Two or three days after Mr. Gregg had talked over the principles of the

wheel and axle, with the children, Fred received notice that a consignment

of wood-work was at the station awaiting his orders. Mr. Gregg made

immediate arrangements with the railway people, and by the time he got

home from his office, the stuff was being unloaded by the boys, who

carried it piece by piece into the workshop, each section being laid

by itself in the order in which it was to be put in place in the boat.

Printed instructions were in the equipment for laying the keel, setting up

the frames, and even for taking the stuff out of the packages and putting

it in heaps, so that it could be readily picked out when wanted for use.

Each rib was numbered, and marked or stamped "right" or "left," and all

the pieces were cut off to the right length and to the right bevel or

angle to suit the positions they were to occupy, as specified in the

printed instructions. This made the setting up an easy matter, requiring

only care, patience, and a fair knowledge of the use of wood-working

tools. That Fred possessed these qualities, was partly due to the training

he had received in the technical school, and partly to his natural

aptitude for picking up methods, ideas, and new applications.

Fred, George, and Mr. Gregg himself, were much interested in the selection

of the various materials, and when the plank that was to form the keel

had been unpacked, George was anxious that it should be laid down on the

bed that had been prepared for its reception. He was quite disappointed

when he found it considerably shorter than he had expected the boat to

be. It was explained to him, however, that the overhanging of the stern,

and therefore shortening of the forefoot, or stem, necessitated the keel

being shorter than the boat would be when measured over all on top. The

keel was found to be a fine piece of tough oak, nicely dressed, made the

proper shape at each end, bored and gained to receive the stern post, the

stern ribs, and side stanchions. Everything was marked, and each timber

was sized so that it would fit in place snugly without using a tool on

it, except a hammer or mallet.

At tea time George felt it difficult to keep reasonably quiet, he was so

enthusiastic about the boat--much to the amusement of his father, who knew

exactly how the boy felt.

[Illustration: Fig. 24. Stem of launch]

After tea, all walked to the boat house, and the father assisted Fred to

set up the keel, which was in two pieces, halved together midway and well

fastened with screws. The joint was painted with a heavy coat of white

lead and linseed oil paint, before being put together and screwed up. The

keel is the lowest timber in a boat or ship, and it runs nearly the length

of the craft. Sometimes there is a keelson placed on the top of the keel,

and the ribs of the boat, or stanchions, are made fast to that timber, as

shown in the illustration, (Fig. 24,) in which the gains for the ribs or

moulds are made. This portion of the boat was put together temporarily, so

Fred had no difficulty in assembling the various pieces. The stem, keel,

keelson, and deadwood were all made of oak, and looked strong. The keel

and keelson were properly laid and adjusted, and after some explanations

by Mr. Gregg the manner of setting up the ribs was thoroughly understood.

Fred decided to telephone Walter Scott to come down next day, as it was

Saturday, and help him to set up the skeleton.

As the weather was getting warm, the whole family spent the evening on

the veranda and George introduced the question of naming the boat. He

suggested _Red Bird_, but this did not seem to take well, and several

others were proposed but none seemed to suit everybody. Jessie sat quietly

on the steps till asked by Fred what her choice would be.

"I would like it called after mamma, _Caroline_."

"That's a good idea, Jessie," said her father, "and if the boys or your

mother don't object, I think we'll settle on _Caroline_."

Early next morning the boys were out watching for _The Mocking-Bird_,

which very soon made its appearance. Fred and Walter tied the boat up

to the new dock and went into the boat house, where the latter began to

examine the boat stuff, and to explain the manner of setting it up and

fastening it in place.

Nick, who was on hand to help, did the heavy work, and helped to put up

the stanchions. Walter seemed quite familiar with the work, and he and

Fred soon had the boat so well in hand that it seemed to grow under their

fingers. The ribs were easily selected, as they were tied together in

pairs and numbered. They were then set in their places according to their

numbers and were fastened to the keelson with the strong copper nails.

All the nails required for the boat were of copper, because that metal is

less likely to corrode than iron or steel.

It was found necessary to brace the ribs in order to keep them in line.

Thin pieces of lath were tacked on the tops to hold the ribs the proper

distance apart, and longer and stronger strips of wood were used for

bracing the boat sideways. These were nailed to the joints in the ceiling

or high up on the walls of the boat house.

[Illustration: Copyright, 1911, by Underwood & Underwood, N. Y.

MAKING A MOTOR LAUNCH

"All the Nails Required for the Boat Were of Copper, Because That

Metal is Less Likely to Corrode Than Iron or Steel"

]

[Illustration: Fig. 25. Section of launch--abeam]

At noon the boys had the skeleton of the boat well advanced, and to one

standing in front of the bow, it presented an appearance like the sketch

shown at Fig. 25.

[Illustration: Fig. 26. Methods of sheathing]

The launch might be called "carvel ribbon built," or nearly so, and it

would have a displacement of 14 or 15 hundred-weight when fairly loaded.

This weight would bring her down to the third W. L., as shown in the end

sketch. To load her to the fourth W. L., would give her a load far beyond

these figures. The sections had to be closely spaced, and the ribbons or

slats let into the temporary section moulds before the outside boarding

could be put on, the edges of the boarding being clinch fastened, as shown

in the ribbon carvel, Fig. 26. Other styles of sheathing boats, as shown,

are often used, but the _Caroline_ was "ribbon carvel."

It is usual to lay off the sheer profile on a suitable floor, and line

in the rebate line, scarf of stem, deadwoods, fork timbers, etc., making

thin moulds of each member to be lined off, sawn, and bolted together.

The section moulds, from which the boat derives its shape, are also laid

off, and the planking, 3/8-in. thick, deducted when making them.

The stem, of crooked oak, was 2-1/4 in. thick by about 3 in., shaped as

shown in Fig. 24. The fore deadwood was 2-1/2 in. thick, moulded about

3 in., and through-bolted to the stem and keel with 3/8-in. copper

bolts; and the stern-post, 3-1/2 in. thick, was wrought to shape, as

shown. The centre line of the shaft, as shown, is subject to alteration,

since different makes of motors have different sizes of propellers and

flywheels. The fork timbers were let into the stern-post, and carried the

transom, wrought out of a flitch of elm 3-1/2 in. thick. The planking,

of 3/8-in. cedar, was closely jointed and varnished, and secured to the

ribbons. The timbers were of rock elm, 7/8 in. by 1/2 in., steamed and

bent or sawn to shape, and through-fastened at the top and bottom edges

of the planking. These were spaced on 7-1/2-in. centres, with two clinch

nails into the ribbons between them. Three or four solid floorings should

be worked into the motor space; fitting of the motor bed thwartships gives

great support to the boat.

The thwarts were of oak, 8 in. wide and 1 in. thick, with the side seats,

7/8 in. thick, supported by turned legs of oak. The decks at each end

should be of 1/2-in. oak or cherry reeded into 3 in. widths, and filled

with marine glue. The covering board, 2-1/2 in. wide, with a nosing worked

on the edges, and 1/2 in. thick, was carried by a clamp or binding stake,

2-1/2 in. by 5/8 in., through-fastened at every timber. The knees were of

oak, 1 in. thick, about 10 in. on the foot by about 3 in. at the head,

and through-fastened. A breast hook 2 in. thick should be fitted. The

floor boards may be of 3/4-in. spruce, elm, or ash grating, as preferred.

The centre of the motor was at No. 6 section, as indicated, the gasolene

being stored in a strong tank under the forward deck, just high enough

to feed by gravitation. After being cleaned off and sandpapered, a coat

of good shellac varnish, may be followed, if desired, by three coats of

best yacht varnish. The spacing of the sections was: No. 1, from face to

stem, 1 foot 2 in.; No. 2, from No. 1, is 1 ft. 2 in., the other sections

to No. 11 each 1 ft. 6 in.; No. 12 was 1 ft. 1 in. from No. 11 (see Fig.

25). The water-lines were 5 in. apart, and the buttock-lines, A and B, 1

ft. and 1 ft. 9 in. respectively from the middle line.

The boys followed these directions, and with the help of the following

table, managed to get the boat ready to varnish and finish up. The

following table, which refers more particularly to the section shown

in Fig. 25, shows the sheer lines, counting from L W L (low water

line). While all the work and calculations regarding the plan had been

already done, Mr. Gregg, who had watched the work's progress for a

week, thought they should know the principles on which the craft was

being built, and therefore advised them to examine the illustration and

table, so that they would have some knowledge of the science required

to build a boat intelligently. Fred and George did this, and were

helped along by Walter, who seemed to have mastered the subject pretty

thoroughly.

TABLE OF OFFSETS

===============+=========+=========+=========+=========+=========

| |

| _Stem_ | _Section Numbers_

---------------+---------+---------+---------+---------+---------

| | 1 | 2 | 3 | 4

---------------+---------+---------+---------+---------+---------

|_ft. in._|_ft. in._|_ft. in._|_ft. in._|_ft. in._

| | | | |

Sheer heights | | | | |

above L.W.L. | 1 7 | 1 6 | 1 5 | 1 4-1/8| 1 3-1/4

| | | | |

L.W.L. to | | | | |

rebate line | | 7 | 8-3/4| 9 | 9-1/4

| | | | |

Half-breadths | | | | |

at gunwale | | 8-1/4| 1 3-1/8| 1 9-1/2| 2 1-1/8

| | | | |

Half-breadths | | | | |

at 4 W.L. | | 6-7/8| 1 1-1/2| 1 8 | 2 0-1/2

| | | | |

Half-breadths | | | | |

at 3 W.L. | | 5-7/8| 11-5/8| 1 6-3/8| 1 11

| | | | |

Half-breadths | | | | |

at L.W.L. | | 4-3/8| 9-3/8| 1 3-5/8| 1 8-3/4

| | | | |

Half-breadths | | | | |

at 1 W.L. | | 2-1/2| 5-3/4| 10-1/2| 1 3

| | | | |

Buttock A | | | | |

from L.W.L. | | | 5-1/2| 4-1/8| 6-3/8

| | | | |

Buttock B | | | | |

from L.W.L. | | | | | 3/8

---------------+---------+---------+---------+---------+---------

===============+=========+=========+=========+=========+=========

|

| _Section Numbers_

---------------+---------+---------+---------+---------+---------

| 5 | 6 | 7 | 8 | 9

---------------+---------+---------+---------+---------+---------

|_ft. in._|_ft. in._|_ft. in._|_ft. in._|_ft. in._

| | | | |

Sheer heights | | | | |

above L.W.L. | 1 2-3/4| 1 2-1/4| 1 2-1/8| 1 2-1/8| 1 2-1/2

| | | | |

L.W.L. to | | | | |

rebate line | 9-1/2| 9-7/8| 10 | 10-1/2| 10-3/4

| | | | |

Half-breadths | | | | |

at gunwale | 2 3-1/2| 2 4-1/2| 2 4-3/8| 2 3-5/8| 2 2-1/8

| | | | |

Half-breadths | | | | |

at 4 W.L. | 2 2-7/8| 2 4 | 2 3-7/8| 2 3-1/4| 2 1-3/4

| | | | |

Half-breadths | | | | |

at 3 W.L. | 2 2 | 2 3-1/4| 2 3-1/4| 2 2-1/2| 2 0-3/4

| | | | |

Half-breadths | | | | |

at L.W.L. | 2 0 | 2 1-1/2| 2 1-1/2| 2 0-5/8| 1 9-1/2

| | | | |

Half-breadths | | | | |

at 1 W.L. | 1 6-3/4| 1 8-1/2| 1 8-1/2| 1 6-1/2| 1 0-7/8

| | | | |

Buttock A | | | | |

from L.W.L. | 7-5/8| 8 | 8 | 7-1/2| 5-1/4

| | | | |

Buttock B | | | | |

from L.W.L. | 3-3/8| 4-3/4| 4-3/4| 3-1/2| 3/8

---------------+---------+---------+---------+---------+---------

===============+=========+=========+=========+=========

| | _End of_

| _Section Numbers_ |_Transome_

---------------+---------+---------+---------+---------

| 10 | 11 | 2 |

---------------+---------+---------+---------+---------

|_ft. in._|_ft. in._|_ft. in._|_ft. in._

| | | |

Sheer heights | | | |

above L.W.L. | 1 3 | 1 3-5/8| 1 4-1/4| 1 6

| | | |

L.W.L. to | | | |

rebate line | 11 | | |

| | | |

Half-breadths | | | |

at gunwale | 2 0 | 1 9-1/2| 1 6-3/4|

| | | |

Half-breadths | | | |

at 4 W.L. | 1 11-3/8| 1 7-1/4| |

| | | |

Half-breadths | | | |

at 3 W.L. | 1 9-1/4| 8-1/2| |

| | | |

Half-breadths | | | |

at L.W.L. | 1 2-1/8| | |

| | | |

Half-breadths | | | |

at 1 W.L. | 5-3/4| | |

| | | |

Buttock A | | | |

from L.W.L. | 1 | 6 | 11-3/4|

| | | |

Buttock B | | | |

from L.W.L. | | | |

---------------+---------+---------+---------+---------

It was necessary, before installing the motor, that a foundation should

be laid for it, so varnishing and the final finish were left over until

the engine and propeller should be put in and tried.

[Illustration: Fig. 27. Starboard side of motor]

[Illustration: Fig. 28. Port side of motor]

The engine was brought to the boat house from Newark, and the expert,

engaged by Mr. Gregg some time previous, came along with it, bringing

such tools as he might want. He examined the bed for the engine, and saw

that all was properly fastened and in good condition to place the engine

and the propeller shaft. Mr. Watts (the machinist) laid off a line for

the propeller shaft and with a long auger bored a hole from the engine

bed through to the stern-post, large enough to permit the shaft of the

propeller to revolve in it easily. A bearing, or "box," was adjusted to

the stern-post in which the shaft ran, and the "box" was made water-tight

to prevent any inflow. The propeller was made of bronze, had been nicely

fitted to the shaft before it came, and had a set screw in its hub to hold

it firmly on the shaft. The diameter of the propeller wheel measured 15

inches and it had two blades. The shaft and wheel being properly adjusted,

the next thing was to place the engine, which weighed about 200 lbs. The

blocks and tackle used in taking down the old barn were rigged up to the

ceiling by cutting a hole through the floor, laying a short timber across

the joists, hitching a rope around the timber, and letting a loop hang

down through the hole made in the floor. The hook of the upper block was

attached to the loop, a sling was fastened to the engine, the whole was

hoisted by Nick with the greatest ease, and the machine dropped on its

bed. As it did not lie quite level, it was raised again and held suspended

until the bed was trued up, when it was permanently lowered into place

and fastened down. Two views of the engine are shown in Figs. 27 and 28.

[Illustration: Fig. 29. Carburetor]

In "shop talk," the engine may be described as follows--Bore of cylinder

4-1/2 in. Stroke 4-1/2 in. Crank shaft 1-3/8 in. Revolutions per minute

from 60 to 750. Propeller shaft one inch. About 15 or 16 horse-power.

A float-feed carburetor, Fig. 29, was installed at the same time. This

carburetor is an excellent one. It insures a regular supply of gasolene

and air, in proper proportion, and prevents trouble when the motor is in

use. The float guarantees an even level of gasolene in the float chamber

at all times. The proper balance of the cork float closes the supply of

gasolene automatically when it reaches the proper level. This prevents

waste of fuel, every drop being thoroughly vaporized and mixed with the

proper amount of air. The spraying nozzle is higher than the gasolene

in the float chamber, and prevents the gasolene from getting into the

engine, unless it is running. The throttle valve on the carburetor gives

the operator the power to change instantly the speed, without changing

the timer, and affords him absolute control of the engine.

When all the machinery was in place, and the propeller attached, Mr. Watts

told the boys that he would finish up the work of installing the next day,

and would then run the engine "dry" for an hour or two, to get everything

working nicely before declaring the _Caroline_ ready for sea.

It was just two weeks from the day the stuff arrived when the engine was

finally installed.

"That's pretty quick work," declared Walter, "and if the boat were

varnished, we could have her in the water in a couple of days."

In the evening, as all the Greggs were seated on the veranda, Fred tried

to explain to his father the installation of the engine, but he failed to

make himself quite clear.

Mr. Gregg said to him: "You seem to have grasped the theory of the matter,

but I see you don't understand some important points, so I think a few

suggestions may be of use to you. I will not confine myself to marine

motors altogether, as gasolene engines are used for many purposes, more

and more every day. With regard to installing an engine in a boat, the

first question is the bed, as you have seen in your own case, where your

foundation is made good and solid.

"Small engines may be supported upon a single cross piece at each end of

the bed, but this method should be employed only for the smallest sizes.

"The heaviest, and in most cases the hardest, pipe to fit up is the

exhaust. It runs from the exhaust nozzle on the engine to the muffler and

thence outboard.

"The muffler is commonly placed in the stern with the outlet directly

outboard. It may, however, be in any convenient position, like under the

seats in the standing room, and the piping led outboard. In any case, the

piping for the exhaust should be as direct and as free from sharp bends

as possible.

"When the motor is near the middle of the boat, a good practice is to

lead the exhaust pipe out through the bottom, and along it to a point near

the stern, where it again enters the boat and connects with the muffler.

The outlet from the muffler then leads directly outboard as before. This

method, especially on a large cabin boat, avoids much loss of space and

the disagreeable heat of the exhaust pipe. The surrounding water quickly

cools the exhaust, reduces the pressure and makes the exhaust almost

noiseless.

"The particular function of the muffler is to afford a comparatively large

space into which the exhaust may pass and expand, greatly reducing the

pressure. The gas, under the reduced pressure, then passes out with little

disturbance. The muffler need be of no particular shape, as long as the

volume is sufficient. It is usually made of cast iron in the smaller sizes

and of sheet iron in the larger. In many cases a long piece of rather

large pipe will answer the same purpose.

"The muffler may be dispensed with and much space saved by carrying the

exhaust directly through the bottom of the boat and exhausting under

water. Although this is a very convenient and many times satisfactory way,

great care must be used or poor results will be obtained. When the exhaust

leads directly out, a certain amount of pressure is used in displacing

the water. This pressure is, of course, supplied by the piston and is a

'back pressure,' retarding the piston and decreasing its power.

"A small expansion chamber or muffler should be provided between the

engine and the outlet, in order to break up the violent pulsations and

make the flow fairly constant. Some form of shield should be fitted over

the outer end of the exhaust pipe to guide the stream of the exhaust aft

and prevent the water being forced into it by the movement of the boat.

Several forms of these are on the market in the shape of brass castings

which bolt on to the outside of the hull and have a thread on the inside

to take the exhaust pipe.

"When the under water exhaust is fitted, a pet cock should be put in the

exhaust pipe near the engine. This is opened when the engine is stopped,

thus preventing the water from being drawn up into the cylinders by the

vacuum caused by the cooling of the gases in the pipe and cylinders.

"The under water exhaust is a very neat and simple method, when correctly

installed, as all noise and heat from the exhaust pipe are avoided. The

exhaust may be considerably cooled and the noise reduced by dispersion.

"With regard to stationary engines, used for domestic or other purposes,

any old place is considered good enough to put them in. Now, this is one

of the biggest and most expensive mistakes one can make, for as soon as

some small screw gets loose in the far corner, the engine, salesman and

manufacturer are unjustly blamed, simply because the present owner has not

left enough room to make the small adjustments necessary in every engine

and piece of machinery. Therefore, it pays always to install the engine in

a light, dry place, easy of access and with sufficient space all round to

enable all parts to be reached and to give plenty of room for turning the

fly wheels in starting. Whenever possible, place the engine on the ground

floor. On an upper floor, the necessary provision should be made to avoid

vibration; if installed in the basement, place it in the best light.

"Without a good foundation, an engine may be expected to give more or

less trouble from vibration, since it is subjected to forces, suddenly and

repeatedly exerted, which produce violent reactions. Care should be taken

to excavate down to good soil and to line the bottom with a substantial

thickness of concrete in order to form a single mass of artificial stone.

The foundations may then be built up of either concrete, brick, or stone.

Anchor plates should be extended to the bottom of the masonry and fastened

so as to prevent turning while the nuts are being screwed up. Place gas

pipes or tubes with an inside diameter twice the diameter of the bolts

around them, while the foundation is being built; this allows the bolts

to be adjusted, and any variations between the tubes may be filled with

thin cement after the engine is set.

"The top of the foundation should be finished perfectly flat and level

with a dressing of cement, and after this is thoroughly dry the engine

may be placed in position. When bolting down the engine, it is better

to draw each bolt down a little at a time until all are tight and thus

avoid straining the engine crank. After the nuts are drawn tight, if the

crank turns unreasonably hard without loosening the main bearing caps,

it may indicate an uneven foundation, which is a strain in the engine bed

casting.

"When setting up large engines, for farm or other purposes, especial care

must be taken to avoid straining the bed castings. Foundations hung from

an upper floor, or built upon it, should be placed as close to the wall

as possible. For the smaller sizes of engines it is a good plan to lay

wooden beams on top of the foundations and then to place the engine on

top of them so that when the frame is bolted down it beds itself into the

timber. The timber cap often saves an annoying vibration when it can be

overcome in no other way.

"All the connections should be as short and as free from turns as

possible, and no mistake can be made by having plenty of unions, so as to

disconnect with ease. The gasolene tank should be set as near the engine

as is convenient, with the top of the tank, preferably, not more than

a foot or two below the base of the engine. In cases where the gasolene

tank must be set from forty to fifty feet away, it is necessary to place a

check valve in the suction pipe near the tank. Both suction and overflow

pipes must have a gradual rise all the way from the tank to the pump and

should be as straight as possible to avoid the air traps, which prevent

a steady flow of gasolene. It is most essential to clean thoroughly all

pipes and fittings before they are put together, by hammering lightly to

loosen any scale and washing out with gasolene, as solid matter of this

nature may be responsible for some of the simple, but hard-to-get-at

troubles common to gasolene engines.

"Shellac is best for joints in gasolene piping, but when this cannot be

obtained common laundry soap will answer the purpose just about as well.

Remember, also, that gasolene is a rubber solvent, and should never be

applied to joints where rubber is used. In some cases it will be found

advisable to use gravity feed instead of a pump, except in the case of the

tank, which must be so arranged that its lowest point is slightly above

the generator valve.

"The exhaust pipe must be of full size, free from turns and short as

possible, since the shorter it is the more economically the engine will

run. It will be found advisable to place the muffler and exhaust piping

away from combustible material, and never to turn the exhaust into any

chimney or flue.

"There are two general methods of supplying the water, the first being

that of the cooling tank commonly used with small engines. For convenience

in piping, the tank should be slightly elevated, and both pipes, having as

few bends as possible, should slope from the tank to the engine, a valve

being placed in the bottom pipe near the tank. By using a circulating

pump, fitted to the engine or shaft, water may be used from an underground

cistern or tank.

"The other method is to use a continuous cooling stream from water-works

or other source. When city water is used, it is a good plan to have a

break and funnel inserted in the drain pipe so that the current of water

flowing through the cylinder jacket may be seen. For making joints in

water pipes, either thick lead or graphite may be used with almost equal

success. It may be well to place particular emphasis on the fact that

it will pay to get into the habit of always shutting off the water at

the tank and draining the cylinder every time the engine is stopped--not

necessary in summer, but absolutely essential in winter--as a fair

percentage of gasolene users know to their cost.

"The greatest care must be employed in using and handling gasolene, as it

is dangerous and highly explosive. It has been known to explode when 20

or 30 feet from light, the vapours having reached the fire in the way of a

gas, igniting and firing the liquid. And, now, right here, let me impress

on you this warning; never handle gasolene near a fire or light under any

circumstances, and be very careful with it under all conditions.

"Fortunately, there are few accidents resulting from gasolene, when we

consider the large amount used since it has become almost a universal

fuel for engines, and it is also used largely for domestic heating and

lighting.

"It is a product of petroleum, of which in its crude form about 76 per

cent. is turned into kerosene, 11 per cent. into gasolene, 3 per cent.

into lubricating oils, and the balance into vaselines, paraffine, coke

and so forth.

"Different petroleums produce different proportions of the various

products, some of them being considerably richer in gasolene than 11 per

cent.

"Gasolene is usually designated according to its specific gravity by an

arbitrary measure, known as Baume's hydrometer scale. This designation

is in degrees, the most common gasolene ranging between 65 degrees and

85 degrees, and the average being 70 degrees, the usual density used in

engines.

"You will find it somewhat difficult at first to start up your engine when

you wish to, so I will give you a few hints to show how this difficulty

may often be overcome.

"There is always a reason why a gas engine refuses to obey the behest of

its driver.

"In the first place, see that the compression is right and the admission

valve so tight that it will admit only enough of the mixture (gasolene

and air) to make a charge that will take fire from the sparker and move

the piston forward. Next see that the sparker is clean, that it will make

a bright spark at white heat when the contact is broken, and at the right

time. 'In time' means to go if everything else is right, and 'out of time'

means not to go even when everything else is right.

"The valve of the engine must be kept well ground down with emery and oil

so as to preclude the possibility of a leak, as one would very seriously

weaken the power of the engine even after it had started. The spark must

be made when the connecting rod of the engine is on the 'up stroke,' with

the crank shaft about three inches below the horizontal line of the centre

of the index, and herein lies the whole secret of the greatest efficiency

from the least amount of gasolene. As there is an interval of time after

the spark is made until it ignites the charge, it is very evident that the

movement of the machinery continues and the moment of ignition should take

place when the compression is greatest. This will be when the piston is

on its farthest 'in stroke,' _i. e._, in perfect line with the centre of

the cylinder. But if the charge be ignited at this point the engine will

not develop the greatest power, as the interval spoken of will elapse and

the piston will have started on its 'out stroke', thereby not getting its

full force of the expansive gases liberated by combustion of the air and

gasolene.

"So you will readily see that you must allow for the interval spoken of,

if you would get full returns for the energy used in propelling the motor.

I have tried to make this plain, and I hope my efforts will help you out

with your engine, either in starting or developing the power at which it

is rated."

It was not yet late, so the boys took down from the book shelf a code of

yacht flag signals, and found the following:

"There are no hard and fast rules regarding shapes and colours of yacht

bunting, but the following are generally accepted by the prominent clubs

in the United States and in foreign countries.

1. The "pennant" (a triangular shaped flag) is used for the club burgee.

2. The "shallow tail" is adopted for the private signal.

3. The rectangular flag is chiefly used for a flag officer's signal.

4. The shape, consequently, at once denotes whether a flag is that of a

club, a flag officer, or a member.

5. The majority of flag officers' signals are coloured: Blue for

commodore, red for vice-commodore, and white for rear-commodore.

6. The international code of signals enables yachts to communicate with

each other, and is also used for dressing ship.

The ensign should be flown from the peak of the main-sail on a sailing

yacht, when under way, and from a stern flag pole when moored.

On a yawl, it should be hoisted at the mizzen truck.

On a steamer, launch, or dinghy, it should be flown from a stern flag

pole, when under way or at anchor.

_Club Burgee._--The burgee should measure in length about one-half inch

for each foot of height of truck from the water; width to be two-thirds

of the length. Private signals may be smaller.

The burgee should be flown from the mast-head or truck of a cutter,

sloop, or cat-rigged yacht, the main truck of a yawl, the fore truck of

a schooner and steamer, and from the bow pole of a launch or dinghy.

Flag officers' and private signals should be flown from the truck of a

cutter, sloop, or cat-rigged yacht, the main truck of a schooner, yawl,

or steamer, and from the bow pole of a launch or dinghy.

The following flags are not considered as colours:

_Night Pennant_ (_blue_).--Is hoisted at the main truck from sundown to

8 A. M.; also occasionally used as a tell-tale when racing or sailing.

_Owner's Absent Flag_ (_blue rectangular_).--Is flown from the main

starboard spreader when yacht is at anchor only. It denotes owner is not

on board, but should never be flown when under way.

_Owner's Meal Flag_ (_white rectangular_).--Is flown from the main

starboard spreader, and denotes the owner is at meals--boarding a yacht

when this flag is flying is considered bad form.

_Crew Meal Flag_ (_red triangular_).--Is flown from the foreport spreader

on schooners and main-port spreader on single-masted yachts. This denotes

that the crew is at meals.

_The Ensign._--Displayed on a vessel indicates distress and want of

assistance.

_Flag "B,"_ of the International Code of Signals, is used for a protest

flag, and is conspicuously displayed in the rigging of a yacht protesting

during a race.

A yacht, on withdrawing from any race, should at once lower its racing

colours, and allow yachts still competing the right of way.

This code was studied by the boys until both of them thoroughly understood

its full meaning, and George became so enthusiastic over it that he

exclaimed: "Fred, I am going to be an admiral of the navy!"

V

A TALK ABOUT ENGINES

Mr. Watts was early at the Gregg residence next day, and busied himself

preparing the engine to start up. A big tub was taken to the boat house

filled with water by a hose attached to the suction pipe, and dropped

into the water. This was a mystery to George, who inquired about the use

of the water and the other attachments. It was explained to him, that

outside the cylinder there was a hollow space, called the "water jacket,"

extending over the top of the cylinder, and this had to be kept full of

cold water by continual circulation. It was pumped in by the engine and

forced out by the same means, a simple contrivance being arranged for the

purpose. This circulation of water is necessary to keep the inside of the

cylinder cool, otherwise the walls would soon become red hot, on account

of the rapid explosions of gas and air employed in the cylinder to keep

the piston moving to and fro.

George seemed to grasp the idea thoroughly. Mr. Watts also explained

the use of the carburetor, the spark coil, the battery, and the method

of contact to produce a spark at the proper moment. After some screwing

of bolts, adjusting the piston, and trying the valves, the tank in the

carburetor was supplied with gasolene and Mr. Watts tried the engine for

a few revolutions, as gently as it could be done. It was a little stiff

at first, some of the connections fitting too tight, and the piston,

being new and harsh, did not work smoothly. By the judicious use of

good lubricating oil and a few turns of some of the nuts on the bolts,

a little more freedom was given to the machine and the starting was easy

and smooth. George and Jessie were delighted with the rapid movement of

the machine, the buzz of the propeller, and particularly interested in

the movement of the water in the tub.

Mr. Watts allowed the engine to run quite a little while, and arranged the

exhaust so as to beat regularly and to "pop! pop!" as little as possible.

He then called Fred into the boat and taught him how to run the machine,

arrange the contact breaker, and regulate the feeding of fuel. The engine

was stopped to cool and to be examined again by Mr. Watts, who pronounced

it all right. Mr. Gregg, who had arrived just before the engine was

stopped, examined all its parts and watched it work for a minute or so.

Fred arranged his pots and brushes, and he and George went to work

varnishing, so that before sunset the _Caroline_ looked quite smart and

trim. The boys were very careful in applying the varnish to put it on

light and thin so as not to let the coats lap over one another as they

went along. They finished each "streak" from end to end, before starting

on the next, and following this method they obtained a nice, even surface.

The varnish did not look "blotchy" or patched, as it would have done had

the ends of the varnish lapped. To avoid "lapping" is one of the most

essential operations in varnishing, when a nice piece of work is desired.

[Illustration: Copyright, 1911, by Underwood & Underwood, N. Y.

FINISHING THE MOTOR LAUNCH

"To Avoid 'Lapping' is One of the Most Essential Operations in

Varnishing"

]

It was decided to give the little craft two more coats of shellac varnish

before launching her, and the following spring to give her a good coat of

marine varnish. Mr. Gregg thought that in another week, say the following

Wednesday, the _Caroline_ might be launched with safety, as the varnish

would get dry and hard, and the inside paint would also be hard enough.

Jessie and the boys were given permission to invite a few friends each to

the boat launching, and were promised suitable refreshments to be served

on the new grounds, if the weather was favourable. Fred asked his father

if he could not build up some temporary picnic tables and seats for the

occasion, as there was plenty of material still left unused from the old

barn stuff. Permission was granted, and after counting up the number that

would probably be present, it was found that three tables, each about

fifteen feet long, with necessary seats, would give ample room for the

accommodation of the proposed guests, with a good allowance for overflow.

Just then the whistle of a small steam tug, that often plied on the river,

gave warning of her approach; and all went down to the river edge to watch

her pass and to see what effect her "wash" would have on the new pier and

the boat house "skid" or slides. She came up stream rapidly against the

tide--which was on the ebb--and there was a considerable "wash" from her

wheel, but it struck the bank, the pier, and the "skids" without doing

the least harm or giving any evidence that trouble would result from any

reasonable wash. The little steamer's exhaust, as she passed, made quite

a noise and Jessie was somewhat puzzled at this, as the exhaust from the

gas engine of the _Caroline_ only made a plaintive puff in comparison.

Her father promised to explain the reason after tea.

Returning to the boat house, George suggested that the name of the boat

be painted on both sides of the bow, in large letters, but Mr. Gregg and

Fred, thought it better to have "Caroline" placed on the second streaks

of sheathing, in gold, the letters to be not more than two inches over

all. This was agreed upon, and a young artist, who was a near neighbour,

was suggested as the person to do the work.

[Illustration: Fig. 30. Hero's steam engine]

After tea, Jessie and the boys followed their father into the den, where

Mr. Gregg gave the children a brief history of the steam engine, as far

back as known, commencing with the Colipyle, the invention of Hero of

Alexandria about 130 B.C. An illustration of this is shown in Fig. 30. It

was simply a pot or boiler, partly filled with water, the lid or cover

being fastened down tightly. On the top of this was attached a hollow

bent tube having a tap fitted to it, which supported and communicated

with a hollow metal ball hung on another tube or bearing on the other

side in such a manner that the ball could revolve easily. Attached to

this hollow ball or sphere were four other hollow tubes, so fastened as

to project from the surface two or three inches, and these were bent at

their outer end, as shown in the illustration. These tubes were of course

attached and bent in a direction at right angles to the axis of rotation.

The tap leading to the hollow ball, when turned open, allowed the steam

from the boiler to rush into the ball and fill it up. If it was closed

entirely, the ball would remain still, but the steam exerting an equal

pressure on all points of the inner surface, and finding the openings,

escaped through with a rush and noise as it condensed in the air, which

it pressed against, causing the ball to revolve in an opposite direction

to the outflow of steam. This Hero engine or Colipyle, was doubtless the

beginning of steam motors, but during the 2,000 or more years since Hero's

toy engine was invented, great strides have been made toward bringing the

steam engine to its present efficiency.

"But I do not intend," said Mr. Gregg, "to give a history of the growth

and development of the machine, at this time. There are numerous works on

the subject, obtainable in any fairly-equipped library."

[Illustration: Fig. 31. Steam cylinder and piston]

Steam, as everybody knows, is generated by heat being applied to a closed

metal kettle or boiler containing water. This boiler must be strong and

properly arranged so as to admit more water--which is usually injected

with a force pump--and it must have an outlet for the release of the steam

to the cylinder of the engine. Generally, there is a small dome on the top

of the boiler, called the "steam dome," and to this the steam outflow pipe

is attached. The actual use of this dome is to hold a volume of steam that

will remain unmixed with water, as it is placed considerably above water

level. On the top of the dome there is an automatic arrangement called

a "safety valve," so that when there is too much pressure of steam in

the boiler, it will open and allow the over-pressure to escape, and thus

prevent the boiler from exploding or being over strained. This valve is

controlled by a simple device, somewhat similar to a steelyard. A movable

weight is arranged to slide on a long arm which is loosely fixed to the

valve flange by a bolt and nut, and extends some distance past the seat

of the valve. The arm or lever has an iron pin attached to it directly

over the valve seat, which holds down the valve and keeps the steam from

escaping. The movable weight on the arm is adjusted so as to regulate

the pressure on the valve. When there is too great a pressure, the valve

forces up the lever, and at the same time opens a passage for the extra

pressure of steam to escape. There are several other contrivances for

relieving the boiler of over stress, but the one described, or rather the

principle on which it is built, is most in use on this country. There are

many kinds of boilers, or steam generators, but the best, and very likely

the strongest, are those employed on our first-class railway locomotives.

These are frequently under a pressure of 200 or more pounds to the

square inch, which seems an enormous load for a hollow shell to carry,

yet, so near perfection are they, we rarely hear of a locomotive boiler

explosion. As there are many kinds of boilers, so also are there many

kinds of steam engines, but all of these latter, with very few exceptions,

have a cylinder and piston for converting the force of the steam into

useful and effective motion. The manner of using this force and keeping

it under proper control is somewhat complex and difficult to describe

briefly, without elaborate diagrams, but Mr. Gregg explained, in his own

way, how the great force was converted into motion. On the blackboard he

drew a rough diagram of a cylinder and valve or steam-chest, with piston

and slide-valve, about as shown in Fig. 31, which gives a longitudinal

section of the whole arrangement. Here we see near each end, the opening

of a double conduit aa, made in the thickness of the side; these are the

openings by which the steam comes alternately to work on one end, then on

the other, of the piston. These are called the steam-ports. These two open

outward on a well-polished surface, and between the two a third opening,

E, is seen, which serves to let the steam escape when it has done its

work, and is called for that reason the exhaust port. C is the pipe by

which the steam gains access to the open air or to the condenser, where

it parts with its elastic force.

Here is shown by what contrivance the distribution is effected,

consisting, as it does, of two partial operations; the admission of the

steam and its escape, which must be repeated twice to obtain a complete

phase of the to-and-fro movement of the slide-valve. There are various

methods employed according to different engines--but the first described

is the one represented by the illustration.

In the valve chest, BB, is seen a prismatic box, open on one side, called

the slide-valve, and this is applied by its open face to the well-polished

plane on which, as mentioned before, the three ports open. The space BB,

is called the valve or steam chest. The steam coming from the boiler by

the pipe C spreads out freely in it, but the inside of the slide-valve, on

the contrary, is always closed to the entering steam, though constantly in

communication with the escape pipe and also with first one then the other

of the entrances to the cylinder. Lastly, the movement of the slide-valve

is produced by the engine itself, aided by a rod and an eccentric fixed

to the shaft of the fly-wheel.

[Illustration: Fig. 32. Steam valves--different positions]

By following the successive and alternating motions of the slide-valve,

as represented in Fig. 32, we can easily comprehend the different phases

of the distribution of the steam.

This is the machinery for the distribution of steam generally. There

are other engines, such as rotary and oscillating, that are supplied by

other contrivances, but most of these have fallen, or are fast falling

into disuse, as they are not so satisfactory as the ordinary slide-valve.

It will be seen upon examination of the sketch, shown in Fig. 32, how

the steam enters and leaves the cylinder and the position of the piston

under the various positions of the valves. The arrows show the direction

of the slide, also the direction of the piston and its position when the

slide covers the ports X, or leaves them open, or partly so. The ports

for egress or ingress are shown at X, the slide-valve at V, and the

cylinder at C. When the piston is near one end of the cylinder, the steam

is admitted and forces the piston in the opposite direction, while the

valve is so arranged that when the piston starts in that other direction,

it begins to open the port at the other end of the cylinder through which

the exhausted steam escapes. This makes the noise Jessie asked her father

about. There are some engines so devised that the exhaust is made to

assist in driving another engine.

Of course, there are many kinds of steam engines, but all are run on the

same principle, or nearly so. As you know, steam is generated in boilers

by fire being applied to the outside and the water made hot enough to

raise steam. A steam engine is said to be externally heated, while gas,

oil, and other similar engines are internally heated, because instead of

the steam driving the piston, the gas, oil, or other explosive matter

is admitted into the clearance or space between the piston and the

end of the cylinder, where it is exploded by an electric spark from a

battery provided for the purpose, and this is called the "ignition." The

explosion causes the gas and air in the cylinder to expand, bringing a

great pressure on the piston, forcing it to move toward the other end of

the cylinder, and making the whole machine move. One great advantage of

employing a gas engine is that no boiler is required, a very important

matter, as boilers take up a great deal of space. The coal or wood

necessary to keep up steam also takes space that could be used for other

purposes, all of which make the use of steam objectionable when it is

possible to employ suitable gas engines. Besides, the make-up of a steam

engine is of such a character that it is very expensive, while the first

cost of gas engines is much lower.

All gas, oil, or other explosive engines are internal heaters, because

the heat is generated in the cylinder at each explosion, and this is one

of the main features that distinguishes the gas from the steam engine.

Of course, there are many attachments and connections to steam and gas

engines that would take too long to describe, and in a great measure be

unnecessary. A few items may prove both useful and profitable and it is

well to know firstly: How to estimate the horse-power of an engine.

When steam engines were first introduced they were largely used to take

the place of the horses previously employed for raising water from mines.

Naturally people inquired, when buying an engine, what amount of work it

would perform as compared with horses. The earliest engine builders found

themselves very much at a loss to answer this question so they had to

ascertain how much a horse could do.

The most powerful draught horses and the best of any then known were the

London brewers' horses. These, it was ascertained, were able to travel at

the rate of two and a half miles per hour and work eight hours per day.

The duty, in this case, was hoisting a load of 150 pounds out of a mine

shaft by means of a cable. When a horse moves two and a half miles per

hour, he travels 220 feet in a minute, and, of course, at the speed named,

the 150-pound load would be raised vertically that distance. That is equal

to 300 pounds lifted 110 feet per minute, or, 3,000 pounds lifted 11 feet

or 33,000 pounds lifted one foot high in one minute. That is the standard

of horse-power, as we all know. It is much more, however, than the average

horse can do, and therefore the builders were confident that the engines

would take the place of fully as many horses as the horse-power would

indicate that they should.

Of course, 33,000 pounds lifted 1 foot per minute is much more convenient

for calculation than 150 pounds lifted 220 feet, and therefore the former

rate has been adopted. The amount of work, or number of "foot-pounds,"

is the same in either case. A foot-pound represents the amount of

power required to lift one pound one foot high. To find the number of

horse-power in any engine, we multiply the area of the piston by the

average pressure per square inch upon it; multiply this result by the

distance which the piston travels per minute in feet and the result is

the number of foot-pounds per minute which the engine can raise. Divide

by 33,000 and the result will be the number of horse-power. The number

of feet per minute travelled by the piston is twice the number of strokes

per minute multiplied by the length of the stroke. This gives the amount

of horse-power sufficiently accurate for all practical purposes.

It necessarily takes time to do work, but the amount of work done has

nothing whatever to do with the time taken to do it.

If a man, weighing 150 pounds, walks up the 900 steps leading to the

highest attainable level in the Washington Monument, 500 feet high, he

does work against gravity equal to 75,000 foot-pounds, irrespective of the

time taken in the ascent. Then the work done in a given time, divided by

the time, is called the power of activity.

Power is the time rate of doing work. In the English gravitational system,

the unit of power is the horse-power (H.P.); it is the rate of doing work

equal to 33,000 foot-pounds a minute, or 550 foot-pounds a second.

In the centimetre-gramme-second (C.G.S.) system (in which the unit is 1

gramme moving at the rate of 1 cm. a second), the unit of power is the

watt. It equals work done at the rate of one joule (10,000,000 ergs) a

second.

One horse-power is equivalent to 746 watts.

A kilowatt (K.W.) is 1,000 watts.

It is therefore nearly 1-1/3 horse-power.

To convert kilowatts into horse-power add one-third; to convert

horse-power into kilowatts, subtract one-fourth.

For example, 60 K.W. equals 80 H.P. and 100 H.P. equals 75 K.W.

The expression foot-pound is in general use among English-speaking

engineers, and as explained it is the unit of work done by a force of one

pound working through a distance of one foot. It is not a fixed standard

of measurement, since the weight of a pound is not the same in all heights

above sea level, and on this ground it is open to objection. It is the

nearest constant, however, we have yet discovered, hence its general

adoption.

"Dry steam" is the steam in which no condensation is visible, and it

may generally be obtained at a 10-pound pressure per inch, but no exact

dividing line of pressure can be defined between dry steam and wet. If

care is taken in covering pipes and cylinders, to prevent condensation, a

pressure of 10 pounds should make steam as dry as gas, and if the steam

pipe is carried through a good, hot fire at some point, the fire will

superheat the steam and render it more dry. Wet steam, of course, is steam

that can be seen, through having been more or less condensed by contact

with air or cold. There can be no steam without heat, but steam does not

require as much heat as is generally supposed. Suppose we take one pound

of water at 32 degrees Fahrenheit and apply a fixed and known quantity of

heat until it boils; we will assume that it takes 20 minutes, and we have

supplied the water 180 heat units, which, added to the 32 contained in the

water at the start, makes 212 degrees Fahrenheit or heat units, and is the

sensible heat of steam at atmospheric pressure. Now let us continue the

same quantity of heat per minute until all the water has evaporated into

steam, and we will then find that it has taken five and one-third times as

long, or 107 minutes to do this work. Consequently we have used five and

one-third times 180 or 960 heat units; or, to be exact, 966 heat units.

Now the temperature of the steam is the same as the water from which it

has evaporated, or 212 degrees Fahrenheit, and this 966 heat units is the

latent heat of steam at atmospheric pressure. All steam has a sensible

heat corresponding with the temperature of the water it has evaporated

from. If you boil water under a pressure of five atmospheres, or 75 pounds

pressure, the sensible heat is 306 degrees Fahrenheit, the boiling point

at that pressure, but the latent heat has decreased by the same number of

heat units that the boiling point increased, so the total is the same in

all cases. In the first instance we have 212 degrees minus 32, plus 966,

or 1,146; and in the second 306 degrees minus 32, plus 872 or 1,146 heat

units. This may be considered a fair description of latent heat.

The most useful quality of steam yet discovered is its power of expansion.

It follows what is known as Marriott's Law of Expanding Gases, which means

one-half the pressure double the volume. So if we let steam into an engine

cylinder, at 80 pounds' pressure, and cut it off at one-fourth stroke, it

is at 80 pounds up to the point of cut-off. At one-half stroke, because it

has doubled its volume, it is reduced to one-half pressure, or 40 pounds;

while at three-fourths stroke the volume has trebled and the pressure

has dropped to nearly 27 pounds, and this is why it is economical to run

engines that use steam expansively. Steam at 27 pounds' pressure is very

much cooler than steam at 80 pounds, and this difference in temperature

has been converted into mechanical work by our steam (heat) engine.

There are many other peculiarities about steam and steam engines that a

young boy should know, and the information can readily be obtained from

books in any good library.

The steam turbine, of which so much has been heard lately, is not

constructed like an ordinary steam engine with cylinder, slide-valve and

other attachments; but more like the Hero engine, with this difference

that the steam jet or jets act on a wheel having vanes or blades, the

expansion producing a velocity which rotates the wheel containing the

vanes. A modern turbine, of the Parsons type, such as are employed on the

great Atlantic steamers, is a tremendously high speed engine. It does not

derive its power from the static force of steam expanding behind a piston,

as in a reciprocating engine. In this case the expanding steam produces

kinetic energy of the steam particles, which receive a high velocity by

virtue of the expansion, and, acting upon the vanes of a wheel, force it

around at a high speed of rotation in the same manner as a stream of water

rotates a water-wheel. The expansion produces velocity in a jet of steam,

and this is the main difference between the ordinary engine and the modern

steam turbine.

Among gas and internal explosion engines there exist some differences,

both in construction and in the manner of supplying fuel. The

gas-producing engine may be considered the better class, though it has

not as yet gained the popularity of the gasolene one. The gas by which

this style of engine is operated is produced by a special process, namely,

by passing air and steam through a fire of hot coals. After generation

the gas passes over a flash-boiler and a portion of its great heat is

withdrawn, thus permitting it to enter a scrubber--a cylinder filled with

coke and sawdust--while fairly cool. In passing over the flash-boiler

the great heat raises all the steam necessary for the production of gas

required in the operation of the engine and plant. In passing through

the scrubber the gas is not only cooled, but is freed from particles

of suspended matter, the coke removing the heavier particles, and the

sawdust, the tar, or any other volatile matter that may be left.

One of the most important requirements in a gas-producer is that it shall

be adapted to the work it has to do. Its construction should be compact

and simple, so as to permit the easy removal of worn out parts. The

feeding device should be such as to secure a uniform distribution of fuel.

The blast should be so introduced as to burn out all the carbon in the

ash zone, and yet not produce localized combustion along the walls. The

construction should permit the easy removal of ashes, and render the

machine safe, while the entire process of gasification should be clean.

The radiation loss should be low, and the producer must be made efficient

to insure satisfaction.

It should be borne in mind that because of the presence of carbon

monoxide, producer gas will always be more or less poisonous. The carbon

monoxide has a specific toxic effect on the human system, and when inhaled

enters into direct combination with the blood, and brings about very

dangerous effects.

As water is always required for cooling purposes when running a gasolene

engine, it is well to know about how much will be required. One authority

says: "The quantity of water required at the ordinary temperature of 60

degrees F. inlet and 150 degrees outlet, to keep the cylinder of gas

engines cool is 4.5 to 5 gallons per indicated horse-power-hour. The

jacket pipe should be from 1 to 2 inches diameter for engines up to 20

horse-power, while for larger engines the sizes are generally 2 to 3

inches for the inlet and 2.5 to 3.5 inches for the outlet. Tanks for

circulating the water are generally made with a capacity for furnishing 20

to 30 gallons per indicated horse-power. This rule may be taken as about

correct, but, if anything, it is rather an over-estimation of quantity

necessary."

All the foregoing was made as clear as possible to the listeners by Mr.

Gregg before the children went to bed.

Next morning Fred called up his artist friend, and got him to come down

to gild the name "Caroline" on the boat before the next coat of varnish

should be applied. The artist made an outline of the name while George

and Jessie stood by and watched the process with considerable interest.

They saw him measure off each letter, outline it with a pencil lightly,

and then paint inside the lines with a substance known as "gold size,"

obtained from any store dealing in painters' supplies. While the size was

still sticky the artist applied "gold leaf," which he had brought in a

little book along with him. Jessie was surprised to see him cut the gold

with a thin pallette knife, having a blunt but smooth edge. She watched

him pick up the small pieces of gold with a camel's hair brush, which he

rubbed in his own hair now and again whenever it would not pick up the

gold. The metal was applied bit by bit over and beyond the lines of the

letters, and a light puff of breath forced it down to the size. When one

side of the boat was finished, so far as laying on the coat of gold was

concerned, Jessie was very much disappointed, as the name seemed merely

a smudge. She could not make out the letters, but the artist told her to

wait until to-morrow and he would show her how well they could be seen.

Next day with a flat camel's hair brush he dusted away the surplus gold,

and the letters showed up in good style, much to the gratification of

Jessie and George. This part of the work being done, the boys took down

their varnish pots, and gave the little craft another coat, to make her

quite spruce and gay.

Fred, and Nick, who was still in the employ of Mr. Gregg, laid off a space

on the ground for tables and seats to accommodate the young folks who

were coming to the launch on the following Wednesday. Nick found a number

of old cedar posts, and with a saw cut off 18 pieces about two feet long

and as many more twice that length. The first were intended to place the

seats on; the second lot were to sustain the tables. The spots for the

tables were chosen, measured off, and small stakes driven into the ground

to show where the posts were to be placed. Five posts were intended for

each table--two at each end, two feet apart, and nine feet apart in the

length of the table. The single post was placed in the centre of the table

both ways. When the stakes were all in place, Nick made holes deep enough

to take in the posts so that their tops measured just two feet and two

inches above the level of the ground. The tables were to be two feet and

six inches high when finished, as that is the regulation height. It was

attained, in this case, as follows--First by the height of the posts from

the ground, two feet two inches; then by a plank two inches thick laid

across the two posts, making the height two feet four inches, and the

table top, two inches thick, laid on these cross planks, which brought it

up to the required height. A piece of plank the same thickness was nailed

on the centre post across, so that it would support the table top. Planks

that had been used in the loft of the old barn did service for the table

tops, bearing pieces, and the bench seats. The last were constructed

in the same manner as the tables, the short posts being let into the

ground--three under each seat--and fourteen inches above ground so that

when the plank seat was nailed on top of them, the seats were just sixteen

inches, the regulation height of stools, benches, and chairs, though it

is sometimes varied to suit conditions. The benches were placed about

four inches out from the edge of the table and were found to be "just the

thing."

When Nick had planted the first post for the tables and got it the right

height, he took that one for his guide and by the aid of a long parallel

straight edge which he laid on the guide post and the one he was setting,

and also a spirit-level on the straight edge, he managed to get all the

posts alike in height and this made the tops of the three tables nice

and level. It was quite an achievement to have three large tables and six

long seats placed in "picnic style" at so small a cost and with so little

effort.

In order to have the tables and seats neat and clean, George turned on the

garden hose and gave them a good wash off, and when they were dry again

the place was as inviting as a country hotel dining-room. When Mrs. Gregg,

Jessie, and Grace Scott had the tables set and garnished for the launch,

the lay out was charming, none the less so because it was a little rustic.

Another coat of varnish, the third, was given the boat the day before she

was to be launched, and Fred had a strong rope attached to the winch, with

a heavy iron hook fastened to the end of it. A stout iron ring was bolted

to the stern of the boat and made secure. Mr. Gregg had purchased a number

of small flags and "burgees" and had one made with the name "Caroline"

in large letters wrought on it, ready to be unfurled when the launch was

made, and Walter Scott, his mother and sister Grace, and others had been

invited to attend.

A number of temporary swings were fixed up by Nick and Fred to the trees,

some for the large folks, others for the smaller ones, and everything was

at last ready for the great event, which was to take place the next day

at two o'clock.

VI

PROPELLER AND OTHER SCREWS

Wednesday morning was light and sunny and the boys were up and dressed

somewhat earlier than usual, so, while waiting for breakfast, they took

a stroll down to the river, where they found their father looking over

the grounds and examining tables, benches, swings, and particularly the

foot-bridge; for, as he told Fred, "it was very likely all the guests

might be on the bridge at one time and the combined weight would be rather

trying if it had not been securely put together." He satisfied himself,

however, that the bridge was strong enough to support three times the

weight it would be called upon to sustain. Everything else seemed to be

sufficiently strong, to apprehend little danger, no matter how much the

children romped.

Nick had the grounds nicely raked off; the decayed branches and shrubs

he moved, and made everything about the place as clean and as neat as

possible. Flags and other decorations were hung or placed about the

grounds, on the trees and buildings, but particularly about the tables

and the boat house. Newspapers were spread over the tables, linen covers

above them, and the whole surroundings took on a most festive appearance.

It was just 11 o'clock when _The Mocking-Bird_ arrived and tied up to

the new dock. On board were Mrs. Scott, Grace, and the maid, who came to

help, besides several of the invited guests whom Walter had brought down

with him. All were welcomed by Fred, Jessie, and George and then the women

visitors went to the house to assist Mrs. Gregg.

Mr. Gregg came home from his office earlier than usual and took a half

holiday in honour of the occasion. The guests, in little groups, arrived

on time, and before the clock struck two Nick had everything prepared for

the launch. He and Fred and George had the _Caroline_ nicely placed on

the skid, ready to "let go" the winch, and a flag pole was fixed up on the

bow of the boat. To this the flag with the name on it was lightly tied, in

such a manner that when a string was pulled it would unfurl, and show the

name. The string looping up the flag was left long enough to enable Mr.

Gregg, standing on the dock, to hold the end in his hand, and by pulling

it to loosen the flag as soon as the boat touched the water.

Everything being ready, Walter Scott invited as many of the young people

to get into the _Mocking-Bird_ as could crowd on board with comfort,

and each was provided with a whistle or a horn, as he ran his boat half

way across the river. The children on shore were also given horns and

whistles, and all were told to blow as loud as they pleased when the boat

touched the water. Mr. Gregg, having Mrs. Gregg and Mrs. Scott standing

beside him, gave the word, "Ready!" Nick and Fred answered, "Aye, aye,

sir!" and the master of ceremonies called out in a loud voice: "Let her

go!"

Nick freed the winch, Fred and George gave a little push, and the

_Caroline_ slid down the skids, into the water, without the least hitch.

The horns and whistles made a great din, and when the flag was let free to

open up and show the name "Caroline" there was another blast of noise by

horns and whistles, mingled with voices of the younger people, who cried

out with all their might, "Hurrah for the _Caroline_!"

The launch being over, and everything having gone all right, the young

people were called to lunch. They all sat at the tables which were nicely

garnished and well supplied, and there was plenty of small talk, and much

laughter and jollity. After lunch, Fred, Walter and George boarded the

_Caroline_, supplied her with gasolene, and tried to run her. They found

a little difficulty in starting, but after the engine was warmed up a

little, she went off beautifully, and answered her tiller in fine style.

The boys ran her up and down the river for a while, then tied her to the

dock, and Walter and Fred invited all the girls to "Come and have a sail."

The boys were promised one when the two boats returned, which they did

in the course of half an hour. The swings were put in use, dancing and

romping began, and the afternoon was passed in fun and frolic.

In the evening, Mr. Gregg, Jessie, and the boys took a trip, and Mr.

Gregg was well pleased with the boat's performance, particularly with

the working of the screw. In mentioning this, he awakened the curiosity

of George, who reminded his father that he had not yet explained to them

about the screw as a mechanical power.

[Illustration: Fig. 33. Theory of screw]

That evening George was told to bring his blackboard and equipment

into the den, and the father at once began explaining the mechanical

qualities of the screw. He told of its great usefulness in the industrial

arts. As one of the mechanical powers, it may be considered an inclined

plane, wrapped spirally round a solid cylinder. The advantage gained by

it depends on the slowness of its forward or backward progress, that

is, on the number of turns or threads, as they are called, in a given

distance. It is always used in combination with a lever of some sort. When

employed as a lifting machine it has great power, and is used to produce

compression or to raise or move heavy weights. If a screw is formed on

the inside surface of a hollow cylinder, it is called a nut, and used

to overcome a resistance; either the screw or the nut may be fixed and

the other movable. The acting force is generally applied at the end of

a lever or wrench or rim of a wheel. Fig. 33 represents a screw and nut

operated by a lever or length of radius _r_; _p_ is the pitch of the screw

or height of the inclined plane for one revolution of the screw. W is

the resistance at the nut and P is the force at the end of the lever _r_.

Remembering that, while the resistance W is raised the distance _p_ the

force P revolves around a complete circle and moves a distance 2[pi][nu].

Let us now apply the condition [sum] work = 0 and we have

P2[pi][nu] - Wp = 0 or -- = P2[pi][nu]/p (6).

[Illustration: Fig. 34. Worm wheel and screw]

The worm gear (Fig. 34) is a special case of screw and nut, where the

latter is replaced by a toothed wheel called a worm wheel. The teeth work

in with the thread of the screw or worm, and thus, as the worm revolves,

the worm wheel revolves about its axis. P is the force acting on the worm

at a radius _r_. _r´_ is the pitch radius of the teeth in the worm wheel

and _r´´_ is the radius of the drum on which W acts. Let K, corresponding

to W in equation W P (6), be the force at the pitch circle and worm

threads due to the force P; then

K = P2W/p (7).

Now apply [sum]m = 0 to the worm wheel and we have

Kr´´ = Wr´´ or K = wr´´ (8).

Substituting the value of K in (7) in equation (8) we have

P2[pi][nu] = Wr´´ or P2[pi][nu] = Wr´´p (9).

Now it is evident that the distance _p´_ moved by W while K moves

through the distance _p_ is to _p_ as _r´´_ is to _r´_ or

_p´_ :_p_ :: _r´´_ : _r´_ or _p´_ = _pr´´_/_r´_ (10).

Substituting this value of _pr´´_/_r´_ in equation (9) we have

P2[pi][nu] = Wp´ or the condition [sum] work = 0, since 2[pi][nu] is the

distance moved by (P) while W moves the distance _p´_.

No provision for friction has been made in any of the examples given,

so that allowance must be made for this propensity whenever any of the

foregoing rules are applied to practice. The amount of allowance required

will vary and must be made to suit conditions.

An endless screw is sometimes used as a component part of graduating

machines, counting machines, etc. It is also employed in conjunction with

a wheel and axle to raise heavy weights. The distance between the threads

of the screw is called the pitch or step. These threads are sometimes

square, sometimes acutely pointed or edged, sometimes rounded off on the

edges. Power is often applied by means of a lever or other contrivance

attached to the end of the screw, or by a long handled wrench (a monkey

wrench for instance), which, when turned, moves forward in the direction

of its axis, overcoming resistance. In the case of the screw-jack, it may

be used to raise a heavy weight. The relation between the force applied

and the resistance to be overcome is important to note, for every time the

screw performs one revolution it moves forward through a distance equal

to the space between one thread and the next.

[Illustration: Fig. 35. Archimedian screw]

The Archimedian screw we have read and heard so much about is simply a

hollow pipe wound around a cylinder. It was often used in olden times for

raising water, but is now only occasionally applied. The lower end of the

spiral pipe is, of course, left open and immersed in water, as shown in

the illustration (Fig. 35), a device for raising water, the supply stream

being the motive power. The oblique shaft of the wheel has extending

through it a spiral passage, the lower end of which is immersed in water;

and the stream, acting upon the wheel at its lower end, produces its

revolution, by which the water is conveyed upward continuously through

the spiral passage and discharged at the top. An arrangement like this

could easily be constructed at the edge of most rivers to raise water to

irrigate the grounds, if so desired, and the little flutter wheel at the

bottom of the inclined shaft would be powerful enough to lift all the

water required. Fred thought that would be a great scheme, and determined

to try his hand at it one of these days, but he was told that a wheel

of that kind could only work at intervals, as the river's flow was often

running in opposite directions owing to the inflow of the tidal water.

[Illustration: Fig. 36. Spiral conveyor]

These Archimedian water raisers are often fitted with a crank handle on

top, and a man, standing on a platform, turns the crank and thus lifts up

all the water the machine will carry. The Archimedian screw is used for

many other purposes than raising water. With wide, thin wings, similar to

the construction shown at Fig. 36, and enclosed in a case or jacket, it

is employed by millers to convey grain and other mill requirements, and

it is also good for moving coal, ore, gravel, and like material, but when

used for these coarser purposes the propelling blades are made of steel,

riveted or bolted to a strong iron shaft. The case or jacket containing

the revolving blades, if horizontal, need not be covered on top, as the

blades will propel the material without jamming or clogging, if the jacket

is smooth inside, and fits fairly close to the blades.

This style of a screw may be used as a sort of turbine water wheel, if

cased in a cylindrical penstock or tube, and a body of water allowed to

fall into the upper end of the tube. The force of the water will give a

rotary motion to the blades and shaft, and, the latter having a geared

wheel or pulley attached to its top, motion is imparted to other shafts

and wheels.

[Illustration: Fig. 37. Theory of screw and gear]

Another application of the screw is shown at Fig. 37, where one is

arranged on a shaft or axle to give a rotary motion. This device is called

a "worm and wheel," and is frequently used in the make-up of machine

engines and mathematical instruments. The illustration shows how the power

or force of a screw may be conceived. For instance, suppose the wheel C

has a screw on its axis working in the teeth of the wheel D, having 48

teeth. It is plain that for every time the wheel C and screw are turned

round by the handle or crank A, the wheel D will be turned once round.

Then, as the circumference of a circle, described by the crank A, is equal

to the circumference of a groove round the wheel D, the velocity of the

crank will be 48 times as great as the velocity of any given point in

the groove. Consequently, if a line C goes round the groove, and has a

weight of 48 pounds hung to it, a power equal to one pound at the handle

will balance and support the weight. To prove this by experiment, let

the circumference on the grooves of the wheels C and D be equal to one

another; and then if a weight H, of one pound, is suspended by a line

going round the groove of the wheel C, it will balance a weight of 48

pounds hanging by the line G; and a small addition to the weight H will

cause it to descend, and to raise the other weight.

If a line C, instead of going round the groove of the wheel D, goes

round its axle I, the power of the machine will be as much increased as

the circumference of the groove exceeds the circumference of the axle,

supposing which to be six times 8, then one pound at H will balance 288

pounds, hung to the line on the axle; thus showing the advantage of this

machine as being 288 to 1. A man who can lift by his natural strength

alone, 100 pounds, by making use of this combination, will be able to

raise 28,800 pounds alone, and if a system of pulleys were applied to the

cord H, the power would be further increased to an amazing degree.

When a screw and wheel are attached, as shown, the screw is sometimes

called a "worm" and sometimes an "endless screw."

The propeller wheel (Fig. 38) is a screw having a large helical dimension.

The example shown has four blades, each of which, when rotated, may be

said to make one quarter of a revolution and when at work in the water

has the same effect as the working of a nut, producing motion in direction

of the axis and so propelling the boat or vessel. The action of the wheel

pressing backward against the water tends to push the craft forward.

[Illustration: Fig. 38. Complete screw propeller]

This figure shows a propeller with four blades, but two and three bladed

ones, particularly for small craft, are mostly used. The _Caroline_

carries a two bladed screw and her performances will be entirely

satisfactory. The blades, of course, are exactly in line with each other

on the shaft, and equally balanced, or of equal weight. A three-bladed

propeller should have its extreme points in a horizontal plane, so that

they will form an equilateral triangle.

The principal features of a propeller may be described as: diameter,

pitch, area, speed of revolution, and slip. The diameter is that of the

circle described by the tips of the blades. The pitch, considering the

propeller to be a portion of a screw, is the amount which it advances in

one turn, supposing it to travel in a solid medium. The blade area is the

actual area of all the blades.

The speed of the revolution is customarily reckoned in turns per minute.

The slip is the difference between the amount which the propeller actually

advances per turn and the amount which it would advance if turning in

a solid medium. For example, if the pitch of a screw is 30 in. it would

advance 30 in. at each turn if there were no slip. Suppose that it only

advances 20 in. per turn, then the slip is 10 in. per turn, or as usually

figured, 33-1/3 per cent. As a further example, suppose a propeller of 30

in. pitch, turning 300 turns per minute, drives a boat at the rate of 6

miles per hour. The advance of the propeller in feet per minute is 30/12

× 300 = 750 while the advance of the boat is 6 × 5,280/60 = 528 ft. per

minute. The slip is then 750 - 528 = 222, or as a percentage, 222/750

= 29.6 per cent. It might seem at first sight, that a perfect screw

propeller should have no slip; but this is a practical and theoretical

impossibility.

The most important dimension, from the standpoint of the absorption

of power, is the blade area. A certain blade area may be obtained by

a relatively wide blade on a small diameter, or by a narrow blade on a

relatively large diameter. In the former case the area of the blades bears

a greater proportion to the area of the circle through the tips than in

the latter case. There are certain limits for this proportion of blade

to disc area for well-designed wheels, beyond which it is not well to go.

These are as follows:

For two blades .20 to .25.

For three blades .30 to .40.

For four blades .35 to .45.

This means that for a 24 in. diameter propeller, whose disc area is 452

sq. in. the blade area should not, for ordinary use, be made greater than

these proportions, as the blades then become so wide as to interfere

one with another. Of course where a propeller, for shallow draft, must

be unusually small in diameter, the proportion of blade area can be

increased, but with some loss in economy. Strictly speaking, for a well

balanced propeller, the blade area fixes the amount of power which the

propeller can deliver, while the pitch, combined with the turns per

minute, governs the speed. As a matter of fact, for the average propeller

the two are closely related, each having a certain influence upon the

other. To illustrate, a propeller may have a small blade area and so great

a pitch that the blades act somewhat like fans and simply churn the water,

offering great resistance and absorbing the power of the engine, but doing

little effective work toward driving the boat.

To get the measurements for a wheel required to perform a given service,

say a three-bladed propeller for a small boat or tug of 20 nominal or 75

indicated horse-power:-- assume that the size determined on is 4 ft. 6

in. in diameter and 7 ft. 6 in. pitch, the diameter of loss may be assumed

to be 8 in. swelled to be 11 in. in the middle, and 11 in. long. The tug

would be, say, 60 ft. long, 12 ft. beam, and 7 ft. deep. First delineate

the path of the point and root of one blade through half a revolution as

in Fig. 39. This should be drawn to a scale of not less than 1-1/2 in. to

1 ft. by the ordinary method of projecting a screw thread. The semicircle

shows the half plan with twelve equal divisions, and the half elevation

is divided into the same number of equal parts. The helix or thread is

then obtained by drawing the curves through the intersections of similar

divisions. Then _a b_ will be the helix for point of the blade, and _c d_

the helix for the root of the blade. These will be found to be practically

straight lines which might have been obtained in a simpler manner if

intended for a working drawing only; but it is useful to have demonstrated

the proper nature of the full curve.

[Illustration: Fig. 39. Diagram screw lines]

The practical way of setting off the blade follows: First for dimensions:

as 20-in. (pitch) is to 11 in. (length of boss and therefore virtual

length of propeller), so is 169.6 in. (circumference due to outer

diameter) to the length of circumference occupied by the blade, 169.6 ×

11/9 = 20.73, say 20-3/4 in. In Fig. 40 describe a circle equal to the

diameter of the propeller, and on each side of the centre line step off

20-3/4 in. to half the scale, making the whole length of arc to scale

20-3/4 in. Draw vertical lines from the ends of the arc, and from the

arc on the centre line set up a height of 11 in. and draw horizontal

lines. Join _a b_, and this will be the angle of the end of the blade.

On the elevation of the propeller circle describe a small circle equal

in diameter to the faces of the boss; draw radial lines from the ends of

the arc first found, and from the intersection with the boss circle draw

vertical lines to cut the horizontal lines of the plan of boss. Join _c

d_, and this will be the angle of the blade at the root.

[Illustration: Fig. 40. Part of screw blade]

Now describe an arc at every three inches from the circumference within

the radical lines; or for large propellers every 6 in. Draw vertical lines

from the intersections of the arcs with the radical lines to meet _a c_

and _b d_, as shown, and joining the points thus found, the diagonal lines

will represent the plan or angle of the blade to each 3 in. difference of

radius--in other words, its real width at the different points, supposing

it to be a plain geometrical portion of a screw thread. As a matter of

fact, the blades are always more complex than this, the edge being curved

to enter the water more easily, to avoid vibration, and also to lessen

the risk of fracture in the event of striking any object in the water.

Sometimes the blades are curved in the opposite direction, as if the

points were being left behind while the blade is advancing.

[Illustration: Fig. 41. Plan of screw blade]

The next step is to draw a flattened elevation or development of one

of the blades, in order to give the actual curves of its outline, and

afterward its thickness at various points. Draw a horizontal line from

_c_ and _f_ (Fig. 41), and through this a centre line. This will give the

length of the blade from the boss, and the centre line of the propeller

shaft may be added below. Then take the lengths _a b_ and _c d_ from Fig.

40, and set them off on Fig. 43, as shown, joining all four points. This

figure would be the true outline of the blade if there were no curves. The

actual outline is found by drawing the curves according to the dimensions.

[Illustration: Fig. 42. Propeller lines complete]

Lay out the propeller, as shown in Fig. 42, which will give the elevation

of the blades, all being alike.

To find the area of a propeller blade, mark it off in parallel lines,

say 3 in. apart, and note the width at the centre of each portion. Add

the widths together, and divide by the number of widths. This will give

the mean width, which must then be multiplied by the length of blade to

obtain the area. If the measurements are all in inches, the result should

be divided by 144 to give the area in square feet, and then be multiplied

by the number of blades to give the total area.

[Illustration: Fig. 43. Angle of propeller blade]

To measure the pitch of a propeller, lay it down on a level surface, hold

a straight edge level across centre of blade with a square up from the

lower edge, as in Fig. 43. Measure the distance B and H and the radius

R from the centre to the part where the measurement is taken; then

B : 2wR :: H to pitch, P or P = 2wRH/B. The measurements may be made in

more than one place and the average taken, as the blades are

sometimes twisted slightly.

Scaling only from the drawing,

P = 2wRH/B

2 × 3.1416 × 1.6 × 1/1.27 = 7.74,

say 7 ft. 9 in. pitch, whereas the intended pitch was 7 ft. 6 in.

A good illustration of the use of the screw may be seen in the carpenter's

auger, used for making or boring holes in wood. These tools are provided

with a small tapered screw on their points, and this is followed by

cutting edges and a larger spiral. The larger spiral is for the purpose

of drawing up the chips or shavings. Another tool is made having two

blades attached to the bottom of an iron bar formed like the blades of a

propeller, which is sometimes employed for boring or digging post holes

in clayey or soft soil. The machine is turned by a cross handle on top,

and is frequently drawn up to bring out the soil until the hole is deep

enough. The ordinary wood screw is one of the most useful of contrivances

for fastening wood together, and for attaching to surfaces, hardware,

ornaments, or other materials. The adhesive strength of nails is already

shown, and the adhesive strength of wood screws, according to Bevan, is

set down as follows:

WOOD SCREWS

The following are the thicknesses or diameters corresponding to

the list numbers. Other thicknesses can be interpolated, each size

varying in succession 1/64 in.--

============+====+====+====+====+====+====+====+====+====+====+====

No. | 00 | 0 | 1 | 5 | 10 | 14 | 18 | 22 | 27 | 32 | 40

------------+----+----+----+----+----+----+----+----+----+----+----

Thicknesses | | | | | | | | | | |

in parts | | | | | | | | | | |

of inches |1/32|3/64|1/16| 1/8|3/16| 1/4|5/16| 3/8|7/16| 1/2| 5/8

------------+----+----+----+----+----+----+----+----+----+----+----

An ordinary 2-in. wood screw, driven through a 1/2-in. board into hard

wood, was found to be 790 lbs., and a force of about 395 lbs. was required

to extract it from soft wood.

When screws are hard to drive or screw in place, a long screw-driver

should be used, as screw-drivers with long handles seem to have a much

greater leverage than short handled ones in driving screws home. Screws,

however, are often split at the head, if care is not taken when using a

long driver.

If a screw is rusted, hard to move or withdraw, it can be loosened by

applying a hot iron to the head and making it hot. The heat expands the

screw and, of course, makes the hole larger, and when the screw cools it

contracts a trifle so that it may be withdrawn quite easily.

VII

AEROPLANES

George and Fred were so much interested in the _Caroline_ that they

neglected to do some work Mr. Gregg had suggested, but a hint or two

from him reminded them that sailing the new boat every day would get so

monotonous it would cease to be a pleasure. Fred, therefore, set to work

to put the new property in apple-pie order, by cleaning up the grounds,

burning the rubbish, and tidying the place generally. Nick, not being

needed longer, was allowed to go, with the promise that whenever a man

was required about the place, he would be chosen. His departure left all

the work to Fred and George, both of whom gladly accepted the duty.

The first thing was to set up three or four long benches on the river

bank. These were built exactly in the same manner as the seats alongside

the tables. Three short posts were let into the ground for each seat, and

a good, sound plank spiked solid to their tops. One of the seats was made

four or five inches lower than those at the tables, so as to accommodate

the smaller children. The two boys did the work well, though they found

it a little hard to dig the holes in the ground and saw off the posts.

George's hands became a little blistered and sore, but his mother soon

cured them, though she warned him against working too hard or too long at

a kind of labour to which he was not accustomed.