exist, the
earth would soon become a barren and uninhabitable
waste. The moisture of rains could not be retained
by the particles of the soil, but would immediately

ASCENT OF SAP. 49

sink far down into the earth, leaving the surface at all
times as dry and unproductive as a desert ; vegetation
would cease ; brooks and rivers would lose the gradual
supplies which the earth affords them through tliis in-
fluence, and become dried up ; and all plants and all
animals die for want of drink and nourishment. Thus
the very existence of the whole human race evidently
depends on a law, apparently insignificant to the un-
thinking, but pointing the observing mind to a striking
proof of the creative design which planned all the
works of nature, and fitted them with the utmost ex-
actness for the life and comfort of man.

ASCENT. OF SAP.

The following interesting experiments serve to ex-
plain the cause of the ascent of sap in plants and trees :
Take a small bladder, or bag made of any similar
substance, and fasten it tightly on a tube
open at both ends {Fig. 17) ; then fill them
with alcohol up to the point C, and im-
merse the bladder into a vessel of water.
The alcohol will immediately rise slowly
in the tube, and if not more than two or
three feet high, will run over the top. This
is owing to the capillary attraction in the
Apparatus ex- mluute porcs of tho bladder, drawing the
lisingofsap. water within it faster than the same at-
traction draws the alcohol outward. One liquid will
thus intrude itself into another with great force. A
bladder filled with alcohol, with its neck tightly tied,
will soon burst if plunged under water. If a bladder
is filled with gum-water, and then immersed as before,
C

50 MECHANICS.

the Water will find its way within against a very heavy
pressure.

In this manner sap ascends through the minute tubes
in the body of trees. The sap is thickened like gum-
water when it reaches the leaves, and a fresh supply,
therefore, enters through the pores in the spongelets of
the roots by capillary attraction, and, rising through the
stem, keeps up a constant supply for the wants of the
growing tree.

SECTION III.

CENTRE OF GRAVITY.

The centre of gravity is that point in every hard
substance or body, on every side of which the different
parts exactly balance each other. If the body be a
globe or round ball, the centre of gravity will be ex-
actly at the centre of the globe ; if it be a rod of equal
size, it will be at the middle of the rod. If a stone or
any other substance rest on a point directly under the
centre of gravity, it will remain balanced on this point;
but if the point be not under the centre of gravity, the
stone wiU fall toward the heaviest side.

Some curious experiments are performed by an in-
genious management of the centre of gravity. A
light cylinder of cork or
pasteboard contains a con-

9^ 2 -^ cealed piece of lead, g

{Figure 18). The lead,
being heavier than the rest,
will cause the cylinder to
roll up an inclined plane, when placed as shown by the

CENTRE OF GRAVITY.

51

Fig. 20.

lower figure on the preceding en-
graving, until it makes half a revo-
lution and reaches the place of the
upper figure, when it will remain
stationary. If a curved body, as
shown in Fig. 19, be loaded heav-
ily at its ends, it will rest on the
stand, and present a singular ap-
pearance by not falling, the cen-
tre of gravity lying between the
I singuiarhj haianccd by two hcavy portlous ou the end of
the stand. A light stick of some
length may be made to stand
on the end of the finger, by
sticking in two penknives, so
as to bring the centre of grav-
ity as low as the finger-end
{Fig. 20).

If any body, of whatever
shape, be suspended by a hook
or loop at its top, it wiU neces-
sarily hang so that the centre
of gravity shall be directly un-
der the hook. In tliis way the
centre in any substance, no
matter how irregular its shape
may be, is ascertained. Suppose, for
instance, we have the irregular plate
or board shown in the annexed figure
{Fig. 21) : first hang it by the hook
«, and the centre of gravity will be
somewhere in the dotted line a b.

Centre of gravity maintained by two
penknives.

52 MECHANICS.

Then hang it by the hook c, and it wUl be somewhere
in the line c d. Now the point e, where they cross
each other, is the only point in both, consequently this
is the centre sought. If the mass or body, instead of
being flat like a board, be shapeless Uke a stone or lump
of chalk, holes bored from different suspending points
directly downward wOl all cross each other exactly at
the centre of gravity.

LINE OP DIRECTION.

An imaginary line from the centre of gravity perpen-
dicularly downward to where the body rests is called
the line of direction.

Now in any sohd body whatever, whether it be a
wall, a stack of grain, or a loaded wagon, the line of
direction must fall within the base or part resting upon
the ground, or it will immediately be thrown over by
its own weight. A heavily and evenly loaded wagon
on a level road will be perfectly safe, because the line
of direction falls equally between the wheels, as shown
in Fig. 22, by the dotted
line, c being the centre. But
if it pass a steep side-hill
road, throwing this line out-
side the wheels, as in Fig.
r, , ^ , , , ^ , ^ 23, it must be instantly

Centre of gravity on level and inclined ' J

^""^^ overturned. If, however,

instead of the high load represented in the figure, it be
some very heavy material, as brick or sand, so as not
to be higher than the square box, the centre will be
much lower down, or at b, and thus, the line falling
within the wheels, the load will be safe from danger,

LINE OP DIRECTION. 53

unless the upper wheel pass over a stone, or the lower
wheel sink into a rut. The centre of gravity of a large
load may be nearly ascertained by measuring with a
rod ; and it may sometimes happen that by measuring
the sideling slope of a road, all of which may be done
in a few minutes, a teamster may save himself from a
comfortless upsetting, and perhaps heavy loss. Again,
a load may be temporarily placed so much toward one
side, while passing a sideling road, as to tlu'ow the line
of direction considerably more up liill than usual, and
save the load, which may be adjusted again as soon
as the dangerous point is passed. This principle also
shows the reason why it is safer to place only light
bundles of merchandise on the top of a stage-coach,
while all heavier articles are to be down near the
wheels ; and. why a sleigh will be less likely to upset
in a snow-drift, if all the passengers will sit or lie on
the bottom. Wlien it becomes necessary to build very
large loads of hay, straw, wool, or other light sub-
stances, the " reach," or the long connecting-bar of the
wagon, must be made longer, so as to increase the
length of the load ; for, by doubling the length, two
tons may be piled upon the wagon with as much secu-
rity from oversetting as one ton only on a short wagon.
Fig. 24. Fig. 25. Where, however, a high

load can not be avoided,
great care must be taken
to have it evenly placed.
vp;_^ip wi^i'^^j- ^ f^j. instance, the load
of hay represented by

Centre of gravity of an even and one-sided Figure 24 be skillfully

'""'' bunt, the line of direc-

54

MECHANICS.

tion will fall equally distant within each wheel ; but a
shght misplacement, as in Fig. 25, p. 53, will so alter
this line as to render it dangerous to drive except on a
very even road.

Thus every one who drives a wagon should under-
stand the laws of nature sufficiently to know how to
arrange the load he carries. It is true that experience
and good judgment alone will be sufficient in many
cases ; but no person can fail to judge better, with the
reasons clearly, accurately, distinctly before his eyes,
than by loose conjecture and random guessing.

Every farmer who erects a wall or building, every
teamster who drives a heavy load, or even he who
only carries a heavy weight upon his shoulder, may
learn something useful by understanding the laws of
gravity.

It is familiar to every one, that a body resting upon
a broad base is more difficult to overset than when the
For instance, the square block {Fig.

is narrow.

Fig. 26.

26) is less easily thrown over than
the tall and narrow block of equal
weight, because, in turning the
square block over its lower edge,
the centre of gravity must be lift-
ed up considerably in the curve
shown by the dotted line c ; but
with a tall, narrow block, this
curve being almost on a level,
very little lifting is required. Hence the reason that
a liigh load on a wagon is so much more easily over-
turned than a low one.

Of all forms, a pyramid stands the most ffi-irdy on its

LINE OF DIRECTION.

55

Fig. 27.

The centre of gravity, c (Fig. 26), being so
near the broad bottom, it must be elevated in a very-
steep curve to throw the line of direction beyond the
base. For tliis reason, a stone wall, or the dam for a
stream, will stand better when broad at bottom and
tapering to a narrow top than if of equal thickness
throughout.

When a globe or round ball is placed upon a smooth
floor, it rests on a single pomt. If the floor be levels
the line of direction will fall exactly
at this resting-point {Fig. 27). To
move the ball, the centre will move
precisely on a level, without being
raised at all. This is the reason that
a ball, a cylinder, or a wheel is rolled
forward so much more easily than any flat-sided or ir-
regular body. In all these cases, the line of direction,
although constantly changing its place, still continues
to fall on the very point on which the round body rests.
But if the level floor is exchanged for a slope or in-
clined plane {Fig. 28), the Ime of
direction no longer falls at the touch-
ing-point, but on the side from it
downward ; the ball will therefore,
by its mere weight, commence roll-
ing, and continue to do so till it
reaches the bottom of the slope.
Wheel-carriages owe their comparative ease of
draught to the fact that the centre of gravity in the
load is moved forward by the rolling of the wheels, on
a level, or parallel with the surface of the road, just in
the same way that the round ball rolls so easily. Each

56

MECHANICS.

wheel supporting its part of the load at the hub, the
same rule applies to each as to a ball or cylinder alone.
Hence, on a level road, the line of direction falls pre-
cisely where the wheels rest on the ground, but if the
road ascend or descend, it falls elsewhere; this ex-
plains the reason why it will run by its own weight
down a slope.

"Whenever a stone or other obstruction occurs m a
road, it becomes requisite to raise the centre by the
force of the team and by means of oblique motion, so
Fie. 29. as to throw the wheel over it,

as shown by Fi^. 29. One
of the reasons thus becomes
very plain why a large wheel
Fig. 30. will run with

^^^~" more ease on
a rough road
than a small-
er one ; the

larger one mounting any stone or obstruction without
lifting the load so much out of a level or direct line, as
shown by the dotted lines in the annexed figures {Figs.
29 and 30). Another reason is, the large wheel does
Fig. 31. Fig. 32. not siuk iuto the smaller

cavities in the road.

A self-supporting fruit-
ladder [Figure 31) (the
centre of gravity, when
in use, being at or near
the top) must have its
A dangerous- Icgs morc wldcly Spread,
uddlr^'^' to be secure from fall-

A Jirmly-set fruit-ladder.

LINE OP DIRECTION. 57

ing, than if the centre were lower down. Hence such
a position as in Fig. 32 would be unsafe.

The support of the human body, in standing and
walking, exhibits some interesting examples in rela-
tion to this subject. A child can not learn to walk till
he acquhes skill enough to keep his feet always in the
line of direction. When he fails to do this, he topples
over toward the side that the line falls outside liis feet.
A man standing with his heels touching the wash-
board of a room can not possibly stoop over without
faUing, because, when he bends, the hne of direction
falls forward of liis toes, the wall against which he
stands preventing the movement of his body backward
to preserve the balance.

In walking, the centre rises and falls shghtly at
Pi^ 33 each step, as shown by the waved line

in Fig. 33. If it were not for the
bending of the knee-joints, this exer-
cise would be much more laborious,
as it would then become needful to
tlurow the centre mto an upward curve
at every step. For this reason, a wood-
en leg is more imperfect than the nat-
ural one {Fig. 34). Hence the reason
why walking on crutches is laborious and fatiguing,
because at every onward step the body must be thrown
upward in a curve, like a wagon mounting repeated
obstructions.

"When a load is carried on the shoulder, it should be

so placed that the Ime of direction may pass directly

through the shoulder or back down to the feet. Fig.

35, p. 58. An unskillful person will sometimes place

C2

58

MECHANICS.

Fig. 36. a bag of grain as shown in Fig.
36. Ths line falling outside his
feet, he is compelled to draw
downward with great force on
the other end of the bag. A man
who carries a heavy pole on his
shoulder should see that the centre is directly over his
shoulder, otherwise he will be compelled to bear down
upon the Ughter end, and thus add in an equal degree
to the weight upon his body.

If an elliptical or oval body,
Fig. 37, rest upon its side a, roll-
ing it in either direction elevates
the centre, c, because it is nearest
the side on wliich the body rests.
If, when raised, it be suffered to
fall, its momentum carries it be-
yond the point of rest, and thus it
contmues rocking until the force is
spent. The course of the centre
dming these motions is shown
by the curved dotted line, c. If
it be placed upon end, as in Fig.
38, then any motion toward ei-
ther side brings the centre of
gravity nearer the touching-point,
that is, causes it to descend, and the body consequently
falls over on its side. This may be easily illustrated

falls when set on either end.

The rockers of chairs, cradles, and cribs are formed
on the principle just explained. If so made that the

LINE OF DIRECTION.

59

centre of gravity of the chair or cradle is nearer the
middle of the rocker than to the ends, the rocking mo-
tion will take place ; and when the distance from the
centre of gravity to the ends of the rockers is but little
Fig. 39. Fig. 40. greater than the distance to the
middle, c, as in Fig. 39, the mo-
tion will be slow and gentle ; but
if this difference be greater, as in
Fig. 40, it will be rapid. When
the centre is high, the rockers must have less curvature
than where it is low and near the floor. If the centre
of gravity be nearer the ends than to the middle, the
chair will immediately be overturned. This principle
should be well understood in the construction of all in-
struments which move by rocking.

' \

(

' 1 -

'^y

oe

\

y<S-.

J

60 MECHANICS.

CHAPTER IV.

SIMPLE MACHINES, OR MECHANICAL POWERS.

SECTION I.
ADVANTAGES OF MACHINES.

The moving forces which are appHed to various use-
ful purposes commonly require some change in veloc-
ity, direction, or mode of acting before they accom-
plish the desired end. For example, a running stream
of water has a motion in one direction only ; by the
use of machinery, we change tliis to an alternating mo-
tion, as in the saw of the saw-mill, or to a rotatory or
whirling motion, as in the stones of a grist-mill. The
direct or straightforward power of a yoke of oxen is
made, by the employment of the plow, to produce a
side-motion to the sod as well as to turn it through
half a circle. The thrashing-machine converts the
slowly-acting pace of horses to the swift hum of the
spiked cyhnder.

Any instrument used for thus changing or modify-
ing motion is called a machine^ whether it be simple
or complex in its structure. Thus even a crowbar^
used in hfting stones from the earth, by diminishing
the motion given by the hand and increasing its power,
may be strictly termed a machine ; while a harrow^
which neither alters the course nor changes the veloci-
ty of the force applied, may with more propriety be re-
garded as simply an implement or tool. In common

THE LAW OF VIRTUAL VELOCITIES. 61

language, however, these distinctions are not accurate-
ly observed, and a machine is usually considered to he
any instrument consisting of different moving parts.

AU machines, however complex, may he resolved into
two simple parts, or simple machines. These are,

1. The Lever ;

2. The Inclined Plane.

The wheel and axle, and the pulley, are modified ap-
plications of the LEVER ; and the wedge and the screiv
of the INCLINED PLANE, as will he shown on the follow-
ing pages. These six are usually termed the mechan-
ical poivers. As they really do not possess any power
in themselves, but only regulate power, the term " sim-
ple macliines" may be regarded as most correct.

THE LAAV OF VIRTUAL VELOCITIES.

Before proceeding to the simple machines, it may be
well to explaia a very important truth, which should be
considered as lying at the foundation of all mechanical
philosophy, and which renders plain and simple many
things which would otherwise seem strange or contra-
dictory. This is, that the force required to lift any
given body is always in proportion to the weight of
that body, taken together with the height to be raised.
For instance, it requires twice the force to raise two
pounds as to raise one pound, three times the force to
raise three pounds, and so forth. Also, twice as great
a force is needed to elevate any weight two feet as one
foot, or three times as great for three feet, and so on.
Agam, combining these together, four times as great a
force is required to raise two pounds to a height of two
feet as to raise one pound only one foot ; eight times

62 MECHANICS.

as great for four feet, and so on. This holds true, no
matter by what kind of machinery it is accomphshed.
Now this may all seem very simple, hut it serves to ex-
plain -many difficult questions in relation to the real
power possessed by all machines.

Take another example. Suppose that one wishes to
raise a weight of 1000 pounds to a height of one foot.
If his strength is only equal to 100 pounds, the weight
would he ten times too heavy for him. He might,
therefore, divide it into ten equal parts of 100 pounds
each. Raising each part separately the required height
of one foot, would he the same as raising one of them
ten feet high. The weight is lessened ten times, hut
the distance is increased ten times. But there are
some bodies, as, for example, blocks of stone or sticks
of timber, which can not well be divided into parts in
actual practice. He therefore resorts to a machine or
mechanical power, through which the same result is
accomplished by raising the whole weight in one mass
with his single strength ; but in this case as well as
the other, the moving force which he applies must pass
through ten times the space of the weight. We arrive,
therefore, at the general rule, that the distance moved
by the weight is as much less than that moved by the
power as the power is less than the weight. This rule
is termed by some writers the " rule of virtual veloc-
ities,'''' virtual meaning not apparent or actual, but
according to the real effect, because the increase in
the velocity of the power makes up for increase in the
size of weight. This rule will be better understood
after considering its application to the different simple
machines.

THE LEVER.

SECTION II.

THE LEVER

The simplest of all machines is the lever. It con-
sists of a rod or bar, one end resting upon a prop ox ful-
crum, F {Fig. 41), near which is the weight, W, moved

Fig. 41.

Lever of the second kind.

by the hand at P. The stone may weigh 1000 pounds ;
yet, if it is ten times as near the fulcrum as the man's
hand is, a force of 100 pounds will lift it ; but it will
be moved only a tenth part as high as the hand has
been moved, as shown by the dotted lines. By placing
the stone stiU nearer the fulcrum, still less will be the
power required to raise it, but then the distance ele-
vated would be also still less. By sufficiently increas-
ing the disproportion between the two parts of the le-
ver, the strength of a child merely might be made to
move more than many horses could draw.

These performances of the lever often excite aston-
ishment at what appears to be out of the common
course of things ; yet, when examined by the princi-
ples of mechanics, instead of appearing matters of as-
tonishment, they are formd to be only the natm-al and
necessary results of the laws of force. In the case of
the lever just described, it is often incorrectly supposed
that the power itself sustains the weight. But this is

64 MECHANICS.

not the case ; nearly the whole of it rests upon the ful-
crum. We often see proofs of this error in common
practice, where fulcrums or props entirely insufficient
to uphold the enormous weight to be raised are at-
tempted to be used. If the weight, for instance, be
ten times as near the fulcrum as to the power, then
nine tenths of the weight rests upon the fulcrum, and
the remaining tenth only is sustained by the lifting
power. The lever only allows the power to expend it-
self through a longer distance, and thus, by concentra-
ting itself at the weight, to elevate the latter through
the shorter distance, according to the rule of virtual
velocities already explained.

The fulcrum may be placed between the weight and
Fig. 42. the power, as in

__^^ Fig. 42, or the

Lever of the first kind. placed between

Fig. 43. the fulcrum and the

// L weight, as in Fig:

^ - ^- 48, the same princi-

Lever of the third kind. ^^Q of virtual Veloci-

ties applying in all cases.

Where the fulcrum is between the power and the
weight, as in Fig. 42, it is called a lever of the first
kind.

Where the weight is between the fulcrum and the
power, as in Fig. 41, it constitutes a lever of the
seco7id kind.

Where the power is between the fulcrum and the
weight, as in Fig. 43, it is termed a lever of the third
kind.

THE LEVER. 65

1. Many examples occur in practice of levers of the
first kind. A crowbar, used to raise stones from the
earth, is an instance of this sort ; so is a handspike of
any kind used in the same way. A hammer for draw-
ing a nail operates as a lever of the first kind, the heel
being the fulcrum, the nail the weight, and the hand
the power ; the distance through wliich the handle
passes being several times greater than that of the
claws, the force exerted on the nail is increased in like
proportion. A pair of scissors consists of two levers,
the rivet being the fulcrum ; and in using them, as ev-
ery one has observed, a greater cutting force is exert-
ed near the rivets than toward the pomts. This is ow-
ing to the power being expended through a greater dis-
tance near the points, according to the rule ah-eady
explained. Pincers, nippers, and other similar instru-
ments are also double levers of the first kind.

A common steelyard is another example, the shding
weight becoming gradually more effective as it is moved
further from the fulcrum or hook supporting the instru-
ment. The brake or handle of a pump is a lever of
this class, the pump-rod and piston being the weight.
The common balance is still another, the two arms
being exactly equal, so that
one weight will always bal-
ance the other, and on this
its usefulness and accuracy
entirely depends. The most
sensitive balances have light
beams with long arms, and
the turning-point of hardened steel or agate, in the
form of a tliin wedsre, on which the balance turns al-

66 MECHANICS.

most without friction. Small balances have been so
skillfully constructed as to turn with one thousandth
part of a grain,

2. Levers of the second kind are less numerous, but
not uncommon. A handspike used for rolling a log is
an example. A wheel-barrow is a lever of the second
kind, the fulcrum being the point where the wheel rests
on the ground, and the weight the centre of gravity of
the load. Hence, less exertion of strength is required
in the arm when the load is placed near the wheel,
except where the ground is soft or muddy, when it is
found advantageous to place the load so that the arm
shall sustain a considerable portion, to prevent the
wheel sinking into the soil. A two- wheeled cart is a
similar example ; and, for the same reason, when the
ground is soft, the load should be placed forward to-
ward the horse or oxen ; on the other hand, on a smooth
and hard, or on a plank road, the load should be more
nearly balanced. An observance of this rule would
often save a great deal of needless waste of strength,
A sack-barrow, used in barns and mills for convey-
Fig. 45. ing heavy bags of grain from one

part of the floor to another, is a le-
ver nearly intermediate between
the first and second kind, the
weight usually resting very near-
ly over the fulcrum or wheels.
When the bag of grain is thrown
forward of the wheels, it becomes
a lever of the first kind ; when
back of the wheels, it is a lever
'sach-barrow. of thc sccond kind. As it is

ESTIMATING THE POWER OF LEVERS. 67

used only on hard and smooth floors, and not, like the
wheel-barrow, on soft earth, the more nearly the load
is placed directly over the wheels, the more easily they
will run.

3. In a lever of the third kind, the weight being
further from the fulcrum than the power, it is only
used where great power is of secondary importance
when compared with rapidity and dispatch. A hand-
hoe is of this class, the left hand acting as the fulcrum,
the right hand as the power, and the resistance over-
come by the blade of the hoe as the weight. ^ A hand-
rake is similar, as well as a fork used for pitching hay.
Tongs are double levers of this kind, as also the shears
used in shearing sheep. The limbs of animals, gener-
ally, are levers of the third kind. The joint of the bone
is the fulcrum ; the strong muscle or tendon attached
to the bone near the joint is the power ; and the weight
of the limb, with whatever resistance it overcomes, is
the weight, A great advantage results from this con-
trivance, because a slight contraction of the muscle
gives a swift motion to the Hmb, so important m walk-
mg and running, and in the use of the arms.

SECTION III.

ESTIMATING THE POWER OF LEVERS.

The power of any lever is easily calculated by meas-

Fig- 46. uring the length of

--r---'|k' its two arms, that

,,-.;^--'- £\ p w is, the two parts in-
to which it is divi-
of the first kind. dcd by the wcight,

68 MECHANICS.

fulcrum, and power. In a lever of the first kind, if
the weight and power he equally distant from the ful-
crum, they will move through equal distances, and
nothing will be gained ; that is, a power of 100 pounds
will lift a weight of 100 pounds only. If the power be
Fig. 47. twice as far as the

'[^'-"-"-T-... weight, its force

' ;' ""'■:.- . will be doubled;

' I I '^ ~c^^-i^^^.._ if three times, it
^ )K^ will be tripled;

Lever of the second kind. and SO forth. In

a lever of the second kind, if the weight be equidistant
between the fulcrum and power, the power will move
through twice the distance of the weight, and the pow-
er of the instrument will therefore be doubled ; if twice
as far, it wiU be tripled, and so on, as shown in the an-
nexed figures. The same mode of reasoning wiU ex-
plain precisely to what extent the force is diminished
in levers of the third kind.

These rules will show in what manner a load borne
on a pole is to be placed between two persons carrying
it. If equidistant between them, each will sustain a
like portion. If the load be twice as near to one as to
the other, the shorter end wiU receive double the weight
of the longer. For the same reason, when three horses
are worked abreast, the two horses placed together
should have only half the length of arm of the main
whipple-tree as the single horse. Fig. 48. The farmer
who has a team of two horses unlike in strength, may
thus easily know how to adjust ithe arms of the whip-
ple-tree so as to correspond with the strength of each.
If, for instance, one of the horses possesses a strength

ESTIMATING THE POWER OF LEVERS.

Fig. 48.

-6-

69

as much greater than the other as four is to tliree,
then the weaker horse should be attached to the arm
of the whipple-tree made as much longer than the oth-
er arm as four is to three.

In all the preceding estimates, the influence of the
weight of the lever has not been taken into consider-
ation. In a lever of the first kind, if the thickness of
the two arms he so adjusted that it will remain bal-
anced on the fulcrum, its weight will have no other
effect than to increase the pressure on the fulcrum ;
but if it be of equal size throughout, its longer arm,
being the heaviest, will add to its power. The amount
thus added will be equal to the excess in the weight
of this arm, applied so far along as the centre of grav-
ity of tliis excess. If, for example, a piece of scantling
Fig. 49. twelve feet long,

a b, Fig. 49, be
used as a lever to
lift the corner of
a building, then
the two portions, a c, c d, will mutually balance each
other. If these be each a foot m length, the weight of
ten feet will be left to bear down the lever. The cen-

70 MECHANICS.

tre of gravity of this portion will be at e, six feet from
the fulcrum, and it will consequently exert a force un-
der the building equal to six times its own weight.
If the scantling weigh five pounds to the foot, or fifty
pounds for the excess, this force will be equal to three
hundred pounds.

In the lever of the second kind, its weight operates
against the moving power. If it be of equal size
throughout, this will be equal to just one half the
weight of the lever, the other half being supported by
the fulcrum.

With the lever of the third kmd, the rule appHed to
the first must be exactly reversed.

COMBINATION OF LEVERS.

A great power may be attained without the incon-
venience of resorting to a very long lever, by means of
p. 5(j Qi combination of levers.

; :x/ In Fig. 50, the small

&; ; jk' "^^rj^^ weight P, acting as a

'^ moving power, exerts a
three-fold force on the next lever ; this, in its turn, acts
in the same degree on the third, which again increases
the power three times. Consequently, the moving
power, P, acts upon the weight, W, in a twenty-seven-
fold degree, the former passing through a space twen-
ty-seven times as great as the latter.

A combination of levers hke this is employed in self-
regulating stoves. It is in this case, however, used to
multiply instead of to diminish motion. The expan-
sion of a metallic rod by heat the hundredth part of an
inch acts on a set of iron levers, and the motion is in-

WEIGHING MACHINE.

71

creased, by the time it reaches the draught-valve, to
about one hundred times.

A more compact arrangement of compound levers
is shown in Fig. 51, where the power, P, acts on
the lever A, exerting a force
on the lever B five times as
great as the power, B acts
on the lever C with a force
increased three times, and
this, again, on the weight,
W, with a four-fold force.
Multiplying 5, 3, and 4 to-
gether, the product is 60 ;
hence a force of one pound
at P will support 60 pounds
at W. By graduating (or
marking into notches) the le-
ver C, so that the distance is measured as the weight
is moved along it, a compact and powerful steelyard for
weighing is formed.

Compound levers.

WEIGHING MACHINE.

A valuable combination of levers is made in the con-
struction of the weighing machine^ used for weighing

Fig. 52.

Weighing Machine.

72 MECHANICS.

cattle, wagons loaded with hay, and other heavy arti-
cles. The wagon rests on the platform A {Fig. 52,
p. 71), and this platform rests on two levers at W, W,
which presses their other ends both on a central point,
and this again hears on the lever D, the other end of
which is connected by means of an upright rod with
the steelyard at F.

There are two important points gained in this com-
bination. In the first place, the levers multiply the
power so much that a few pounds' weight will balance
a heavy load of hay weighing a ton or more ; and, in
the next, the load resting on both the levers, commu-
nicates the same force of weight to the central point,
from whatever part of the platform it happens to stand
on ; for if it presses hardest on one lever, it bears light-
er, at a corresponding rate, on the other. In practice,
there are always two pairs, or four levers, which pro-
ceed from each corner of the platform, and rest on one
point at the centre. We have taken the two only, to
simplify the explanation.

. STUMP MACHINES.

A simple contrivance for allowing a succession of
efforts in the use of the lever is represented in the ac-
companying figure {Fig. 53), and is used for tearing
out the roots of partly decayed stumps. It may be
also applied to lifting heavy weights, and to various
other purposes. Two pieces of strong, three-inch white-
oak plank, eight inches wide and seven feet long, are
connected at the ends, and are furnished with the
movable leg, d. Two rows of holes are bored through
them, to receive iron pins, which are to serve as ful-

STUMP MACHINE.

Fig. 53.

73

^fe

crums. A strong lever, a, is furnish-
ed at one end with a thick iron hook
(shown in Fig. 54), which is first fast-
ened on the root of the stump, and then
one of the pins is inserted under the
lever. The lever is now elevated, and
the other bolt is placed under it. It is
next pressed down, and the first bolt
elevated one hole higher, and so on tOl
the stump is torn out. To prevent the lever slipping,
a notch is made in its under side, on each side of the
hook, as shown in Fig. 54.

A more powerful stump-extracting machine, made
on precisely the same principle, is exhibited by Fig.
55, p. 74. The lever, a, should be a strong stick of
timber, furnished with three massive iron hooks, se-
cured by bolts passing through, as represented in the
figure. Small or truck wheels are placed at each end
of the lever, merely for the purpose of moving it easily
over the ground. The stump, b, used as a fulcrum,
has the chain passing round near its base, while an-
other chain passes over the top of the stump, c, to be
torn out. A horse is attached to the lever at d, and,
moving to e, draws the other end of the lever back-
D

74

MECHANICS.

Fig. 55.

ward, and loosens the stump ; while in this position,
another chain is made to connect gtoh, and the horse
is turned ahout, and draws the lever backward to i,
which still further increases the loosening ; a few rep-
etitions of this alternating process tears out the stump.
Very strong chains are requisite for this purpose.
Large stumps may require an additional horse or a
yoke of oxen. Where the stumps are remote from
each other, iron rods with hooks may he used to con-
nect the chains.

The power which may be given to this and to all
other modes of using the lever, as we have already
seen, depends on the difference between the lengths of
its two arms. A yoke of oxen, drawing with a force
of 500 pounds on the long arm of a lever 25 feet long,
will exert a force on the short arm of six inches equal

WHEEL AND AXLE. 75

to 50 times 500 pounds, or 25,000 pounds, on the
stump.

It was after an examination of the great power
which may be given to the lever by increasing this dif-
ference that Archimedes exultmgly exclaimed, " Give
me but a fulcrum whereon to place my lever, and I
will move the earth !" Admitting the theoretical truth
of tliis exclamation, and supposing there could be a
lever which he might have used for this purpose, its
practical impossibility may be quickly understood by
computing the whole bulk of the globe ; for such is
its enormous size and cubical contents, that Archim-
edes must have moved forward his lever with the
strength of a hundred pounds and the swiftness of a
cannon ball for eight hundred million years to have
moved the earth the thousandth part of an inch !

SECTION IV.
WHEEL AND AXLE.

In treating of the lever, it was shown to be capa-
ble of exerting a force through a small distance only.
Hence, if a heavy body were required to be elevated
to any considerable height, it would be necessary to
accomplish it by a succession of efforts. This incon-
venience is removed by a constant and unremitted
action of the lever in the form of the ivheel and axle.

Let the weight, w {Fig. 56, p. 76), be suspended by
a cord from the end of the lever, a b, and a wheel at-
tached to the lever, so that this cord may wind upon
it as the weight is elevated ; then let the power be ap-
plied at the other end by means of a cord, and a larger

76

MECHANICS.

Fig. 56. wheel be attached, so that

this cord too may wind upon
the larger wheel. These two
wheels (fastened together so
as to form one), as they are
made to revolve on their axis,
will now constitute, in a man-
ner, a succession of levers, act-
ing through an indefinite dis-
tance according to the length
of the cords. The levers here
successively acting are of the
"fhst kind," and the axis of
the wheel is the fulcrum. This arrangement consti
tutes in substance the wheel and axle ; and its power.
Hke that of the simple lever, depends on the compara
tive velocity of the weight and the movmg force. If,
for example, the larger wheel is four times the circum
ference of the smaller, a force of one hundred applied
to the outer cord will raise a weight of four hundred
pounds.

The annexed figure exhibits at one view the pow-

Fig. 57.

Wheel and axle, showing the heavier weight foi
less motion.

er exerted through
the wheel and axle,
where a small weight
of 6 pounds will wind
up (or balance) oth-
er weights separate-
ly, weighing 8, 12,
or 24 pounds, as the
difference increases
between the size of

WHEEL AND AXLE. 77

the wheel and of the axle, according to the rule of vir-
tual velocities already explained.

The thickness of the rope has not been taken into
consideration. This is very small when compared with
the diameter of the outer wheel, but often considerable
when compared with that of the inner. To be strictly
accurate, therefore, the force must be considered as act-
ing at the centre of the rope ; hence the diameter of
the rope must be added to the diameter of the wheel.

There are various forms of the wheel and axle. In
the common windlass, motion is given to the axle by
means of a winch, which is a lever like the handle of
a grindstone. The windlass used in digging wells
has usually four projecting levers or arms. The wheel
used in steering a vessel is furnished with pins in the
circumference, to which the hand is applied m turning
it. In the capstan (for weighing anchor) the axis is
vertical, and horizontal levers are applied around it, so
that several men may work at once. The power of
all these forms is easily calculated by the rule of vir-
tual velocities — that is, that the velocity with which
the power moves is as many times greater than the ve-
locity of the weight, as the weight exceeds the power.
A simple and convenient rule for computing in num-
bers the power of wheel- work is the following : Multi-
ply all the numbers together which express either the
circumferences or diameters of the large wheels, and
then multiply together all the numbers which express
the diameters of the smaller wheels or pinions ; divide
the greater number by the lesser, and the quotient will
be the power sought.

78

MECHANICS.

MOLE PT.OW.

A good example of the power of the wheel and axle
is furnished in the English Mole Plow for draining
land {Fig. 58). It has a wooden beam, sheathed with

BAND AND COG WHEELS. 79

iron on the lower side, which moves close to the ground,
below which a thin, broad coulter extends downward,
and to the lower end of this coulter a sharp iron cyhn-
der is attached. This moves horizontally, point fore-
most, through the soil, producing a hollow channel be-
neath the plow for the escape of the water, the only
trace on the surface being a narrow sht left by the
coulter. It is dragged forward by means of a chain
and capstan worked by a horse, the machine itself be-
ing fixed with strong iron anchors. This mode of
draining is only adapted to clay soil, and is very cheap-
ly performed, but is now little used since the introduc-
tion of tile -draining. Foivler^s Draining- Ploiv, de-
scribed hereafter, is a great improvement on the mole
plow, and draws the tile-tubing into the channel as
fast as it is made, forming a perfect drain by one op-
eration.

BAND AND COG "WHEELS.

Where great power is required, several wheels and
axles may be combined in a manner corresponding
with that of the compound system of levers already
explained. In this case the axis of one wheel acts on
the circumference of the next, producing a continued
slower motion, and increasing the power in a corre-
sponding degree. The wheels
are made thus to act by means
of cogs or teeth, or of bands
{Fig. 59). In ordinary prac-
tice, however, combined wheels
are made use of to multiply
Combined cog-wheels. motion instead of to diminish

80

MECHANICS,

it, familiar instances of which occur in the grist-mill
and thrashing-machine.

In connecting a system of wheels, the cord or strap
may be used where great force is not required, the
friction round the circumference being sufficient to pre-
vent slipping. Bands are chiefly useful where motion
is to be transmitted to a distance ; as, for example,
from a horse-power without a barn to a thrashing-ma-
chine within it. Liability of sliding is sometimes use-
ful, by preventing the machinery from breaking when
a sudden obstruction occurs. Where the force is great,
the necessary tension or tightness of the cord produces
too great a friction at the axle. In such cases, cogs or
teeth must be resorted to.

The term teeth is usually applied when they are
formed of the same piece as the wheel, as in the case
of cast-iron wheels. Cogs are teeth formed separate-
ly and inserted into the wheel, as with wooden wheels.
Pinions are the small wheels, or, more properly, teeth
set on axles.

Fig. 60.

Form of cogs — a, bad/i/
formed; b, proper Jo:

FORM OF TEETH OR COGS.

The form of the teeth
has a great influence on
the amount of friction
among wheel- work. Bad-
ly-formed teeth are repre-
sented by the wheel- work
at a, in the annexed fig-
ure, consisting of square
projecting pins. Wlien
these teeth first come into

FORM OF TEETH OR COGS. 81

contact with each other, they act
and thus a part of their force is lost, and they continue
scraping together with a large amount of friction so
long as they remain in contact. These eifects are
avoided hy giving to them the curved form represented
by b. Here, instead of pressing each other obliquely,
they act at right angles, that is, not obhquely ; and in-
stead of scraping, they roll over each other with ease.
These curves are ascertained by mathematical calcu-
lation, which can not be here given ; it may be enough
to state that they should be so formed that the points
in contact shall always work at right angles to each
other. For ordinary practical purposes, however, they
Fig. 61. may be made as is

_ ^.- '/''■■--, i y''^\ "X— , shown in the annex-

/ "">( /K V" \ ed figure {Fig. 61),

! the teeth thus form-

Mode of giving the bestform to cogs. ed arc rcmoved, leav-

ing a blunt extremity, according to the figure.

There are a few other rules that should always be
observed in constructing wheel- work, in order that the
wheels may run easily together, without jerking or
ratthng, the most important of which are the follow-
ing:

1. The teeth must be of uniform size and distance
from each other, through the whole circumference of
the wheel.

2. Any tooth must begin to act at the same instant

D2

82 MECHANICS.

that the preceding tooth ceases to touch its correspond-
ing tooth on the other wheel.

3. There must he sufficient space hetween the teeth
not only to admit those of the other wheel, but to al-
low a certain degree of play, which should he equal to
at least one tenth of the thickness of the teeth.

4. The pinions should not he very small, unless the
wheels they act on are quite large. In a pinion that
has only eight teeth, each tooth begins to act before it
reaches the line of the centres, and it is not disengaged
as soon as the next one begins to act. A pinion of ten
teeth will not operate perfectly if working in a wheel
of less than 72 teeth. Pinions of less than six teeth
should never be used.

5. To give strength to the teeth of wheels, make the
wheels themselves thicker, which increases the breadth
of the teeth.

6. Wheel- work is often defective in consequence of
the relative number of teeth working together not be-
ing such as to equalize the wear of all alike. If the num-
ber of teeth on a wheel is divided without a remainder
by the number of the pinion, then the same teeth will
repeatedly engage each other, and they wdl often wear
unevenly. The number should be so arranged that
every tooth of the pinion may work in succession into
the teeth of the wheel. This is best effected by first
taking a number for the wheel that will be evenly di-
vided by the number on the pinion, and then adding
one more tooth to the wheel. This will effect a contin-
ual change, so that no two shall be engaged with each
other twice until all the rest have been gone through
with. This odd tooth is called the hunting-cog.

THE PULLEY.

83

Cog-wheels are most usually made with the teeth
on the outside or circumference of the wheel ; these
are termed spur-ivheeh. If the teeth are set on one
side of the wheels, they are termed crown-
wheels. When they are made so as to
work together obliquely, they are called
bevel-wheels, as in Fig. 62. vig. es.
Where the obliquity isi
Bevei-whe'eis. small, the motiou may be
communicated by means of the univer-
sal joint., as shown in Fig. 63. This is
commonly used in the thrashing-ma-
chine, where there is a slight change
in the direction of motion between the

horse-power and the tlirasher.

Universal joint.

SECTION" V.

Fig. 64.

THE PULLEY.

Let a cord fixed at one end pass round a movable
grooved wheel, and be grasped by the hand at the other
end ; then, in hfting any weight attach-
ed to the wheel, by drawing up the cord,
the hand will move with twice the ve-
locity of the weight. It will, therefore,
exert double the degree of force. This
operates precisely as a succession of le-
vers of the second kind, the fixed cord
being the fulcrum, and the cord drawn
up by the hand the power. It thus con-
stitutes one of the simplest kinds of the

Pulley doubling the ^^ -n- n t

force. pulley, l^lg. 64.

84

MECHANICS,

Fig. 65.

The wheel is called a sheave ; the term pulley is
applied to the block and sheave ; and a
combination of sheaves, blocks, and ropes
is called a tackle.

There are various combinations of sin-
gle pulleys for increasing powder, the most
common of which, and least liable to be-
come deranged by the cord being thrown
off the wheels, is shown in Fig. ^fi. In
this and in all similarly constructed pul-
leys, the weight is as many times great-
er than the power as the number of cords
which support the lower block. If there

be six cords, as in
the figure, the weight
will be six times the

Fig. 66.

^i^ljgiij/

Pulley of six-fold
power.

power.

Where a cord is
over a single fixed wheel,
as in Fig. 66, or over two or more
wheels, as in Fig. 67, no power is
gained, the moving force being the
same in velocity as the weight.
Such pulleys are sometimes, how-
ever, of use by altering the direc-
tion of the force. The latter is
applied with advantage to unload-
ing or pitching hay by means of a horse power, saving
much time and labor, as shown in Fig. 67. The head
of the fork {Fig. 68) is about 28 inches long, and is
fitted with steel prongs 20 inches long. The rope at-
tached at a passes over the pulley above, by which the

Pulley with no increase of

THE PULLEY.

85

Fig. 67

Pitching hay with horse-power.

fork, after being thrust into the hay, is lifted by the
strength of the horse workmg just without the barn
door. It is kept level by means of the rope, b, until the
fork is high enough to unload, when this rope is slack-
ened, and the hay deposited. The man on the mow
can give any direction to the hay he pleases while it
remains suspended. The horse is backed, and the op-
eration repeated. The arrangement is cheap, and with
it six tons have been pitched 20 feet high in an hour.
The usefulness of the pulley depends mainly upon
its Hghtness and portable form, and the facility with
which it may be made to operate in almost any situ-
ation. Hence it is much used in building, and is ex-
tensively applied in the rigging of ships. In the com-
putation of its power there is a large drawback, not
taken into account in the preceding calculation, which
materially lessens its advantage ; this is the friction of

86 MECHANICS.

the wheels and blocks and the stiffness of the cordage,
which are often so great that two tliirds of the power
is lost.

SECTION VI.
THE INCLINED PLANE.

The inclined plane or slope possesses a power which
is estimated by the proportion which its length bears
to the height. If, for example, the plane be twice as
long as the perpendicular height,
then in rolling the body, «, up
the inclined plane {Fig. 69), it
will move through twice the dis-
tance required to lift it directly
from b to c. Therefore only one half the strength else
required need be exerted for this purpose. The same
reasoning will apply to any other proportion between
the height and length ; that is, the more gradual or
less steep the slope becomes, the greater will be the
advantage gained. A familiar example occurs in lift-
ing a loaded barrel into a wagon : the longer the plank
used in rolling it, the less is the exertion needed.

A body, in rolling freely down an inclined plane, ac-
quires the same velocity that it would attain if dropped
perpendicularly from a height equal to the perpendic-
ular height of the plane. Thus, if an inclined plane
on a plank road be 100 yards long and 16 feet high, a
freely running wagon, left to descend of its own accord,
will move 32 feet per second by the time it reaches
the bottom, that being the velocity of a stone falling
16 feet. Or, a rail-car on an inclined plane 145 feet

ASCENT IN ROADS. 87

high will attain a speed of 96 feet per second, or more
than 65 miles an hour, at the foot of the plane, which
is equal to the velocity of a stone falhng three seconds,
or 145 feet.

ASCENT IN ROADS,

All roads not perfectly level may he regarded as in-
chned planes. By the application of the preceding
rule, we may discover precisely how much strength is
lost in drawing heavy wagons up hill. If the load
and wagon weigh a ton, and the road rise one foot in
height to every five feet of distance, then the increased
strength required to draw the load will be one fifth of
its weight, or equal to 400 pounds. If it rise only one
foot in twenty, then the increase in power needed to
ascend this plane will be only 100 pounds. The great
importance of preserving as nearly as practicable a per-
fect level is very obvious.

There are many roads made in this country, rising
over and descending hills, which might be made near-
ly level by deviating a little to the right or to the left.
Suppose, for example, that a road be required to con-
nect the two points a and b {Fig: 70), three miles

Fig. 70.

^^i^^^^^.A'n^if. ,,-i

apart, but separated by a lofty hill midway between
them, and one mile m diameter. Passing half a mile
on either side would entirely avoid the liill, and th&
road thus curved would be only one hundred and forty-

so MECHANICS.

eight yards, or one twelfth of a mile longer. The same
steep hill is ascended perhaps fifty to five hundred times
a year by a hmidred different farmers, expending an
amount of strength, in the aggregate, sufficient to ele-
vate ten thousand tons annually to this height, as a
calculation will at once show — more than enough for
all the increased expense of making the road level.

It is interesting and important to examine how
much further it is expedient to carry a road through
a circuitous level course than over a hiU. To ascer-
tain this point, we must take into view the resistance
occasioned by the rough surface or soft material of the
road. Roads vary greatly in this particular, but the
following may be considered as about a fair average.
In drawing a ton weight (including wagon) on freely
running wheels, on a perfect level, the strength exert-
ed will be found about equal to the following :

On a hard, smooth plank road 40 pounds.

On a good Macadam road 60 "

On a common good hard road 100 "

On a soft road about 200 "

Now let us compare this resistance to the resistance
of drawing up hill. First, for the plank road — forty
pounds is one fiftieth of a ton ; therefore a rise of one
foot in fifty of length will increase the draught equal
to the resistance of the road. Hence the road might
be increased fifty feet in length to avoid an ascent of
one foot ; or, at the same rate, it might be increased a
mile in length to avoid an ascent of one hundred and
five feet. But in this estimate the increase in cost of
making the longer road is not taken into account. If
making and keeping in repair be equal to three hund-

ASCENT IN ROADS. 89

red dollars yearly per mile, and one hundred teams
pass over it daily, at a cost for traveling of four' cents
each per mile, being four dollars daily, or twelve hund-
red dollars per annum, then the cost of making and re-
pair would be one quarter of the expense of travelmg
over it. Therefore the mile should be diminished one
quarter in length to make these two sources of expense
counterbalance each other. Hence a road with this
amount of travel should, with a reference to public ac-
commodation, be made three fourths of a mile longer
to avoid a hill of one hundred and five feet. This es-
timate applies to loaded teams only. For light car-
riages the advantages of the level road would not be
so great. One half to five eighths of a mile would,
therefore, be a fair estimate for all kinds of travehng
taken together.

The following table shows the rise in a mile of road
for different ascents :

For a rise of 1 foot in 10, the road ascends 528 feet per mile.

do.

do.

13,

do.

406

do.

do.

do.

15,

do.

352

do.

do.

do.

20,

do.

264

do.

do.

do.

25,

do.

211

do.

do.

do.

30,

do.

116

do.

do.

do.

35,

do.

151

do.

do.

do.

40,

do.

132

do.

do.

do.

45,

do.

117

do.

do.

do.

50,

do.

100

do.

do.

do.

100,

do.

53

do.

do.

do.

125,

do.

42

do.

The same kind of reasoning applied to a common
good road will show that it will be profitable for the
public to travel about half that distance to avoid a hill
of one hundred and five feet. In this case the whole

90 MECHANICS.

yearly cost of the road, including interest on the land,
and the cost of repairs, would not usually be more
than a tenth part of the same cost for plank, or would
not exceed thirty dollars.

On rail-roads, where the resistance is only about one
fifth part of the resistance of plank roads, the dispro-
portion between the draught on a level and up an as-
cent becomes many times greater. Thus, if a single
engine will move three hundred and fifty tons on a lev-
el, then two engines will be required for an ascent of
only twenty feet per mile, four engines for fifty feet per
mile, and six engines for eighty feet per mile.

Such estimates as these merit the attention of the
farmer in laying out his own private farm roads. It
may be worthy of considerable eflbrt to avoid a liill of
ten or twenty feet, which must be passed over a hund-
red times yearly with loads of manure, grain, hay, and
wood. The greatly-increased resistance of soft mate-
rials, also, is too rarely taken into account. A few
loads of gravel, well applied, would often prevent ten
times the labor in plowing through deep ruts, to say
nothing of the breaking of harness and wagons by the
excessive exertions of the team.

FORM AND MATERIALS FOR ROADS.

The depth of the mud in common roads is often un-
necessarily great, in consequence of heaping together
with the plow and scraper the soft top-soil for the raised
carriage-way. When heavy rains fall, this forms a
deep bed of mud, into which the wheels work their
way, and cause extreme labor to the team. A much
better way is to scrape off and cart away into the fields

FORM AND MATERIAL FOR ROADS. 91

adjoining all the soft, rich, upper surface, and then to
form the harder subsoil into a slightly-rounded car-
riage-way, with a ditch on each side. Such roads as
this have a very hard and firm foundation, and they
have heen found not to cut up into ruts, nor to form
much mud, even in the wettest seasons. On this hard
foundation six inches of gravel will endure longer and
form a hotter surface than twelve inches on a raised
" turnpike" of soft soil and nmd.

It frequently happens that the form of the surface
increases the quantity of mud in a road, by not allow-
ing the water to flow off freely. The earth is heaped
up in a high ridge, but having little slope on the top
{Fig-. 71), where the water lodges, and ruts are formed,

Fi£. 71.

Badly-formed road.

the only dry portions being on the brink of the ditches,
where the water can escape. Instead of this form,
there should be a gradual inclination from the centre
to the ditches, as shown in Fig. 72. This inclination

Fis. 72.

Well-formed road.

should not exceed 1 foot in 20. On hillsides the slope
should all be toward the higher ground, as in Fig. 73.

Fiff. 73.

Road for side-hill.

92 MECHANICS.

Hard and durable roads are made on the plan of
Telford. Their foundation is rounded stones^ placed
upright, with the smaller or sharp ends upward. The
smaller stones are placed near the sides, and the larger
at the centre, thus giving to the road a convex form.
The spaces are then filled in with small broken stone,
and the whole covered with the same material or with
gravel. The pressure of wagons crowds it compactly
between the stones, and forms a very hard mass.

IMPORTANCE OF GOOD ROADS.

The principles of road-making should be better un-
derstood by the community at large. Farmers are
deeply interested in good roads. Nearness to market,
and facilities for all other kinds of commmiication, are
worth a great deal, often materially affecting the price
of land and its products. The difference between trav-
elmg ten miles through deep mud, at two miles per
hour, with half a load, and traveling ten miles over a
fuie road, at five miles per hour, with a fuU load, should
not be forgotten.

" In the absence of such facilities," says Gillespie,
" the richest productions of nature waste on the spot
of their growth. The luxuriant crops of our Western
prairies are sometimes left to decay on the ground, be-
cause there are no rapid and easy means of conveying
them to market. The rich mines in the northern part
of the State of New York are comparatively valueless,
because the roads among the mountams are so few
and so bad, that the expense of the transportation of
the metal would exceed its value. So, too, in Spain
it has been known, after a succession of abundant har-

THE WEDGE. 93

vests, that the wheat has actually been allowed to rot,
because it would not repay the cost of carriage."
Again, "When the Spanish government required a
supply of grain to be transferred from Old Castile to
Madrid, 30,000 horses and mules were necessary for
the transportation of four hundred and eighty tons of
wheat. Upon a broken-stone road of the best sort, one
hundredth of that number could easily have done the
work." He further adds, in speaking of the improve-
ments in roads made by Marshal Wade in the Scottish
Highlands, " His military road is said to have done
more for the civilization of the Highlands than the
preceding efforts of all the British monarchs. But the
later roads, under the more scientific direction of Tel-
ford, produced a change in the state of the people wliich
is probably unparalleled in the history of any country
for the same space of time. Large crops of wheat now
cover former wastes ; farmers' houses and herds of cat-
tle are now seen where was previously a desert ; estates
have increased seven-fold in value and annual returns ;
and the country has been advanced at least one hund-
red years."

SECTION VII.
THE WEDGE.

The wedge is a double inclined plane, the power
.being apphed at the back to urge it forward. It be-
comes more and more powerful as it is made more
acute ; but, on account of the enormous amount of
friction, its exact power can not be very accurately es-
timated. It is nearly always urged by successive

94 MECHANICS.

blows of a heavy body, the momentum of which im-
parts to it great force.

All cutting and piercing instruments, as knives, scis-
sors, chisels, pins, needles, and awls, are wedges. The
degree of acuteness must be varied according to cir-
cumstances ; knives, for instance, which act merely by
pressure, may be made with a much sharper angle
than axes, which strike a severe blow. For cutting
very hard substances, as iron, the edge must be form-
ed with a still more obtuse angle.

The utility of the wedge depends on the friction of
its surfaces. In driving an iron wedge into a frozen
or icy stick of wood, as every chopper has observed, the
want of sufficient friction causes it immediately to re-
coil, unless it be previously heated in the fire. The
efficacy of naUs depends entirely on the friction against
their wedge-like faces.

THE SCREW.

The screw may be regarded as nothing more than
Fig- '74. an inclined plane winding round the surface
^^g^r^ of a cylinder {Fig: 74). This may be easily
understood by cutting a piece of paper in
such a form rig. 75.

that its edge,
a b {Fig. 75),
may represent
the inclined plane ; then, ''^-
beginning at the wider end, and wrapping it about the
cylindrical piece of wood, c, the upper edge of the pa-
per will represent the thread of the screw.

Although the friction attending the use of the screw

THE SCREW.

95

is considerable, and without it "it would not retain its
place, yet the slope of its inclined thread being so gi-ad-
ual, it possesses great power. This power is multiplied
to a still greater degree by the lever which is usually
employed to drive it, a {Fig. 76). If,
for example, a screw be ten inches in
circumference, and its threads half an
inch apart, it exerts a force twenty
times as great as the moving power.
If it be moved by a lever twenty
times as long as the diameter of the
screw, here is another increase of
twenty times in force. Multiplying
20 by 20 gives 400, the whole amount gained by this
combination, and by which a man applying one hund-
red pounds in force could exert a pressure equal to
twenty tons. About one tliird or
one fourth of this should, how-
ever, be deducted for friction.

When the screw is combined
with the wheel and axle {Fig-
ure 77), it is capable of exert-
ing great power, which may be
readily calculated by multiply-
^ , , ing the power of the screw and

Screw, lever, and wheel " ^

combined. ifg Icvcr luto the power of the

wheel and axle.

96

MECHANICS.

CHAPTER V.

APPLICATION OP MECHANICAL PRINCIPLES IN THE STRUC-
TURE OF THE PARTS OF IMPLEMENTS AND MACHINES.

In contriving the more difficult and complex ma-
chines, the principles of mechanics must be closely
studied, to give every part just that degree of strength
required, and to render their operation as perfect as pos-
sible. But in making the more common and simple
implements of the farmer, mere guess-work too often
becomes the only guide. Yet it is highly useful to ap-
ply scientific knowledge even in the shaping of a hoe-
handle or a plow-beam.

The simplest tool, if constantly used, should be form-
ed with a view to the best application of strength.
The laborer who makes with a common hoe two thou-
sand strokes an hour, should not wield a needless
ounce. If any part is heavier than necessary, even to
the amount of half an ounce only, he must repeatedly
and continually lift this half ounce, so that the whole
strength thus spent would be equal, in a day, to twelve
hundred and fifty pounds, which ought to be exerted
in stirring the soil and destroying weeds. Or, take
another instance : A farm wagon usually weighs near-
ly half a ton ; many might be reduced fifty pounds
in weight by proportioning every part exactly to the
strength required. How much, then, should we gain
here? Every farmer who drives a wagon with its

APPLICATION OF MECHANICAL PRINCIPLES, ETC. 97

needless fifty pounds, on an average of only five miles
a day, draws an unnecessary weight every year equal
to the conveyance of a heavy wagon-load to a distance
of forty miles.

Now a knowledge of mechanical science will often
enable the farmer, when he selects and buys his im-
plements, to judge correctly whether every part is prop-
erly adapted to the required strength. "We shall sup-
pose, for instance, that he intends to purchase a com-
mon pitchfork. He finds them differently formed, al-
though aU are made of the best materials. The han-
dles of some are of equal size throughout. Some are
smaller near the fork, as in Fig. 78, and others are

Fi-. 78.

, w

Badly-formed fork handle.

larger at the same place, as in Fig. 79. Now, if he

S^^

Badly -formed fork handle.

understands the principle of the lever, he knows that
both of these are wrongly made, for the right hand
placed at a is the fulcrum, where the greatest strength
is needed, and therefore the one represented by Fig. 80

Fig. 80.
r- a, „^^ ^

Well-formed fork handle.

is both stronger and Ughter than the others. Again,
hoe handles, not needing much strength,, chiefly re-
quire hghtness and convenience for grasping. Hence,
in selecting from two such as are represented in the
E

98 MECHANICS.

annexed figures, the one should be chosen which is
lightest near the blade, nearly all the motion being in
that direction, because the upper end is the centre of
motion. The right hand, at a, acting partly as the
fulcrum, the hoe handle should be slightly enlarged at
that place. Fig. 81 represents a well-formed handle,

Fig. 81.

r^T — ' —

CI

Well-formeA Iwe .

Fig". 82 a clumsy one. Rake handles should be made

O"

Fig.

P

Badly-formed hoe handle.

largest at the middle, or where the right hand presses.
Rake-heads should be much larger at the centre, and
tapering to the ends, where the stress is least, the two
parts operating as two distinct levers, acting from the
middle. Horse-rakes might be made considerably
lighter than they usually are by observing the same
principles. The greatest strength required for ploW'
beams is at the junction with the mould-board, and
the least near the forward end, or furthest from the ful-
crum or centre of motion.

Now it may be that the farmer who has had much
experience may be able to judge of all these things
without a knowledge of the science. But this scien-
tific knowledge would serve to strengthen his experi-
ence, and enable him to judge more accurately and
understandingly by showing him the reasons ; and in
many cases, where neiv implements were introduced,
he might be enabled to form a good judgment before

APPLICATION OF MECHANICAL PRINCIPLES, ETC.

99

he had incurred all the expense and losses of unsuc-
cessful trials.

Even so simple a form as that of an ox-yoke is often
made unnecessarily heavy. Fig. 83 represents one

Fig. 83.

that is faulty in this respect, by having heen cut from
a piece of timber as wide as the dotted lines a c, and
being thus weakened, it requires to be correspondingly
large. Fig: 84 is equally strong, much hghter, and is

Fig. 64.

easily made from a stick of timber only as wide as a b
in the former figure.

In the heavier machipes, it is necessary to know the
degree of taper in the different parts with accuracy.
A thorough knowledge of science is needed to calcu-
late this with precision, but a superficial idea may be
given by figures. • If a bar of wood, formed as in a
{Fig. 85, p. 100), be fixed in a wall of masonry, it will
possess as much strength to support a weight hung on
the end as if it were the same size throughout, as b.

100 MECHANICS.

Fig. 85.

'n:

~^^^

1

^5 ^ ^

The first is equally strong with the second, and much
lighter.* The same form doubled must be given if
the bar is supported at the middle, with a weight at
each end, or with the weight at the middle, supported
at each end, as c. This form, therefore, is a proper
one for many parts of implements, as the bars of whip-
pie trees, the rounds of ladders, string-pieces of bridges,
and any cross-beams for supporting weights. One
half of this form, as a, is the proper form for rake-
teeth, wheel-barrow handles, spade handles, &o. On
fence-posts, the pressure being nearly alike on all parts,
they should be nearly in the form of a wedge. There-
fore a post of equal size throughout contains nearly
twice as much timber as is needed for strength only.

The form of these parts must, however, be modified
to suit circumstances ; as whipple-trees must be large
enough at the ends to receive the iron hooks, wagon-

* The simple style of this work precludes an explanation of the
mode of calculation for determining the exact form. Where the
stick tapers only on one side, it is a common parabola ; if on all
sides, a cubic parabola.

APPLICATION OF MECHANICAL PRINCIPLES, ETC. 101

tongues for ironing at the end, and spade handles for
the easy grasp of the hand.

The axle-trees of wagons must he made not only-
strong in the middle, or at centre of pressure, hut also
at the entrance of the hub ; because the wheels, when
thrown sideways in a rut, or on a sideling road, operate
as levers at that point, a and h {Fig. 86), show the
manner in which the axles of carts may be rendered
lighter without lessening the strength, a being the
common form, and b the improved one.

Fig. 86.

Sometimes several forces act at once on different
parts. For example, the spokes of wagon- wheels re-
quire strength at the hub for stiffening the wheel ; they
must be strong m the middle to prevent bending, and
large enough at the outer ends, where they are soonest
weakened by decay. Hence there should be nearly a
uniform taper, slightly larger at the middle, and with
an enlargement at the outer end, as c {Fig. 86).

A very useful rule in practice, in giving strength to
structures, is this : the strength of every square beam
or stick to support a weight increases exactly as the
width increases, and also exactly as the square of the
depth increases. For example, a stick of timber eight

lOS MECHANICS.

inches wide and four inches deep (that is, four inches
thick), is exactly twice as strong as another only four
inches wide, and with the same depth. It is twice as
wide, and consequently twice as strong ; that is, its
strength increases just as the width increases, accord-
ing to the rule given. But where one stick of timber is
twice as deep^ the width heing the same, it is, four times
stronger ; if three times as deep, it is nine times strong-
er, and so on. Its strength increases as the square of
the depth, as already stated. The same rule will show
that a board an inch thick and twelve inches wide will
be twelve times as strong when edgewise as when lying
flat. Hence the increase in strength given to whipple-
trees, fence-posts, joists, rafters, and string-pieces to
farm-bridges, by making them narrow and deep.

Again, the strength of a round stick increases as the
cube of the diameter increases ; that is, a round piece
of wood three inches in diameter is eight times as
strong as one an inch and a half in diameter, and twen-
ty-seven times as strong as one an inch in diameter.
This rule shows that a fork handle an inch and a half
in diameter at the middle is as much stronger than
one an inch and a quarter in diameter, as seven is
greater than four. Now this rule would enable the
farmer to ascertain this without breaking half a dozen
fork handles in trying the experiment, and it would
enable the manufacturer to know, without the labor of
trying many experiments, that if he makes a fork han-
dle an mch and a half at the middle, tapering a quar-
ter of an inch toward the ends, it will enable the work-
man to lift with it nearly twice as much hay as with
one an inch and a quarter only through its whole length.

ROLLING FRICTION,

CHAPTER VI.

103

SECTION I.

The ' subject of friction has been postponed, or has
been merely alluded to, in treating heretofore of ma-
chines, to prevent the confusion of considering too many-
things at once. As it has often an important influence
on the action of machines, it is worthy of careful in-
vestigation.

It is famihar to most persons, that when two sur-
faces slide over each other while pressing together, the
minute unevenness or roughness of their surfaces causes
some obstruction, and more or less force is required.
This resistance is known as friction.

ROLLING FRICTION.

The term is also apphed to the resistance of one body
rolling over another. This may be observed in various
degrees by rolling an ivory ball successively over a car-
pet, a smooth floor, and a sheet of ice ; the same force
which would impel it only a few feet on the carpet,
would cause it to move as many yards on a bare floor,
and a still greater distance on the ice. The two ex-
tremes may be seen by the force required to draw a
carriage on a deep sandy or loose-gravel road, and on
a rail-road.

104 MECHANICS.

NATURE OF FRICTION.

If two stiff bristle brushes be pressed with their faces
together, they become mutually interlocked, so that it
will be quite difficult to give them a shding motion.
This may be considered as an extreme case of friction,
and serves to show its nature. In two pieces of coarse,
rough sandstone, or of rouglily-sawed wood, asperities
interlock in the same way, but less in degree ; a di-
minished force is consequently required in moving the
two surfaces against each other. On smoothly-planed
wood the friction is still less ; and on poUshed glass,
where the unevenness can not be detected without the
aid of a powerful magnifying glass, it is reduced still
further in degree.

ESTIMATING THE AMOUNT OF FRICTION.

In order to determine the exact amount of friction
between different substances, the following simple and
ingenious contrivance is adopted : an inclmed plane,
a b {Fig: 87), is so formed that it may be raised to any

Fig. 87.

desired height by means of the arc of a circle and a
screw. Lay a flat surface of the substance we wish
to examine upon this inclined plane, and another small-

ESTIMATING THE AMOUNT OF FRICTION. 106

er piece or block of the same substance upon this
surface ; then raise the plane until it becomes just
steep enough for the block to slide down by its weight.
Now, by measuring the degree of slope, we know at
once the amoimt of friction. Suppose, for example, the
two surfaces be smoothly-planed wood : it will be found
that the plane must be elevated about half as high as
its length ; therefore we know, by the properties of the
inchned plane, heretofore explained, that it requires a
force equal to one half the weight of the wooden block
to slide it over a smooth wooden surface. Some kinds
of wood have more firiction than others, but this is about
the average.

From the result of this experiment we may learn
that to shde any object of wood across a floor requires
an amount of strength equal to one half the weight of
the object. A heavy box, for instance, weighing two
hundred pounds, can not be moved without a force
equal to one hundred pounds. It also shows the im-
propriety of placing a heavy load upon a sled in winter
for crossing a bare wooden bridge or a dry barn floor,
the friction between cast-iron sleigh-shoes and rough
sanded plank being nearly equal to one third of the
whole weight.* Hence a load of one ton (including
the sled) would require a draught equal to more than
six hundred pounds, which is too much for an ordina-
ry single team. On bare unfrozen ground the friction
would be still greater. On a plank bridge, with run-
ners wholly of wood, it would be equal to half the load.
All these facts may be readily proved by actually

* On clean hard wood, with polished metallic shoes, the friction
would be much less, or a fourth, or fifth.

105 MECHANICS.

placing the sled on slopes of plank and of earth, and
hy observing the degree of steepness required for slid-
ing down by its own weight.

In a similar way, we are enabled easily to ascertain
the force required to draw a wagon upon any kind of
level surface. Suppose, for example, that we wish to
determine the precise amount of force for a wagon
weigliing, with its load, one ton, on a plank road. Se-
lect some slight descent, where the wagon will barely
run with its own weight. Ascertain by a level just
what the degree of descent is ; then divide the weight
of the wagon by the degree of the slope, and we shall
have the force sought for. To make this rule plainer
by an example : it will be found that a good, newly-
laid plank track, if it possess a descent of only one foot
in fifty feet distance, will be sufficient to give motion
to an easy-running wagon ; therefore we know that
the strength required to draw it on a level will be only
one fiftieth part of a ton, or forty pounds.

The resistance offered to the motion of a wagon by
a Macadam road, by a common dry road, and by one
with six inches of mud, may be readily determined in
the same way by selecting proper slopes for the exper-
iment. If by such trials as these the farmer ascer-
tains the fact that a few inches of mud are sufficient
to retard his wagon so much that it will not run of its
own weight down a slope of one foot in four (and few
common roads are ever steeper), then he may know
that a force equal to one fourth the whole weight of
his wagon and load will be required to draw it on a
level over a similar road — that is, the enormous force
of five hundred pounds will be needed for one ton, of

RESULTS WITH THE DYNAMOMETER.

107

which many wagons will constitute nearly one half.
Hence he can not fail to see the great importance, for
the sake of economy, and humanity to his team, of pro-
viding roads, whether public or private, of the hardest
and best materials.

SECTION II.

RESULTS WITH THE DYNAMOMETER.

Another mode of determining the resistance of roads
is by means of the Dynamometer* It resembles a
spring-balance, and one end is fastened to the wagon
and the other end connected with the horses. The
force applied is measured on a graduated scale, in the
same way that the weight of any substance is meas-
ured with the spring-balance. A more particular
description of this instrument will be given hereafter.

Careful experiments have been made with the dyna-
mometer to ascertain accurately the resistance of va-
rious kinds of roads. The following are some of the
results :

On a new gravel road, a horse will draw eight times
as much as the force applied ; that is, if he exerts a
force equal to one hundred and twenty-five pounds, he
will draw half a ton on such a road, including the
weight of the wagon, the road being perfectly level.

On a common road of sand and gravel, sixteen times
as much, or one ton.

On the best hard-earth road, twenty-five times as
much, or one and a half tons.

On a common broken-stone road, twenty-five to thir-

* From two Greek words, dunamis, power, and metreo, to measure.

108 MECHANI(5S.

ty-six times as much, or one and a half to two and a
quarter tons.

On the best broken-stone road, fifty to sixty-seven
times as much, or three to four tons.

On a common plank-road, clean, fifty times as much,
or three tons.

On a common plank -road, covered thinly with sand
or earth, thirty to tliirty-five times as much, or about
two tons.

On the smoothest oak plank-road, seventy to one
hundred times as much, or four and a half to six tons.

On a highly-finished stone track-way, one hundred
and seventy times as much, or ten and a half tons.

On the best rail-road, two hundred and eighty times
as much, or seventeen and a half tons.

The firmness of surface given to a broken-stone road
by a paved foundation was found to lessen the resist-
ance about one thhd.

On a broken-stone road it was found that a horse
could draw only about two thirds as much when it was
moist or dusty as when dry and smooth ; and when
muddy, not one half as much. When the mud was
thick, only about one quarter as much.

The character of the vehicle has an influence on the
draught. Thus, a cart, a part of the load of which is
supported by the horse, usually requires only about
two thirds the force of hori2ontal draught needed for
wagons and carriages. On rough roads the resistance
is slightly diminished by springs.

On soft roads, as earth, sand, or gravel, the number
of pounds draught is but little affected by the speed ;
that is, the resistance is no greater in driving on a trot

WIDTH OP WHEELS. 109

than on a walk ; but on hard roads it becomes greater
as the velocity increases. Thus a carriage on a dry
pavement requires one half greater force when the
horses are on a trot than on a walk ; but on a muddy
road the difference between the two rates of speed is
only about one sixth. On a rail-road, where a draught
of ten pounds will draw a ton ten miles an hour, the
resistance increases so much at a high degree of speed
as to require a force of fifty pounds per ton at sixty
miles an hour — that is, it would require five times as
much actual power to draw a train one hundred miles
at the latter rate as at the former ; but as the speed
is six times as great, the actual force during a given
time would be five times six, or thirty times as great.

WIDTH OF WHEELS.

Wheels with wide tire run more easily than narrow
tire, on soft roads ; on hard, smooth roads, there is no
sensible difference. Wide tire is most advantageous
on gravel and new broken-stone roads, both by causing
the vehicles to run more easily, and by improving the
surface. For the latter reason, the New York turnpike
law allows six-inch wheels to pass at half price, and
twelve-inch wheels to pass free of toll. Wheels with
broad tire on a farm would pass over clods, and not
sink between them ; or would only press the surface
of new meadows, without cutting the turf. But where
the ground becomes muddy, the mud closes on both
sides of the rim, and loads the wheels. On clayey
soils, narrow tire unfits the roads for broad wheels.
For these reasons, broad wheels are decidedly objection-
able for clayey or soft soils, and they are chiefly to be

110 MECHANICS,

recommended for broken-stone roads, and gravelly, or
dry, sandy localities. They are also much the best for
the wheels of sowing or drilling machines, which only
pass over mellowed surfaces.

The larger the wheels are made, the more easily they
run ; thus a wheel six feet in diameter meets with only
half the resistance of a wheel three feet in diameter.

A flat piece of wood, sliding on one of its broad sur-
faces, is subject to the same amount of friction as when
shding upon its edge. Hence the friction is the same,
provided the pressure be the same, whether the surface
be small or large.* Or, in other words, if the surfaces
are the same, a double pressure produces a double
amount of friction ; a triple pressure, a triple amount,
and so on.

A narrow sleigh-shoe usually runs with least force,
for two reasons : first, its forward part cuts with less re-
sistance through the snow ; and, secondly, less force is
required to pack the narrow track of snow beneath it.
The only instance in which a wide sleigh-shoe would be
best, is where a crust exists that would bear it up, and
through which a narrow one would cut and sink down.

Friction is entirely independent of velocity ; that is,
if a force of ten pounds is required to turn a carriage
wheel, this force will be ten pounds, whether the car-
riage is driven one or five miles per hour. Of course,
it will require five times as much force to draw five

* Generall}' speaking, this is very nearly correct ; but when the
pressure is ielense, the friction is slightly less on the smaller sur-
face.

FRICTION AT THE AXLE.

Ill

miles per hour, because five times the distance is gone
over ; but, measured by a dynamometer or spring-bal-
ance, the pressure would be the same. In precisely
the same way, the weight of a stone remains the same,
whether lifted slowly or quickly by a lever. If the
friction of the wheels of a wagon on their axles be
equal to ten pounds, driving the horse fast or slowly
will not increase or diminish it. But fast driving will
require more strength, for the same reason that a man
would need more strength to carry a bag of wheat up
two flights of stairs than one, in one minute of time.

FRICTION AT THE AXLE.

A carriage wheel, or any other wheel revolving on an
axle, will run more easily as the axle is made smaller.
This is not owing to the rubbing surfaces being less in
size, as some mistakenly suppose, for it has just been
shown that this makes very Uttle or no difference, pro-
vided the pressure is the same ; but it is owing to the

leverage of the wheel
on the friction at the
axis ; and the smaller
the axle, the greater
is this leverage ; for,
if the axle, a {Fig-
ure 88), be six inches
in circumference, and
the wheel, 6 c, be ten
feet in circumference,
then the outer part of
the wheel will move
twenty times further than the part next the axle.

112 MECHANICS.

Therefore, according to the rule of virtual velocities,
one ounce of force at the rim of the wheel will over-
come twenty ounces of friction at the axle ; or if the
axle were twice as large, then, according to the same
rule, it would requu-e two ounces to overcome the same
friction acting between larger surfaces.

For this reason, large wheels in wheel-work for mul-
tiplying motion, if not made too heavy, run with less
force than smaller ones, the power acting upon a larger
lever. Horse-powers for thrashing-machines, consist-
ing chiefly of a large, light crown-wheel, well stiffened
by brace-work, have been found to run with remarka-
ble ease ; a good example of which exists in what is
known as Talpin's horse-power, when made in the
best manner.

FRICTION-WHEELS.

On the preceding principle, friction-wheels or fric-
tion-rollers are constructed, for lessening as much as
possible the friction of axles in certain
cases. By this contrivance, the axle, a
{Fig. 89), instead of revolving in a sim-
ple hole or cavity, rests on or between
Friction-wheels. ^^^ ^^^^^ ^f ^^^^ ^^^iey: whccls. As the

axle revolves, the edges turn with it, and the rubbing
of surfaces is only at the axles of these two wheels.
If, therefore, these axles be twenty times smaller than
the wheels, the friction will be only one twentieth the
amount without them. This contrivance has been
strongly recommended and considerably used for the
cranks of grindstones {Fig. 90), but it was not found
to answer the intended purpose so well as was expect-

LUBRICATING SUBSTANCES.

113

Fig. 90.

Grindstone on Friction-wheels.

ed, for the very
plain reason that,
in using a grind-
stone, nearly all
the friction is
at the circumfer-
ence, or between
the stone and the
tool, which fric-
tion-wheels could

not, of course, remove.

SECTION III.

LUBRICATING SUBSTANCES.

LuBRiCATiNa substances, as oil, lard, and tallow, ap-
phed to rubbing surfaces, greatly lessen the amount of
friction, partly by filling the minute cavities, and partly
by separating the surfaces. In ordinary cases, or where
the machinery is simple, those substances are best for
this purpose which keep their places best. Finely-
powdered black-lead, mixed with lard, is for this reason
better for greasing carriage wheels than some other ap-
pUcations. Drying oils, as linseed, soon become stiff
by drying, and are of little service. Olive oil, on the
contrary, and some animal oils, which scarcely dry at
all, are generally preferred. To obtain the full benefit
of oil, the application must be frequent.

According to the experunents made with great care
by Morin, at Paris, the friction of wooden surfaces on
wooden surfaces is from one quarter to one half the
force applied ; and the friction of metals on metals, one

114 MECHANICS.

fifth to one seventh — varying in both cases with the
kinds used. Wood on v^ood was diminished by lard
to about one fifth to one seventh of what it was before ;
and the friction of metal on metal was diminished to
about half what it was before ; that is, the friction be-
came about the same in both cases after the lard was
apphed.

To lessen the friction of wooden surfaces, lard is bet-
ter than tallow by about one eighth or one seventh ;
and tallow is better than dry soap about as two is to
one. For iron on wood, tallow is better than dry soap
about as five is to two. For cast iron on cast iron,
polished, the friction with the different lubricating sub-
stances is as follows :

Water 31

, Soap 20

Tallow 10

Lard 1

Olive oil 6

Lard and black-lead 5

When bronze rubs on wrought iron, the fi-iction with
lard and black-lead is rather more than with tallow,
and about one fifth more than with olive oil. With
steel on bronze, the friction with tallow and with olive
oil is about one seventh less than with lard and black-
lead.

As a general rule, there is least friction with lard
when hard wood rubs on hard wood ; with oil, when
metal rubs on wood, or metal on metal — being about
the same in each of all these instances.

In simple cases, as with carts and wagons, where
the friction at the axle is but a small portion of the re-

ADVANTAGES OF FRICTION. 115

sistance,* a slight variation in the effects in the lubri-
cating substance is of less importance than retaining
its place. In more complex machinery, as horse-pow-
ers for thrashing-machines, friction becomes a very
large item, unless the parts are kept well lubricated
with the best materials.

Leather and hemp bands, when used on drums for
wheel-work, should possess as much friction as possi-
ble, to prevent slipping, thus avoiding the necessity of
tightening them so much as to increase the friction of
the axles. Wood with a rough surface has one half
more friction than when worn smooth ; hence moisten-
ing and rasping small drums may be useful. Facing
with buff leather or with coarse thick cloth also ac-
complishes a useful purpose. It often happens that
wetting or oiling bands will prevent slipping, by keep-
ing their surfaces soft, and causing them to fit more
closely the rough surface of the drum.

ADVANTAGES OF FRICTION.

Although friction is often a serious inconvenience, or
loss, in lessening the force of machines, there are many
instances in which it performs important offices in na-
ture and in works of art. " Were there no friction, all
bodies on the surface of the earth would be clashing
against each other ; rivers would dash with an un-
bounded velocity, and we should see little besides col-

* If the friction at the axle be one twelfth of the force, and the
diameter of the wheels ten times as great as the diameter of the axle,
the friction at the axles will be reduced to one twelfth of a tenth, or
one hundred and twentieth part of the force, according to the law
of virtual velocities as applied to the wheel and axle.

116 MECHANICS.

lision and motion. At present, whenever a "body ac-
quires a great velocity, it soon loses it by friction
against the surface of the earth. The friction of water
against the surfaces it runs over soon reduces the rap-
id torrent to a gentle stream ; the fury of the tempest
is lessened by the friction of the air on the face of the
earth, and the violence of the ocean is subdued by the
attrition of its own waters.

" Its offices in the works of art are equally import-
ant. Our garments owe their strength to friction, and
the strength of ropes depends on the same cause ; for
they are made of short fibres pressed together by twist-
ing, causing a sufficient degree of friction to prevent
the sliding of the fibres. Without friction, the short
fibres of cotton could never have been made into such
an infinite variety of forms as they have received from
the hands of ingenious workmen."* Deprived of this
retaining force, the parts of stone walls, piles of wood
and lumber, and the loads of carts and wagons, as well
as the wheels themselves, would slide without restraint,
as if their surfaces were of the most icy smootliness,
and walking without support would be impossible.

The tractive power of locomotives depends on the
friction between the wheels and iron rails, which is
equal to about one fifth of the weight of the engine ;
that is, a locomotive weighing twenty-five tons will
draw with a force of five tons, without producing slip-
ping of the wheels.

* Eneyclopsedia Americana.

PRINCIPLES OF DRAUGHT. 117

SECTION IV.

PRINCIPLES OF DRAUGHT.

An examination of the nature or laws of friction en-
ables us to ascertain the best line of draught for teams
when attached to wagons and carriages. If there were
no friction whatever upon the road, the best direction
for the traces would be parallel to the road, that is, on a
level with the wagon ; but as there is always some fric-
tion, the line of draught should be a Uttle rising, so as
to tend to lessen the pressure of the wheels on the road.
Now this upward direction of the draught should al-
ways he exactly of such a slope, that if the same slope
were given to the road, the wagon would just descend
by its iveight. The more rough or muddy the road is,
the steeper should be this line of draught or direction
of the traces.* On a good common road it would be
much less, and on a plank road but slightly varied
from a hori2ontal direction. On a rail-road the line
should be about level. On good sleighing, some of the
strength of the team is commonly lost by too steep a
Une of draught.

The reason of this rule may be understood by the
following explanation: Let the ob-
struction, a, in the annexed figure
{Fig. 91), represent the friction the
wheel constantly meets with in roll-
ing over a common road. To over-
come this friction, the wheel must

* Provided the wheels are not made smaller for this purpose, in-
creasing their resistance.

118 MECHANICS.

rise in the direction of the dotted line. Therefore, if
the force is made to pull in this direction, it will act
more advantageously than in any other, because this
is the course in which the centre of the wheel must
move. Now if a downward slope were given to the
road at this obstruction, the wheel and the obstruction
would be brought both on a level, and the wheel would
move with the slightest degree of force.

It will be understood from the preceding rule that a
sled ruiming on bare ground should be drawn by traces
bearing upward in a large degree. The same remark
will apply to the plow, which slides upon the ground
in a similar way, with the pressure of the turning sod
as a load. Hence the reason that a great saving of
strength results from the use of short traces in plowing.
An experiment was tried for the purpose of testing this
reasoning ; first, with traces of such length that the
horses' shoulders were about ten feet from the point of
the plow ; and secondly, with the distance increased to
about fifteen feet. With the short traces a strength
was required equal to 2| cwt., but with the long traces
it amounted to 3^ cwt.

But the draught-traces may be made too short.
When this is the case, the plow is necessarily thrown
too much upon its point to keep it from flying out of
the ground, by which means it works badly in turning
the furrow. In addition to this evil, the plowman is
compelled to bear down heavily, adding to the friction
of the sole on the bottom of the furrow, and greatly in-
creasing his labor.

The line of draught should be so adjustsd that the
plow may press equally all along on its sole or bottom,

PRINCIPLES OF DRAUGHT.

119

which will cause it to run evenly and with a steady mo-
tion. This end will be effected by giving the traces or
draught-chain just such a length that the share of the
plow (or centre of resistance), the clevis, and the point
of draught at the horses' shoulders (or the ring of the
ox-yoke) shall all form a straight line. This is shown
in the annexed figure, where A is the place of the ox-
ring or of the for-
A^.-' ward extremity of
the traces {Figure
92).

The centre of re-
sistance will vary with the depth of plowing. When
the furrow is shallow (as shown by the lines G H, Fig.
93), the centre of resistance will be at A, requiring the

Fig. 93.

Fig. 92.

Line of draught for the plow.

team to be fastened to the lower side of the clevis, C ;
but when the depth is greater (as shown by F H), the
centre of resistance will be at B, requiring a higher at-
tachment to the clevis; the point of draught, E, re-
maining the same in both cases.

So great is the difference between an awkward and
skillful adjustment of the draught to the plow, that
some workmen with a poor instrument have succeeded
better than others with the best ; and plows of second
quality have sometimes, for this reason, been preferred
to those of the most perfect construction.

120 MECHANICS.

COMBINED DRAUGHT OF ANIMALS.

AVTien several animals are combined together, it is
of great importance that they should be exactly match-
ed in gait. Much force is often wasted when they
draw unsteadily or unevenly. It is more difficult to
divide the draught equally among several animals when
placed one before the other, or ad tandem^ than when
arrayed abreast, for some may hang back, and others
do more than their share, unless a skillful driver is
always on the watch. It also happens, when thus
arranged, that the forward horses draw horizontally,
while the hindmost one draws in a sloping line, and
the line of draught between them thus being crooked,
more or less force is lost. This may be, however, rem-
edied in part by placing the taller animals forward, and
the smaller behind.

For these reasons, when only three horses are used,
they should always be placed abreast. The force re-
quired for each may be rendered exactly equal by the
whipple-trees usually employed for this purpose, and
represented in Fig. 94, where two horses are attached

Fig. 94.

Whipple-tree for three horses.

to the shorter end, and the third to the longer end of
the common bar. Another ingenious but more com-
plex arrangement is shown by Fig-. 95, where also the
central horse has only half the two others, by being

PRINCIPLES OF DRAUGHT.

121

Whipple-trec for three horses.

attached to the longer ends of the intermediate bars.
Fig. 96 represents the mode of attaching four horses in
draught, their force being equalized by passing the

Fig. 96.

Whipple-tree for four horses.

chain round the wheel in the pulley-block, a, security
being provided that the hindmost pair shall not en-
croach on the forward pair, by connecting the end of
the chain at the same time to the plow.
F

122 MECHANICS.

SECTION V.
CONSTRUCTION AND USE OF THE DYNAMOMETER.

The dynamometer, or force-measurer, has been al-
ready briefly alluded to, but a more particular descrip-
tion will be useful. In the construction and selection
of all machines and implements that require much
power in their use, the dynamometer is indispensable,
although at present but little known. As an example
of its utility, the farmer may wish to choose between
two plows which, so far as he can perceive, may do
their work equally well ; but this instrument, when
applied, may show that the team miist draw with a
force equal to 400 pounds in moving one of them
through the soil, while 300 pounds would be sufficient
for the other. He would, therefore, select the one of
easiest draught, and by doing so would save the labor
of one day in four to his team, or twenty-five days in
a hundred, which would be worth many times the cost
of the trial. The same advantage might be derived
in the selection of harrows, cultivators, horse-rakes,
straw-cutters, and all other implements drawn by
horses or worked by men. Again, the farmer may be
in doubt in choosing between two thrashing-machines,
which in other respects may work equally fast and
well; but the dynamometer may show that one re-
quires a severer exertion fi:om the team, and conse-
quently is less valuable for use.

The operation of this instrument may be readily un-
derstood by Figure 97, where b represents the dyna-
mometer, made precisely similar to a large and stiff

CONSTRUCTION AND USE OF THE DYNAMOMETER.

123

Fig. 97.

Dynamometer, or Force-measurer.

spring balance, with one hook attached to the plow
and the other to the whipple-tree. The amount of
force required to draw the plow is accurately meas-
ured on the scale by the index or pointer, a.

Sometimes the motion of this index is multiphed,or
made greater and more easily seen, by means of a cog-
wheel and rack-work ; but this renders the instrument,
at the same time, more complex.

Another form of this instrument is shown in Fi^. 98,

Ellipt

where the ends of the oval spring, Q, Q,, are attached
to the plow and draught. The harder the force exert-
ed by the team, the closer together will the sides of
this spring be brought, causing the rod, E, to press
against the index or pointer, and showing the precise
degree of force on the circular scale.

124

MECHANICS.

An improvement, by rendering the instrument more
compact, is shown in Fig. 99, where S S is the spring,
and directly over it is the graduated scale.

Fig. 99.

Elliptic Dynamometer, in compact form : S S, spring ; F, cross-lever for moving
index.

An inconvenience occurs in the use of the instru-
ments now described from the rapid vibration of the
index, resulting from the quick changes in the force,
partly from inequahties in the soil, and partly from the
unsteady motion of the horses. The vibration is some-
times so great that the index can be hardly seen, ren-
dering it difficult to measure the average force. This
inconvenience has been removed, in a great degree, by
attaching to one end of the index, E {Fig: 99), a pis-
ton working in a cylinder filled with oil, G ; this piston
has a small hole through it, through which the oil pass-

SELF-RECORDING DYNAMOMETER.

125

es from one side to the other as the draught varies, but
not fast enough to allow any sudden motion.

SELF-RECORDING DYNAMOMETER.

A less simple but more perfect instrument is the Self-
recording Dynamometer, which marks accurately all
the vibrations on a sHp of paper while the plow is in
operation. A pencil is fixed to the index, and presses,
by means of a spring, against the paper, thus giving a
true register of the force exerted. To prevent the pen-
cil from constantly marking on the same line, the pa-
per is made to move slowly in a side direction, so that
all the vibrations are shown, as represented in Fig. 100,

«r — *:^sSSr Motion (^/^aper ,^J

300

; ^ 280

,..- r\ . ^:

1 ^,'-1 n:

1, '^

ll,!:: :;.i,.J:^

220

i;i A ii

■' '•...''ir^''iii 1

200

'liViIrl!!)!,:.'!

1

ffln

!!.|lii'illlil

ii^m

ll

|ii^

■140

120

1

100

80

60

40

20

The markings of the Self-recording Dynamometer.

and they may be accurately examined and read off at
leisure, a and b representing the forces of two different
plows, drawn through a single furrow across the field.
The motion of the paper is effected by being placed on
two rollers, one of which unwinds it from the other.

126 MECHANICS.

This roller is made to turn by means of a wheel run-
ning on the ground, which gives motion to the roller
through an endless chain, working a cog-wheel by
means of an endless screw. The cylindrical dynamom-
eter, shown in Fig. 101, is used for this purnose, length-
Fig. 101. wise upon which the two
rollers are placed for hold-
ing the paper. With this in-
strument a permanent reg-
ister might be made of the
Self-recording Dynamometer. forcc required for different
plows, the accuracy of which none could dispute.

DYNAMOMETER FOR ROTARY MOTION.

All these dynamometers apply only to simple, on-
ward draught, as in plowing, drawing wagons, harrow-
ing, &c. There is another, represented in Fig. 102, of
very ingenious but complex construction, which shows
the force required in working any rotary machine, such
as thrashers, straw-cutters, and mills, and showing,- at
the same time, the velocity, and recording the number
of revolutions made.

The whole machine is supported by a cast-iron frame-
work, on four small wheels with flanges, like the
wheels of rail-cars, that it may be conveniently run up
on a temporary rail-way to the thrashing or other ma-
chine to be tried.

The band- wheel, /, on the shaft, e, is connected with
the machine under trial, and the force is supposed, in
this instance, to be applied by hand to the handle, a,
on the fly-wheel.

"When the fly-wheel is turned in the direction shown

DYNAMOMETER FOR ROTARY MOTION. IZ /

by the arrow, it causes the two cog-wheels to levolve,

Dynamometer for measuring the force and velocity of thrashing-machines.

and moves the band in the direction shown by the oth-
er arrow. Now, whatever force is required to turn the
wheel,/, connected with the machine under trial, must
be overcome by a corresponding force applied to the
handle, a, because the wheel-work is so adjusted that
this handle moves with the same velocity as the band
on the band- wheels.

The wheel, /, being connected by the band to the
wheel, d, which is on the same axis or shaft as the cog-
wheel, /, the resistance of the machine under trial tends
to keep the cog-wheel, /, from turning, until enough
force is apphed to the handle, a, to set the cog-wheel,
k, in motion. Now the greater the resistance, the
greater will be the power needed at the handle. This

128 MECHANICS.

power, therefore, is measured accurately in the follow-
ing manner :

The axle, g; of the cog-wheel, /, rests at its further
end in an oblong hole or mortise, that allows it liberty
to play, or rattle up and down within narrow limits.
This same axle, g, passes through a hole in the lever,
i, so that when it rattles up and down, it carries this
lever up and down with it. The other part of the lev-
er turns on the shaft, h, of the other cog-wheel.

Now when the man at the fly-wheel applies his
force to the handle, a, the resistance of the machine
under trial causes the cog-wheel, /, to refuse to turn ;
consequently, his force, instead of turning it, hfts it up
in the mortise, and raises the lever with it. As he in-
creases his force against the handle, let weights be
hung on the lever, until, at the very moment that the
wheel begins to revolve, the weights shall be just heavy
enough to keep the lever down in the mortise. This
weight, therefore, will measure the exact force need-
ed to turn the machine : the greater the resistance of
the machine, the greater must be the weight.

There is another weight, J, used to balance the
lever and cog-wheel, /, while the machine is at rest, or
before the force is applied to it, so that the weight at
m shall represent the force truly. The weight, m, is,
of course, to be multipUed by the power it exerts on
the lever, i, which should be graduated like the bar of
a steelyard.

There are a few other parts of this dynamometer not
yet described. One is the cyHnder, o, filled with oil,
in which a perforated piston works, preventing the
rapid vibration of the lever, i, as the force varies, pre-

DYNAMOMETER FOR ROTARY MOTION. 129

cisely similar to the cylinder of oil described in Fig.
99. Another part is the pendulum, j9, with the wheel,
r, which measures the time.

The use of this instrument has been already attend-
ed with some important results in detecting the great
amount of friction existing in some thrashing-machines
of high reputation, which has been found to amount,
in certain cases, to more than one half of the whole
power applied. It is only by detecting so great a
waste that we are enabled to take measures for its
prevention.

F2

130 MECHANICS.

CHAPTER VII.

CONSTRUCTION AND USE OF FARM IMPLEMENTS AND MA-
CHINES.

SECTION I.

The application of meclianical principles in the
structure of the simpler parts of implements and ma-
chines has been treated of in a former part of this
work. It remains to examine more particularly those
machines chiefly important to the farmer, and to show
the application of these principles in their use and op-
eration.

PLOWS AND PLOWING.

One great difference between good and had plows is
in the form of the mould-hoard. To understand the
best form, it must be observed that the slice is first cut
by the forward edge, and then one side is gradually
raised until it is turned completely over, or bottom side
up. To do this, the mould-board must combine the
two properties of the wedge and the screw.

The position of the furrow-slice, from the time it is
first cut till completely inverted, may be represented
by placing a leather strap flat upon a table, and then,
while holding one end, turning over the other, so as
to bring that also flat upon the table, as in Fi^. 103.
Now the mould-board should have just such a shape
as will fit the furrow-slice while in the act of turning

PLOWS AND PLOWING.

131

over, else it will wear unequally, become clogged with
soil where the earth rubs slightly, and require greater
strength in the team. By examining, it will be found
that, although the strap {Fig. 103) twists like a screw.

Fig. 103.

yet all parts wiU be straight if measured across at right
angles, as shown by the dotted lines. Therefore, by
applying this principle, the farmer can judge of one im-
portant quality in selecting a plow. If, for example,
he finds that a straight-edged stick will be flat upon
Fig. 104. the face at right angles to the

line of motion, as shown by the
dotted lines in Fig. 104, the
mould-board will be so far
right ; but if the straight edge
must be placed in other posi-
tions, as in Fig. 105, it is de-
fective in form. A mould-
board may be much modified,
with this principle pre^^erved in every instance ; that is,
it may be short, so as to raise the earth abruptly, or it
may be long, so as to raise it gradually; it may be
adapted to a deep furrow, lifting the furrow-slice to a
considerable height, or to a shallow one, tin-owing it
quickly over. These modifications are required for dif-
ferent soils and for different purposes. When, for ex-
ample, it is desired to break up the slice and pulverize
a heavy soil, the twist must be short and abrupt ; when
a sod in hght soil is to be inverted smoothly, the mould-
board must be longer, and the twist more gradual. In

132

MECHANICS.

all mould-lDoards, care must be taken that the soil is
not lifted so abruptly as to throw it forward, instead of
simply turning it over.

Another defect in some plows is too blunt or thick a
wedge formed by the share and mould-
board. By the plow represented in
Fig. 106, the earth must be thrown
from the land-side into the furrow
with a velocity about equal to the
motion of the team; but by the
one shown by Fig. 107, the team
moves twice as fast as the earth is
thrown by this longer wedge. C on-
sequently, according to the rule of virtual velocities
(aheady explained), as applied to the wedge, there is
a great gain in power. Care must be taken, how-
ever, not to make this wedge too long, else the friction
of a greater length of sod may overbalance the advant-
age.

An attention to such principles as these has result-
ed in an extraordinary improvement within the past
thirty years. Plows are made with one third the for-
mer cost, that will do more than twice as much work
with the same strength of team, and do it so much
better, that larger crops may be reaped from the same
land. These advantages are so great, that on all the
arable land of the Union there must be a yearly sav-
ing of ten millions of dollars in the work of teams, one
million in the price of plows, and millions of bushels
in the aggregate increase of crops by good tillage. In
the two annexed figures we have a representation of
an old and an improved plow.

PLOWS AND PLOWING. 133

Fig. 108 is such a plow as is now used in some

parts of Grermany.

Fig. 109 is one of the hest im-

Fig. 109.

proved cast plows. Nearly as great a difference ex-
ists between the plows used here fifty years ago and
at the present time. Some portion of this great im-
provement may have heen effected by persons not fa-
miliar with science ; but if such persons were enabled
to achieve so much, with the few truths which they
had themselves laboriously discovered, how much more
they might have accomplished if they had enjoyed the
advantages of all that strong-minded men have discov-
ered during the course of ages, and wliich is collected
together in the form of modern science. How much
more, too, would be saved in time and tedious exper-
iments, by applying the principles of science already

134 MECHANICS.

discovered, than by ascertaining what we wish to know
only by long-repeated trials.

TRENCH AND SUBSOIL PLOWING.

When the common two-horse plow alone is used by
farmers, it pulverizes the soil only a few inches in
depth, and its own weight, and the tread of the horses
on the bottom of the furrow, gradually form a hard
crust at that depth, through which the roots of plants
and the moisture of rains do not easily penetrate.
Hence the roots have only a few inches of good soil on
the surface of the earth for their support and nourish-
ment ; and when heavy rains fall, the shallow bed of
mellow earth is soaked and injured by surplus water.
Again, in time of drought, this shallow bed of moist-
ure is soon evaporated, and the plants suffer in conse-
quence.

But, on the other hand, when the soil is made deep,
it absorbs, Uke a sponge, all the rains that fall, and
gradually gives off the moisture as it is wanted dur-
ing hot and dry seasons. For this reason, deep soils
are not so easily injured by excessive wetness, or by ex-
treme drought, as shallow ones. In addition to this
advantage, they allow a deeper range for the roots in
search of nourishment.

Soils are deepened by trench-plowing and by suh-
soiling. By trench-plowing, the common plow with
a mould-board is made to enter the earth to an unu-
sual depth, and to throw up a portion of the subsoil,
covering with it the top-soil which is thrown under.
A subsoil plow, on the contrary, only loosens the sub-
soil, but does not lift it to the surface.

THE DOUBLE MOULD-BOARD TRENCH-PLOW. 135

"When a mixture of the subsoil with the surface tends
to render the whole richer, trench-plowing is best ; hut
when the subsoil is of a more sterile character, it should
be only loosened with the subsoil plow, and more cau-
tiously intermixed with the richer portion above.

It often happens that the subsoil plow is very use-
ful in loosening the soil for the purpose of allowing the
trench-plow to run more freely through it.

THE DOUBLE MOULD-BOARD TRENCH-PLOW.

This plow, sometimes called the Michigan Double
Ploio, is represented in Fis:. 110. It has two mould-

boards on one beam. The forward or small one pares
off the surface or sod, and throws it into the previous
furrow, usually to a depth of three to five inches. The
larger one follows closely, lifting the under-soil upon
the top, and in sward land completely burying the sod
with the mellow earth from below. This is the best
implement for trench-plowing yet introduced into prac-
tice, and with double the ordinary amount of team,
will cut to a depth of nine to twelve inches.

136

MECHANICS.

THE SUBSOIL PLOW,

represented in Fig. Ill , consists of a narrow, horizon-

Fig. 111.

Subsoil plow.

tal, wedge-like share for loosening the earth, and con-
nected with the beam by a strong plate of metal run-
ning edgewise, so as to cause little resistance through
the soil. This plow follows in the furrow after a com-
mon plow, loosenmg but not lifting out the earth. The
operation is shown in Fig. 112. The benefit of sub-

Subsoil plowing in the furrow of a common plow.

soiling will last three or four years ; but it is of gi-eat
importance that land be well underdrained, for if the
earth becomes heavily soaked with water, it settles
down into one compact mass, and the advantages of
the operation are lost.

fowler's draining plow.

The mole-plow, for forming a small hollow passage
beneath the soil, by means of a sharp iron plug forced
through it at the lower end of a thin coulter, has been

fowler's draining plow. 139

already described. A great improvement has "been
made in this machine by the invention of the Draining
ploiv, Fig. 113, opposite, which not only forms a hole
through the subsoil, but fits into it at the same ope-
ration earthen pipe or tubular tile, forming at once a
perfect and durable under-drain. The pieces of tile or
pipe, which are about a foot long, are strung on a rope,
as shown m the foreground of the engraving. This
rope is attached to the back end of the iron plug, and
is drawn forward through the earth as the plug ad-
vances, thus fitting the hole with tile as fast as it is
formed. The only trace left on the surface of the earth
is a narrow sht made by the coulter, an invisible drain
being formed beneath it.

The frame-work to which the coulter and plug are
attached is drawn forward by an iron rope (made of
twisted wire) wound upon a windlass or capstan work-
ed by horses. Drains forty rods long are completed at
one operation. A short piece of ditch is fu'st dug for
the admission of the plug, and strings of pipe, each fifty
feet long, are successively added, and when done the
whole of the rope is withdrawn.

When the surface of the ground is uneven, an in-
genious contrivance preserves a straight and uniform
slope to the drain. The coulter is w^orked up or down
by the man who stands on the frame, by means of a
wheel and screw, his eye being guided by a try-sight
on the frame, and a cross-staff at the end of the field,
set so as to give a proper slope. This machine, when
tried in England, has been found to accomplish the
work of draining with less than one half the ordinary
expense.

140 MECHANICS.

THE PARING PLOW

consists merely of a flat blade, which runs beneath the
surface, shaving off the roots, but not moving the soil
{Fig". 114). It is used in cutting turf for burning,

Fig. 114.

and for destroying thistles and other deep-rooted weeds.
When made light for a single horse, it is sometimes
used advantageously for cutting the grass and weeds
between rows of corn. A two-horse paring plow has
been lately constructed, in which the depth of cutting
is accurately regulated by wheels placed on an axle
like those of a cart. The cast-iron blade, which cuts
about three feet wide, is raised or depressed by means
of screws passing through the axle. Its chief utility
is in destroying grass and weeds before the sowing of
broadcast crops.

THE GANG PLOW

consists of three or four small mould-boards placed side
by side {Fig. 115), and is used for shallow plowing, or
burying manure or seed on inverted sod, without dis-
turbing the turf beneath. In those of the best con-
struction, the depth is regulated by wheels, and the
breadth of the furrows by turning the cross-beam more

THE HARROW.

Fis. 115

141

Gang plow.

or less obliquely, by means of a fixed contrivance for
this purpose.

SECTION II.

PULVERIZERS.

The fine pulverization of the soil, for the ready ex-
tension of the fine roots of plants, and for the thorough
intermixture of manure, is of great importance to the
farmer. It is but partially accompHshed by the plow,
which crumbles the soil only so far as may be done by

the act of turning it over,

Fi?. no.

Scotch or square harrow.

Hence additional imple-
ments are needed for this
purpose, among which are
the harrow, the cultiva-
tor, and the clod-crusher.

THE harrow

The common form of
the harrow is represented
by Fig. 116, which con-
sists of two parts hung

142

MECHANICS.

together by hinges, so as to hend and fit an uneven
surface of land, and to he folded for carrying in a cart
or wagon. The dottted lines show the track of each
tooth. The Geddes Harrow, rep-
resented in Fig. 117, is supe-
rior to the square harrow on ac-
count of its drawing more stead-
ily from a centre, and its wedge-
form frame passing more freely
past any unusual obstruction.
To prevent the central part from
being lifted by the ^^'e-^ in-
draught, the draught-
Geddes Harrow. chaiu is fastcucd to the (j;-///j I K^\i

side-beams, as in Fig. 118. ''''' hi >"''

The teeth of harrows are often made too large and
too few in number. Small and very numerous teeth
pulverize the soil more finely and rapidly. They
should be so placed that the corners, like wedges,
and not the sides, may cut the soil in their onward
progress ; and if the forward half of the teeth were
made sharp and flat, similar to the coulter of a plow,
they would not only run more easUy, but cut and pul-
verize clods more efficiently. This form of the teeth
would admit of the use of cast-iron, which would be
cheap and durable.

The Norwegian Harrow., Fig. 119, is a new ma-
chine for pulverizing the soil, which performs the work
in a very perfect manner, by turning up instead of
packing down the earth. Two rows of star-shaped
tines play into each other, and produce a complete self-

CULTIVATORS.
Fig. 119.

143

Nonvegian Harrow, kept from clogging- hy two cylinders of teeth
playing into each other.

cleaning action, preventing clogging even in quite ad-
hesive soils.

CULTIVATORS.

The cultivator is used for loosening and pulverizing
the soil, and for cutting and destroying weeds. The
usual form is represented in Fi^. 120, v^^here the wheel

Common Cultivator.

in front regulates the depth of the teeth. The width
is altered by expanding or contracting the. two outer
beams.

Various sorts of teeth are used, according to the na-
ture of the work, and they are made of steel or cast-

144

MECHANICS.

iron. The cast-iron teeth, represented in Fig. 120,
are well adapted for cultivating the rows of Indian
corn and other hoed crops, where the soil is aheady
moderately mellow. For harder soils, the teeth should
he in the form of claws, as shown in Fig. 121, their

Fig. 121

Claw-toothed cultivator for hard ground.

sharp, wedge-form points penetrating and loosening the
earth with comparative ease. A very efficient culti-
vator is made by using hoth kinds of teeth in the same
implement, placing the claws forward for breaking the
hard earth, and the broader teeth behind for stirring it.
Steel plates, with sharp or " duck-feet" edges screw-
ed at the lower extremities of the teeih. Fig. 122, are

Fig. 122,

useful for paring, or cutting the roots of weeds ; and
formed like the mould-board of a plow, they are some-
times used for throwing the mellow earth toward the
row, or, when reversed, from it.

In all cases, the teeth should be so long and the
frame-work high enough above ground to allow room

CLOD-CRUSHERS.

145

for the weeds to gather and fall off, even when the
teeth are deepest in and the land the foulest.

Two-horse cultivators are very useful in pulverizing
the surface of inverted sod, and fitting it for the recep-
tion of seed. They run on wheels, and an apparatus
is attached for lowering or raising the frame-work and
regulating the depth of the teeth.

GarretVs Horse-hoe, an English invention, is a mod-
ification of the cultivator, and is used for cultivating
carrots and other root-crops in drills, cleaning eight or
ten rows at once. It is furnished with sharp horizon-
tal hlades, which run heneath the surface, and shave
off" and destroy all the weeds within an inch of the
rows of young plants. These rows, having been planted
by means of a drilling-machine, are straight and per-
fectly parallel, and the operator has only to watch one
row and guide the blades for that row, the apparatus
being so contrived that the blades for the other rows
shall run at the same distance from them.

Fi^. 123 represents an end view of this implement.

Fig. 123.

rJt's Horse-hoe — E7id view.

G

146 MECHANICS.

It exhibits the apparatus by which the length of the
axle is altered to suit all kinds of planting ; by which
each hoe is kept independent of the others, so as to suit
the inequalities of the ground, and by which they can
be set any width, from seven inches to thirty. It
shows the oblique angle at which they run — this obliq-
uity being easily altered to any desired degree : this is
effected by a movement of the upper handle represent-
ed in the figure. By the lower handle the whole is
accurately guided. It is said that two men, one to lead
the horse, and the other to guide the implement, will
dress ten acres of root-crops in a single day, and that it
has proved eminently a labor-saving machine.

CLOD-CRUSHERS.

In clayey soils, clods are often formed in abundance
during the process of cultivation. These become very
hard in dry weather, and prevent the proper extension
of the fine roots of plants in search of nourishment, and
also the intermixture of manure with the soil, without
which it has been found that two thirds or even three
fourths of the value of manure is lost to growing crops.

Different modes of pulverizing the clods have been
adopted. The simplest is the " drag-roller,'^'' repre-
sented in Fig. 124. It is made of a log or portion of

Fig. 124.

Clod-crusher.

a hollow tree, into which a common two-horse wagon

CLOD-CRUSHERS.

147

tongue has been fitted, by which it is dragged over
the ground without rollmg, gi-inding to powder, in
its progress, every clod over which it passes. The
greater the diameter of the log, the less will be the lia-
bility of its clogging by gathering the clods before it.
It may also be made of a half log with the round side
downward. Fig. 125 represents a similar implement

Fig. 125.

One-horse Clod-crusher.

for one horse, and is used for working between the
rows of corn in cloddy ground.

The use of these simple implements, by reducing
rough fields to a condition as mellow as ashes, has in
some instances been the means of doubhng the crop.
It is necessary that the soil be dry when they are used,
to prevent its packing together.

CrosskilVs Clod-crusher is a more powerful and

Fig. 126.

Cross/' ill's ''lod-rtiislifr

148

MECHANICS.

more costly implement {Fig. 126). It consists of
about two dozen circular cast-iron disks, placed loosely
upon an axle, so as to revolve separately. Their outer
circumference is formed into teeth, w^liioh crush and
grind up the clods as they roll over the surface of the
field. Every alternate disk has a larger hole for the
axle, which causes it to rise and fall while turning
over, and thus prevent the disks from clogging. It
can be used only when the ground is dry.

SECTION III.
SOWING-MACHINES.

Sowing-machines, for wheat and other grains, pos-
sess great advantages over hand-sowing. All the seed
being deposited by them at nearly a uniform depth,
and completely covered with earth, it vegetates and
grows evenly, and the plants are uniformly strong and
vigorous. A less quantity of seed is required, and the
crop is heavier.

Small seeds, such as carrots and turnips, can be
sown evenly and rapidly only by means of drills adapt-
ed to these seeds, and hence drilling-machines are in-
dispensable in the cultivation of such root-crops.

A great number of different drills have been made
for sowing grain, the general principles of which can
be only noticed in this treatise. The seed is delivered
by means of a revolving cylinder, in the surface of
which small regular cavities have been made, which
constantly carry off and drop measured portions of the
grain. The motion of this cylinder is increased or less-
ened by means of wheel- work, according to the quan-

Grain-drillms Machine.

SOWING-MACHINES.

151

tity of seed to be sown. As soon as the seed drops
from the revolving cyUnder, it falls down either through
a hollow coulter, or through a tube which opens just
behind a coulter, into the bottom of the furrow, and is
immediately buried by the earth falhng back upon it
after the coulter has passed.

Drills for sowing small seeds are usually furnished
with a spindle having circular brushes, which press
the bottom of the hopper, and force the seed through
small holes made for its escape.

For planting corn, beans, and other crops cultivated
in drills and hills, the machines are so regulated as to
drop either in hills or in uniform rows, and they do
the work more evenly than when performed by hand.
The coulters or tubes for depositing the seed should,
in all machines of this kind, be made sharp and not
rounded on the forward part, that the draught may be
easier.

A simple grain-drill is represented in operation by
Fig. 127, and one of more finished construction by
Pig. 128, showing the cog-wheel gearing for regulat-
ing the quantity of seed, and the chains for lifting up
the discharging tubes from the ground when not in use.

A very simple
machine for sow-
ing grass, as well
as other small
seed, by hand, is
shown in the an-
nexed figure. It
consists of a light
trough, contain-

Fig. 129.

152 MECHANICS.

ing the seed, which is distributed through holes in the
zinc bottom by the vibrations of a notched rod, and
any desired quantity of seed accurately regulated.

HORSE-RAKES.

In all labor-saving contrivances, the greatest advant-
age is gained where the work originally performed by
the hand is light, or where much exertion of strength
is not required. An example of this kind occurs in the
use of hand-drills for sowing small seeds, such as tur-
nips and carrots. These, when planted by the unas-
sisted hand, require but little power, but the operation
is very slow. A hand-drill enables the laborer to apply
his whole strength profitably, with an increase in ef-
fect of at least forty or fifty times. A similar advant-
age is gained by the use of the horse-rake, where the
full strength of a horse is made to accomplish the
moderate labor of the hand-rake, and to perform an
amount equal to at least ten men. With the simplest
form of the horse-rake, sixteen acres of heavy hay have
been collected by one horse in a day, and with the re-
volving-rake, twenty to twenty-five acres.

The simplest form of the horse-rake is represented in
Fig. 130. It is made of a piece of strong scantling
three inches square, tapering slightly toward the ends,
for the purpose of combining strength with lightness,
and in which are set horizontally about fifteen teeth,
twenty-two inches long, and an inch by an inch and
three fourths at the place of insertion, tapering on the
under side, with a shght upward turn at the points, to
prevent their running into the ground. The two outer
teeth should be cut off to about one third their first

HORSE-RAKES.

Fig. 130.

153

Simple Horse-rake.

length, and draught-ropes attached. If they are too
short, the teeth will be hard to guide ; if too long, the
rake is unloaded with difficulty. Handles serve to
guide the teeth, to Uffc the rake from the ground in
avoiding ohstructions, and to empty the accumulated
hay.

In using this rake, the teeth, instead of moving on
their points as in the common hand-rake, run flat upon
the ground, passing under and collecting the hay.
When full, the horse is stopped, the handles thrown for-
ward, the rake emptied and lifted over the winrow thus
formed. The winrows are made at right angles to the
path of the rake, as each load is deposited opposite the
last heap formed in previously crossing the meadow.
A few hours' practice enables any one to use this rake
without difficulty ; the only skiU required is to keep the
teeth under the hay and above the ground. When
small obstructions occur, the handles are depressed, and
the points of the teeth rise and pass freely. Over large
obstructions, the rake must be lifted. By shortening
the teeth, it may be used on the roughest ground.

In addition to raking, this implement may be em-
G2

154

MECHANICS.

ployed for sweeping the hay from the winrow and
drawing it to the stack. It is also useful for cleaning
up the scattered hay from the meadow at the close of
the work, for raking grain-stubble, and for pulling and
gathering peas.

Its cliief advantages over other horse-rakes are its
simplicity, cheapness, and little liability to get out of
order — adapting it to small farms — and its superior
fitness for uneven surfaces. If made of the toughest
wood, and with the proper taper in the main parts for
Hghtness and strength, according to the principles al-
ready pointed out in a previous chapter, it is easily
lifted, and its use not attended with severe labor.

The Revolving Horse-rake, Fig. 131, is similar in

Fig.

Revolving Horse-rake.

its mode of operation, possessing, however, the great
advantage of unloading without lifting the rake or stop-
ping the horse. It has a double row of teeth, pointing
each way, wliich are brought alternately into use as
the rake makes a semi-revolution at each forming win-
row in its onward progress. They are kept flat upon
the ground by the pressure of the square frame on their
points beneath the handles ; but as soon as a load of
hay has collected, the handles are slightly raised, throw-

HORSE-RAKES. 155

ing this frame backward off the points, and raising
them enough for the forward row to catch the earth.
The continued motion of the horse causes the teeth to
rise and revolve, tlirowing the backward teeth fore-
most over the winrow. In this way each set of teeth J
are alternately brought into operation. J^

The cost of the revolving rake, well made, is about ^
four times that of the simple horse-rake, but on large
meadows it possesses the superior advantages of expe-
dition and ease in working.

The Spring-tooth Horse-rake, Fig-. 132, has been

Spring-tooth Horse-rake.

much used, and has proved a valuable implement. The
teeth are made of stiff, elastic wire, on the points of
which the rake runs, and not on the flat sides, as in the
two already described. They bend in passing an ob-
struction, and spring back again to their place. This
rake is unloaded by simply lifting the handles, which
is easUy done, the rake being light, and about one half
the weight being sustained by the horse. It is pecu-

156 MECHANICS.

liarly adapted to raking stubble, its upright teeth pre-
venting the collection of portions of the soU with the
straw.

All horse-rakes used on meadows are not only use-
ful by the immediate saving of labor, but sometimes
still more so by the expedition with which a crop of
well-dried hay may be rescued from an approaching
storm.

MOWING AND REAPING MACHINES.

The cutting part of all the best mowers and reapers

Fig. 1 33. made at the present day

^i^^^Ml^,^;^^;^^ consists of a serrated

blade, as shown at a

^ A A A _f\_J\_ (-^^■^- 133)' ^^i^^ P^««-

I— —I _ gg through narrow slits

in each of the fingers shown in 6, forming, when thus
united, the cutting apparatus, as exhibited in the an-
nexed figure of KetcJmm's Mowing-machine {Fig.
134). "When the machine is used, the motion of the

Fig. 134.

Ketchum's Mowing-machine.

wheel on which the machine runs is multiplied by
means of the cog-wheels, imparting quick vibrations

MOAVING AND REAPING MACHINES.

157

endwise to this blade, shearing off the grass smoothly
as it advances through the meadow, like a large num-
ber of scissors in exceedingly rapid motion. Fig. 135

Fig. 135.

Back view of Ketchum^s Mower m operation.

represents Ketchum's mower in operation as seen from
behind, cutting an even swath five feet wide as fast as
the horses advance.

In the mowing-machine the cutting apparatus is
narrow, causing the newly-cut grass to fall evenly be-
hind it, covering the whole surface of the ground. The
reaping-machine is similar in construction, Avith the
addition of a platform for holding the grain as it falls,
as shown in the figure oiHussey^s Reaper {Fig. 136).

Hussey's Reaping-machine.

158 MECHANICS.

As the straw collects on this platform, it is raked off
in successive bunches for binding by a man who rides
on the machine for this purpose.

Most reaping-machines are provided with a revolv-
ing reel, which strikes backward against the standing
grain, holds it there while the blade is cutting, and
throws it backward on the platform. This reel is dis-
tinctly shown in the representation {Fig. 137) oiMan-

Fig. 137.

Manny's Mowing and Reaping Machine, showing the reel distinctly.

np^s Mowing and Reaping Machine, where the cut-
ting blade is placed midway between the forward and
back wheels.

Mowing machines require but one man for their
management, who merely drives the horses that draw
it. Reapers, as usually made, require another man be-
sides the driver, to rake off the bunches of cut grain,
which is severe labor. Various self-raking contriv-
ances have been tried to obviate this labor, one of the
most ingenious and best of which is Atkins' Self-raker,
represented by Fig. 138, and sometimes called the
Automaton Raker. An ingenious piece of mechanism
causes the rake to sweep the platform, and presses the
fallen grain against another rake, when both of them,
with the bundle of grain firmly inclosed, swing round
behind, and then open wide, and drop it on the ground
ready for binding. It may be so regulated as to drop

THE KNEE-JOINT POWER.

Fig. 138.

159

Atkmb Automaton Reaper in operation

the bunches more frequently where the crop is heavy,
or more remotely where it is light.

SECTION IV.

THE KNEE-JOINT POWER APPLIED TO MACHINES.

The knee-joint or toggle-joint is usually regarded
Fig. 130. as a compound lever, and consists of two
rods cormected hy a tm-ning joint, as rep-
resented in Fig. 139. The outer end of
one of the levers is fixed to a soUd beam,
and the other connected with a movable
block. When the joint a is forced in the''
direction indicated by the arrow, it pro-
Knee-jomt power, duces a powcrful prcssurc upon the mov-
able block, which increases as the lever approaches a
straight hne. This is easily understood by the rule of
virtual velocities, for the force moves with a velocity
many times greater than the power given to the block,
and this relative difference increases as the joint is
made straighter.

This power is made use of in the lever printing-press,
where the greatest force is given just as the pressure
is completed. Another example occurs in the Lever

160

MECHANICS.

Washing-machine {Fig. 140), which is worked by
the alternating motion of the handle, A, pressing a
swinging-board, perforated with holes, with great force

Fig. 140.

Lever Washing-machine.

against the clothes next to one side of the water-
box. Like the printing-press, this machine exerts the
greatest power just as the motion of the lever is
completed, and at the time it is most needed. The
same principle is exhibited in KendalVs Cheese-press
[Fig. 141), where the lever and the wheel-and-axle
are corribined with the two knee-joints, one on each
side of the press, drawing down a cross-beam upon the
cheese with a greatly multiplied power. Fmer'ifs
Hay-press., for compressing hay into bales for distant
conveyance, is another example {Fig. 142). The hay
is thrown into a space in a strong box by opening the
top doors, and when trodden down, the doors are closed
and secured by buttoning down the cross-bars. Horse-

THE KNEE-JOINT POWER.

Fig 141

161

Emery s Hay press

power is then applied to chains, which draw down the

162 MECHANICS.

raised levers, operating on a knee-joint, and compress-
ing the hay into a small and compact mass, the great-
est force being given when most needed, at the termi-
nation of the pressure. Side-doors are then thrown
open, and the hay secured by bands and taken out.
Two hundred and fifty pounds of hay may be thus re-
duced to a space of sixteen cubic feet, or a little more
than half a cubic yard, by a single horse ; and several
tons may be pressed in a day. Dederick's improve-
ment in this press consists in placing the levers at one
end only, compressing the hay into the other end, and
thus simplifying the machine. Double levers, press-
ing equally against the upper and lower part of the
slide or piston, keep it always upright and even, al-
though the hay may be unequally compact. These
double levers are connected and kept parallel by con-
necting hinged bars.

The power exerted by a rolling-mill, where bars of
iron are flattened in their passage between two strong
roUers, is precisely like that of the knee-joint. The
only difference is, that the rollers, which may be con-
sidered as a constant succession of levers coming into
play as they revolve, are both
fixed, and consequently the
bar has to yield between them
[Figure 143). The greatest
power is exerted just as the
bar receives the last pressure
from the rollers. The most
, ^ , , . . . , powerful and rapidly-workina:

Principle of the knee-jomt m the ^ i ./ o

roiiing-miii. straw-cuttcrs are those which

draw the straw or hay between two rollers, one of

THE KNEE-JOINT POWER.

163

which is furnished with knives set around it parallel
with its axis, and cutting on the other, which is cover-
ed with untanned ox-hide {Fig. 144). The only de-

Fig 146.

feet in this machine is its inability to cut shorter than
one inch in length, which is not sufficient for corn-
stalks and other coarse fodder.

Dick's Cheese-press {Fig: 145,
on the following page) operates on
a similar principle. Figure 146
shows the structure of its working
part, the dotted lines indicating the
position of the lever, which is in-
serted into a roller or axle, and, by
turning, drives the movable iron
blocks asunder, and raises the
cheese against the broad screw-
head above, as shown in Fig. 145. In Fig. 146, the
raised lever shows that the blocks are at first near to-
gether, but are crowded asunder as the lever is press-
ed downward. This cheese-press is made of cast-iron,

164

MECHANICS.
Fig. 145.

Dick's cast-iron Cheese-press.

and has great power ; to try it, weights were increased
upon the lever, until the iron frame broke with a force
equal to sixteen tons.

ENDLESS-CHAIN POWERS.

A convenient and compact machine for applying ani-
mal power is by means of the endless chain, working
in the position of an inclined plane, as represented in
the annexed cut {Fig: 147), where the weight of a
large dog is used for driving a churn-dasher. The
platform on which the animal stands is formed of strips
of light wood riveted to two India-rubber straps, and
their constant downward motion turns the fly-wheel,
to which a rod is attached for working the dasher.

ENDLESS-CHAIN POWERS. 165

Fig. 147.

Chv,rn worked by dog-power.

The same principle has been lately adopted with
great success in the application of horse-power to driv-
ing thrashing-machines, sawing wood, and to various
other purposes. Instead of India-rubber straps, strong
cast-iron chains are used, which are made to run
smoothly and with very little friction over a succession
of small iron wheels, which support the weight of the
horses on the moving platform {Fig. 148, on the fol-
lowing page).

The power of these, machines, and the amount of
friction in running them, may be easily ascertained by
the rule, already given in a former part of this work,
for determining the power of the inclined plane ; for
the only difference between the endless-chain and a
common inclined plane is, that in one the plane is
fixed, and the body moves up its surface, and in the
other the plane itself moves downward, and the weight
or animal upon it remains stationary. The same prin-

166

MECHANICS.

ciple applies in both
cases.

First, to ascertain
the friction, let the
platform he placed on
^ a level, with the horse
I upon it ; then gradual-
f ly raise the end until
I theweight of the horse
I will just give it mo-
r„ tion. This will show
I the precise amount of
c the friction ; for if the
I. end he elevated one
I twentieth of its length,
I then the friction is one
X twentieth the weight
I of the horse and plat-
^ form.

Secondly, to deter-
mine the power, when
the end is still further
raised, measure the
difference between the
height thus given and the length of the platform. If,
for instance, the height of the inclination is one eighth
of its length, and the horse is found to weigh eight
hundred pounds, then the power is one hundred pounds,
or one eighth the weight of the horse.

This rule will not, however, apply, when the draught
of the horse is added to its weight ; for it usually hap-
pens that the weight alone is not sufficient, without

APPLICATION OF LABOR. 167

placing the platform in too steep a position for a horse
to work comfortably. He is therefore attached to a
whipple-tree placed on the frame of the machine, so
that in drawing he pushes the platform backward with
his feet. In this case, the power can be only ascer-
tained by the use of the dynamometer, already de-
scribed.

SECTION V.

APPLICATION OF LABOR.

Most of the moving powers applied by the farmer to
accomplish labor are the exertions of animal strength.
A principal object of the preceding pages is to point out
how this strength can be applied in the most econom-
ical manner, and to aid in the substitution of cheap
horse-power for more costly human labor. It will
doubtless contribute to the end to exhibit the relative
efficiency of each, as well as the results of strength
differently apphed.

The amount of work which any machine is capable
of performing is denoted by comparing this amount
with the power of a single horse ; hence the common
expressions of twenty, or fifty, or a hundred horse-
power engines. The strength of different horses varies
greatly, but the expression, as commonly understood,
indicates a force equivalent to raising or pressing with
a force equal to 150 pounds 20 miles a day, at the rate
of two and a half miles an hour. This is the same as
33,000 pounds raised one foot in one minute. The re-
sults of numerous experiments in different places give
the actual power of the average of horses at somewhat

168 MECHANICS.

less than this ; and there is no doubt that, for most of
the farm-horses of this country, the result would be
considerably less. The power of a strong English
draught-horse has been ascertained to be about 143
pounds for 22 miles a day, at 2| miles an hour. Many
American horses are scarcely more than half as strong.
The strength of a man, working at the best advantage,
is estimated at one fifth that of a horse. As the speed
of a horse increases, his strength of draught diminishes
very rapidly, till at last he can only move his own
weight. This is owing to three reasons : first, the load
moves over a greater space in a given time, and if, for
instance, the speed be doubled, half the load only can
be carried with the same quantity of power, according
to the law of virtual velocities ; secondly, the horse
has to carry the full weight of his body, whatever his
speed may be, and the force expended for this purpose
alone must, therefore, be doubled as the speed is
doubled ; thirdly, a very quick and unaccustomed mo-
tion of the muscles is in itself more fatiguing than the
ordinary or natural velocity.

The following table shows the amount of labor a
horse of average strength is capable of performing in a
day at different degrees of speed, on canals, rail-roads,
and on turnpikes. The force of draught is estimated
at about 83 pounds. This is considerably less than
the horse-power used in estimating the force of machin-
ery, but it is as much as an ordinary horse can exert
without being improperly fatigued with continued ser-

APPLICATION OF LABOR. 169

Velocity
per hour.

Duration of the
day's work.

Hours.

Work accomplished for one day,
one mile.

in tons, drawn

Miles.

On a canal.

On

a rail-road.

On a turnpike.

2i

IH

520

115

14

3

8

243

92

12

3^

4

5A

4^

153
102

82
V2

10
9

5
6

2

52
30

57

48

7.2
6

7

n

19

41

5.1

8

n

12.8

36

4.5

9
10

1%
■1

9
6.6

32

28,8

4
3.6

From the preceding table it will be seen that a horse,
at a moderate walk, will do more than four times as
much work on a canal as on a rail-road ; but the re-
sistance of the water increases as the square of the ve-
locity, and therefore when the speed reaches five miles
an hour, the rail-road has the advantage of the canal.
On the rail-road and turnpike the resistance is about
the same, whether the speed be great or little, the
chief loss with fast driving resulting from the increased
difficulty with which the horse carries forward his own
body, which weighs from 800 to 1200 pounds. The
•table also shows that when it becomes necessary to
drive rapidly with a load, it should be continued but
for a very short space of time ; for a horse becomes as
much fatigued in an hour, when drawing hard at ten
miles an hour, as in twelve hours at two and a half
miles an hour ; because, when a boat is driven through
the water, to double its velocity not only requires that
twice the amount of water should be moved or dis-
placed in a given time, but it must be moved with
twice the velocity, thus requirmg a four-fold force.

The muscular formation of a horse is such that he
H

170 MECHANICS.

will exert a considerably greater force when working
horizontally than up a steep inclined plane. On a
level, a horse is as strong as five men, but up a steep
hill he is less strong than three ; for three men, carry-
ing each 100 pounds, will ascend faster than a horse
with 300 pounds. Hence the obvious waste of power
in placing horses on steeply-inclined tread-wheels or
aprons. The better mode is to allow them to exert
their force more nearly horizontally, by being attached
to a fixed portion of the machine. For the same rea-
son, the common opinion is erroneous that a horse can
draw with less fatigue on an undulating than on a level
road, by the alternations of ascent and descent calling
different muscles into play, and relieving each in turn ;
for the same muscles are alike exerted on a level and
on an ascent, only in the latter case the fatigue is much
greater than the counterbalancing rehef. Any person
may convince himself of the truth on this subject by
first using a loaded wheel-barrow or hand-cart for one
day on a level, and for the next up and down a hill ;
bearing in mind, at the same time, that the human
body is better fitted for climbing and descending than
that of a horse.

A draught-horse can draw 1600 pounds 23 miles in
a day on a good common road, the weight of the car-
riage included. On the best plank-road he will draw
more than twice as much.

A man of ordinary strength exerts a force of 30
pounds for 10 hours a day, with a velocity of 2 J feet
per second. He travels, without a load, on level ground,
during 8^ hours a day, at the rate of 3.7 miles an hour,
or 31^ miles a day. He can carry 111 pounds 11

APPLICATION OF LABOR. 171

miles a day. He can carry in a wheel-barrow 150
pounds 10 miles a day.

Well-constructed machines for saving human labor
by means of horse-labor, when encumbered with little
friction, will be found to do ahout Jive times as much
work for each horse as where the same work is per-
formed by an equal number of men. For example : an
active man will saw twice each stick of a cord of wood
in a day. Six horses, with a circular saw, driven by
means of a good horse-power, will saw five times six,
or thirty cords, working the same length of time. In
this case the loss by friction is about equal to the ad-
ditional force required for attendance on the machine.

Again : a man will out with a cradle two and a half
acres of wheat in a day. A two-horse reaper should
therefore cut, at the same rate, ten times two and a
half, or twenty-five acres. This has not yet been ac-
comphshed. We may hence infer that the machinery
for reaping has been less perfected than for sawing
wood. It should, however, be remembered, that great
force is exerted, and for many hours in a day, m cut-
ting wheat with a cradle, and therefore a Uttle less
than twenty-five acres a day may be regarded as the
maximum attainment of good reaping-machines, when
they shaU become perfected.

Applying the same mode of estimate, a horse-culti-
vator will do the work of five men with hoes, and a
two-horse plow the work of ten men with spades. A
horse-rake accomplishes more than five men, because
human force is not strongly exerted with the hand-rake.

In using different tools, the degree of force or press-
ure applied to them varies greatly with the mode in

172 MECHANICS.

which the muscles are exerted. The following table
gives the results of experiments with human strength,
variously applied, for a short period :

Force of the hands Force of the tool

on the tool. on the object.

With a drawing-knife 100 lbs. 100 lbs.

" a large auger, both hands 100 " about 800 "

" a screw-driver, one hand 84 " 250 "

" a bench-vice handle 72 " about 1000 "

" a windlass, with one hand 60 " 180 to 700 "

" a hand-saw 36 " 36 "

" a brace-bit, revolving 16 " 150 to 700 "

Twisting with thumb and fingers, but-
ton-screw, or small screw-driver. ... 14 " 14 to 70 "

The force given in the last column will, of course,
vary with the degree of leverage applied ; for example,
the arms of an auger, when of a given length, act v/ith
a greater increase of power with a small size than
with a large one. This degree of power may he calcu-
lated for an auger of any size, by considering the arms
as a lever, the centre screw the fulcrum, and the cut-
ting-blade as the weight to be moved. The same
mode of estimate will apply to the vice-handle, the
windlass, and the brace-bit.

Every one is aware that a heavy weight, as a pail
of water, is easily lifted when the arm is extended
downward, but with extreme difficulty when thrown
out horizontally. In the latter case, the pail acts with
a powerful leverage on the elbow and shoulder-joint.
JFor this reason, all kinds of hand-labor, with the arms
pulling toward or pushing directly from the shoulders,
are most easily performed, while a motion sidewise or
at right angles to the arm is far less effective. Hence
great strength is applied in rowing a boat or in using

MODELS OF MACHINES. 173

a drawing-knife, and but little strength in turning a
Lrace-bit or working a dasher-churn. Hence, too, the
reason that, in turning a grindstone, the pulling and
thrusting part of the motion is more powerful than
that through the other parts of the revolution. This
also explains why two men, working at right angles to
each other on a windlass, can raise seventy pounds
more easily than one man can raise thirty pounds
alone. Tliis principle should be well miderstood in the
construction or selection of all kinds of machines for
hand labor.

SECTION VI.
MODELS OF MACHINES.

Serious errors might often be avoided, and some-
times gross impositions prevented, by understanding
the difference between the working of a mere model,
on a miniature scale, and the working of the full-sized
machine. It is a common and mistaken opinion that
a well-constructed model presents a perfect representa-
tion of the strength and mode of operation of the ma-
chine itself.

AVlien we enlarge the size of any thing, the strength
of each part is increased according to the square of the
diameter of that part ; that is, if the diameter is twice
as great, then the strength will be four times as great ;
if the diameter is increased thi*ee times, then the
strength will be nine times, and so on. But the weight
increases at a still greater rate than the strength, or
according to the cube of the diameter. Thus, if the
diameter be doubled (the shape being similar), the

174 MECHANICS.

weight will be eight times greater ; if it be tripled,
the weight will be twenty-seven times greater. Hence,
the larger any part or machine is made, the less able
it becomes to support the still greater increasing
weight. If a model is made one tenth the real size
intended, then its different parts, when enlarged to full
size, become one hundred times stronger, but they are
a thousand times heavier, and so are all the weights
or parts it has to sustain. All its parts would move
ten times faster, which, added to their thousand-fold
weight, would increase their inertia and momentum
ten thousand times greater. For this reason, a model
will often work beautifully when made on a small
scale ; but when enlarged, the parts become so much
heavier, and their momentum so vastly greater, from
the longer sweep of motion, as to fail entirely of suc-
cess, or to become soon racked to pieces.

This same principle is illustrated in every part of
the works of creation. The large species of spiders
spin thicker webs, in comparison with their own diam-
eter, than those spmi by the smaller ones. Enlarge a
gnat until its whole weight be equal to that of the
eagle, and, great as that enlargement would be, its
wing will scarcely have attained the thickness of writ-
ing-paper, and, instead of supporting the weight of the
animal, would bend down from its own weight. The
larger spiders rarely have legs so slender in form as
the smaller ones ; the form of the Shetland pony is quite
different from that of the large cart-horse; and the
cart-horse has a slenderer form than the elephant.

The common flea will leap two hundred times the
length of its own body, and the remark has been some-

MODELS OF MACHINES. 175

times made that a man equally agile, with his present
size, would vault over the highest city-steeple, or across
a river as wide as the Hudson at Albany. Now, if the
flea were increased in size to that of a man, it would
become a hundred thousand times stronger, but thirty
million times heavier ; that is, its weight would be-
come three hundred times greater than its correspond-
ing strength. Hence we may infer that the enlarged
flea would be no more agile than a man ; or that, if a
man were proportionately reduced to the size of a flea,
he could leap to as great a distance.

All this serves to illustrate in a striking manner the
distinction between models and machines.

PART II.

HYDRODYNAMICS.*

Hydrostatic st treats of the weight and pressure of
liquids when not in motion ; Hydraulics,1: of liquids in
motion, as, conducting water through pipes, raising it
by pumps, &c. ; and Hydrodynamics includes both, by
treating of the forces of the liquids, whether at rest or
in motion.

CHAPTER I.

HYDROSTATIC

SECTION I.
UPWARD PRESSURE.

A REMARKABLE property of liquids is their pressure
in all directions. If we place a solid body, as a stone,
in a vessel, its weight will only press upon the bottom ;
but if we pom- in water, the water will not only press
upon the bottom, but against the sides. For, bore a
hole into the side, and the side pressure will drive out
the water in a stream; or, bore small holes into the
sides and bottom of a tight wooden box, stopping them

* From two Greek words, hudor, water, and dunamis, power,
t From two Greek words, hudor, water, and statos, standing, or at
rest. t From two Greek words, hudor, water, and aulas, a pipe.

UPWARD PRESSURE. 177

with plugs ; then press this hox, empty, bottom down-
ward, into water, allowing none to run in at the top.
Now draw one of the side plugs, and the water will be
immediately driven into the box by the pressure out-
side. If a bottom plug be drawn, the water will im-
mediately spout up into the box, showing the pressure
upward against the bottom. Hence the pressure in
all directions^ upward, sideways, and downward, is
proved.

The upward pressure of liquids may be shown by
pouring into one end of a tube, bent in the shape of the
letter U, enough water to partly fill it ; the upward
pressure will drive it up the other side till the two
sides are level.

On tliis principle depends the art of conveying water
in pipes under ground, across valleys. The water will
rise as high on the opposite side the valley as the spring
which supplies it. The ancient Romans, who were
unacquainted with the manufacture of strong cast-iron
pipes, conveyed water on lofty aqueducts of costly ma-
sonry, built level across the valleys. Even at the pres-
ent day, it has been deemed safest to build level aque-
ducts for conveying great bodies of water, as in very
large pipes the pressure would be enormous, and might
result in violent explosions.

If the valleys are deep, the pipes must be correspond-
ingly strong, because, the higher the head of water, the
greater is the pressure. For the same reason, dams
and large cisterns should be strongest at bottom. Res-
ervoirs made in the form of large tubs require the
lower hoops to be many times stronger or more numer-
ous than the upper.

H2

178

HYDRODYNAMICS.

MEASUREMENT OF PRESSURE AT DIFFERENT HEIGHTS.

The amount of pressure which any given height of
water exerts upon a surface below may be understood
by the following simple calculation :

If there be a tube one inch square (with a closed

end), half a pound of water poured into it will fill it to

a height of fourteen inches ;* one pound will fill it

twenty-eight inches ; two pounds, fifty-six inches ; ten

Fig. 149. pounds, twenty -three feet; twenty

2ibs. 5Gin. pounds, forty-six feet, and so on.

Now, as the side pressure is the same

as the pressure downward for the

., ^ .„. same head ofwater, the same column

• !/2lbs.42in. . '

will, of course, exert an equal press-
ure on a square inch of the side of
the tube. Or, if the tube be bent, as
lib 20 ill. shown in the annexed figure {Fig".
149), the pressure upward on the end
of the tube, at a, will be the same for
the various heights.
V2 lb. Id: in. Now, as the pressure of a column
fifty feet high is about twenty-two
pounds on a square inch, the pressure
on the four sides is equal to eighty-
j ll eight pounds for one inch in length.

Hence the reason that considerable
strength is required in tubes which have much head
of water, to prevent their being torn open by its force.

* This is nearly correct, for a cubic foot (or 1728 cubic inches) of
water weighs 62 lbs. Consequently, one pound will be 27.9 cubic
inches, and will fill the tube nearly 28 inches high.

SPRINGS AND ARTESIAN WELLS. 179

DETERMINING THE STRENGTH OF PIPES.

The question may now arise, and it is a very import-
ant one, How thick must be a lead tube of this size to
prevent danger of bursting with a head of fifty feet, or
of any other height ? To answer it, let us turn to the
table of the Strength of Materials in a former part of
this work, where we find that a bar of cast lead one
fourth of an inch square will bear a weight of fifty-five
pounds. If the tube be only one sixteenth of an inch
thick, one inch of one of its sides will possess an equal
strength, that is, will bear fifty-five pounds only, and
the tube would consequently burst with fifty feet head.
If one tenth of an inch thick, the tube would just bear
the pressure, and, to be safe, should be about twice as
thick, or one fifth of an inch. Half this thickness
would be sufficient for twenty-five feet of water, which
would require to be doubled for one hundred feet. A
round tube, one inch in diameter, having less surface
to its sides, would be about one third stronger. A tube
twice the diameter would need twice the thickness ;
or if less in diameter, a proportionate decrease in thick-
ness might take place. If, instead of cast lead, milled
lead were used, the tube would be nearly four times
as strong, according to the table of the strength of ma-
terials already referred to.

SPRINGS AND ARTESIAN WELLS

Result from the upward pressure of water. Rocks are
usually arranged in inclined layers {Fig. 150, p. 180),
and when rain falls upon the surface, as at c d, it sinks
down in the more porous parts between these layers,

180

HYDRODYNAMICS.

to c. If the layers happen to be broken in any place
below, the water finds its way up through the crevices
by the pressure of the head above, and forms springs.
If there are no openings through the rocks, deep borings
are sometimes made artificially, through wliich the wa-
ter is driven up to the siu-face, as at a, forming what
are termed Artesian Wells. The head of water which
supphes them may be many miles distant, the place
of discharge being on a lower level. It has sometimes
been found necessary to bore more than a thousand
feet downward before obtaining water which will flow
out fireely at the surface of the earth.

SECTION II.

DETERMINING THE PRESSURE ON GIVEN SURFACES.

The pressure of liquids upon any given surface is
Pig 151 always exactly in proportion

to the height, no matter what
the shape of the vessel may
be. If, for instance, the ves-
sel a {Fig. 151), be one inch
in diameter, and the vessel b
be three inches in diameter,

DETERMINING THE PRESSURE ON GIVEN SURFACES. 181

the water being equally high in both, the pressure on
the whole bottom of b will be nine times as great as
on the bottom of a ; or any one inch of the bottom of
h will receive as great a pressure as the bottom of a.
Again, if the vessel c, broad at the top, be narrowed to
only an inch in diameter at bottom, the pressure upon
that inch will still be the same, most of the weight of
its contents resting against the sides, d d.

If the vessel, A {Fig. 152), be filled with water to a
height of fourteen inches, the press-
ure will be half a pound on every
square inch of the bottom, or upon
every square inch of the sides four-
teen inches below the surface. If
the tube, C, be an inch square, the
water wiU be driven into it with a
force of half a pound, and will press
with that force against the one-inch
surface of the stop-cock, C. If the tube, B, be now
filled to an equal height, the same force will be exert-
ed against the other side. To prove this, let the stop-
cock be opened, when the two columns of water will
remain at an exact level.

If enough water be now poured into the tube, B, to
fiU it to the top, it will immediately settle down on a
level with the water m A, raising the whole surface
in the latter. This result has seemed very strange to
many, who can not conceive how a small column of
water can be made to balance a large one, and it has
been therefore termed the Hydrostatic Paradox. But
the difficulty entirely vanishes, and ceases to appear a
paradox, when we remember that the water in the

182

HYDRODYNAMICS.

larger vessel rises as much more slowly than it de-
scends in the smaller, as the large one exceeds the
smaller ; thus acting on the principle of virtual veloci-
ties in precisely the same manner that a heavy weight
on the short end of a lever is upheld by a small weight
on the long end. The great mass of water is support-
ed directly by the bottom of A, in the same way that
nearly all the weight on the lever is supported by the
fulcrum. A man who was seeking a solution to the
absurd mechanical problem of perpetual motion, and
Fig 153. who supposed that the large mass in A
would overbalance the small column in
B, and drive it upward, constructed a
vessel in the form shown in Fig. 153, so
that the small column, when forced up-
ward, wovild flow back into the larger
vessel perpetually. He was, however,
greatly surprised to see the fluid in both

Attempted Perpetual o .y x

Mutiun. divisions settle at the same level.

This principle may be further explained by the fol-
lowing experiment : A B {Fig'. 154) repre-
sents the inside of a metalhc vessel, with
a bottom, C, which slides up and down,
water-tight. If water be poured in to fill
the lower or larger part only, it will be
found to press on the sliding bottom with
a force exactly equal to its own weight ;
that is, if there is a pound of water, it will
^' press on the botton with a force equal to
one pound. Now, if the bottom be pushed upward, so
as to drive the water into the narrow part of the ves-
sel, the pressure upon the bottom becomes instantly

Fig. 151.

A

t}

'%

D

---

D ■

.^Ti ----- - - --

-;"b-""

mfr"-^-^"«

1

HYDROSTATIC BELLOWS.

183

much greater, or equal to many pounds, the water be-
ing the same in quantity, but with a much higher
head than before. Suppose the narrow part of the ves-
sel is twenty times smaller than the larger part, then,
m pushing the bottom up one inch, the water is driven
twenty inches upward in the tube. So then, accord-
ing to the rule of virtual velocities, it will require
twenty times the force, because it moves upward twen-
ty times faster.* This, then, is precisely similar to the
instance where a pound on the longer end of a steel-
yard balances twenty pounds on the shorter end. In
this instance, the upper parts, D D, of the vessel oper-
ate as the fulcrum of a lever, and offer resistance to the
sliding part as soon as the water begins to ascend the
tube.

HYDROSTATIC BELLOWS.

This principle is shown in the Hydrostatic Bellows
Fig. 155. {Fig. 155), which consists of two round
•^^ pieces of board, connected by a narrow
strip of strong leather ; into it is inserted
a long narrow tube, B, with a small fun-
nel, e, at the top. When water is poured
into this tube, it will raise a weight as
much greater than the weight of the
water in the tube as the surface of the
upper board exceeds the cross-section of
the tube. Thus, if a pound of water fills
Hydrostatic Bellows. ^ tubc half QXi iuch in diamctcr, and the
bellows is two feet in diameter, then this pound will

* The pressure will be as great upon the bottom as if the vessel
continued a uniform size all the way up, as shown by the dotted lines.

184 HYDRODYNAMICS.

raise more than two thousand pounds on the bellows
(if it is strong enough), because the surface of the bel-
lows is more than two thousand times greater.

In the same way, a strong, iron-bound hogshead may
be burst with the weight of a single gallon of water by
pouring it into a long and narrow tube set upright
into the bung of the hogshead. If, for instance, the
inner surface of the hogshead be 20 square feet, or
2880 square inches, a tube of water 23 feet high will
press with a force of 10 pounds on every square inch,
or equal to a force of 28,800 pounds, or 14 tons, on the
whole surface.

HYDROSTATIC PRESS.

The Hydrostatic Press owes its extraordinary power
to a similar principle ; but, instead of a bellows, there
is a moving piston in a strong metallic cylinder ; and
instead of being worked by the mere weight of the
water, it is driven into the cylinder by means of the
lever of a powerful forcing-pump. An instrument of
this sort, possessing enormous power, was used to ele-
vate the great tubular iron bridge in England. It was
found necessary to make the sides of the cylinder into
which the water was driven no less than eleven inches
thick, of solid iron ; and so great was the pressure giv-
en to the confined water, that it would have forced it
up through a tube higher than the summit of Mont
Blanc. In the port of New York, vessels of a thousand
tons burden have been lifted by the hydrostatic press.

This machine is applied in compressing hay, cotton,
and other bulky substances into a compact form, so
that they may occupy but little space for conveyance

HYDROSTATIC PRESS.

185

to distant markets. The following figure {Fig: 156)
exhibits the different parts of this powerful machine.

Fig. 156.

Ifi/drost jtir Press.

A is a cistern to supply water, which is raised by work-
ing the handle, B, of the forcing-pump; the water
passes through the valve, C, opening upward, and
through the spring valve, D, opening toward the large
cylinder, E. Being thus driven into the space, E, it
raises the piston, F, and exerts a prodigious pressure
upon the mass of hay or cotton, G. The piston is low-
ered by turning the screw, H, which allows the water
to pass back into the cistern at I. In the figure the
hay is sho\^ai as visible to the sight, in order to repre-
sent the whole more plainly; but in practice it is

186 HYDRODYNAMICS.

thrown into a square box or chamber of strong plank,
of the size of the intended bundle. One side is hung
upon stout hinges, and is opened for the removal of the
hay when the pressing is completed.

To estimate the power of this machine, divide the
square of the diameter of the piston, F, by the square
of the diameter of the piston of the forcing-pump, and
multiply the quotient by the power of the lever, B.
For example, suppose the piston, F, is 16 inches in di-
ameter, and the piston of the forcing-pump is 2 inches
in diameter ; then the square of 16 is 256. Divide
this by 4, the square of 2, and the result will be 64.
If the lever, B, increases the power five times, the
whole power of the machine will be 320 ; that is, a
force of one pound applied to the lever will raise the
large piston with a force equal to 320 pounds ; or, if a
force of 100 pounds be given to the lever, the power
will be 32,000 pounds, or 16 tons. Reducing the di-
ameter of the smaller piston to half an inch, and in-
creasing the force of the lever to twenty times, the
whole power exerted will be thirty -two times as great,
or equal to 960 tons. In ordinary practice, it is more
convenient and economical to reduce the diameter of
the larger piston to a few inches only, making the
forcing-pump correspondingly small, the power depend-
ing entirely on the disproportion between them. Such
presses may be worked rapidly by horse, water, or steam
power.

One great advantage which the hydrostatic press
possesses over those worked by screws results from
the little friction among liquids, nearly the only fric-
tion existing: in the whole machine being that of the

SPECIFIC GRAVITIES.

18:

two pistons, which is comparatively small. Another
is the smallness of the compass within which the whole
is comprised ; for a man might, with one not larger
than a tea-pot, standing before him on a table, cut
through a thick bar of iron with as much ease as he
could chip pasteboard with a pair of shears.

SECTION III.

SPECIFIC GRAVITIES.

In connection with Hydrostatics, the subject of the
specific gravities of bodies is one of importance. The
specific gravity of a substance is its comparative
weight with some other substance, an equal bulk of
each being taken. Water is usually the standard for
comparison.

To ascertain the specific gravity, weigh the body
both in and out of water, and observe the difference ;
then divide the whole weight by this difference, and
the quotient will be the specific gravity of the body.
For example, if a stone weighs 12
lbs. out of water and 7 lbs. in
water, divide 12 by 5, and the
quotient is 2.4, which shows that
the stone is 2^ times heavier than
water. Figure 157 shows the
mode of weighing the body in
water, by suspending it beneath
•"^, a balance on a hair or thread.

It was in a similar way that

Instrument fr taking Specific i i • i .

Grainttes. Archimcdcs succeeded in detect-

ing the suspected fraud in the manufacture of the gold-

188 HYDRODYNAMICS.

en crown of the ancient king of Syracuse. He first
weighed it, and then found that it displaced more wa-
ter when plunged in a vessel just filled, than a piece of
pure gold, and also that it displaced less than silver,
whence he inferred the mixture of these two metals.

When the specific gravity of a substance hghter than
water is to be ascertained, it is loaded down by a
weight, so as to sink in water, for which allowance is
made in the calculation. A very simple way to deter-
mine this in different kinds of wood is to form them
into rods or sticks of uniform size throughout, and then
to observe what portion of them sink when placed end-
wise in water.

A knowledge of the specific gravities of various sub-
stances becomes useful in many ways, among which
is ascertaining the weight of any structure, machine,
or implement, according to the material used in its
manufacture ; determining the cost, by the pound, of
such material ; or knowing the bulk or size of any load
for a team. The latter may often become of great use
in ordinary practice, by enabling the teamster to cal-
culate beforehand the amount of load to give his horses,
whether in timber, plank, brick, lime, sand, or hon,
without first subjecting them to overstraining exer-
tions in consequence of error in random guessing.

Tables of specific gravities, for this purpose, and
weights of a cubic foot of different substances, are giv-
en in the Appendix.

VELOCITY OF FALLING WATER. ibl9

CHAPTER 11.

HYDRAULICS.
SECTION I.

VELOCITY OF FALLING WATLR.

Liquids in motion are subject to the same laws as
solids in motion. Falling water increases in velocity
at the same rate that the motion of falhng solids is ac-
celerated, as already explained under the head of Grav-
itation. Thus a perpendicular stream of water de-
scends one foot in a quarter of a second, four feet in
half a second, nine feet in three fourths of a second,
and sixteen feet in one second. Like falhng sohds,
the velocity at the end of the first quarter will be eight
feet per second ; at the end of the second quarter, six-
teen feet per second ; at the end of the thud quarter,
twenty-four feet per second ; and at the end of the
fourth quarter, thirty-two feet per second.

Now, if there be an orifice made in the side of a ves-
sel of water, the water will spout out with the same
swiftness as if it fell perpendicularly from an equal
height, were it not retarded a little by friction. For
example, if the head of water is one foot above the
orifice, the velocity would be at the rate of eight feet
per second, but for friction, which reduces it to about
five and a half feet* per second. The velocity for any
other height of head may be easily found by deduct-
ing the same proportionate rate from the velocity of a

Or, more accurately, 5.4 feet per second.

190 HYDRODYNAMICS.

falling body. Thus, for example, if the head he six-
teen feet, the speed would be thirty-two feet (as shown
under Gravitation), from which, deducting the fric-
tion, the real velocity would be about twenty-two feet
per second.

It has been already shown that the velocity of a fall-
ing body increases at the same rate as the increase in
the time of falling ; for instance, the speed is twice as
great in two seconds as in one ; three times as great in
three seconds ; four times as great in four seconds, and
so on. But the distance fallen through increases as
the square of the time ; that is, it is four times as great
in two seconds, nine times as great in three seconds,
sixteen times as great in four seconds, &c. Thus we
see that, in order to produce a two-fold velocity, a four-
fold height is necessary, &c. So also in the escape of
water under a head: to double the velocity of the
stream, the head must be four times as high ; to triple
it, the head must be nine times as high, &c.

DISCHARGE OF AVATER THROUGH ORIFICES AND PIPES.

The discharge of water from a vessel is greatly in-
fluenced by the nature of the orifice through which it
flows. If, for example, a vessel or cistern have a thin
bottom of tin, with a smooth circular hole, we might
naturally suppose that the discharge would be as easy
as it could be made, and that water would pass as rap-
idly through it as through any orifice of an equal size.
But this is not the fact. As the particles approach
this orifice, their motion throws them across, and they
partly obstruct the opening ; it will be seen that they
converge toward a point just under the orifice, where

DISCHARGE OF WATER THROUGH ORIFICES AND PIPES. 191

Fig. 158. ^ ^|-^g stream will be considerably con-
tracted {Fig. 158). If a short tube be
inserted into the hole (the head being
the same), this crossing of particles will
be partly prevented, and the liquid will
flow more rapidly. The greatest ef-
fect is produced Fi?. iso. Fig. leo.
when the tube
is twice as long
as its diameter
(F«V. 159). If
the tube be en-
larged at its
, ,,» upper and low-
'I'lll'l er end, similar
to the form of the contracted
stream of water in Fig. 158, the quantity
discharged is greatly increased {Fig. 160).

When water flows down an inclined plane, the same
law applies as to the motion of a sohd body rolling down
a plane. The velocity increases as the square of the dis-
tance, and is the same as the velocity of a body falling
freely downward from a height equal to the perpendic-
ular height of the plane. Unless the stream, however, is
very large, its speed is quickly diminished by the friction
of its chamiel,* until this friction becomes as great as
the descending force, after which the motion becomes
uniform. Hence the reason that large streams, with an
equal degree of descent, flow so much more rapidly than
small ones, the gravitating force being so much great-
er that friction has a less retarding effect upon them.

* Which increases as the square of the velocity.

192 HYDRODYNAMICS.

In pipes which wholly surround the flowing stream,
the friction becomes still greater, and the difficulty is
only obviated by making the pipe of larger dimensions
than would otherwise be necessary, so as to allow a free
passage of a sufficient quantity of water through, the
centre of the tube, while a ring or hollow cyUnder of
water is nearly at rest all around it. The tables in
the Appendix exhibit this decreased velocity in tubes
of various sizes.

SECTION III.
VELOCITY OF WATER IN DITCHES.

It is often of great practical utility to know what
amount of water may be carried off in draining or sup-
plied in irrigation by channels of any given size and
descent. The following rule will apply to all cases,
from the plow-furrow to the mill-race, or even to the
large river, and may be used by any boy who under-
stands common arithmetic, and which is illustrated
and made plain by the example that follows the rule.

To ascertain the mean [or average) velocity of wa-
ter in a straight channel of equal size throughout :

Let/=the fall in two miles in inches;

Let d—WxQ hydraulic mean depth;

Let v = the velocity in inches per second;
then the rule is thus expressed, v — 0.^1\^fd, or, in
plain words, the velocity is equal to the hydraulic mean
depth multiplied by the fall, with the square root of
this product extracted, and then multiplied by 0.91.

The " hydraulic mean depth'''' is found by dividing
the. cross-section of the channel by the perimeter or

VELOCITY OF WATER IN DITCHES. 193

border. The perimeter is the aggregate breadths of
the sides and bottom of the channel.

The rule will be rendered quite plain by an exam-
ple. Suppose a smooth furrow is cut six inches wide
and four inches deep, with perpendicular sides, and
that it descends one inch in a rod ; to find the quanti-
ty of water that will flow through it. One inch fall in a
rod is 320 inches in a mile, or 640 in two miles. The
perimeter in contact with the water will be six inches
on the bottom, and four inches in each side = 14 inches.
The area of the cross-section will be 6 times4 = 24, which
divided by 14, the perimeter, gives 1.7 = the hydraulic
mean depth. Then, by applying the preceding rule :

V = 0.91^640x1.7, or t^ = 0.91 X 33 = 30 inches,
the velocity per second, which would be about three
gallons per second, or three hogsheads per minute.

An open ditch, therefore, with smooth sides, convey-
ing a stream of this size, would carry oft' in one hour,
from an acre of land, all the water which might fall
by half an inch of rain during the wet season ; for half
an inch of ram would be 180 hogsheads per acre, which
would pass oft" in one hour ; or it would supply in one
hour, by the process of irrigation, as much water as a
heavy shower of half an inch. Where the descent is
greater, the increased quantity may be readily calcu-
lated by the rule given. The capacity of smooth-sided
underground channels may be determined in the same
way; but if built of rough stones, great allowance
must be made, as they will retard the flow of water.

In common practice, too, even with straight, open
ditches, the velocity will be much dmiinished by the
rough sides,

I

194

HYDRODYNAMICS.

LEVELING INSTRUMENTS,

The simplest mode of leveling, or ascertaining the
for ditches, is to cut a few yards of the ditch so
that water may stand in it, and then to set two sticks
perpendicularly, both rising to an equal height above
the surface. The sticks should be measured at equal
distances from the top downward and marked, and

Fig. 16L

Simple method of taking levels.

then pressed into the earth till the water reaches the

mark. The level may then be determmed with much

accuracy by "sighting" over the tops of these sticks.

Pig 162. Figure 161 exhibits this

] arrangement. The shorter

the sticks, and the longer

the piece of water, the less

will be the liability to error.

The following simple

mode may be sufficiently

accurate where the descent

of the ditch is considerable.

A {Fig. 162) is a common

square, placed in a slit in

the top of the stake, B. By

means of a plumb-hne, the

square is brought to a level,

when a thumb-screw at C

fixes it fast. If the square

Simple Leveling Instrument.

LEVELING INSTRUMENTS.

195

is two feet long, and is so carefully adjusted by means
of the plumb-line as not to vary more than the twen-
tieth of an inch from a true level, which is easily ac-
complished, then a twentieth of an inch in two feet
will be one inch in forty feet, a sufficient degree of ac-
curacy for many cases.

Where greater accuracy is required, as in long and

nearly level ditches, the "water level" may be used.

Fig. 163. It may be made of a

- g fl^ lead tube about three

A F^ ' ,, ^ B feet long, bent up an

inch or two at each end,
and stiffened by fasten-
ing to a wooden bar,
A, B {Fig-. 16S). Into
each end is cemented,
with sealing-wax, a
small and thm phial
with the bottom broken
off, so that when the tube is filled with water it may
rise freely into the pliials. If the tube be now filled
with water colored with cochineal or any dye-stuff, and
then placed upon the tripod, C, by looking across the
two surfaces of liquid in the phials, an accurate level
may be obtained. "When not in use, a cork is placed
Fig- '64. into each phial. " Sights" of equal height, fast-
ened to pieces of cork floating on the water, as
shown in Fig-. 164, give a more distinct hne for
the eye. The sights are formed of fine threads
or hairs stretched across the square openings.
To ascertain whether these threads are both of
equal heights above the water, let a mark be made

Leveling Instnimcnt.

196 HYDRODYNAMICS.

where they intersect some distant object ; then reverse
the instrument, or turn it end for end, and observe
whether the threads cross the same mark. If they do,
the instrument is correct ; but if they do not, then one
of the sights must be raised or lowered until it be-
comes so.

In laying out canals and rail-roads, where extreme
accuracy is needed, the spirit-level attached to a tele-
scope is used. So great is the perfection of this instru-
ment, that separate lines of levels have been run with
it for sixty miles without varying two thirds of an inch
for the whole distance.

The use of a cheap and simple instrument to determ-
ine the position and descent of ditches with ease and
precision, before commencing with the spade, will save
a vast amount of the trouble and expense which those
often meet with whose only method is to " cut and tryP

SECTION III.

HYDRAULIC MACHINES.
ARCHIMEDEAN SCREW.

Machines for raising water are of frequent use on
every farm. One of the simplest contrivances for this
purpose is the Screw of Archimedes. It may be easily
made by winding a lead tube around a wooden cylin-
der or rod {Fig. 165), in the form of a screw. When
placed in an inclined position, with one end in water,
and made to revolve, the water resting at the lower side
of each turn of the screw is gradually carried from one
end to the other, and discharged at the upper extremi-

ARCHIMEDEAN ROOT-WASHER. 197

Fig. 105.

The Screw of Archimedes

ty. Its simplicity and small liability to get out of
order renders the Archimedean Screw sometimes use-
ful where water is to be raised from an open stream to
a short distance, as for krigation, the motion being
easily imparted to it by means of a small water-wheel
driven by the stream.

ARCHIMEDEAN ROOT-WASHER.

This principle has been successfully applied in the
Archimedean Root-washer {Fig. 166). The roots to

Fig 166

Croskill's Archimedean Root-washer.

be washed are first delivered into a hopper, from which

198 HYDRODYNAMICS.

they pass into an inclined cylinder made of strips of
wood with grate-hke openmgs. The cylinder has two
portions separated by a partition, in the first of which
they remain while the handle is turned for washing
them. As soon as the washing is finished, the motion
of the handle is reversed, which throws them into the
other part, which has a spiral partition, along which
they pass till they drop into a spout outside.

The same principle is adopted in the horizontal corn-
sheller, shown by the annexed figure {Fig. 167), al-

Fig 167

though this machine has no connection with hydraul-
ics. The corn in the ear is thrown into the hopper at
one end, and is quickly separated from the cob by rows
of teeth revolving in a concave bed and set spirally,
which, by this arrangement, carry along the cobs and
eject them from the other end. Tliis is a good corn-
shelling machine for horse-power.

The sausage-mincing machine operates on a similar
principle.

G-reat improvement has been made in the common
pump for farms within the past ten years. The best
cast-iron pumps, made almost wholly of this metal, far

199

exceed in durability and ease of
working those formerly con-
structed of wood, and excel all
others in cheapness. Fig. 168
exhibits the working of the com-
mon pump, the water first pass-
ing through the fixed valve be-
low, and then through the one
in the piston ; both opening up-
ward, it can not flow back with-
out mstantly shutting them.
The water is driven up by the
pressure of the atmosphere, ex-
plained m the next chapter.

The most perfect pump, per-
haps, in present use,
is the best-construct-
ed Chain Pump, a
cross-section of one
of which is here
shown {Fig. 169).
The chain is made

Fig.

Common Pump : b, loiccr or fixed
valve, G, piston with valve, a,
opening upward ; D d, piston-
rod ; F, spout.

to revolve rapidly on the angular wheel by
means of a winch attached to the upper one,
and being furnished with a regular succes-
sion of metallic discs which nearly fit the
bore in the tube, a, the water is carried up
in large quantities. Wlien the motion is
discontinued, the water settles down again
into the well, and consequently this pump is
not Hable to accident by freezing. By
sweeping rapidly through the water, it pre-

200

HYDROBYNAMICS.

serves it in better condition, and prevents stagnation.
The friction being very small, it will last a long time
without wearing out.

Fig 170.

THE WATER-RAM.

One of the most ingenious and useful machines for
elevating water is the Water-ram. It might be em-
ployed with great advantage on many farms, were its
principle and mode of action more generally understood.
By means of a small stream, with only a few feet fall,
a current of water may be driven to an elevation of
fifty to a hundred feet above, and conveyed on a higher
level to pasture-fields for irrigation, or to cattle-yards
for supplying drink to domestic animals, or to the kitch-
en of dwellings for culinary purposes.

Its power depends on the momentum of the
stream. Its principal
parts are the reservoir
or air-chamber, A {Fig'.
170), the supply-pipe,
B, and the discharge
pipe, C. The running
stream rushes down
the supply - pipe, B,
Water-ram. and. Striking the waste

valve, D, closes it. The stream being thus suddenly
stopped, its momentum opens the valve, E, upward,
and drives the water into the reservoir. A, until the
air within, being compressed into a smaller space,
by its elasticity bears down upon the water, and again
closes the valve, E. The water in the supply-pipe, B,
has by this time expended its momentum and stopped

THE WATER-RAM. 201

running ; therefore the valve, D, drops open again, and
permits it to escape. It recommences running, until
its force again closes the waste valve, D, and a second
portion of water is driven into the reservoir as before,
and so it repeatedly continues. The great force of the
compressed air in the reservoir drives the water up the
discharge-pipe, C, to any required height or distance.

The mere weight of the water will only cause it to
rise as high as the fountain-head ; hut like the mo-
mentum of a hammer, which drives a »ail into a solid
team, which a hundred pounds would not do by press-
ure, the striking force of the stream exerts great
power.

The discharge-pipe, C, is usually half an inch in di-
ameter, and the supply -pipe should not be less than an
inch. A fall of two or three feet in the stream, with
not less than half a gallon of water per minute, with
a supply-pipe forty feet long, will elevate water to a
height as great as the strength of common half-inch
lead pipe will bear.* The greater the height in pro-
portion to the fall of the stream, the less will be the
quantity of water elevated as compared with the quan-
tity flowing in the stream.

Unlike a pump, there is no friction or rubbing of
parts in the water-ram, and it will act for years with-
out repairs, continuing thi'ough day and night its

* When water is raised to a considerable elevation by means of the
water-ram, the reservoir must possess great strength. If the height
be one hundred feet, the pressure, as shown on a former page, is about
forty-four pounds to the square inch. With an internal surface, there-
fore, of only two square feet, the force exerted by the column of water,
tending to burst the reservoir, would be equal to more than twelve
thousand pounds.

12

2G2

HYDRODYNAMICS.

constant and regular pulsations, unaltered and unob-
served.

WATER-ENGINES,

including those for extinguishing fires and for irriga-
ting gardens, are constructed on a principle quite sim-
ilar to that of the water-ram. Instead, however, of
compressing the air, as in the ram, by the successive
strokes of a column of running water, it is accom-
plished by means of a forcing-pump, driving the water
into the reservoir, from which it is again expelled with
great power by means of the elasticity of the com-
pressed air. Fig. Ill represents a garden-engine.

Fig. 171.

Gardcu-e?ighie.

movable on wheels, which may be used for watering
gardens, washing windows, or as a small fire-engine.
Fig-. 172 (at the head of the opposite page) is another
of smaller size, for the same purpose, and in a very
neat and compact form, the working part being within
the cylindrical case.

THE FLASH-WHEEL.

Fig. 172.

203

Cylindrical Garden- engine.

THE FLASH-WHEEL

is employed with great advantage where the quantity
of water is large and is to be raised to a small height.
It is like an undershot- wheel with its motion reversed
{Fig. 173, p. 204), where the arrows show the direc-
tion of the current when driven upward. It must, of
course, be made to fit the channel closely, without
touching and causing friction. In its best form its
paddles incline backward, so as to be nearly upright at
the time the water is discharged from them into the
upper channel. It has been much used in Holland,
where it is driven by wind-mills, for draining the sur-
face-water off from embanked meadows. In Enirland

204

HYDRODYNAMICS.

Flash or fen wheel/or raising water rapidly short distances.

it has "been driven by steam-engines ; and in one in-
stance, an eighty-horse-power engine, with ten bushels
of coal, raised 9840 tons of water six feet and seven
inches high in an hour. This is equal to more than
29,000 lbs. raised one foot per minute by each horse-
power, showing that very little force is lost by friction
in the use of the flash- wheel.

Fig. 174.

SECTION IV.

WAVES.
NATURE OF WAVES.

An inverted syphon, or bent tube like
that shown in Fig. 174, may be used
to exhibit the principle on which de-
pends the motion of the waves of the
sea. The action of the waves on shores

THE WATER NOT PROGRESSIVE. 205

and banks, and the inroads which they make upon
farms situated on the borders of lakes and large rivers,
present an interesting subject of inquiry.

If the bent tube [Fig. 174) be nearly filled with wa-
ter, and the surface be driven down in one branch by
blowing suddenly into it, the liquid will rise in the
other branch. The increased weight or head of this
raised column will cause it to fall again, its moment-
um carrying it down below a level, and driving the
water up the other branch. The surfaces will, there-
fore, continue to vibrate until the force is spent. The
rising and falHng of waves depend on a similar action.
The wind, by blowing strongly on a portion of the wa-
ter of the lake or sea, causes a depression, and produces
a corresponding rise on the adjacent surface. The
raised portion then falls by its weight, with the added
force of the wind upon it, until the vibrations increase
into large waves.

THE WATER NOT PROGRESSIVE.

The waves thus produced have a progressive motion
(for reasons to be presently shown), as every one has
observed. A curious optical deception attending this
advancing motion has induced many to believe that
the water itself is rolling onward ; but this is not the
fact. The boat which floats upon the waves is not
carried forward with them ; they pass underneath, now
lifting it on their summits, and now letting it sink into
the hollows between. The same effect may be observ-
ed with the water-fowl, which sits upon the surface.
It often happens, indeed, that the waves on a river roU
in an opposite direction to the current itself

206

HYDRODYNAMICS.

If a cloth be laid over a number of parallel rollers
so far apart as to allow the cloth to fall between them,
and a progressive motion be then given to them, the
cloth remaining stationary, a good representation of
waves will be afforded, and the cloth will appear to ad-
vance ; or if a strip of cloth be laid on a floor, repeated
jerks at one end will produce a similar illusion.

It is only the form of the wave, and not the water
which composes it, which has an onward motion. Let
the dark line in Fig. 175 represent the surface of the

Fig. 175.

water. A is the crest of one of the waves, and being
higher than the surface at B, it has a tendency to fall,
and B to rise. But the momentum thus acquired car-
ries these points so far that they interchange levels.
The same change takes place with the other waves,
and the' dotted line shows the newly-formed surface as
the water thus sinks in one place and rises in another.
The same process is again repeated, and each wave
thus advances further on, and the progressive motion
is continually kept up.

BREADTH AND VELOCITY OF WAVES.

Each wave contains at any one moment particles
in all possible stages of their oscillation ; some rising
and some falling ; some at the top and some at the bot-
tom ; and the distance from any row of particles to the
next row that is in precisely the same stage of oscilla-

BREADTH AND VELOCITY OP WAVES. 207

tion, is called breadth of the wave, that is, the distance
from crest to crest or from hollow to lioUow.

There is a striking similarity between the rising and
falling of waves and the vibrations of a pendulum, and
it is a very interesting and remarkable fact that a wave
always travels its own breadth in precisely the same
time that a pendulum whose length is equal to that
breadth performs one vibration. Thus, a pendulum
39^ inches long beats once in each second, and a wave
whose breadth is 39^ inches travels that breadth in
one second. The length of a pendulum must be in-
creased as the square of the time for its vibrations ;
that is, to beat but once in two seconds, it must be
four times as long as for one second ; to beat once in
three seconds, it must be nine times as long, and so on.
In the same way, waves which travel their breadth in
two seconds are four times as wide as those travehng
their breadth in one second ; and thus their breadth,
and consequently their speed, increases as the square
of the time. Large waves, therefore, roll onward with
far greater velocity than small ones. If only thirty-
nine inches wide, they move about two and a quarter
miles an hour, and pass once each second ; if

13 feet wide, they move 4^ miles an hour, passing once in 2 seconds.

52 do. do. 9 do. do. 4 do'.

209 do. do. 18 do. do. 8 do.

836 do. do. 3G do. do. IG do.

Although the water itself does not advance where
there is much depth, yet when it reaches a shore or
beach, the hard and shallow bottom prevents it from
falhng or subsiding, and it then rolls onward with a
real progressive motion by the momentum it has ac-

208

HYDRODYNAMICS.

quired, and breaks into foam and lashes the earth and
rocks. The sea-billows are sometimes twenty-five feet
in elevation,* and when these advance upon a stranded
ship on a lee shore, with the speed of a locomotive,
their effects are in the highest degree appalling, and
iron bolts are snapped and massive timbers crushed
beneath their violence.

PREVENTING THE INROAD OF WAVES.

To prevent the inroads of lake waves upon land, the
remedies must vary with circumstances. The diffi-
culty would be small if the water always stood at the
same height. The greatest mischief is usually done
when they rise over the beach of sand and gravel which
they have beaten for centuries. Wooden bulwarks soon
decay. Wliere loose stone can be had in large quan-
tities they may be cheapest, but they are not unfre-
quently placed too near low- water mark to protect the
banks. Substances which offer a gradual impediment
to the waves are often quite effectual, though not for-
midable in themselves. It is curious to observe how
so slender a plant as the bulrush, growing in water
several feet deep, will destroy the force of waves. If
it grew only near the shore, where the water has pro-
gressive motion, it would soon be dashed in heaps on
the beach. Parallel hedgerows of the osier willow,
protected by a wooden barrier until well grown and
established, would in many cases prove efficient.

Stones and timber bulwarks are often made need-
lessly liable to injury by being built nearly perpen-

* No authentic measurement gives the perpendicular height of
■waves more than twenty-five feet.

PREVENTING THE INROAD OF WAVES. 209

dioular, and the waves break suddenly and with full
Fig. 176. force, like the blows

of a sledge against
them. A better form
is shown in Fig.
176, where a slope
is first presented to weaken their force without impos-
ing a full resistance, and their strength is gradually
spent as they rise in a curve. A more gradual slope
than the figure represents would be still better. It is
on this principle that the stabihty of the world-renown-
ed Eddystone light-house depends. The base spreads
out in every direction, like the trunk of a tree at the
roots; and although the spray is sometimes dashed
over its lofty summit by the violence of the storm, it
has stood unshaken on its rocky base far out in the sea,
against the billows and tempests, for nearly a century.
An instance occurred many years ago in England,
where the superiority of knowledge over power and
capital without it was strongly exemplified. The sea
was making enormous breaches on the Norfolk and
Suffolk coast, and inundated thousands of acres. The
government commissioners endeavored to keep it out
by strong walls of masonry and breakwaters of timber,
built at great expense ; but they were swept away by
the fury of the billows as fast as they were erected.
A skillful engineer visited the place, and with much
difficulty persuaded them to adopt his simple plan.
Observing the slope of the beach on a neighboring
shore, he directed that successive rows of fagots or
brush be deposited for retaining the sand, which was
carted from the hills, forming an embankment with a

210 HYDRODYNAMICS.

slope similar to that of the natural beach. Up this
slope the waves rolled, and became gradually spent as
they ascended, till they entirely died away. The
breach was effectually stopped, and this simple struc-
ture has ever since resisted the most violent storms of
the G-erman Ocean.

SECTION V.
CONTENTS OF CISTERNS.

Connected with the subject of hydrauUcs is the
collection and security of water falling upon roofs, in
all cases where a deficiency is felt by farmers m the
drought of summer. The amount which falls upon
most farm-buildings is sufficient to furnish a plentiful
supply to all the domestic animals of the farm when
other supplies fail, if cisterns large enough to hold it
were only provided. Generally speaking, none at all
are connected with barns and out-buildings, and even
when they are furnished, they are usually so small as
to allow four fifths of the water to waste.

If all the rain that descends in the Northern States
of the Union should remain upon the surface without
sinking in or running off, it would form each year a
depth of about three feet. Every inch that falls upon
a roof yields two barrels for each space ten feet square,
and seventy-two barrels a year are yielded by three
feet of rain. A barn thirty by forty feet supplies annu-
ally from its roof 864 barrels, or enough for more than
two barrels a day for every day in the year. Many
farmers have in all five times this amount of roof, or
enough for twelve barrels a day yearly. If, however,

RULE FOR DETERMINING THE CONTENTS. 211

this water was collected, and kept for the dry season
only, twenty or thirty barrels daily might be used.

In order to prevent a waste of water on the one hand,
and to avoid the unnecessary expense of too large cis-
terns, their contents should be determined beforehand
by calculation.

RULE FOR DETERMINING THE CONTENTS.

A simple rule to determine the contents of a cistern,
circular in form, and of equal size at top and bottom,
is the following : Find the depth and diameter in
inches ; square the diameter, and multiply the square
by the decimal .0034, which will find the quantity in
gallons* for one inch in depth. Multiply this by the
depth, and divide by 31^, and the result will be the
number of barrels the cistern will hold.

For each foot in depth, the number of barrels an-
swering to the different diameters are.

For 5 feet diameter 4.66 barrels.

6.71
9.13
11.93
15.10
18.65

10

By the rule above given, the contents of barn-yard
cisterns and manure tanks may be easily calculated
for any size whatever.

* This is the standard gallon of 231 cubic inches. The gallon of
the State of New York contains 221.184 cubic inches, or 6 pounds at
its maximum density.

212 HYDRODYNAMICS.

DETERMINING THEIR SIZE.

The size of cisterns should vary according to their
intended use. If they are to furnish a daily supply
of water, they need not be so large as for keeping sup-
plies for summer only. The average depth of rain
which falls in this latitude, although varying consid-
erably with season and locality, rarely exceeds seven
inches for two months. The size of the cistern, there-
fore, in daily use, need never exceed that of a body of
water on the whole roof of the building seven inches
deep. To ascertain the amount of this, multiply the
length by the breadth of the building, reduce this to
inches, and divide the product by 231, and the quotient
will be gallons for each inch of depth. Multiplying by
7 will give the full amount for two months' rain fall-
ing upon the roof. Divide by 31 J, the quotient will
be barrels. This will be about fourteen barrels for
every surface of roof ten feet square when measured
horizontally. Therefore, a cistern for a barn 30 by 40
feet should hold 168 barrels ; that is, as large as one
ten feet in diameter and nine feet deep. Such a cis-
tern would supply, with only thirty inches of rain year-
ly, no less than 630 barrels, or nearly two a day.

Cisterns intended only for drawing from in times of
drought, to hold all the water that may fall, should be
about tliree times the preceding capacity.

PART III.

PNEUMATICS.

CHAPTER I.

PRESSURE OF AIR.

Fig. 17

Pneumatics treats of the mechanical properties of
the air.

The actual weight of the
air may be correctly found by
weighing a strong glass ves-
sel furnished with a stop-cock,
a {Figure 177), after the air
has been withdrawn from it by
means of an air-pump. Let
it be accurately balanced by
weights in the opposite scale ;
then turn the stop-cock and ad-
mit the air, and it will imme-
diately descend, as shown in
the figure. The weight of the
admitted air may be ascertain-
ed by adding weights till it is
again balanced.

Balance for Weighing Ai

HEIGHT AND WEIGHT OF THE ATMOSPHERE.

The atmosphere which covers the earth extends up-
ward to a height of about fifty or sixty miles. At the

214 PNEUMATICS.

surface of the earth the air is about eight hundred times
hghter than the water, and the higher we ascend, the
rarer or lighter it becomes, from the diminished press-
ure of its weight above. At seven miles high, it is
four times lighter than at the surface ; at twenty-one
miles, it is sixty-four times lighter ; and at fifty miles,
about twenty thousand times lighter. At this height
it ceases to refract the rays of the sun so as to render
it visible at the earth's surface ; but if it decreases at
the same rate upward, at a hundred miles high it must
be nearly a thousand miUion times rarer than at the
earth.

If the atmosphere were uniformly of the same dens-
ity, with its present weight, it would reach only five
miles high. Although so much lighter than water,
yet, from its great height, it presses upon the surface
of the earth as heavily as a depth of thirty-three feet
of water. This is nearly equal to fifteen pounds on
every square inch, or more than two thousand pounds
to the square foot. This enormous weight would in-
stantly crush us, did not air, like liquids, press in every
direction, so that the upward exactly counterbalances
the downward pressure, and the air within the body
counteracts that without.

The weight of the atmosphere is strikingly shown
by means of an air-pump, which pumps the air from a
glass vessel, placed mouth downward upon the brass
plate of the machine {Fig. 178). When the air is
pumped out, and the upward or counterbalancing air
removed, so heavy is the load upon the glass vessel,
that a strong man could scarcely remove it from the
plate, although it be no larger than a small tumbler.

HEIGHT AND "WEIGHT OF THE ATMOSPHERE.

215

A glass jar with a
mouth six inches
across would need
a force equal to
nearly four hund-
red jDounds to dis-
place it. If there
he a glass vessel
open at both ends,
the hand placed on
the top may he so
firmly held by the
pressure that it can not be removed Fig. 179.

until the air is again admitted below
{Fig. 179). If a thin plate of glass
be placed on the top of this open ves-
sel, on pumping out the air, the
weight will suddenly crush it with a
noise like the report of a gun.

Some interesting instances occur in nature of the
use of atmospheric pressure. Flies walk on glass by
means of the pressure against the outside of their feet,
the air having been forced out beneath. In a similar
way, some kinds of fishes cling to the sides of rocks
under water, so as not to be swept off" by the current.
Dr. Shaw threw a fish of this kind into a pail of water,
and it fixed itself so firmly to the bottom, that, by tak-
ing hold of the tail, he lifted iip the pail, water and all.
It is the pressure of the atmosphere upon water that
drives it up the barrel of a pump as soon as the air is
pumped out from the inside. Hence the reason that
pumps can never be made to draw water more than

The Hand fastmed
by Air.

216 PNEUMATICS.

thirty-three feet below the piston, a height correspond-
ing to the weight of the atmosphere.

THE BAROMETER.

On the same principle the Barometer is made. It
consists of a glass tube, nearly three feet long, open at
one end, and which is first filled with mercury, a liquid
nearly fourteen times heavier than water. The open
end is then placed downward in a cup of mercury.
The weight of the mercury in the tube causes it to de-
Fig. 180. scend until the pressure of the atmosphere on
the mercury in the cup preserves an equilibrium,
which takes place when the column in the tube
has fallen to about two feet and a half high, the
upper part of the tube being left a perfect vac-
uum, as no air can enter {Fig. 180). Now, as
the height of the column of mercury depends
alone upon the weight of the atmosphere, then,
whenever the air becomes fighter or heavier, as
*'^'"- it constantly does during the changes of the
weather, the rising or falling of the column indicates
these changes ; and, what is very important, it shows
the approaching changes of the weather several hours
before they actually take place. Hence it becomes a
valuable assistant in foretelling the weather. When
the mercury falls, showing that the atmosphere is be-
coming lighter, it indicates the approach of storms or
rain ; when it rises, a settled or fair sky follows. These
are often foreshown before there is any change in the
appearance of the sky. For this reason the barometer
is sometimes called a weather-glass. It is of the
greatest value to navigators at sea. Long voyages

THE BAROMETER. 217

which formerly required a year have been made in
eight months by means of the assistance afforded by
the barometer, admitting a full spread of canvas by
night as well as by day, from the certainty of its pre-
dictions. On land its indications are not so certain, and
at some places less so than at others. Sometimes, and
more commonly during autumn and winter, the sink-
ing of the mercury is followed only by wind instead
of rain. There is, however, no doubt that its use would
be of much advantage in large farming establishments,
more especially during the precarious seasons of haying
and harvesting.

The barometer is an instrument of great value in
determining with little labor, and with considerable ac-
curacy, the heights of mountains, hills, and the leading
points of an extensive district of country. In rising
above the level of the sea, the weight of the air above
us becomes less ; that is, the pressure of the air upon
the barometer decreases, and the column of mercury
gradually falls as we ascend. To determine, therefore,
the height of a mountain, we have only to place one
barometer at its foot while another stands at the top,
and then, by observing the difference in the height of
the mercury, we are enabled to calculate the height of
the mountain. The following table shows how much
the barometer falls at different altitudes, thirty inches
being taken for the sea-level :*

* The mercury rarely stands as high as 30 inches at the level of the
sea, the mean height being about 29.5 inches. But this does not af-
fect the measurement of heights, which is determined, not by the actual
height, but by the difference in heights.

K

218 PNEUMATICS,

At 1000 feet above the sea, the column falls to 28.91 inches.
2000 " " " » " 27.86 "

3000 » " " " " 26.85 "

4000 " " " " " 25.87 "

5000 " " " " » 24.93 "

1 mile " " " " 24.67 "

2 " " " « u 20.29 "

3 " " « " " 16.68 "

4 " u u u u 1373 u

5 " " " " u 11.28 "
10 " " " " " 4.24 "
15 " " " " " 1.60 "
20 " " " " '< 0.95 »

At the level of the sea, the barometer falls about
one hundredth of an inch for a rise of nine feet, or a
little more than the tenth of an inch for a rise of one
hundred feet. At a height of one mile it requires about
eleven feet rise to sink the mercury a hundredth of an
inch.

In selecting land in mountainous districts of the
country, w^here degrees of frost increase with increased
altitudes, and .where the height of one portion above
another has an important relation to the cost of draw-
ing loads up and down hill, the barometer might be-
come of much practical value.

THE SYPHON.

The si/phon operates on a principle quite similar to
that of the pump ; but, instead of pumping out the air
of the tube through which the water rises, a vacuum
is created by the weight of a column of water, in the
following way : Fig: 181 represents a syphon, which is
nothing more than a tube bent in the form of a letter
U inverted. Now, if this be filled throughout with

THE SYPHON.

219

water, and then placed with the short-
er arm in the vessel of water, A, the
weight of the column of water in the
longer arm, which is outside, will over-
balance the weight of the other col-
umn, and will therefore run out in a
stream. This tends to cause a vacu-
um in the tube, which is instantly fill-
ed by the water rushing up the short-
er arm, being driven up by the pressure of the atmos-
phere, A stream will consequently continue running
through the syphon until the vessel is drained.

The syphon may sometimes be very usefully em-
ployed in emptying pools or ponds of water on high
ground, without the trouble of cutting a ditch for this
purpose. For instance, let a {Fig. 182) represent a

Fig. 182.

body of water which it is desirable to drain off; by
placing the lead tube, b c, so that the arm, c, may be
lowest, and applying a pump at this arm to withdraw
the air and fill the syphon with water, it will com-
mence running, and continue till the water has all been
drawn off. Difficulties, however, sometimes occur. If
the tube is small and very long, and the descent is
trifhng, the friction of the water in the tube may pre-
vent success. Water usually gives out small quanti-
ties of air, which collects in the higher part of the sy-

220 PNEUMATICS.

phon, and after a while fills it, causing the stream to
cease running ; but syphons for this purpose, when only
a few rods in length, with several feet descent, are
usually found to succeed well. If the discharging
orifice is several times smaller than the tube, it is fre-
quently of material use, by causing a slow and steady
current through the syphon.

221

CHAl'TER 11.

MOTION OF AIR.

SECTION I.

WINDS.

Wind is air in motion. Its force depends on its
speed. When its motion is slow, it constitutes the
soft, gentle breeze. As the velocity increases, the force
becomes greater, and the strong gale sweeps round the
arms of the wind-mill with the strength of many horses,
and huge ships are driven swiftly through the waves
by its pressure. By a still greater velocity of the air,
its power becomes more irresistible, and solid buildings
totter, and forest trees are torn up by the roots in the
track of the tornado.

The force of wind increases dh*ectly as the square
of the velocity. Thus a wind blowing ten miles an
hour exerts a pressure four times as great as at five
miles an hour, and twenty-five times as great as at two
miles an hour. The following table exhibits the force
of wind at different degrees of velocity :

Description.
Hardly perceptible.
Just perceptible.

rliles an

hour.

1

Pressure in lbs. on
a square foot.
.005

2

.020^
.045 5

3

4

.080^
.125 5

5

6

.180 i
.320 5

7

Light breeze.
Gentle, pleasant wind.

222 PNEUMATICS.

Miles an Pressure in lbs. on n„„„,i„,i..„

hour. a square foot. Description.

10 .500

15 1.125

20 2.000 ;

25 3.125 :

30 4.500 ;

35 6.125 I

40 8.000 ;

45 10.125 I

Pleasant, brisk wind.
Very brisk.
Strong, high wind.
Very high.

50 12.500 Storm or tempest.

60 18.000 Great storm.

80 32.000 Hurricane.

100 50.000 Tornado, tearing up trees, and sweeping off

buildings.

These forces maybe observed at a time when the air
is still, by a forward motion equal to that of the wind.
Thus walking moderately gives the faint breeze against
the face ; riding in a wagon at six miles an hour causes
the sensation of a pleasant wind ; the deek of a steam-
boat at fifteen miles produces a brisk blow ; while an
open rail-car at forty miles an hour occasions a sweep
of the air nearly resembling a tempest.

The preceding table will enable any one to calculate
with considerable accuracy the amount of draught
which a horse must constantly overcome in traveling
with a covered carriage against the wind, adding, of
course, the speed of the horse to that of the wind. For
example, suppose a horse with a covered carriage is
driven against what we term " a very brisk wind,"
blowing 24 miles an hour, and pressing 3 lbs. on the
square foot. The carriage top offers a resisting surface
four feet square, or with sixteen square feet. Three
times sixteen, or 48 lbs., are consequently required to
be overcome with every onward step of the horse.

^ ^VIND-MILLS. 223

Now we have already seen, when treating of " appU-
cation of labor," that a horse traveling three miles an
hour for eight hours, will overcome only 83 lbs. with
ordinary working, which is not double the resistance
of the wind. Hence we perceive that more than half
the horse's strength is lost by driving against such a
current. At six miles an hour, all his strength, with-
out over-driving, would be expended in overcoming
the force of the wind, and the power required for mov-
ing the carriage would be so much excessive labor.
For simplifying the operation, the increased motion of
the wind occasioned by driving against it has not been
taken into account.

Even with a small pressure, the loss in power is con-
siderable for an entire day. When, for example, the
air is perfectly still, travehng six miles an hour will
cause a constant resistance of 3 lbs. on the carriage, or
one fourteenth of the power exerted for a full day's
work. The same speed against a " gentle wind" of six
miles an hour, added, would increase the resistance four-
fold, or equal to 12 lbs. ; more than one fourth of the
horse's strength at six miles an hour through the day.

^VIND-MILLS.

The power possessed by the sails of a wind-mill
may be nearly ascertained in the same way, the area
of the sails being known, and first deducting their av-
erage velocity.

The force of wind may be usefully applied by al-
most every farmer, as it is a universal agent, possess-
ing in this respect great advantages over water-power,
of which very few farms enjoy the privilege.

224

PNEUMATICS.

Wind may be applied to various purposes, such as
Fig- 183. sawing wood by the aid

of a circular saw, turn-
ing grindstones, and
particularly in pumping
water. One of the best
contrivances for pump-
ing is represented by
Fig. 183, where A is
the circular wind-mill,
with a number of sails
set obliquely to the di-
rection of the wind, and
always kept facing it
by means of the vane, B.
The crank of the wind-
mill, during its revo-
lutions, works the pump-rod, I, and raises the water
from the well beneath. In whatever direction the wind
may blow, the pump will continue working. The
pump-rod, to work steadily, must be immediately un-
der the iron rod on which the vane turns. If the di-
ameter of the wind-mill is four feet, it will set the
pump in motion even with a light breeze, and with a
brisk wind will perform the labor of a man. Such a
machine will pump the water needed by a large herd
of cattle, and it may be placed on the top of a barn,
with a covering, to which may be given the architec-
tural effect of a tower or cupola, as shown in Fig. 184,
opposite.

A more compact machine, but of more complex con-
struction, is shown in Fig. 185, opposite, where the up-

Wind-mill for pumping water on farms :
A, wind-mill ; B,vane; \, pump-rod.

WIND-MILLS.
Fig. 184.

225

Bam surmounted with viind-mill for pumping water,
cutting straw, ^c.

Fig. 185.

K2

226 PNEUMATICS.

per circle moves around with the wheel and vane on
the fixed lower circle, to which it is strongly secured so
as to admit of turning freely. In other respects it is
similar to the preceding.

In all wind-mills, it is important that the sails should
have the right degree of inclination to the direction of
the wind. If they were to remain motionless, the angle
would be different from that in practice. They should
more nearly face the wind ; and as the ends of the sails
sweep round through a greater distance and faster, they
should present a flatter surface than the parts nearer
the centre. The sails should, therefore, have a twist
given them, so that the parts nearest the centre may
form an angle of about 68 degrees with the wind, the
middle about 72 degrees, and the tips about 83 degrees.

In order to produce the greatest effect, it is necessa-
ry to give the sails a proper velocity as compared with
the velocity of the wind. If they were entirely un-
loaded, the extremities would move faster than the
wind, m consequence of its action on the other parts.
The most useful effect is produced when the ends move
about as fast as the wind, or about two thirds the ve-
locity of the average surface.

The most useful wind is one that moves at the rate
of eight to twenty miles per hour, or with an average
pressure of about one pound on a square foot. In large
wind-miUs, the sails must be lessened when the wind
is stronger than this, to prevent the arms from being
broken ; and if much stronger, it is unsafe to spread
any, or to run them.

CHIMNKV CURRENTS. 227

CAUSES OF WIND.

The motion of air in producing wind is explained by
the action of heat, although there are many irregular
currents whose cause is not well uuderstood. The
simplest illustration of the effect of heat in causing cur-
rents is furnished by the land and sea breezes in warm
latitudes. The rays of the sun during the day heat the
surface of the land, and the air in contact with it also
becoming heated, and thus rendered hghter, flows up-
ward ; the air from the sea rushes in to fill the vacancy
and causes the sea-breeze. During the night, the ra-
diation of heat from the land into the clear sky above
cools the surface to a lower temperature than that of
the sea ; consequently the air in contact with the sea
becomes heated the most, and rising, causes the wind
from the land to flow in and supply the place. Trade-
winds are caused in a similar way, but on a much
larger scale, by the greater heat of the earth at the
equator, which produces currents from colder latitudes.
These currents assume a westerly tendency, in conse-
quence of the velocity of the earth being the greatest
at the equator, and which, outstripping the momentum
which the winds have acquired in other latitudes, tends
to throw them behind, or in a westerly direction.

SECTION II.

CHIMNEY CURRENTS.

Chimney Currents are produced by the heat of the
fire rarefying the air, which rises and carries the smoke
with it. The taller the chimney is, the longer will be

228

PNEUMATICS.

the column of rarefied air tending upward, and, as a
consequence, the stronger will be the draught. In kin-
dhng a fire in a cold chimney, there is very little cur-
rent till this column becomes heated. The upward
motion of heated currents is governed by laws similar
to the downward motion of water in tubes, where the
velocity is increased with the height of the head. But
as air is more than eight hmidred times lighter than
water, shght causes wiU affect its currents, which would
have no sensible influence on the motion of liquids.
For instance, a strong wind striking the top of a chim-
ney may send the smoke downward into the room ;
and a current can not be induced through a horizontal
pipe without connecting with it an upright pipe of con-
siderable height.

CONSTRUCTION OF CHIMNEYS.

In constructing chimneys to produce a
strong draught, the throat immediately
above the fire, which should have a breadth
equal to that of the fire-place, should be
contracted to a width of about four inches,
so that the column of rising air above may
draw the air up through the throat with
increased velocity, as shown in Fig. 186.
This arrangement also allows the fire to be
built so as to throw the heat more fully out
into the room. By leaving the shoulder
at b square or flat, it will tend to arrest
any reversed or downward current in a bet-
ter manner than if built sloping, as shown
by the dotted line at a, which would act

CHIMNEY-CAPS.

229

like a funnel, and throw the smoke into the room.
Fig. 187. The throat should he about as high as the ex-
treme tip of the flame ; if much higher, the
chimney will not draw so well, and if lower,
too much of the heat will be lost. Fi^. 187
shows a fire-place without a contracted throat,
the current of which is comparatively feeble.
Many chimneys draw badly by being made
too large for the fire to heat sufficiently the
column of air they contain.

CHIMNEY-CAPS.

When wind sweeps over the roof of a high
part of the budding, or over a hill, it often
strikes the top of chimneys below, and drives
the smoke downward. This may be often
prevented by placing a cap over the chim-
ney, like that represented by Fig. 188,
which is supported at its corners, the
smoke passing out at the four sides just
under the eaves of this cap. But it some-
times happens that there is a confusion of
currents and eddies at the top of the cliim-
ney, over which this cap has no influence.
In this case, the cap represented by Fig.
189 furnishes a perfect remedy, and is, in-
deed, perfect in its operation under any cir-
cumstances whatever, for the chimney sur-
mounted by it will always draw when
there is wind from any quarter, with or without any
fire. It has effected a perfect cure in some chimneys
which before were exceedingly troublesome, and were

Fig.

Fig. 189.

230

PNEUMATICS.

Fig. 191.

Fig. 190. regarded as incurable. Fig. 190

is intended to show the mode of
its operation, the wind, as shown
by the arrows, being deflected for
a considerable distance on the lee
side, so as to form a vacancy at
a, which the wind from the other end and from the
chimney both rush in to supply. Being fixed on with-
out turning in the chimney, it is both simpler and less
noisy than any caps furnished with a vane.

EmersoTi's Chimney-cap, lately invented, is differ-
ent in construction, but quite similar in
principle to the preceding. It is shown
by Fig. 191. A sheet-iron pipe is set in
the top of the chimney, furnished with
the conical rim, and a plate or fender
on the top which excludes the rain. Be-
tween the plate and rim is a space

Fig. 192.

quite simi-
lar in form or section to
that represented by Fig.
190.

In exposed situations,
chimneys are found to
draw more imiformly by
contracting the top about
a third less than the rest
of the flue. The current
at the moment of escape
is swifter than below, and
less acted upon by any
downward check from the

CHIMNEY-CAPS.

231

wind, at the same time that the surface is
smaller on which the wind can strike the
current, as shown in Fig. 192. A chim-
ney of this character may he very easily
made by contracting the tiers of brick, thus
giving to it an ornamental appearance, as
seen in Fisr. 193.*

* Where different fires communicate with the same chimney, sep-
arate flues should be built for each fire, and kept separate in the same
chimney-stack, carried up independently of each other. But even
with this precaution, smoky rooms will not be avoided, unless the ter-
mination of the chimney is of the right form, of which the following
illustration is given in Allen's Rural Architecture :

" Fifteen years ago we purchased and removed into a most substan-
tial and well-built stone house, the chimneys of which were construct-
ed with open fireplaces, and the flues carried up separately to the top,
where they all met upon the same level surface, as chimneys in past
times usually were built, thus. Every fireplace in
the house (and some of them had stoves in) smoked
intolerably ; so much so, that when the wind was in
some quarters, the fires had to be put out in every
room but the kitchen, which, as good luck would
have it, smoked less — although it did smoke there —
than the others. After balancing the matter in our
own mind some time whether we would pull down and rebuild the
chimneys altogether, or attempt an alteration — as we had given but lit-
tle thought to the subject of chimney draft, and to try an experiment
was the cheapest — we set to work a bricklayer, who, under our direc-
tion, simply built over each discharge of the several flues a separate
pj^ 195 *°P °^ fifteen inches high, in this wise : the remedy

was perfect. We have had no smoke in the house
since, blow the wind as it may, on any and on all oc-
casions. The chimneys can^t smoke ; and the whole
expense for four chimneys, with their twelve flues,
was not twenty dollars ! The remedy was in giving
each outlet a distinct current of air all around, and on
every side of it."

X

232

PNEUMATICS.

VENTILATION.

Impure air may be breathed for a short time with-
out any serious detriment, but to live in it and respire
it for years can not fail to produce permanent injury to
the health. During the heat of summer, open doors
and windows will usually furnish plenty of fresh air,
as long as this season lasts, which in the Northern
States is not one half of the year. During the rest of
the time rooms are heated with close stoves, and unless
special care is taken to secure fresh air, pale or sickly
inmates will be the most likely results.

Even with a common open fire-place, which causes
more circulation of the air in a room than stoves, the
ventilation is very imperfect. The following figure
{Fig: 196) represents the fresh air as passing in from

Fig. 196.

A badly-ventUated Room.

an open window opposite the fire, producing a direct
current from the window to the chimney, and leaving
all the upper portion of the room filled with bad air,
unaffected by the change. The cold air can not rise,
nor the hot air descend. This difficulty may be easily

VENTILATION. 233

removed by placing a register (which may be closed or
opened at pleasure) at a, in the upper corner, so that
the confined air may escape into the chimney. With-
out this provision, it is nearly impossible to preserve
the air in proper condition for breathing, for the upper
part, being warmest and lightest, remains unchanged
at the top. In rooms heated by stoves, registers for es-
cape of the foul air are still more important, where the
thermometer frequently indicates twenty degrees differ-
ence in the heat above and at the floor, the lower stra-
tum of air resting like a cold lake about the feet, while
the head is heated unduly.

"When the draught of the chimney-fire is not strong,
the smoke may, however, escape through the ventilat-
ing register into the room. To avoid this difficulty, it
is best to provide separate air-flues in the walls when
the house is built, for effecting perfect ventilation. In
rooms strongly heated by fires, the fresh air should be
admitted near the ceiHng, producing descending cur-
rents, and effecting a complete circulation in the air of
the room. But in sleeping apartments and in closets,
not heated artificially, and where the descending cur-
rents will not take place, the fresh air should be admit-
ted through a register or small rolling blind near the
floor, and discharged near the ceiling into an air-flue.
Fig. 197. The excessive warmth of

garrets in mid-summer may be
avoided by placing a ventilator
at the highest part, and admit-
ting air at windows or openmgs
near the eaves {Fig-. 197), thus

Mode of Ventilating Garrets. SWecpUlg aU thc hot air OUt by

234

PNEUMATICS.

the current produced ; or, the oppressive heat of half-
story bedrooms may he similarly avoided, by creating
a current of air between the roof and the plastering
{Fig'. 198). Two modes may be adopted, as repre-
sented on each side of the figure.

Fig. 198.

Mode of Ventilating- half-story Bed-

PART IV.

HEAT.

CHAPTER I.

CONDUCTION OF HEAT.
SECTION I.

CONDUCTING POWER OF BODIES.

"When any substance or body has become heated, it
loses its heat in two different ways, by conduction and
by radiation. When conducted, heat passes off slow-
ly or gradually through bodies, as when a pin is held
by the hand in a candle, the heat advancing from one
end to the other till it burns the fingers ; or, when an
iron poker is thrust into the fire, the heat gradually
passes through it till the whole becomes hot. Iron
and brass are, therefore, said to be good conductors of
heat. The end of a pipe-stem may, however, be heated
to redness, and a wooden rod may be set on fire, with-
out even warming the other extremity, because the
heat is very slowly conducted through them. "Wood
and burned clay are, therefore, poor conductors.

The comparative conducting power of different sub-
stances may be shown by placing short rods of each
with one of their ends in a vessel of hot sand, the oth-
ers to be tipped with wax. The different periods of
time required to melt the wax indicate the relative

236 HEAT.

conducting powers. It will speedily melt on the cop-
per rod ; soon after, on the rod of iron ; glass will re-
quire longer time ; stone or eathenware still longer ;
while on a rod of wood it will scarcely melt at all.
These rods should he laid horizontally, that the hot air
rising from the sand may not affect the wax. The
conducting powers may be judged of likewise, with
considerable accuracy in cold weather, by merely plac-
ing the hand upon the different substances. The best
conductors will feel coldest, because they withdraw the
heat most rapidly from the hand. Iron will feel colder
than stone ; stone colder than brick ; wood still less so ;
and feathers and down least of all, although the real
temperature of all may be precisely the same.

UTILITY OF THIS PRINCIPLE.

A knowledge of this property is often very useful.
For instance, it is found that hard and compact kinds
of wood, as beach, maple, and ebony, conduct heat
nearly twice as rapidly as light and porous sorts like
pine and basswood. Hence doors and partitions made
of light wood make a warmer house than those that are
more heavy and compact. Pine or basswood would,
in this respect, be better than oak or ash.

Porous substances of all kinds are the poorest con-
ductors ; saw-dust, for example, being much less so
than the wood that produced it. For this reason, saw-
dust has been used as a coating around the boilers of
locomotives to keep in the heat, and for the walls of
ice-houses to exclude it. Sand, filled in between the
double walls of a dwelling, renders it much warmer in
winter and cooler in summer than if sandstone were

CONDUCTING POWER OF LIQUIDS. 237

made to fill the same space. Ashes, being more po-
rous, are found to be still better. Tan, which is simi-
lar to saw-dust, is well adapted to filling in the walls
of stables and poultry -houses, where more than usual
warmth in winter is required. Confined air is a very
poor conductor of heat ; hence the advantage of double
walls and double windows, provided there are no crev-
ices for the escape of the confined air. This principle
has been lately applied in the manufacture of hollow
brick for building the walls of dwellings.

The light and porous nature of snow renders it emi-
nently serviceable as a clothing to the earth in the
depth of winter, preventing the escape of the heat from
below, and protecting the roots of plants from injury
or destruction. Hence the very severity of the cold
of the Northern regions, by producing an abundance of
those beautiful feathery crystals which form snow, be-
comes the means of protecting from its own effects the
tender herbage buried beneath this ample shelter.

CONDUCTING POWER OF LIQUIDS.

Liquids are found to conduct heat very slowly, and
they were for a long time considered perfect non-con-
ductors. Some interesting experiments have been per-
formed in illustration of this property. A
large glass jar may be filled with water (Fig.
199), in which may be fixed an air thermom-
eter, which is always very quickly sensitive
to small quantities of heat. A shallow cup
of ether, floating just above the bulb, may be
set on fire, and will continue to burn for
some time before any effect can be seen upon

238 HEAT.

the thermometer. The upper surface of a vessel of wa-
ter has been made to boil a long time, with a piece of
unmelted ice at the bottom. Liquids are found, howev-
er, to possess a conducting power in a very slight degree.
When a vessel of water is heated in the ordinary-
way over a fire, the heat is carried through it merely
by the motion of its particles. The lower portion be-

^. „„„ comes warm and expands ; it immediate-
Fig. 200. _ ^ '

ly rises to the surface, and colder portions
sink down and take its place, to ascend in
their turn. In this way, a constant cir-
culation is kept up among the particles.
These rising and descending currents are
shown by the arrows in Fig. 200. This
result may be easily shown by filling a flask
with water into which a quantity of saw-
dust from some green hard wood has been
thrown, which is about as heavy as water.
It will traverse the vessel in a manner precisely Hke
that shown in the figure.

These results show the importance of applying heat
directly to the bottom of all vessels in which water is
intended to be heated. A considerable loss of heat oft-
en occurs when the flame is made to strike against the
sides only of badly-arranged boilers.

SECTION II.
EXPANSION BY HEAT.

An important effect of heat is the expansion of bod-
ies. Among many ways to show it, an iron rod may
be so fitted that it will just enter a hole made for the

EXPANSION BY HEAT.

239

purpose in a piece of sheet-iron. If the rod be now-
heated in the fire, it expands and becomes larger, and
can not be thrust into the hole. The expansion may
be more visibly shown and accurately measured by
means of an instrument called the Pyrometer {Fig.
201). The rod a b, secured to its place by a screw at

Fig. 201.

if>££^

a, presses against the lever c, and this against the lever,
or index, d, both of which multiply the motion, and
render the expansion very obvious to the eye when the
rod is heated by the lamps. If the rod should expand
one fiftieth of an inch, and each lever multiphes twen-
ty times, then the index (or second lever) will move
along the scale eight inches ; for 20 times 20 are 400,
and 400 50ths of an inch are 8 inches.

Many cases showing the expansion of heated bodies
occur in ordinary practice. One is afforded by the
manner in which the parts of carriage wheels are bound
together. The tire is made a little smaller than the
wooden part of the wheel; it is then heated till, by

240 HEAT.

expanding, it becomes large enough to be put on, when
it is suddenly cooled with water, and by its powerful
contraction binds every part of the wheel together with
great force. Hogsheads are firmly hooped with iron
bands in the same way, with more force than could be
ever given by driving on with blows of the mallet.

This principle was very ingeniously applied in draw-
ing together two expanding brick walls of a large
building in Paris, which threatened to burst and fall.
Holes were drilled in the opposite walls, through which
strong iron bars across the building projected, and cir-
cular plates of iron were screwed on these projecting
ends. The bars were then heated, which increased
their length ; the plates were then screwed closely
against the walls. On cooling, they contracted, and
drew the walls nearer together. The process was re-
peated on alternating bars, until the walls were re-
stored to their perpendicular positions.

All tools, where the wooden handles enter iron sock-
ets, will hold more firmly if the metal is heated before
inserting the wood.

The metallic parts of pumps sometimes become very
difficult to unscrew, and a case has occurred where
two strong men could not start the screws, until a by-
stander suggested that the outer piece be heated, keep-
ing the inner cool, when a force of less than ten pounds
quickly separated them. In other cases, where the
large iron nuts have been thoughtlessly screwed, while
warmed with the hands, on the cold metallic axles of
wood-sawing machines in winter, they have contracted
so that the force of two or three men has been insuffi-
cient to turn them.

THE STEAM-ENGINE.

241

The sudden expansion of todies by heat sometimes
causes accidents. Thick glass vessels, when unequally
heated, expand unequally, and break. Heated plates
of cast iron or cast kettles are very Hable to be frac-
tured by suddenly pouring cold water upon them. The
same effect has been usefully appUed in sphtting the
scattered rocks which encumber a farm, and which
are too large to remove while entire. Fires are built
upon them ; the upper surface expands, while the low-
er remains cold, and large portions are successively
separated in scales, and sometimes the whole rock is
severed. The only care needed is to observe atten-
tively and remove with an iron bar any parts which
may have become loosened by the heat, and which
would prevent the heat from passing to other portions.
One man will thus attend to a large number of fires,
and will split in pieces ten times as many rocks in a
day as by drilling and blasting.

Fig. 202.

THE STEAM-ENGINE.

The Steam-engine owes its power to
the enormous expansion of water at the
moment it is converted into steam, which
is about 1600 times its bulk when in the
form of water. The principle on which
the steam-engine acts may be understood
by a very simple instrument represented
in Fig. 202. A glass tube with a small
bulb is furnished with a solid air-tight
piston, capable of working up and down.
The water in the bulb, a, is heated with
a spirit-lamp or sand-bath ; the rising
L

242 HEAT.

steam forces up the piston. Now immerse the bulb in
cold water or snow, and the steam is condensed again
into water, the tube is left vacant, and the pressure of
the atmosphere forces down the piston. By thus al-
ternately applying heat and cold, it is driven up and
down like the piston of a steam-engine. The only dif-
ference is, the steam-engine is furnished with appara-
tus so that this application of heat and cold is perform-
ed by the machine itself. The bulb represents the
boiler, and the tube the cylinder ; but in the steam-
engine the boiler is separate, and connected by a pipe
with the cyhnder ; and instead of applying the cold
water directly to the cylinder, it is thrown into an-
other vessel called the condenser, connected with the
cylinder.

When Newcomen, who made the first rude regular-
ly-working engine, began to use it for pumping water,
he employed a boy to turn a stop-cock, connected with
the condenser, every time the piston made a stroke.
The boy, however, soon grew tired of this incessant la-
bor, and endeavored to find some contrivance for relief
This he effected by attaching a rod from the piston or
working-beam to the cock, which was turned by the
machine itself at every stroke. This was the origin
of the first self-acting engine.

The different parts of a common steam-engine may
be understood from the following figures, one represent-
ing the boiler, and the other the working machinery.

The boiler, B {Fig. 203), contains water in the low-
er part and steam in the upper ; F B is the fire ; v o is
the feed-pipe ; v, a valve, closed by the lever, b c a,
whenever the boiler is full enough, by means of the ris-

THE STEAM-ENGINE.

243

ing of the float, S, and opened whenever the float sinks
from low water. M, barometer s:aus;e, to show the

Fig. 203,

Boiler of Steam-ensine.

pressure of the steam ; w, weight on the lever, e b, for
holding down the safety-valve : this lever being grad-
uated like a steelyard, the force of the steam may he
accurately weighed. U is a valve opening downward,
to prevent the boiler being crushed by atmospheric
pressure, by allowing the air to pass in whenever the
steam happens to decline. Two tubes with stop-cocks,
c and d, one just below the water-level and the other
just above it, serve to show, by opening the cocks,
whether the water is too high or too low.

The working part of the engine is represented in the
figure on the following page {Fig. 204). The steam
enters by the pipe, s, from the boiler on the other side
of the brick wall, as shown in Fig-. 203. The steam

244

Low-pressure Steam-engine.

passes through what is called Si four-way-cock, a, first
into the lower, then into the upper end of the cylinder,
C, as the piston, P, moves up and down ; this is regu-
lated by the levers, y y. The piston-rod, E, is attach-
ed to the working-heam, B F, turning on the centre, A.
The rod, F R, turns the fly-wheel, H H, and drives
the mill, steam-hoat, or machinery to be put in motion.
The condenser, j, shown directly under the cylinder,
remains to be described. It is immersed in a cistern
of cold water, and is connected by pipes to the upper
and lower end of the cylinder. Through these pipes
the steam passes out of the cyhnder, first from one end
and then from the other, and is condensed into water
by a jet of cold water thrown into it by the injection-
cock. When condensed, it is pumped out by the pump,
0, into the well or reservoir, W, and then again into

THE STEAM-ENGINE. 245

the feed-pipe of the boiler. Warm water is thus con-
stantly supplied to the boiler, and effects a great sav-
ing of fuel.

The supply of steam and the motion of the engine
are regulated by the governor^ Gr. "When the motion
is too fast, the two suspended balls, which revolve on
a vertical or upright axis, and which hang loosely like
pendulums, are thrown out from the axis, producing
the movement of a rod which shuts the steam-valve.
When the motion is too slow, the balls approach the
axis and open the valve.

In high-pressure engines the steam is not condensed,
but escapes into the open air at every stroke of the pis-
ton, which produces the loud, successive puffs of all
engines of this kind.

The steam-engine, in its most perfect form, is a
striking example of human ingenuity, and its qualities
are thus described by Dr. Arnott : "It regulates with
perfect accuracy and uniformity the number of its
strokes in a given time, and records them as a clock
does the beats of its pendulum. It regulates the quan-
tity of steam ; the briskness of the fire ; the supply of
water to the boiler ; the supply of coals to the fire. It
opens and shuts its valves with absolute precision as to
time and manner ; it oils its joints ; it takes out any
air accidentally entering parts which should be vacu-
ous ; and when any thing goes wrong which it can not
of itself rectify, it warns its attendants by ringing a
bell ; yet, with all these qualities, and even when ex-
erting a force of six hundred horses, it is obedient to
the hand of a child. Its aliment is coal, wood, and
other combustibles. It consumes none while idle. It

246 HEAT.

never tires, and wants no sleep. It is not subject to
any malady when originally well made, and only re-
fuses to work when worn-out with age. It is equally
active in all climates, and wiH do work of any kind :
it is a water-pumper, a miner, a sailor, a cotton-spin-
ner, a weaver, a blacksmith, a miUer, a printer, and is
indeed of all occupations ; and a small engine in the
character of a steam pony may be seen dragging after
it, on an iron rail-way, a hundred tons of merchandise
or a thousand persons with the speed of the wind."

Steam-engines have been much used on large farms
in England for thrashing, grinding the feed of animals,
cutting fodder, and for other purposes. They have been
less used here, but may prove useful for large estab-
lishments, where the teams for ordinary tillage are in-
sufficient for stationary labor.

More difficulty exists in their use for plowing, in con-
sequence of the labor and expense of moving frequent-
ly so heavy a machine, and the still greater difficulty
of using a locomotive power like that on rail-roads on
the soft surfaces of farms.

EXCEPTION TO EXPANSION BY HEAT.

A striking exception to the general law of expansion
by heat occurs in the freezing of water.*' During its
change to a solid state, it increases in bulk about one
twelfth, and this expansion is accompanied with a
great force. The bottoms of barrels are burst out, and
cast-iron kettles are split asunder, when water is suf-
fered wholly to freeze in them. Lead pipes filled with

* There are a very few other substances which expand on passing
from a liquid to a solid state.

EXCEPTION TO EXPANSION BY HEAT. 247

ice expand ; but if it is often repeated, they are crack-
ed into fissures. A strong brass globe, the cavity of
which was only one inch in diameter, was used by the
Florentine academicians for the purpose of trying the
expansive force of freezing water, by which it was
burst, although the force required was calculated to be
equal to fourteen tons. Experiments were tried at
Quebec, in one of which an iron plug, nearly tln-ee
pounds in weight, was thrown from a bomb-shell to
the distance of 415 feet ; and in another, the shell
was burst by the freezing of the water which it con-
tained.

This expansion has a most important influence in
the pulverization of soils. The water which exists
tlu-ough all their minute portions, by conversion to
frost, crowds the particles asunder, and when thawing
takes place, the whole mass is more completely mel-
lowed than could possibly be effected by the most per-
fect instrument. This mellowing is, however, of only
short duration, if the ground has not been well drain-
ed to prevent its becoming again packed hard by soak-
ing with water.

But this is not the most important result from the
expansion of water. Much of the existing order of na-
ture and of civilized hfe depends upon this property ;
without it the great mass of our lakes and rivers would
become converted into solid ice ; for, as soon as the
surface became covered, it would sink to the bottom,
beyond the reach of the summer's sun, and successive
portions being thus added, the great body of all large
rivers and lakes would become permanently frozen.
But instead of this disastrous consequence, the ice, by

248 HEAT.

resting upon the surface, forms an effectual screen from
the cold winds to the water below.

SECTION III.

LATENT HEAT.

If a vessel of snow, which has been cooled down to
several degrees below freezing by exposure to the se-
vere cold of winter, be placed over a steady fire with a
thermometer in the snow, the mercury will rise by the
increasing heat of the snow until it reaches the freez-
ing point. At this moment it will stop rising, and the
snow will begin to melt ; and although the heat is all
the time passing rapidly into the snow, the thermom-
eter will remain perfectly stationary till it is all con-
verted to water. The heat that goes to melt the snow
does not make it any hotter ; in other words, it becomes
latent (the Latin word for hidden), so as neither to af-
fect the sensation of the hand or to raise the thermom-
eter. Now it has been found that the time required
to melt the snow is sufficient to heat the same quantity
of water, placed over the same fire, up to 172 degrees,
or 140 degrees above freezing; that is, 140 degrees
have become latent, or hidden, in melting the snow.

This same amount of heat may be given out again
by placing the vessel of water out of doors to freeze.
A thermometer will show that the water is growing
colder by the escape of the heat, till freezing commen-
ces. After this it still continues to pass off, but the
water becomes no colder till all is frozen, as it was
only the latent heat of the water that was escaping.

A simple and familiar experiment exhibits the same

LATENT HEAT OF STEAM. 249

principle. Place a frozen apple, which thaws a little
helow freezing, in a vessel of ice-cold water. The la-
tent heat of the water immediately passes into the
apple and thaws it, and in an hour or two it will be
found hke a fresh apple and entirely free from frost;
hut the latent heat having escaped from the water
next the apple, a thick crust of ice is found to en-
case it.

The amount of latent heat may be shown in still
another way. Mix a pound of snow at 32 degrees, or
at freezing, with a pound of water at 172 degrees.
All will be melted, but the two pounds of water thus
formed will be as cold as the snow, showing that for
melting it the 140 degrees in the hot water were all
made latent.

ADVANTAGES OF LATENT HEAT.

If no heat became latent by the conversion of ice
and snow to water, no time would, of course, be required
for the process, and thawing would be instantaneous.
On the approach of warm weather, or at the very mo-
ment that the temperature of the air rose above freez-
ing, snow and ice would all dissolve to water, and ter-
rific floods and inundations would be the immediate
consequence.

LATENT HEAT OF STEAM.

A still larger amount of latent heat is required for
the conversion of water into steam ; for, again place
the vessel of water with its thermometer on the fire,
it will rise, as the heat of the water increases, to 212
degrees, and then commence boiling. During all this
L2

250 HEAT.

time it will now remain stationary at 212, till the wa-
ter is all boiled away. This is found to require nearly
five times the period needed to heat from freezing to
boiling ; that is, nearly one thousand degrees of heat
are made latent by the conversion of water into
steam.

"When the steam is condensed again to water, this
heat is given out. Hence the use made of steam con-
veyed in pipes for heating buildings, and for boiling
large vats or tubs of water, by setting free this large
amount of latent heat which the fire has imparted to it.

GREEN AND DRY WOOD FOR FUEL.

A great loss is often sustained in burning green
wood for fael, from an ignorance of the vast amount
of latent heat consumed to drive off the water the
wood contains. "VYlien perfectly green, it loses about
one third of its weight by thorough seasoning, which
is equal to about 25 cubic feet in every compact cord,
or 156 imperial gallons. Now all this water must be
evaporated before the wood is burned. The heat thus
made latent and lost, being five times as great as to
heat the water to boiling, is equal to enough for boiling
780 imperial gallons in burning up every cord of green
wood. The farmer, therefore, who burns 25 green
cords in a winter, loses heat enough to boil more than
fifteen thousand gallons of water, which would be
saved if his wood had been previously well seasoned
under shelter.

The loss in using green fuel is, however, sometimes
overrated. It has been found by experiment that one
pound of the best seasoned wood is sufficient to heat

GREEN AND DRY WOOD FOR FUEL. 251

27 lbs. of water from the freezing to the hoihng point.*
This wUl be equal to heating and evaporating four
pounds of water by every pound of wood. The 25
cubic feet of water, therefore, in every cord of green
wood, weighing about 1500 pounds, would require near-
ly 400 pounds of wood for its evaporation, or about one
seventh or one eighth of a cord. Hence we may infer
that seven cords of dry wood are about equal to eight
cords of green. This imperfect estimate will apply
only to the best hard wood, and will vary exceedingly
with the different sorts of fuel ; the more porous the
wood becomes, the greater will be the necessity for
thorough seasoning.

Superficial observation often leads to very erroneous
conclusions. Seasoned wood will sometimes burn with
great rapidity, and, producing an intense heat for a
short time, will favor an over-estimate of its superior-
ity. G-reen wood, on the other hand, kindles with dif-
ficulty, and burns slowly and for a long time ; hence,
where the draught of the chimney can not be control-
led, it may be the most economical, because a less pro-
portion of heat may be swept upward than by the more

* The following results show the heating power of several combust-
ibles :

1 lb. of wood (seasoned, but still holding 20 per cent, of water)

raised from 32° to 212'^ 27 lbs. water.

1 lb. of alcohol 68 " "

1 lb. of charcoal 78 "

1 lb. of oil or wax 90 " "

1 lb. of hydrogen 216 " "

It should be remembered that by ordinary modes of heating water,
a very large proportion of the heat is wasted by passing up the chim-
ney and into surrounding bodies, and the air.

252 HEAT.

violent draught produced from dry materials. Where
the draught can be perfectly regulated, however, seas-
oned wood should be always used, both for convenience
and comfort, and for economy.

Where wood is to be drawn to a distance, the pre-
ceding estimate shows that the conveyance of more
than half a ton of water is avoided in every cord by
seasoning.

RADIATION OF HEAT, 253

CHAPTER 11.

RADIATION OF HEAT.

The passage of heat through conducting bodies has
been aheady explained. There is another way in
which it is transmitted, termed radiation, in which it
is thrown off instantaneously in straight lines from
hot bodies, in the same way that light is thrown off
from a candle. A familiar instance is furnished by
the common or open fire-place, before which the face
may be roasted with the radiated heat, while the back
is chilled with cold. A screen held in the hand will
intercept this radiated heat, showing that it flies in
right lines like the rays of light.

E-adiated heat is reflected by a polished metallic
surface, in the same way that light is reflected by a
looking-glass. A plate of bright tin held near the fire
will not for a long time become hot, the heat being
reflected from it without entering and heating it. But
if it be blackened with smoke, it will no longer reflect,
but absorb the heat, and consequently will speedily
become hot. This experiment may be easily tried by
placing a new tin cup containing water over a char-
coal fire, which yields no smoke. The heat will be
reflected into the fire by the tin, and the water wiU
scarcely become warm. But if a few pine shavings
be thrown on this fire to smoke the surface of the tin,
it will then absorb the heat rapidly, and soon begin to
boil. This explains the reason that bread bakes more

254 HEAT.

slowly in a new tin dish, and that a polished andiron
before a fire is long in becoming hot.

A concave burning-mirror, which throws the rays of
heat to a focus or point, may be made of sheet-tin, by
beating it out concave so as to fit a regularly curved
gauge. If a foot in diameter, and carefully made, it
will condense the rays of heat so powerfully at the fo-
cus, when held several feet from the fire, as to set fire
to a pine stick or to flash gunpowder {Fig-. 205).

The reflection of radiated heat may be beautiful-
ly exhibited by using two such concave tin mirrors.
Place them on a long table several feet apart, and as-
certain the focus of each by means of the light of a
candle. Then place in the focus of one a red-hot iron
ball, or a small chafing-dish of burning charcoal. In
the focus of the other place the wick of a candle with
a small shaving of phosphorus in it. The heat will
be reflected, as shown by the dotted lines {Fig. 206),

Fig. 206.

DEW AND FROST. 255

and, setting fire to the phosphorus, will light the
candle.

If a thermometer be placed in the focus of.one mir-
ror while the hot iron ball is in the other focus, it will
rise rapidly ; but if a lump of ice be substituted for
the ball, the thermometer will immediately sink, and
will continue to do so until several degrees lower than
the surrounding air ; because the thermiometer radi-
ates more heat to the mirrors, and then to the ice, than
the ice returns.

DEW AND FROST.

All bodies are constantly radiatmg some heat, and
if an equal amount is not returned by others, they
grow colder, like the thermometer before the lump of
ice. Hence the reason that on clear, frosty nights, ob-
jects at the surface of the earth become colder than
the air that surrounds them. The heat is radiated
into the clear space above without being returned ;
plants, stones, and the soil thus become cooled down
below freezing, and, coming in contact with the moist-
ure of the air, it condenses on them and forms dew, or
freezes into white frost. Clouds return or prevent the
passage of the heat that is radiated, which is the rea-
son there are no night-frosts in cloudy weather. A
very thin covering, by intercepting the radiated heat,
will often prevent serious injury to tender plants.
Even a sheet of thin muslin, stretched on pegs over
garden vegetables, has afforded sufficient protection,
when those around were destroyed.

256

FROST IN VALLEYS.

On hills, where the wind blows freely, it tends to
restore to plants the heat lost by radiation, which is
the reason that hills are not so liable to sharp frosts as
still valleys. When the air is cooled it becomes heav-
ier, and, rolling down the sides of valleys, forms a lake
of cold air at the bottom ; this adds to the Uability of
frosts in low places. The coldness is frequently still
further increased by the dark and porous nature of the
soil in low places radiating heat faster to the clear sky
than the more compact upland soil.

A knowledge of these properties teaches us the im-
portance of selecting elevated places for fruit-trees, and
all crops liable to be cut off by frost ; and it also explains
the reason that the muck or peat of drained swamps is
more subject to frosts than other land on the same lev-
el. Therefore, corn and other tender crops upon such
porous soils must be of the earliest ripening kinds, so
as to escape the frosts of spring by late planting, and
those of autumn by early maturity.

REMARKABLE EFFECTS OF HEAT ON WATER.

The effects of heat and cold on water are of a very
interesting character. Without its expansion in freez-
ing, the soil would not be pulverized by the frost of
winter, but would be found hard, compact, and diffi-
cult to cultivate in spring ; without its expansion into
steam, the cities which are now springing up, and the
continents that are becoming peopled, through the in-
fluence of rail- ways, steam-ships, and steam manufac-
tures, would mostly remain unbroken forests ; without

REMARKABLE EFFECTS OF HEAT ON WATER, 257

the crystallization of water, the beautiful protection of
plants by a mantle of snow, in northern regions, would
give place to frozen sterility ; without the conversion
of heat to a latent state in melting, the deepest snows
would disappear in a moment from the earth, and
cause disastrous floods ; without its conversion to a la-
tent state in steam, the largest vessel of boiling water
would instantly flash into vapor. All these facts show
that an extraordinary wisdom and forethought planned
these laws at the creation ; and even what aopears at
first glance as an almost accidental exception in the
contraction of bodies by cold, and which causes ice to
float upon water, preventing the entire masses of riv-
ers and lakes from becoming permanently frozen, fur-
nishes one out of an innumerable array of proofs of
creative design in fitting the earth for the comfort and
sustenance of its inhabitants.

APPENDIX,

APPARATUS FOR EXPERIMENTS.

For the assistance of lecturers, teachers, and home students, the fol-
lowing list is given of cheap and simple apparatus and materials for
performing most of the experiments described in this work. These
experiments, although simple, exhibit principles of much practical im-
portance. A few articles of a more costly character are given in a
second list.

1. Inertia apparatus, p. 23. The concave post or stand is sufficient,
the snapping being done by the finger, although a spring-snap performs
the experiment more perfectly.

2. Weight with two hooks and fine thread, p. 23.

3. The inertia of falling bodies may be simply shown, and the pile-
engine illustrated, by placing a large wooden peg or rod upright in a
box of sand, and then dropping a weight upon its head at different
heights, which will drive the rod into the sand more or less, according
to the distance passed through by the falling weight.

4. A straw-cutter, so made that the fly-wheel can be easily taken off,
will show in a very striking manner the efficacy of this regulator of
force.

5. Two lead musket balls will exhibit the experiment in cohesion,
p. 42. Balls or lead weights with hooks may be separated by sus-
pending weights to show the amount of force required to draw them
asunder. Metallic buttons or plates an inch in diameter, with hooks,
vi'ill show the great strength needed to separate them when coated
with grease, p. 42.

6. Capillary tubes of different sizes, two straight small panes of glass,
and a vessel of water, highly colored with cochineal or other dye, to
exhibit capillary attraction.

7. Glass tube, piece of bladder, and alcohol, for experunent described
on p. 49.

8. The cylinder for rolling up the inclined plane, represented by

260 APPENDIX.

Fig. 18, p. 50, may be very easily made by using a round pasteboard
box a few inches in diameter, and securing a piece of lead inside by
loops made with a needle and thread. The object shown by Fig. 19
may be cut in one piece out of a pine shingle, the centre rod being
lengthwise with the grain ; the two extremities are shaved small, and
wound with thick sheet-lead, and the whole then colored or painted a
dark hue, to render the lead inconspicuous. The experiment with the
penknives, p. 51, is very simple, care being taken to insert them low
enough in the stick.

9. Irregular pieces of board, variously perforated with holes, and
furnished with loops to hang on a pin, may be used to determine the
centre of gravity, according to the principle explained by Fig. 21, p. 51.

10. Portions of plank and blocks of wood, with the centre of gravity
determined as in the last experiment, may have a plumb-line (which
may be a thread and small perforated coin) attached to this centre, and
then be placed on differently inclined surfaces, to show their upsetting
just as this line of direction falls without the base. Toy-wagons,
bought at the toy-shops, may be variously loaded and used in experi-
ments of this sort.

1 1 . Experiments with the lever of the first kind may be easily per-
formed by the use of a flat wooden bar, two or three feet in length,
marked into inches, and placed on a small three-cornered block as a
fulcrum. Weights, such as are used for scales, may be variously
placed upon the lever. Levers of the second and third kind, which
are lifted instead of borne down, may have a cord attached to the point
where the power is to be applied, running up over a pulley or wheel,
with a weight suspended to the other end.

12. An axle, furnished with wooden wheels with grooved edges, of
different sizes, may be used to exhibit the principle of the wheel and
axle, in connection with scale-weights that are furnished with hooks.
The power of combined cog-wheels may be shown by a combination
like that represented on p. 76, using weights for both cords.

13. Interesting experiments with the inclined plane, at different de-
grees of slope, by a contrivance similar to that represented by Fig. 87,
p. 104, with the addition of a small wheel at the upper side for a cord
to pass over. This cord is fastened at one end to a light toy-wagon,
running up and down the plane, and at the other to a weight suspend-
ed perpendicularly just beyond the upper edge of the plane. The
wagon is variously loaded with weights to counterpoise the suspended
weight at different degrees of inclination.

APPENDIX. 261

14. A lecturer may quickly demonstrate before a class the small in-
crease in the length of a road, in consequence of a considerable cun'e
to one side of a straight line (as shown by Fig. 70), by using a cord
for measuring, the diagram being marked on a board or the wall.

15. A round stick of wood, and a long, wedge-shaped slip of paper,
easily show the principle of Fig. 75, p. 94.

16. A cog-wheel with endless screw and winch, Fig. 77, p. 95, ex-
hibits distinctly the great power of the screw in this combination.

17. Pine sticks, two feet long, and one fourth to one half inch
through, of different shapes and sizes, supported at each end, and with
weights hung at the middle till they break, may be made to illustrate
the principles described on p. 100, 102.

18. Some of the principles of draught may be shown, and especially
those in relation to the different angles of inclination for hard and soft
roads, by using a common spring-balance as a dynamometer, attached
to a hand-wagon, and also to a sliding block of wood.

19. Bent glass tubes, with arms of different sizes to indicate the up-
ward pressure of liquids, may be procured cheaply at glass-works. The
experiment described by Fig. 154, p. 182, may be rendered easy and
interesting by purchasing a large and perfectly-working syringe, and
attaching to its nose, by means of sealing wax, a slender glass tube
two or three feet long. Fill the syringe with water, leaving the
tube empty ; then, with the tube upright, drive the water up through
it with the piston of the syringe, and the increased weight felt on the
piston as the column of water rises will be very evident.

20. A hydrostatic bellows a foot in diameter, made by any good
mechanic, will answer the purpose well, and exhibit an important
principle.

21. Specific gravities may be shown before a class by a common
balance and a fine cotton or silk thread.

22. A tin pail, with a hole half an inch or an inch in diameter at the
bottom, will show the contracted stream which pours from it, p. 191.
A short tin tube, with a slight flange at the upper end (quickly made
by any tin-worker), fitted into this hole, will increase the discharge, as
shown by Figs. 159, 160, and the difference in time for emptying the
vessel may be measured by a stop-watch.

23. Archimedes' screw is readily made by winding a lead pipe round
a wooden cylinder.

24. A glass syphon, filled with cochineal water, shows distinctly the
theory of waves, by blowuig with the mouth into one end.

262

APPKNDIX.

25. Any vessel, filled with sand which has been heated over a fire,
with rods of different substances, nearly of an equal size and length,
and thrust with one end into the hot sand, in an inclined or nearly
horizontal position, will exhibit the various conducting powers of these
rods by melting pieces of wax or tallow placed on the ends most re-
mote from the sand.

26. The expansion by heat may be demonstrated by fitting an iron
rod to a hole in sheet iron ; on heating the bar, it can not be made to
enter. Or, if a hot iron ring be slipped on a tapering cold iron rod, it
will contract on cooling so that the force of a man can not withdraw
the rod.

27. The rising and descending currents in a vessel of heating water
are easily rendered visible by throwing into a glass vessel, or flask,
over a lamp, particles of sawdust from any hard green wood, whose
specific gravity is about the same as that of water.

28. Instrument figured on p. 241, for showing the principle of the
steam-engine.

29. Experiments in latent heat may be easily exliibited with the as-
sistance of a common thermometer.

30. Tin mirrors for showing radiation, p. 254.

Second List, containing a few of the more costly pieces of appara-
tus for experiments as described in this treatise.

1. A good compound or solar microscope will exhibit the minute
animalcules described under the head o{ Divisibility. The larger of
these animalcules may be seen in old strong vinegar, and the smaller
in a drop of water taken from a vessel in which a portion of raw po-
tato has been soaked a few hours in a warm place. The same instru-
ment will show the pores of wood mentioned under the head Impene-
trability.

2. Atwood's machine, p. 39.

3. A good dynamometer for field experiments is of great value and
importance.

4. An air-pump, with the several pieces of apparatus connected with
it, shows, in an interesting and striking manner, several important
principles.

263

HYDROSTATICS AND HYDRAULICS.

TABLE OF SPECIFIC GRAVITIES.

Metals.

Gold, pure 19.36

" standard 17.16

Mercury 13.58

Lead 11.35

Silver 10.50

Copper 8.82

7.78

" cast

7 20

Steel . . .

7 82

Brass, common ....
Tin

7.82

7.29

Zinc

6.86

Stones and Earths.

Brick 1.90

Chalk 2.25 to 2.66

Clay 1.93

Coal, anthracite, about. . .1.53

Coal, bituminous 1.27

Charcoal 44

Earth, loose, about 1.50

Flint 2.58

Granite, about 2.65

Gypsum 1.87 to 2.1T

Limestone 2.38 to 3.17

Lime, quick 80

Marble 2.56 to 2.69

Peat 60 to 1.32

Salt, common 2.13

Sand 1.80

Slate 2.67

Woods — dry.
Green wood often loses one third of its weight by seasoning, and
sometimes more. The same kind varies in compactness with soil,
growth, exposure, and age of the trees.

Apple 68 to .79

Ash, white 72 to .84

Beech 72 to .85

Box 91 to 1.32

Cherry 71

Cork 24

Elm 58 to .67

Hickory 84 to 1.00

Maple 65 to .75

Pine, white 47 to .56

Pine, yellow 55 to .66

Oak, English 93 to 1.17

" white 85

" live 94 to 1.12

Poplar, Lombardy .40

Pear 66

Plum 78

Sassafras 48

Walnut 67

Willow 58

264 APPENDIX.

MiscellaTieous.

Beeswax 96

Butter 94

Honey 1.45

Lard 94

Milk 1.03

Oil, linseed 94

Oil, whale 92

" turpentine 87

Sea water 1.02

Sugar 1.60

Tallow 93

Vinegar 1.01 to 1.08

Weights of a Cubic Foot of various Substances, from which the Bulk of
a Load of one Ton may be easily calculated.

Cast Iron 450 pounds.

Water 62 "

White pine, seasoned, about 30 "

White oak, " " 52 "

Loose earth, about 95 "

Common soil, compact, about 124 "

Clay, about 135 "

Clay with stones, about 160 "

Brick, about 125 "

Bulk of a Ton of different Substances.
.23 cubic feet of sand, 18 cubic feet of earth, or 17 cubic feet of clay,
make a ton. 18 cubic feet of gravel or earth before digging, make 27
cubic feet when dug ; or the bulk is increased as three to two. There-
fore, in filling a drain two feet deep above the tile or stones, the earth
should be heaped up a foot above the surface, to settle even with it,
when the earth is shoveled loosely in.

DISCHARGE OF WATER THROUGH PIPES.
Table showing the amount of water discharged per minute through
an orifice one inch in diameter ; also through a tube one inch in di-
ameter and two inches long, according to experiment. To ascertain
the cunount in gallons, divide the cubic inches by 231.

265

Height of head
-«f Water.

Amount discharged

1 Par

3

4
5
C

7

tlirough Ori

s foot* 2,722 cub.

3,846

4,710
5,436
G,075
G,654
7,183
7,672
8,135
8,574
8,990
9,384
9,764
10,130
10,472

Amount discharged
througti Tube.

3,539 cub. in.

5,002

0,126

7,070

7,900

8,654

9,340

9,975
10,579
11,151
11,693
12,205
12,699
13,177
13,620

VELOCITY OF WATER IN PIPES.
The following table shows the height of a head of water required to
overcome the friction in horizontal pipes 100 feet long, and to produce
a certain velocity, according to Sme.vton :

Bore of

Pipes. & Inches
in. in.

i 4.5

1/00^.

in.

16.7

Wfcct.
in.

35.1

ft.
4

f^ct.
in.

9.7

ft. in.

10 1.0

ifcet. ,
ft. in.

17 10.0

bfect.
ft. in.

28 0.2

f

3.0

11.1

23.3

3

2.5

6

8.6

11

10.6

18 8.1

1

2.2

8.4

17.5

2

4.9

5

0.5

8

11.0

14 0.0

u

1.8

6.7

14.0

1

11.1

4

0.4

7

1.6

11 2.5

u-

1.5

5.6

11.7

1

7.2

3

4.3

5

11.3

9 4.1

11

1.3

4.8

10.0

1

4.5

2

10.6

5

1.1

8 0.1

2

1.1

4.2

8.7

1

2.4

2

6.2

4

5.5

7 0.0

2i

1.0

3.7

7.8

1

0.8

2

9.9

3

11.6

6 2.7

2i

0.9

3.3

7,0

0

11.5

2

0.2

3

6.8

5 7.2

3

0.7

2.8

5.0

0

9.6

1

8.2

2

11.7

4 8.0

3i

0.6

2.4

5.0

0

8.2

1

5.3

2

6.6

4 0.0

4

0.6

2.1

4.4

0

7.2

1

3.1

2

2.7

3 6.0

Look for the velocity of the water per second in the pipe, in the up-
per line ; and in the column beneath it, and opposite the given diam-
* A Paris foot is about 12 4-5 U. S. inches, and 15 Paris feet are about 16 U. S. feet.

M

266 APPENDIX.

eter of the pipe, is the height of the column or head required to obtain
the required velocity.

To find the quantity of water discharged each minute, multiply the
velocity by 12, which will give the inches per second ; then multiply
this product by 60, which will give the inches per minute ; then, to
change these cylindrical inches into cubic inches, multiply by 4 and
divide by 5.* Divide the cubic inches by 231, and the result will be
gallons.

By comparing this table with the next preceding, we shall perceive
that the water flows from three to four times as fast through the tube
two inches long, as through a tube one hundred feet long, the diameter
of the tube and the head of water being the same.

RULE FOR THE DISCHARGE OF WATER.
The following general formula, or rule applicable to different cases,
has been furnished by a practical engineer. It may be useful in ascer-
taining the quantity required to fill the driving pipe of a water-ram, and
for various other purposes occasionally occurring in practice.

Let A represent the fountain or reservoir from which water is to be
conveyed to the trough B through the pipe L. Let N be the height
of the surface of the water in the reservoir, above the place of dis-
charge, and let D be the diameter of the tube in the smallest part. It
is required to find the quantity Q which will be discharged in a second
of time. The length and height being given in feet,, and the diameter
of the tube in inches, the fonnula, when the quantity is required in
gallons, is as follows :

Q = 0.608 -/(D^^).

* This gives the cubic inches very nearly ; but, to be more accurate, multiply by
the decimal .7854, which represents the difference between the area of a square and
of a circle.

APPENDIX. 267

In order to make the above formula more intelligible :
Let L = 80 rods or 1330 feet.
" H = 50 feet.
" D = 2 inches.
" Q =: gallons.

Then Q=:0.608./(32X^) =0.67; or, the same may be thus

expressed in words.

Divide the height (50) by the length (1320); multiply the quotient
by the fifth power of the diameter (fifth power of 2 = 32) ; extract the
square root of the product, which, being multiplied by 0.608, will give
(0.67) the number of gallons the tube will discharge in one second ;
which in this case is 40 gallons in one minute.

THE END.

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