After tea was over, it being a fine, warm, spring evening, the whole

family went down to the river's edge to sit on the new seats and enjoy

the view. Noticing the current of the river, Jessie questioned her

father about its going one way sometimes, and then turning in the other

direction. Her father explained that it was the movement of the tide that

made the water flow against the stream at times, and that when there was

no tide, the current took its natural course. This explanation did not

seem to satisfy Jessie, and she asked why there were any tides. So Mr.

Gregg promised to explain all that was known about tides to her in the

near future. "I wish you would," said George, "and tell us about kites,

balloons, and flying machines."

"Oh, yes," said the father, "I'll try to do that to-morrow night."

"I'm glad, father," said Fred, "as I want to try and make a model for

George before the Fourth if I can, so he can have one to fly across the

river that day, instead of fooling with fire-crackers and other dangerous

fireworks."

"That's a good idea, Fred," said the father. "A model aeroplane, decorated

with silk flags would give a great deal more real pleasure than firing off

all the fire crackers in the state. It would be quite easy, now you have

a boat, for one of you to be on this side of the river, the other on the

opposite side, and to keep a number of little machines going to and fro

across the water."

George seemed delighted at the prospect. Walter Scott had also been

stricken with the aeroplane fever, and was busy making models, though, as

yet, he had not finished any. Both Fred and George were anxious to hear

all their father had to say concerning these machines, as they knew he

would be thorough, and make it all plain. Mr. Gregg told the boys that to

explain fully the theory and practice of building an aeroplane of any kind

would take some time, but he would willingly give it for their benefit,

and would discuss the subject of aeronautics at length so as to give them

some pointers about the design and practical making of flying machines.

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

THE MONOPLANE MODEL COMPLETE

"A Model Aeroplane, Decorated with Silk Flags Would Give a Great

Deal More Pleasure Than Firing off All the Fire Crackers in the

State"

]

On the following evening, Jessie did not forget to remind her father of

his promise to tell them all about "air-ships and things," as she put it.

"All right, my dear," said Mr. Gregg, "I'll take you all into the 'lion's

den' shortly after tea. But tell me, why is it you are so anxious to know

all about 'air-ships and things'?"

"Oh! that's all right, papa; Fred is going to build a great big ship, as

soon as he knows how, and he has promised to take me up to the clouds in

it for a ride."

"Well, my dear, it will take some time to tell you all about these things

but I will make an attempt. For ages man has wanted to fly, and the Greeks

tell us of a mythical personage named Icarius, and another named Dædalus,

who flew to the sun. There have been many attempts to fly, both with

and without mechanical aid, but history gives us nothing definite on the

subject until about the year 1785, when two Frenchmen, named Montgolfiers,

built a balloon sixty feet high and forty-three feet in diameter, and

filled it with heated air. Attached to the bottom was a light cage made

of wicker-work, into which were placed a lamb, a duck, and a rooster. The

balloon was cut from its moorings and rose to a height of over 1,400 feet

so that these animals were the first that ever went up in a machine made

by hands.

"The Montgolfiers attained considerable notoriety, and out of their

experiments grew the present dirigible Zeppelin, which measures 446

feet in length, over 42 feet in diameter, and is capable of carrying

eight able-bodied men a distance of over 900 miles. This great machine

is charged with gas, and driven by four three-bladed propellers, which

are run by two gas engines of 110 horse-power. This is simply a monster

balloon, suspended in the air by 529 to 700 cubic feet of hydrogen, or

coal gas, which is much lighter than ordinary air.

"It may be said there are four distinct kinds of flying machines, each

unlike the other in construction and in principle. The first is the

old-fashioned balloon which has an envelope or covering of some air-tight

fabric, and is inflated with a light gas. To it is attached a framework of

some kind called a Nacelle, that carries the aviator, the steering gear,

and the necessary engines to operate the propeller or propellers.

"The second kind of flier is the aeroplane, which, as its name indicates,

is supplied with 'air planes,' that give it the power of rising and

falling at the will of the operator when the machine is in motion. These

planes play a very important part in the successful operation of the

machine, as I will explain later. The first type of machine is classed as

a 'lighter-than-air' machine or a balloon, while the planes of all kinds

are classed as 'heavier-than-air' machines. Among other types of 'fliers,'

there is the helicoptere, which is raised by screws or propellers on

vertical shafts. These revolve rapidly, and drive the machine upward,

just as the propeller on the _Caroline_ drives her forward when in rapid

motion. Another type, nearly abandoned, is called the ornithoptere, or

'wing flyer.' These machines are built to operate like the wings of a

bird, and are provided with the necessary contrivances to work the wings,

both vertically and horizontally. This type, like the helicoptere, is

not considered practicable, and is virtually abandoned, so that the

field is now left altogether to the 'lighter-than-air,' and the aeroplane

machines. I do not intend giving you any instruction regarding balloons,

or dirigibles, as I think such is unnecessary, but will confine myself

altogether to the discussion of aeroplanes.

[Illustration: Fig. 44. Aero-curves]

"It must not be supposed because of the name aeroplane, that the so-called

plane is a real plane; it is not. The front edge of an air-ship plane must

always be curved, as shown in Fig. 44, so that the air strikes the under

surface and is forced under the plane, to buoy up the machine as it moves

forward; or, to put it another way, there must be a current of air either

natural or artificial on which the machine must float, or it will be drawn

by gravitation to the earth. While we cannot see air or wind, we know from

experience that it has great power, and for thousands of years ships have

been propelled across the seas by this force, acting on sails of some

kind. We know how difficult it is to travel against a high wind, and it

is this quality in the air that makes it possible to travel through it.

The resistance of the atmosphere makes it possible for the aviator to hold

his machine suspended in opposition to the laws of gravity, and to drive

it forward and upward by means of the revolving propeller acting against

this resistance, the motor acting on the same principle and manner as

the wheel or propeller of a boat when it is urged forward. If, as I have

seen George do, we take a flat stone, a piece of slate, or flat metal,

and throw it along the face of the river, in such a manner that its flat

surface strikes the surface of the water, it will skim along, striking

the water at intervals in its course, until the force given by the hand

that threw it is exhausted, when it will drop and sink. The water, though

lighter in equal bulk than the stone, is aided by the force given by the

hand to buoy up the stone until the force is expended. The curve on the

front edge of the planes, when the machine is in motion, really takes in

more air than the space allowed for it under normal conditions, and it

may be said to be compressed to some extent. If the wind be blowing in the

'teeth' of the machine, the resistance of the air will be greater, and the

buoyancy of the machine increased. So, also, if the machine is travelling

rapidly, the motion will increase the resistance and the buoyancy at the

same time. The moment the propellers stop, gravitation grasps the machine,

and if the planes are kept evenly balanced it will quietly and gently

descend to the earth. You must particularly bear in mind that wind blowing

in the face of a machine tends to hold it up, and that a machine flying

rapidly makes its own wind, so that the results are the same.

"The curve on the front of the planes may be called an 'aero-curve,'

and much of the success of the machine depends on this curvature of

the planes, which gives to the inside of the plane a concave shape of a

peculiar character, and to the outside a convex form.

[Illustration: Fig. 44_a_. Maxim's aero-curve]

"If you examine the rough drawing I made for you on the blackboard (Fig.

44) you will notice that the upper or convex curve is different from the

under or concave one, and it is upon this difference in curvatures that

many of the flying qualities of the machine depend. This little section

showing the different curves is the one used by many of the successful

aviators, though some prefer the form invented by Sir Hiram Maxim, shown

in Fig. 44_a_, which does not differ very materially from the previous

section shown. In all cases, however, the accepted plane is one of a

curved vertical section in which the convex side is uppermost and the

upper surface more curved than the lower. Although different authorities

disagree as to why this shape of plane is best, all agree that it is so.

Sir Hiram Maxim's theory is that the air follows both the upper and lower

surfaces of the plane, as shown in Fig. 44_a_, while Phillips holds that

the air follows the lower surface of the plane, and, striking the hump,

shown at A, Fig. 44, is reflected off the upper surface of the plane, thus

forming a partial vacuum on the upper surface, which gives an additional

upward pull to the plane. There is, however, little doubt that most of

the work is done by the force exerted on the lower surface of the plane.

"Another consideration that enters into the design of the plane is

the aspect ratio, or the ratio between the depth of the plane fore and

aft, and the width or span. Authorities do not agree about this latter

consideration. A practical aspect ratio, one states, is 6 to 1, as, for

instance, a plane 39 feet spread by 6 feet 6 inches in depth. In Santos

Dumont's _Demoiselle_ the aspect ratio is only 3 to 1. The ideal plane,

however, would be a plane of great length and little depth, but this is

impossible in the practical machine, as a plane of excessive length would

greatly weaken the construction of the machine. Again, the different

authorities do not agree as to the shape of the ends of the planes.

Lanchester says that an efficient plane must be of rectangular form, and

the Voisin and Curtiss planes are rectangular, whereas the wings of the

Blériot and the Wright planes are decidedly curved at the tips.

"I will show in other illustrations the method of placing the planes on

such machines, as made by Curtiss and some other noted aviators.

"I think I have said sufficient to give you a fair idea of the reason why

an aeroplane can be made to navigate the air, but I have not told you

how its direction can be controlled. No doubt, if the air were always

still and not subject to change, there would be but little difficulty

in controlling the direction of the machine, but, unfortunately, this

is not the case, so provision has to be made to meet various changes

as they occur. A downward current of air causes the plane to change its

inclination to the horizontal, so that it will not support the weight, and

the machine falls to the ground. To overcome this unsatisfactory state

of things, small auxiliary planes are used to counteract the effect of

varying air currents. They control the movements of the main planes so

that they always bear the same inclination to the horizontal, and they

are also used to elevate the machines so as to clear small obstacles. If

any great increase in altitude is desired, the speed of the engine must be

increased and the planes driven more rapidly through the air, thus giving

them more lifting power.

"It may be that in a short time, additional balancing planes will not be

necessary, as some other scheme may be invented that will regulate the

balance of the aeroplane. Already an Australian inventor, called Roberts,

has applied the gyroscope to the aeroplane in order to solve the problem

of making it balance automatically. It exerts a balancing force equal to

300 pounds, placed 18 inches on either side of the centre of gravity. The

gyroscope is driven by electricity, and controlled by a pendulum which

swings right or left, according to the tilt of the aeroplane. Mr. Roberts

is also working on a small aeroplane which is to be controlled by wireless

telegraphy. His inventions are being tested by the British War Office.

There are many other inventors on three continents busily employed in

trying to solve the balance problem.

"A very important matter in the construction of the aeroplane is the

position of the screw propeller. Sir Hiram Maxim advocates placing it

at the rear of the planes, and this construction is carried out in the

Wright, Curtiss, Voisin and Baldwin-McCurdy machines, while the tractor

screw is used on the Blériot, Antoinette, and Roe fliers. Sir Hiram's

theory is that if the screw is placed in front, the backwash strikes the

machine, which offers a good deal of resistance to the passage of the

air, and retards action; but if the propeller is placed in the rear, the

resistance of the machine imparts a forward motion to the air with which

it comes in contact, and the screw, running in air that is moving forward,

has less slip, and is, therefore, more efficient than the tractor screw.

"While the construction of the aeroplane is yet in an experimental stage,

it is progressing quite rapidly, and though no definite rules covering

the whole ground of construction and management can yet be laid down,

the following points may be well considered before any steps are taken in

making or using any make of aeroplane: (1) That it is useless to construct

the planes of flat vertical section, as much lift is lost in doing so, and

they are best constructed after the manner shown in Figs. 44 and 44_a_.

(2) That the most practical aspect ratio is about 6 to 1. (3) That the

angle of incidence of the inclined planes ought to be somewhere between

1 in 10, and 1 in 20 (_i. e._, the angle by which they are inclined

to the horizontal, the forward or entering edge of the plane of course

being the higher). (4) That a reliable motor, one that is immune from

involuntary stoppages, is absolutely essential to prevent accidents. (5)

That automatic stability of the machine is the theory of aeronautics that

all inventors should study most carefully.

[Illustration: Fig. 45. Blériot monoplane]

"The illustration I show here (Fig. 45) represents the monoplane in which

the Frenchman, Blériot, crossed over the sea from France to England. The

thick curved lines, shown at A, exhibit the main plane which gives the

machine its name of "monoplane"--one plane--and B shows the rear auxiliary

plane, which is also of curved section and curved ends. The plane A has

an area of 150 square feet, and B has an area of 17 square feet, while

the rudder C has an area of 4-1/2 square feet. The total length of the

machine is 25 feet, the sweep of the rudder 6 feet 6 inches. The rudder

is a plane, pure and simple, and may be constructed of any light material

that is strong enough to stand a reasonable wind pressure. The planes must

be covered on both sides with some light fabric, silk preferred, and all

the framework made as light as possible, consistent with safety.

[Illustration: Fig. 46. Plan of Blériot machine]

"The plan I show at Fig. 46 will give you a good idea of the form of this

machine, if you were looking from above at it. E is the point where the

aviator sits, and where the 30 horse-power engine is placed. The ends

of the planes are rounded off, and the ends of the rear plane at DD, are

made adjustable so that the machine may be made easier to manage when in

motion.

"All engines used in aeroplanes are of the internal combustion type,

made purposely for aerial flight, and are as strong and as light as it is

possible to make them.

[Illustration: Fig. 47. Biplane]

[Illustration: Fig. 48. Voisin biplane]

"The biplane, or two plane machine, is fitted up on somewhat the same

lines as the monoplane, having two planes one above the other, as I show

you in Fig. 47. The dark portion A A, shows the positions and curvature

of the planes. The plane B is called the elevator because it keeps up the

head of the machine. C shows the tail with a single plane. D is the part

containing the mechanism and the aviator's seat. E shows the vertical

planes, made of some light fabric stretched over a bamboo frame. The

propeller is shown at F, and it is about six feet in diameter. The two

carrying wheels, shown at G G, are simply light bicycle wheels which tend

to ease the landing of the machine when it comes to the earth. It will

be seen that machines may differ in the style of construction and yet, so

long as they contain the principles I have described, they will fly with

more or less success. The illustration, (Fig. 48), shows the plan of the

biplane, which is somewhat different in arrangement from the monoplane.

This sketch is of the Voisin biplane and shows the tail-piece, something

not used in machines of the Wright type. The Voisin machine is quite

popular in Europe, particularly in France. It is not very difficult to

construct or easy to control; at least, it has that reputation.

[Illustration: Fig. 49. The Santos-Dumont monoplane]

"The Santos Dumont monoplane, _Demoiselle_, shown in Fig. 49, is said

to be the smallest and lightest known practical machine, and there are

no patents on it, the inventor having published sketches and drawings

of all its details. Contrary to the usual plan, the aviator, in this

machine, sits below the motor, so that the propeller blades cut across

the line of sight; but as it revolves very rapidly the vision is not

affected. The whole machine, when complete, weighs only about 250 pounds.

Its length is about 20 feet and its total width over the planes 18 feet,

and it is about 7 feet 6 inches high. It is quite easy to build, as the

framework, or chassis, is fixed to a bent piece of ash or elm--like a

sleigh runner--which answers very well, because when the machine begins to

move the rear end rises first. If desired, the frame can be made so that

the whole thing can be taken apart. Sockets, like those used on finishing

rods, may be attached at the joints and junctions to hold the structure

together. The two spars that constitute the main support of the planes are

formed of ash, this having been found the best material for the purpose,

as it is also for the making of the propeller blades. One of the spars

should be fixed about nine inches from the front edge, and the other about

twelve inches from the back. Bamboo cross pieces are fastened about nine

or ten inches apart between the two main spars. All is covered with oiled

silk, applied in two thicknesses. The area of the main plane is some 115

square feet, and that of the tail-piece about 50 square feet. To cover

all this would require about 400 square feet of silk.

"I have heard it said that aeroplanes are hard to manage, difficult to

drive, and extremely dangerous. This is not true entirely, but there is

some truth in it. An amateur has to go through a 'course of sprouts' and

must learn all about his machine before beginning to use it practically.

Once he becomes master of it and can keep it well under control, he need

not fear accidents, if he does not lose his head, nor venture out in half

a gale. When we consider the number of experiments that have been made

from time to time with imperfect machines, we find that fatal accidents

have been very few, less, indeed, than the number recorded in the early

stages of automobile history.

"I have been compelled to draw a number of the points I have given

you from many sources, particularly from the writings of Messrs.

Fetherstonhaugh and Lanchester, which does not detract from what I have

told you, but rather guarantees its correctness.

"Well, children--it is getting late, but, before bidding you good-night,

I think I should finish my talk on aeroplanes by showing you how to make

a small model of a flying machine, if you are not too tired to listen

further?"

[Illustration: Fig. 50. A model aeroplane]

"Please, father," said Fred, "do keep on." George, also, wanted to hear

more, so Mr. Gregg decided to continue.

[Illustration: Fig. 51. Section model aeroplane]

"I have given you an outline of the reason why an aeroplane can be made to

rise from the ground and navigate the air; but I have not told you of all

the kinds of machines that can be made to fly, for there are many others

than those I have spoken of. One is the glider, which does not carry an

engine, but, as its name indicates, glides along in the air at a distance

not far from the earth. These are not capable of travelling very far

and, therefore, are not likely to come into general use. They have to be

started either by gliding off a high tower, by sliding down a hill or by

being propelled by hand or towed by some rapidly moving machine. Some day,

perhaps, a machine will be evolved on the same or similar lines as the

glider, that can be propelled by natural forces, but the time is not yet.

Beside the monoplane and the biplane, there is the triplane, constructed

on the same lines as the other flying planes, that is to say, the three

planes used on the machine are made the same as the planes on the others,

each having a convex and concave side of different curvatures.

[Illustration: Fig. 52. Blade of propeller]

"The monoplane which I am about to describe and illustrate, and which

I show in Figs. 50-51-52, can be easily and cheaply made, and can be

guaranteed to fly, after a little experimenting to get the correct balance

and angle of the planes. The frame A will first be treated. Get two pieces

of yellow or white pine (the lightest and most easily procured wood), cut

them to the shape shown, 1 foot 6 inches long, 1/2 inch by 1-3/16 inches

in the middle, and thickened at the ends to take the screws from the end

bars B and C (Fig. 50). Take great care to make them exactly alike. The

end pieces B and C, which are 2-1/2 inches by 7/16 inch by 1/4 inch can

then be screwed to the side pieces A, and a rectangular frame is the

result. Should the screws split the wood in the slightest degree, new

pieces must be made, as the plane is sure to get rough usage in falling

on the ground a few times.

[Illustration: Photograph by Brown Brothers

MAKING AN AEROPLANE MODEL

"If the Screws Split the Wood in the Slightest Degree, New Pieces

Must be Made"

]

"The planes are also made of yellow pine. They must be exactly equal

to one another in weight, one being right handed and the other left.

The wood must not be more than 1/22 inch thick, and, if possible, even

thinner. A large circular chip box will be the best thing from which to

make these. Gum a piece of tracing cloth on top of the planes, and allow

about 2 inches to overlap at the large ends, to twist and glue round the

main frame when fixing. The cloth will fulfil two useful and necessary

purposes. It will strengthen the planes and curve them to a very large

extent. This curvature is essential to the flight of the machine. A wooden

block curved to suit, and inclined at about 5 degrees, is fixed between

the back planes and the frame.

"The front or small plane is 8 inches by 3 inches, and made in the same

way as the others. It must be adjustable, and is, therefore, mounted on

two wooden blocks, 2 inches by 1/4 inch by 1/2 inch and fastened by means

of copper wire which acts as a hinge. Four silk cords are fixed to the

movable end of the plane, two being fastened to nails at the rear end of

the frame and two to the front, to hold the plane at any desired angle.

[Illustration: Fig. 53. Connections of propeller blade]

"The propeller blades (Fig. 52) are made of thin aluminum. Two sheets are

cut out the same size and shape, and placed with their ends overlapping

(see Fig. 53). A piece of steel wire 1/16 inch in diameter is bent and

placed between them to form the shaft. The whole is then fixed in a piece

of light copper tube, which is slotted by means of a hack saw or fret saw

to receive them. The blades are bound crosswise to the tube by means of

thin wire or strong thread; then twisted to a pitch of about 6 inches. It

is also advisable to place a washer between the copper tube and the end

bar of the frame.

"This method of fixing the propeller blades is not the same as that shown

in Fig. 50 but it is the better way.

"The drive for the propeller is elastic (a rubber band), which, when

twisted and released, will rapidly revolve the shaft for a short time.

The best kind to use is the gray variety, and when in the form of bands,

say 3/8 inch by 1/16 inch by 6 inches, is ready for use without jointing.

The wire carrying the elastic should be made so that the elastic is just

in tension when untwisted.

"The monoplane, when complete, should be tested without the propeller

until it will glide perfectly. The front of the plane will need weight

added if there is a tendency to somersault; but if the back rises ahead

of the forward end, more weight is necessary there. The best glide to be

expected is about a 1 in 6 slope. The propeller should then be tried, and

a flight of 50 or 100 feet, or more, should result. If there is a tendency

to twist, owing to the side pull of the propeller, a screw should be fixed

to the end of the plane to counteract it.

"A much longer flight can be given the model, if the spring is made

so that the tension may continue a longer period. Sometimes a rubber

attachment can be applied and twisted so that the propeller can be kept

running long enough to carry the machine a much greater distance than

here stated. The dimensions of all the parts of the machine are marked on

the illustrations, so that you will find no difficulty whatever in making

a model monoplane that will fly from the start. In the making of little

models of this kind, you will encounter many things that will tax your

skill and ingenuity, as amateur workmen.

"Now, children, I have told you all about aeroplanes that I intended,

though I may take up the subject again, when I try to explain the

recognized theory of flight, and the making and flying of kites."

VIII

KITES, SUNDIALS, PATENTS

The next day, just as Mr. Gregg returned from his office, Fred, Jessie,

and George landed on their new dock from the _Caroline_. They had been

for a sail on the river, and Jessie was quite enthusiastic over the trip.

"Fred was a real good captain. Why, papa, he let me steer the boat all by

myself, and taught me so well I didn't have any collisions."

An hour or so later the boys, Jessie, and Mr. Gregg, retired to the den.

After questioning the boys regarding the previous talk, to discover if

they remembered the main points, Mr. Gregg said he would now tell them

something of kites and kite flying.

"The highest kite ascent yet recorded was made at the aeronautical

observatory at Lindenburg, (Prussia) on November 25, 1905, 21,100 feet

being attained. Six kites were attached to one another with a wire line

of nearly 16,000 yards in length. The minimum temperature recorded was 13

degrees, F.; at starting the reading was 41 degrees. The wind velocity

at the surface of the earth was eighteen miles an hour, and the maximum

altitude it reached was fifty-six miles an hour. The previous height

record by a kite was nearly 1,100 feet lower, and it had been reached

from a Danish gunboat in the Baltic. These ascents were wonderful, for it

is not an easy matter to train a kite higher than a given altitude, for

several reasons. The higher a kite rises the more string it will require,

and this tends to weight down the plane or kite.

The wind, too, acting on the string, tends to retard the upward flight and

to cut short further ascent. When an ordinary kite reaches a height of

1,200 or 1,500 feet, it is doing very well; and few exceed this height.

When Benjamin Franklin angled in the clouds for lightning, his kite did

not attain an altitude of more than 1,000 feet, which was quite sufficient

for the purpose he had in view. When Franklin flew his kite, he was so

afraid of ridicule that he took a small boy with him to carry the kite

and string, in order to prevent his neighbours from thinking he was going

'kite flying.' In these days when a man is seen flying a kite, people

very naturally imagine him to be an aeronaut, studying the science for

the purpose of improving or inventing a flying machine of some kind--for

which there seems to be ample room.

[Illustration: Fig. 54. Science of kite-flying]

"The first thing a beginner in the science of aeronautics will want to

know is, 'Why does the kite or machine lift itself off the ground?' If you

take a kite and hold it in an inclined position, the wind on the lower

side will have a tendency to blow it backward; but as it is held by the

kite string, this movement is impossible, and so it is inclined to rise

in the air (see Fig. 54). If we construct a large plane and equip it with

a motor operating a screw which pushes or pulls the plane along through

the air, the result is the same as if the plane were anchored, and the

wind hits the lower surface of the inclined plane, thus forcing it up.

Also, we find, within certain limits, the more you incline a plane the

more lift or upward thrust will it give; but it will take more power to

drive it through the air, and the faster the plane is driven through the

air the less surface is required to support the weight. A matter of great

importance in the construction is the shape of the plane, and the shape

of the vertical section through the same. The shape of these planes has

been explained in Figs. 43 and 44, and the reasons were given why these

shapes were considered the proper ones for the purpose.

"It does not follow," said Mr. Gregg, "that all kites should have the

same kind of a surface or plane, though the flat planes of the toys of

our school days were all of the flat surface kind; these being of various

shapes and sizes from the lozenge to the square, bow top, octagon, and

many others, according to the whim or skill of the maker. One of the

conditions of these planes or flat kites, was that each one must have

at least one tail attached to the bottom of it. This tail was flexible,

simply a piece of string having paper similar to 'curl papers' tied to it

at intervals. The tail was a necessity, for without it the equipoise would

be impossible. In China and Japan, where the natives have been kite-flying

for more than twenty centuries, they make kites that fly and maintain the

aerial equipoise without having tails hung to them, no matter whether the

shape be that of a dragon, a lion, or an eagle.

[Illustration: Fig. 55. Box kite]

"A kite is simply an aeroplane on a small scale, and should be considered

as such, as it has a fixed fulcrum in the belly band, a constant pressure

when flying, and an angle which is varied in proportion to the load it

may have to carry. The common kite is easily made, but it does not always

fly as desired; for it seems almost impossible to make two kites that

will fly in the same manner under similar conditions. Box kites are the

most reliable, and not so very difficult to make, as you will discover by

examining Figs. 55, 56, and 57 and following the directions I give you.

First, procure four straight strips of light wood, preferably spruce,

2 ft. 6 in. by 3/8 in. by 1/8 in.; these dimensions should be full (see

Fig. 55.) Obtain also four other pieces, each 1 ft. 7-1/2 in. long, but

1/16 in. wider and thicker than the foregoing, and halve their ends to a

depth of 1/8 in. by 1/4 in., in order that when the false end A (Fig. 56)

is tightly bound on, these cross sticks will firmly grip the long pieces

edgewise, the sides of the cells being indicated by the dotted lines. The

long sticks should be notched at a distance of 4 in. from their ends to

receive the forks of the cross sticks.

[Illustration: Fig. 56. Making a kite]

"The width of the cloth or paper cells should be 8 in., and they should be

separated by a distance of 1 ft. 1 in. or 1 ft. 2 in., their edges being

bound with fine twine. The easiest way to make the cells is to cut two

strips of the material, 10 in. wide and 4 ft. 8-1/2 in. long. Turn over

the edges 1/2 in. along each side, and insert fine strong twine! If paper

is used, glue the fold; if cloth, stitch the hem. When completed, either

glue or stitch the ends of the strip with a 3/4 in. lap, so as to form a

continuous band. By folding, divide this accurately into four equal parts

and at each of the creases glue one of the long sticks edgewise (see Fig.

56). When dry, the whole can be put together and the flying line attached,

without a bridle, as in Fig. 55. For additional clearness an enlarged

detail of one end of the kite is shown at Fig. 57.

[Illustration: Fig. 57. Single box kite]

[Illustration: Photograph by Brown Bros

MAKING KITES

"Box Kites Are the Most Reliable, And Not so Very Difficult to

Make"

]

"It is advisable in all cases to make the cross pieces a trifle too long,

to insure their straining the band tightly. They may also be shortened by

cutting away the shoulder formed by the halving.

"These kites are easy to fly. Avoid an enclosed space, where the wind

whirls in invisible eddies; having let out 20 yds. or 30 yds. of line,

get some one to throw up the kite in the usual fashion. If several large

kites are sent up in tandem, steel wire should be used.

[Illustration: Fig. 58. Square cellular kite]

"Another kind of a kite, known as the cellular kite is shown in Fig.

58. This is made by forming two square frames N. O., divided into nine

compartments each and connected together by a light rod at _r_, the

fulcrum or string being at P, the air pressure at T. The whole forms a

good, strong kite, but it is not able to carry much weight, on account

of the equipoise being self adjusted in accordance with the constant

pressure and surface. The equipoise is due to the current being cut by the

edges _a a´_, and diverted into the cellular divisions of each area.

This being the case, any upward or downward tendency of _a a´_, would

be counterbalanced by the effect on the other side and the kite would

naturally adjust itself on the opposite side. We are not dependent upon

any particular shape for obtaining a good serviceable kite--like the plane

made kite, the cellular one may be of any shape. I show you one here, at

Fig. 59, having a circular rim, with thin tubes inserted in such a manner

that the current of wind will rush through when the machine is in the air.

The two portions, A and B, are held together by a rod in a similar manner

to the square kites, and the cord or fulcrum is fastened to the rod at R.

[Illustration: Fig. 59. Circular cellular kite]

"A number of kites may be sent up at once, all attached to the same

string, if properly adjusted. Here are six square cellular kites looped

together, shown at Fig. 60. They may be made of any suitable size, but

need not be all of one size, though each pair would be better if made the

same size. They may be looped up, as shown, and the point S may be loaded

lightly; it will help to steady the kite and keep it from swaying.

[Illustration: Fig. 60. Group of kites]

"A peculiar kite, called 'a war kite,' is very popular in some parts of

Europe, and in some parts of our country also. It is easily made and

gives good results. It is on the principle of the 'cellular' or 'box'

kite, being cubical or box-shaped, and, when used for carrying weights,

usually has several cells built together, or several kites may be coupled

when a heavy load, such as that of a man, is to be raised. These kites

are made of light wood or cane covered with nainsook or fine cotton,

and strengthened with cross pieces which hold the frames tight and keep

the kite in shape. They can be taken to pieces and the covering material

rolled up so that they occupy very little space. Two forms of box kites

are shown in Figs. 61 and 62, and it will be seen that an attachment is

made each side of the frame. This is fine steel wire, very light compared

with its strength, wound on a drum by means of a small engine. Large kites

of the ordinary form can be used for the same purpose, but their lifting

power is not equal to that of the box kite. A small box kite is used for

taking photographs, a camera being carried by a separate wire connection

to the attachment wire, and the shutter released at the proper time by an

ingenious arrangement, similar to the pieces of paper called 'messengers'

which boys used to send up on the cords of ordinary kites. This kite is

a little more expensive to make than most of those shown, but it gives an

excellent result when properly handled.

[Illustration: Fig. 61. Sextuple kite]

[Illustration: Fig. 62. War kite]

"In making kites of any kind, the lightest materials consistent with

sufficient strength, should be employed. The frames should be split bamboo

or cane. The joints may be lashed together with fine wire or silk thread,

and the envelope in each case should be fine silk or similar material that

would be close, light, and strong. These qualities, in all sorts of kites

and aeroplanes, are absolutely essential to accomplish the best results.

"Before leaving the subject of aeronautics, I think it would not be amiss

to tell you something of bird flight. There are different modes of flying,

just as men have different gaits in walking or running.

"Rapid wing movement does not always imply speed in flight, any more

than does rapid leg movement imply speed in walking or running. With

us it is the length of the stride that tells ultimately. What tells,

correspondingly, in the flight of the bird is not known.

"Speaking broadly, long-winged birds are strong and swift fliers;

short-winged birds are feeble in flight. When we consider that a cumbrous,

slow-moving bird like the heron moves its wings twice per second when in

flight, it is evident that many birds have a very rapid wing movement.

Most small birds have it, combined with feeble powers of flight. The

common wren and the chipping sparrow, for instance, have a flight like

that of a young bird.

"What can give one more exquisite pleasure than to watch seagulls

swooping round the edge of a cliff, to see them drift down wind with wings

motionless, then suddenly dart downward, turn to meet the breeze, and beat

up against it with all their ingenuity and skill?

"The beauty of a ship depends on the way it glides through the water.

Watch a liner, and you can see that it is being driven by its screws, but

look at a racing yacht: there is no sense of effort whatever. She seems

to move like a bird, by natural means.

"Here is the secret of the beauty of the aeroplane. It seems to be

completely master of the element in which it moves. It flies with no

visible effort and at a little distance one could imagine it endowed with

magic power, moving by natural force, like a bird.

"All the early attempts at flying were made on the theory of wing motion,

and the failures resulting were doubtless due to careless study of what

nature could teach. There was a great deal more to be learned from nature

than from mathematics. An examination of the different types of birds

testifies, among other things, to their rigid backs, and to the fact that

nearly all their bones are hollow and have air cavities. An erroneous

deduction had been drawn from this that the hollows were purely for the

sake of lightness, and that the cavities were for hot air to make the

bird light when it wanted to fly. The amount of lightness so obtained,

however, was so small as not to be worth consideration. The passages are

simply reservoirs for air, and they allow the bird more energy than a less

freely breathing animal. The wing of the bird does a double duty: it is

an aeroplane and a propeller combined. The valvular action has nothing at

all to do with the flight. Some explanation of how a sparrow can rise from

the gutter to the eaves may be seen by the difference in the construction

of its wings from those of the swallow, which cannot rise from the ground

like a sparrow, but has to get initial velocity. The swallow, however,

has much more mastery over its movements in the air than the sparrow has.

These, and many other things in connection with bird flight, under proper

methods of scientific investigation, may show us the whole theory of

aviation. I am inclined to think that scientific men will soon be able to

solve the problem, and to give us better control of the coming aeroplanes,

or even direct their flight by the aid of electric waves or other natural

forces.

"In kite-flying, it is well to know something of the wind and its

pressure, and, in this connection, the following short table will give

some idea of the force exercised on objects in its path: A light air

current presses 0.004 lbs. per square foot.

Light wind has a pressure of 0.125 lbs. per sq. foot

Light breeze 0.246 lbs. per sq. foot

Moderate breeze 0.406 lbs. per sq. foot

Strong breeze 2.00 lbs. per sq. foot

Moderate gale 2.98 lbs. per sq. foot

"This last should be the limit, as a kite or aeroplane of any kind will

find it hard to manoeuvre in a breeze stronger than a moderate gale.

Of course, there are winds sometimes that have a velocity of 60 to 75

miles an hour, and a pressure of over 40 pounds to the square foot, but

these would prove disastrous to any kind of a flying machine, if it was

in action."

"Father," asked Fred, "how can one tell the velocity of the wind,

without one of those expensive machines I see at the weather office, an

anemometer, I think it is called?"

"I am glad," said the father, "that you have noticed those and other

instruments for gauging and foretelling weather conditions. It is an

indication that you keep your eyes open when you visit such places, and

to learn by observation is almost as effectual as to obtain knowledge

by experience. I have in mind a very simple contrivance you can make

yourself, for measuring wind pressure from a couple of ounces to four

pounds to the foot. I will make a sketch of it, which I am sure you will

understand.

[Illustration: Fig. 63. Wind gauge]

"It consists of a light pine or cedar wood frame on a strong stand,

supporting on a centre two bent wires, carrying at one end a 3-in. square

of thin wood, A, and on the other a thin bar of wood, to the centre of

which is attached a fine string tied to a spring balance scaled to 1/8 of

an ounce and up to 4 ounces (Fig 63). As the square of 3 inches is the

16th of a foot, each ounce on the spring is equal to 1 lb. pressure on

the square foot. The latter balance slides in the V-frame at the back so

as always to keep the square parallel to the face of the frame, whether

the wind is strong or light, and the balance must be slidden in or out

until the face of the square is so placed before registering the force of

the wind. By attention to this it will register very truly up to 4 lbs.,

which is the extent of an ordinary spring balance. There is also a front

view, a side view, and a bird's-eye view, also one of the bent wires and

the 3-inch square. I think this requires no further explanation."

Fred was satisfied with the description of the register and promised to

make one at an early date.

The following evening when they were all sitting on the river bank,

Fred suddenly asked his father if it was difficult, or costly, to secure

patents. He wanted to know, because he had been thinking of making a kite

on a new principle--that of a funnel, and he was so sure it would prove

a success that he would like to have it patented.

Mr. Gregg thought the scheme rather an ambitious one, but, while he could

not see it as Fred did, he determined not to say anything that would be

likely to discourage the boy. So he explained, as well as he could, the

patent laws: "In order to apply for a patent it is necessary to file

in the Patent Office at Washington, D. C., a petition, affidavit of

invention, drawings, and specifications, all of which must be prepared

in legal form and in accordance with official rules and practice of the

office.

"This can best be done by a reliable attorney but an applicant should

understand some of the requirements as well.

"The Patent Office does not require a model to be furnished in order to

apply for a patent, but if the attorney is not near enough to see the one

made by the inventor, then one should be sent him, unless good photographs

and drawings can be supplied.

"Since the drawing attached to the specifications and claims is to be

on a sheet of a special size, no attention need be paid to having the

original sketches of a uniform size. When ready to apply for a patent,

secure as much evidence as possible of the reliability of some attorney

you have heard of and consult him about the matter, explaining as much

as is necessary for him to prepare an outline that will suffice for a

preliminary search through the records in the Patent Office to see that

no interference will take place should the application be made.

"This usually costs $5.00, and an attorney often supplies copies of

existing patents that look the most like the one in question.

"If it is thought that there will be no interference, the case is then

prepared for the examiners, and the application duly made.

"The drawings should be made and lettered, so that the specifications can

be written up, including the proper reference to the different parts.

"The drawings should be made upon paper stiff enough to stand in a

portfolio, the surface of which must be calendered and smooth. The best

kind is patent office bristol, though there is a style on the market

printed with margin and headings all ready for use, but the surface is

not of the best.

"The size of the sheet on which a drawing is made should be exactly 10 ×

15 inches with margin lines one inch from all the edges, leaving a clear

space of 8 × 13 inches.

"One of the smaller sides is regarded as its top, and measuring downward

from the margin, or border line, a space of not less than 1-1/4 inches is

to be left blank for the insertion of title, name, number and date, to be

put in by the patent officials.

"All drawings must be made with the pen only, using the blackest India

ink. Every line and letter, including the signature must be absolutely

black.

This applies to all lines, however fine, to shading and to lines

representing cut surfaces in sectional views. All lines must be clean,

sharp, and solid, and they must not be too fine or crowded.

"Surface shading, when used, should be left very open. Sectional shading

should be by oblique parallel lines, which may be about one-twentieth

of an inch apart. Drawings should be made with the fewest lines possible

consistent with clearness, for the drawings are subjected to photographic

reduction, which decreases the space between the lines.

"Shading (except on special views) should be used only on convex and

concave surfaces, and there sparingly, or it may be dispensed with if the

drawing is otherwise well made.

"The plane on which a sectional view is taken should be indicated on the

general view by a broken or dotted line.

"Heavy lines on the shade sides of objects should be used, except where

they tend to thicken the work and obscure the reference letters.

"The light is always supposed to come from the upper left hand corner, at

an angle of forty-five degrees.

"Imitations of wood or surface graining should not be attempted.

"The scale to which a drawing is made ought to be large enough to show

the mechanism without crowding, and two or more sheets should be used if

one does not give sufficient room to accomplish this end; but the number

of sheets must never be increased unless it is absolutely necessary.

"Sometimes the invention, although constituting but a small part of a

machine, has to be represented in connection with other and much larger

parts. In a case of this kind, a general view on a small scale is

recommended, with one or more of the invention itself on a much larger

scale.

"Letters or figures may be used for reference, but they should be well

made, and when at all possible should not be less than one eighth of an

inch in height, that they may bear reduction to one twenty-fourth of an

inch; or they may be much larger when there is sufficient space.

"Reference letters must be so placed in the close and complex parts of

a drawing as not to interfere with a thorough understanding of the same,

and to this end should rarely cross or mingle with the lines.

"The illustrations on pages of current topics under the head of new

patents show the manner of putting in the reference lines from the letters

to the part indicated.

"These are carried out some distance, but if placed on the face of the

object where sectioned, a blank space should be left in the shading for

the letter.

"If the same part of the invention appears in more than one view, it

should always be represented by the same letter.

"Great care should be exercised in the matter of drawings, or they will be

returned to the applicant, but, at his suggestion and cost, the officials

will make the necessary corrections.

"The time required to procure an allowance of a patent averages from six

weeks to two months.

"United States patents are granted for a term of seventeen years, and

cannot be extended. The patent remains good whether the invention is

worked or not, and no additional payments are required beyond the cost of

first taking out the patent. Patents are not subject to taxation. Reissues

of patents are granted whenever one is inoperative or invalid, by reason

of a defective or insufficient specification, or by reason of the patentee

claiming more than he had a right to claim as new, provided the error

arose by inadvertence, accident, or mistake, without fraudulent intent.

A fee of $30.50 must be forwarded upon application for patent.

"As stated before, a patent is obtained by a petition to the Commissioner

of Patents accompanied by a description, including drawings and a model,

when the invention will admit of these. A fee of $15 is required when the

application is made, and a further fee of $20 when the patent is issued.

Postage on model is at the rate of 1 cent per ounce.

"A patent for a design is granted to any person who has invented or

produced any new and original design for the printing of woollen, silk,

cotton, or other fabrics; any new and original impression, ornament,

pattern-print, or picture to be printed, painted, cast, or otherwise

placed on or worked into any article of manufacture; or any new, useful,

and original shape or configuration of any article of manufacture, the

same not being known or used by others before this invention or production

thereof, or patented or described in any printed publication, upon payment

of the duty required by law, and other required proceedings the same as

in cases of inventions or discoveries. These are granted for three and

one-half years, seven years or fourteen years, for which the respective

fees of $10, $15, and $30 are paid the government.

"A caveat is a provisional protection to any person who has thought of

an invention and desires the time to complete or perfect the same. It is

procured at an expense of $10, and runs for one year with the permission

of renewal from year to year.

"In Canada the patent office is a branch of the Department of Agriculture,

and the Minister of Agriculture for the time being is the Commissioner of

Patents.

"Any intending applicant for a patent who has not yet perfected his

invention, and is in fear of being despoiled of his idea, may file in

the patent office a description of his invention so far, with, or without

plans, of his own will, and the Commissioner, on payment of the prescribed

fee, shall cause the said document, which shall be called a caveat, to

be preserved in secrecy, and, if application is made by any other person

for a patent interfering in any way therewith, the Commissioner shall

forthwith give notice, by mail, of such application to the person filing

such caveat, who shall, within three months thereafter, if he wishes to

avail himself of the caveat, file his petition, and take the other steps

necessary on application for a patent. The application for the patent

must be made within one year from the filing of caveat, otherwise the

Commissioner is relieved from the obligation of giving notice.

"The following fees are payable: Full fee on patent for 18 years, $60.00;

partial fee for 12 years, $40.00; partial fee for 6 years, $20.00; on

filing caveat, $5.00; on registering assignment patent, $2.00; for copy

of patent, with specification, $4.00.

"The disbursements for filing an application in Great Britain are

$25.00; France, $20.00; Germany, $5.00, and $7.50 before issuing patent;

Australia, $20.00; Russia, $75.00; British India, $20.00. The German and

French patents cover not only Germany and France but their colonies also.

The Russian patent extends to all of the Russian possessions.

"The disbursements for filing an application in the Australian states,

namely, Queensland, Victoria, New South Wales, South Australia, Western

Australia and Tasmania are $5.00 on filing the application, $10.00 on

allowance of same, and $25.00 for preparation of the sealing of patent;

New Zealand, $20.00; Mexico, $75.00; Natal, $50.00; Japan, $75.00;

Jamaica, $150.00."

This talk on patents was quite interesting to Fred, and very instructive

to George, and they thanked their father for it.

[Illustration: Photographs by C. M. D'Enville

A SUN DIAL MADE OF CONCRETE

An excellent illustration of the possibility which concrete offers

in ornamental as well as practical construction. This sun dial,

complete, cost approximately ten dollars, and may be duplicated

by any clever boy. See formula for concrete on page 20.

]

"Boys," he said to them next morning, "why not try your hands on a

sundial? You will find it easy to make, and if properly set up it will

keep accurate time. There is a nice place for one near the bridge on the

new grounds, as there is a stump there, the top of which can be cut off

smooth, and it stands out full in the sun.

[Illustration: Fig. 64. Sundial]

"Go to our jeweller in the city and get him to give you an old tin

clock-dial, like the one shown in Fig. 64. If you cannot get one, make a

dial out of cardboard yourself, printing the hours in ink. Slit the dial

from the centre to a point directly underneath the number 12, if you have

Arabic numerals on your dial.

"Then cut out a triangular blade or gnomon, like the one shown. If your

dial is of tin, make the blade of tin, or cardboard if your dial is of

cardboard.

"Insert the blade in the slit of the dial and secure it to the top of

the stand you have selected--with tacks if your dial is cardboard, with

small nails if it is tin. Then your sundial will be completed and ready

for business.

"At 12 o'clock, there will be only the shadow of the thin edge of the

blade over the dial, but as the sun moves, so will the shadow, so as

to tell always the correct time of day. You will find this not only a

useful but a quaint and artistic addition to the grounds, and not at all

expensive."

"Papa," said George, "mamma wants a flower bed made in the front garden,

and she would like to have it an oval or elliptical shape. I have promised

to make it for her, but I do not know how to make the shape, and I wish

you would tell me."

"Certainly, my boy, I will show you. It can be done easily with a string

and two wooden pegs. Follow the lines I make on the blackboard. First

we must decide on the length and width of the oval or rather ellipse

required. Then draw two straight lines, A B and C D, Fig. 65, equal to

the two axes, and bisect or halve each at right angles. Set off from C

half the length of the great axis at E and F, which are the two foci of

the ellipse. Take an endless string, as long as the three sides of the

triangle, C E F, fix two pins or nails in the two foci, one at E and one

at F. Lay the string around E and F, stretch it with a marker G, and it

then will describe the desired ellipse.

[Illustration: Fig. 65. Drawing an ellipse]

"This is not at all difficult, and will answer for any kind of an ellipse,

short or long, narrow or wide. This is called the "gardener's method." The

main thing is to get the two points, E and F. This distance is always half

of the long diameter A B, no matter what that may be, and this distance is

then transferred by taking C as the starting point, measuring from there

until the other point of measurement cuts the long diameter, as at E and

F.

"The ellipse has many peculiar and useful qualities, which you will

doubtless discover before long."

IX

TIDES

"Now, papa!" said Jessie the following evening, after Mr. Gregg and the

family had strolled down to the river bank to enjoy the cool air, "you

promised to tell me about the tides and the moon--when you could spare

time. Haven't you got time now?"

"I may as well say all I intended now, my dear, and leave some other

matters for future consideration. As this subject may tax your patience,

I hope you, Fred, and George, will give me your earnest attention.

"In order to have a clear understanding of the movements of the tides and

their supposed causes, you must know something of the moon's influence

over them; as this knowledge will aid you very much in remembering what

I am about to say.

"The earth is a globular body. One reason for this belief, among many

others, is that sailors or others who go to sea soon observe that as

they sail from shore, the lower portions of mountains, steeples or other

high objects, are gradually lost sight of while the higher parts do not

so soon disappear. Persons on shore first notice the upper portions of

masts, and the smoke-stacks of approaching vessels, which would not be

the case, if the earth were a plane, but is very easily accounted for, on

the supposition of its being a sphere, as you can readily understand by

looking at Fig. 66. Several navigators have sailed completely round the

earth by continuing in the same direction, and coming at last to the same

place from which they started. The earth, however, is not a perfect sphere

but a spheroid like an orange; having its equatorial longer than its polar

diameter or axis. It is flattened at the poles, and more protuberant at

the equator. The diameter at the equator is 7,977 miles, and at the poles

7,940, a difference of 37 miles.

[Illustration: Fig. 66. Proof of earth's rotundity]

"You know that the cause of day and night is the rotation of the earth

on its own axis. It shows a large portion of its surface to the sun

continually, or in other words, the sun is always shining on some portion

of the earth's surface. You are also aware of the earth and its satellite,

the moon, both being held in their orbits by the sun's attraction, the

moon being further kept in her orbit by the attraction of the earth. Now

the earth is composed of three main elements, air, water, and land, and if

you consider, for a moment, that the daily rotatory movement of the earth

is something like 1,000 miles an hour, this rapid speeding through space

must have some effect on air and water in assisting or retarding their

flow.

[Illustration: Fig. 67. Phases of the moon]

"Nature has divided time, and man has named and subdivided it into years,

months, and days. The natural month, however, does not consist of four

weeks, nor is the natural year made up of the twelve calendar months

given us by the almanac. A natural, or lunar, month is the time the moon

takes to perform her journey round the earth, which is 27 days 7 hours,

and 43 minutes; this is called the periodical month, while the average

calendar or synodical month consists of 29 days 12 hours and 44 minutes.

The light of the moon is borrowed from the sun, for if it were her own

light, she would shine all the time and not be subject to her present

phases. The moon is seen by means of the light which comes to it from

the sun being reflected from it. Its changes, or phases, depend upon its

relative position to the earth and the sun. When the moon is in opposition

to the sun at A (Fig. 67) the lighted side is turned toward the earth,

as A, and it appears full. When the moon is in conjunction at E with the

sun, its dark side is turned toward us, and it is invisible, as at _e_.

As it proceeds in its orbit, as at F, a small part of the light side is

seen, and then we have what is called a new moon; and we continue to see

more and more of the light side, as the moon approaches at G and H, to

the state of opposition or full moon. The waning or decreasing of the

moon takes place in the same manner, but in a contrary order. The earth

must perform the same office to the moon that the moon does to us; and

it will appear to the inhabitants of the moon (if there be any), like

a very magnificent moon, being to them about thirteen times as large as

the moon is to us and it will also have the same changes or phases. Hence

it is evident, that one half of the moon is never in darkness, the earth

constantly affording it a strong light, during the absence of the sun;

but the other half has a fortnight's light and darkness by turns.

"The moon's orbit is elliptical, and she also rotates on her axis and

takes the same time to circle the earth, consequently every part of the

moon is successively presented to the sun, yet the same hemisphere is

always turned to the earth. This has been discovered by observation with

good telescopes. The length of a day and night in the moon is more than

twenty-nine and a half days of ours; and while her year is the same length

as ours, being measured by her journey around the sun with us, so she has

but twelve days and a third in a year. Another remarkable circumstance

is that the moon's hemisphere next the earth is never in darkness, for

when it is turned from the sun, it is illuminated by light reflected from

the earth in the same manner as we are lighted by a full moon. The other

hemisphere of the moon however, has a fortnight's light and darkness

by turns. If there are inhabitants in the moon, which is doubtful, the

satellite will appear to them to be about thirteen times as large as the

moon does to us, and when it is new moon to the earth, it is full earth

to the moon.

"There are many things regarding our relationship to the moon that would

be of interest, if I had time to explain them, such as eclipses, the

moon's surface as seen through telescopes, its supposed influence on the

weather, etc., but I fear too much moon might prove tiresome. Beside I

have shown you sufficient to enable you to understand the relationship

existing between the moon and the tides, generally accepted as the true

theory.

"If we agree that the tides are occasioned by the attraction of sun

and moon, more particularly the latter, we can readily understand their

dependence on some known and determinate laws. Our almanacs published

long in advance give the exact time of high water at any prominent port

in the United States on the morning and afternoon for every day in the

year; and seafaring men can tell you when the tide will be high or low,

notwithstanding the fact that these movements are not fixed. They know

from experience that the time of ebb and flow varies about three quarters

of an hour each day.

"The first person who clearly pointed out the accepted cause of the

tides and showed its agreement with the effects, was Sir Isaac Newton.

He discovered a relationship between the moon and the tides, and by the

application of his new principles of geometry, the attraction was made

clear.

"The ocean, it is well known, covers more than one half the globe; and

this large body of water is found to be in continual motion, ebbing and

flowing alternately, without the least intermission. For instance, if the

tide is now at high water mark, in any port or harbour which lies open to

the ocean, it will presently subside, and flow regularly back for about

six hours, when it will be found at low water mark. After this it will

again gradually advance for six hours; and then recede in the same time

to its former situation, rising and falling alternately twice a day, or

in the space of about twenty-four hours. The interval between its ebb

and flow is not precisely six hours, for there is a little difference in

each tide; so that the time of high water does not always happen at the

same hour, but is about three quarters of an hour later each day, for

about thirty days, when it again recurs as before. For example, it is

high water to-day at noon, it will be low water at eleven minutes after

six in the evening; and, consequently, after two changes more, the time

of high water the next day will be at about three quarters of an hour

after noon; the day following it will be at about half an hour after one,

the day following that at a quarter past two, and so on for thirty days;

when it will again be found to be high water at noon, as on the day the

observation was first made. This exactly answers to the motion of the moon

which rises every day about three quarters of an hour later than upon the

preceding one, and by moving in this manner round the earth, completes

her revolution in about thirty days, and then begins to rise again at the

same time as before.

"To make the matter still plainer; suppose, at a certain place, it is high

water at three o'clock in the afternoon, upon the day of the new moon; the

following day it will be high water at three quarters of an hour after

three; the day after that at half an hour past four; and so on till the

next new moon, when it will again be high water exactly at three o'clock,

as before. By observing the tides continually at the same place, they will

always be found to follow the same rule; the time of high water, upon the

day of every new moon, being exactly at the same hour, and three-quarters

of an hour later every succeeding day.

"The change of the tides is in such exact conformity with the motion of

the moon that, independently of mathematical calculations, a thoughtful

person would certainly be induced to look to her as their cause.

[Illustration: Fig. 68. Theory of the tides]

"The waters at Z, on the side of the earth, A, B, C, D, E, F, G, H, next

the moon M, (Fig. 68) are more attracted by the moon than the central

parts of the earth, O, and the central parts are more attracted by her

than the waters on the opposite side of the earth at _n_; and therefore

the distance between the earth's centre and the waters on its surface

under and opposite to the moon will be increased. Let there be three

bodies at H, O, and D; if they are all equally attracted by the body M,

they will all move equally fast toward it, their mutual distance from

each other continuing the same. If the attraction of M is unequal, then

that body which is most strongly attracted will move most quickly and will

increase its distance from the other body. M will attract H more strongly

than does O, by which the distance between H and O will be increased, and

a spectator on O will perceive H rising higher toward Z. In like manner,

O being more strongly attracted than D, it will move farther toward M

than D does; consequently the distance between O and D will be increased;

and a spectator on O, not perceiving his own motion, will see D receding

farther from him towards N; all effects and appearances being the same,

whether D recedes from O, or O from D.

"Suppose now there is a number of bodies, as A, B, C, E, F, G, H, placed

round O, so as to form a flexible or fluid ring; then, as the whole is

attracted toward M, the parts at H and D will have their distance from O

increased; whilst the parts at B and F being nearly at the same distance

from M as O is, these parts will not recede from one another; but rather

by the oblique attraction of M, they will approach near to O. Hence, the

fluid ring will form itself into an ellipse Z, _n_, L, N, whose longer

axis _n_, O, Z, produced will pass through M, and its shorter axis B, O,

F, will terminate in B and F. Let the ring be filled with fluid particles,

so as to form a sphere round O; then, as the whole moves toward M, the

fluid sphere being lengthened at Z and _n_ will assume an oblong or oval

form. If M is the moon, O the earth's centre, A, B, C, D, E, F, G, H, the

sea covering the earth's surface, it is evident, by the above reasoning,

that whilst the earth by its gravity falls toward the moon, the water

directly below at B will swell and rise gradually toward her; also the

water at D will recede from the centre, (strictly speaking, the centre

recedes from D) and rise on the opposite side of the earth; whilst the

water at B and F is depressed, and falls below the former level. Hence as

the earth turns round its axis from the moon to the moon again in 24-3/4

hours, there will be two tides of flood and two of ebb in that time, as

we find by experience.

"That this doctrine may be still more clearly understood, let it be

considered that, although the earth's diameter bears a considerable

proportion to the distance of the earth from the moon, yet this diameter

is almost nothing when compared to the distance of the earth from the sun.

The difference of the sun's attraction, therefore, on the sides of the

earth under and opposite to him, will be much less than the difference

of the moon's attraction on the sides of the earth under and opposite to

her; and, for this reason, the moon must raise the tides much higher than

they can be raised by the sun. The effect of the sun's influence, in this

case, is nearly three times less than that of the moon. The action of the

sun alone would, therefore, be sufficient to produce a flow and ebb of

the sea; but the elevations and depressions caused by this means would be

about three times less than those produced by the moon.

"The tides, then, are not the sole production of the moon, but of the

joint forces of the sun and moon together. Or, properly speaking, there

are two tides, a solar one and a lunar one, which have a joint or opposite

effect, according to the situation of the bodies which produce them. When

the actions of the sun and moon conspire together, as at the time of new

and full moon, the flow and ebb become more considerable; and these are

then called the spring tides. But when one tends to elevate the waters

while the other depresses them, as at the moon's first and third quarters,

the effect will be exactly the contrary: the flow and ebb, instead of

being augmented, as before, will now be diminished; and these are called

the neap tides.

"To explain this more completely, let Fig. 69 represent the sun, Z, H,

R, the earth, and F and C the moon at her full and change. Then, because

the sun S, and the new moon C, are nearly in the same right line with the

centre of the earth O, their actions will conspire together, and raise

the water above the zenith Z, or the point immediately under them, to a

greater height than if only one of these forces acted alone. But it has

been shown that when the ocean is elevated to the zenith Z, it is also

elevated to the opposite point, or nadir, at the same time; and therefore

in this situation of the sun and moon, the tides will be augmented. And

again, whilst the full moon F raises the waters at N and Z, directly under

and opposite to her, the sun S, acting in the same right line, will also

raise the waters at the same point Z and N, directly under and opposite

to him. Therefore, in this situation also, the tides will be augmented;

their joint effect being nearly the same at the change as at the full;

and in both cases they occasion what are called the spring tides.

[Illustration: Fig. 69. Attractions of the moon]

"On this theory, the tides ought to be highest directly under and

opposite to the moon; that is, when the moon is due north and south;

but we find that in open seas, where the water flows freely, the moon

is generally past the north and south meridian of the place where it is

high water. The reason is obvious; for though the moon's attraction were

to cease altogether when she was past the meridian, the motion of ascent

communicated to the water before that time would make it continue to rise

for some time after; much more must it do so when the attraction is only

diminished. A little impulse given to a moving ball will cause it still to

move farther than otherwise it could have done; and experience shows that

the day is hotter about three in the afternoon than when the sun is on

the meridian, because of the increase made to the heat already imparted.

"Tides do not always answer to the same distance of the moon from the

meridian at the same place, but are variously affected by the action of

the sun, which brings them on sooner when the moon is in her first and

second quarters, and keeps them back later when she is in her third and

fourth; because, in the former case, the tide raised by the sun alone

would be earlier than the tides raised by the moon; and in the latter

case, later.

"The sea, being put in motion, would continue to ebb and flow for several

times, even though the sun and moon were annihilated, and their influences

at an end, on the same principle that if a basin of water is once

agitated, the water will continue to move for some time after the basin

is left to stand still. A pendulum, put in motion by the hand, continues

to make several vibrations without any new impulse. When the moon is at

the equator, the tides are equally high in both parts of the lunar day,

or time of the moon's revolving from the meridian to the meridian again,

which is 24 hours 50 minutes. But as the moon declines from the equator

toward either pole, the tides are alternately higher and lower at places

having north or south latitude. One of the highest elevations, which is

that under the moon, follows her toward the pole to which she is nearest,

and the other declines toward the opposite pole; each elevation describing

parallels as far distant from the equator, on opposite sides, as the

moon declines from it to either side; and consequently the parallels

described by those elevations of the water are twice as many degrees from

one another as the moon is from the equator; then increase their distance

as the moon increases her declination, till it is at the greatest, when

these parallels are, at a mean state, 47 degrees from one another; and on

that day the tides are most unequal in their heights. As the moon returns

toward the equator, the parallels described by the opposite elevations

approach toward each other, until the moon comes to the equator, and then

they coincide. As the moon declines toward the opposite pole, at equal

distances, each elevation describes the same parallel in the other part

of the lunar day which its opposite elevation described before. Whilst the

moon has north declination, the great tides in the northern hemisphere are

when she is above the horizon; and the reverse whilst her declination is

south.

"In open seas, the tides rise to very small heights in proportion to what

they do in wide-mouthed rivers, opening in the direction of the stream of

tide. In channels growing narrower gradually, the water is accumulated by

the opposition of the contracting bank--like a gentle wind, little felt

on an open plain, but stronger and brisk in a street; especially if the

wider end of the street is next the plain, and in the way of the wind.

"The tides are so retarded in their passage through different shoals and

channels, and otherwise so variously affected by striking against capes

and headlands, that in different places they happen at all distances of

the moon from the meridian, consequently at all hours of the lunar day.

"There are no tides in lakes because they are generally so small that

when the moon is vertical she attracts every part of them alike; and,

therefore, by rendering all the waters equally light, no part of them can

be raised higher than another. The Mediterranean and Baltic Seas suffer

very small elevations, because the inlets by which they communicate with

the ocean are so narrow that they cannot, in so short a time, receive or

discharge enough to raise or sink their surface sensibly.

"Air being lighter than water and the surface of the atmosphere being

nearer to the moon than the surface of the sea, it cannot be doubted that

the moon raises much higher tides in the air than in the sea. Therefore

many have wondered why the mercury does not sink in the barometer when

the moon's action on the particles of air makes them lighter as she

passes over the meridian. But we must consider, that as these particles

are rendered lighter, a greater number of them are accumulated, until

the deficiency of gravity is made up by the height of the column; and

then there is an equilibrium, consequently an equal pressure upon the

mercury as before; so that it cannot be affected by the aerial tides. It

is probable, however, that stars seen through an aerial tide of this kind

will have their light more refracted than those which are seen through

the common depth of the atmosphere; and this may account for the supposed

refractions of the lunar atmosphere that have been sometimes observed.

"You see now how the tides are caused; while there may be some influences

at work other than those exerted by the sun and moon, the latter are the

chief ones, so I will not attempt to explain any other.

"Here, on the Passaic River, we do not have excessive tides, as the

highest on the coast near us seldom rise over ten or twelve feet.

As a rule, tides rise highest and strongest in those places that are

narrowest. In the Black Sea and the Mediterranean, the tides are scarcely

perceptible, while at the mouth of the Indus, in the Bay of Fundy, and

other places, they rise thirty or more feet at times. The general rise,

however, in mid-ocean, is from eleven to twelve feet.

"The diameter of our moon is nearly 2,200 miles, and her distance from

the earth is about 240,000 miles; so you see it is not her size, but her

proximity to the earth that gives her so much influence over the tides;

for the sun, which is many times larger than the earth and moon combined,

because of its being some ninety-three millions of miles away, exerts only

one sixth of the attraction on the earth that the moon does.

"These facts, children, should be remembered, as you may often be called

upon to make use of them.

"Oh, papa!" said Jessie "how many wonderful things there are in this

world."

"But I have not told you all, my dear. There is much more to learn, but

I hope the knowledge you have now acquired will act as an incentive, and

cause you to pursue this study further."

Next morning Fred asked his father to enlighten himself and George

regarding the making of a few simple meters, such as barometer,

hygrometer, and a thermometer. He also wished to know if it would be

possible for him to make a boomerang. Mr. Gregg told him he would be

pleased to help him, and that there would be no difficulty in making a

boomerang if he went to work at it earnestly.

On the arrival of his father that evening, the subject was again

introduced, and Mr. Gregg using the blackboard, laid out the following

drawing and wrote the accompanying instructions.

"The best hygrometer of absorption is (according to Deschanel) that

of De Saussure, consisting of a hair deprived of grease, which by its

contractions moves a needle. When the hair relaxes, the needle is caused

to move in the opposite direction by a weight which serves to keep the

hair always tight as seen in the illustration, Fig. 70. The hair contracts

as the humidity increases. In the accompanying illustration A A and B B

represent the frame; e f, the scale; a, screw for tightening the hair; b,

the hair; O, weight; H, thermometer.

[Illustration: Fig. 70. Hygrometer]

[Illustration: Fig. 71. Index of Hygrometer]

"A neater hygrometer, and one on the same principle, may be made by taking

an old tooth powder box (as deep a one as possible, since the longer the

string, the more sensitive it is), and boring a hole through the centre of

the top and bottom. Paste a kind of dial in paper on the top of the box;

take a piece of catgut, or small fiddle string, and push it up through

the hole in the bottom and out at the one in the lid. Glue the bottom

end immovably, and let the top end move freely: make a small index of a

strip of whalebone (Fig. 71); bore a hole in the centre, and fix it on the

catgut with glue. Wet the catgut, see which way it turns, and mark 'wet'

and 'dry', accordingly on the dial.

"So much for the hygrometer. Now about that curious thing, the boomerang.

If the following directions are closely adhered to, and the proper shape

followed, a regular Australian boomerang will result. It is not difficult

to make. Take a piece of hard wood, the natural shape of one of the

segments of an ordinary wheel felloe, or bend in the wood; let it be 1/4

inch thick, shaped as at Fig. 72, to be held in the right hand at A, which

shows the way the edges of the side facing the left hand must be bevelled

off. It requires a slight curve on the flat side; so that, if on a table,

each end would turn about 1/8 inch. It is then a part of a very fine pitch

screw, in motion similar to a piece of slate jerked into the air, the sole

difference being due to the slight curve in the back, which gives the

screw motion, in conjunction with the forward and rotatory motion given

by the hand. Sheet-iron would not do, as there would not be thickness to

show the bevelled edge. The boomerang was made in the form of a cross,

with four legs of equal length, bevelled, but it does not work as well as

the regular form. You must be careful in throwing it as it may strike you

on return."

[Illustration: Fig. 72. Boomerang]

George asked his father to describe one and to explain its uses. Mr. Gregg

told the boys that a boomerang, as used by the aborigines of Australia

for a weapon or missile of war or in the chase, consisted of a flat piece

of hard wood bent or curved in its own plane, and from 16 inches to 2

feet long. Generally, but not always, it is flatter on one side than on

the other. In some cases the curve from end to end is nearly an arc of

a circle; in others it is rather an obtuse angle than a curve, and in a

few specimens there is a reverse curve toward each end. In the hand of

a skilful thrower, the boomerang can be projected to a great distance,

and made to ricochet almost at will. It can be thrown in a curved path,

somewhat as a ball can be "screwed" or "twisted," and it can be made to

return to the thrower, striking the ground behind him. It is capable of

inflicting serious wounds.

"It is very good of you, father," said Fred, "to tell and show us all

these things; I'd like very much to have a very common, every-day matter

explained: the theory of the pump." The following questions also were

asked by one or another on the same line: What is the greatest distance

or height a pump of any type can be placed away from the water? Is there

any limit to the length of the delivery pipe to the tank? What is the

difference between a lift and a plunger or force pump? Is it the sucker of

the pump that draws the water up, or does it flow because the air being

drawn out of the pump barrel and forced on the water outside, causes it

to flow into the pump?

Mr. Gregg started in at once to give them the facts desired:

"Theoretically, the greatest height a pump can be fixed above the water

level depends on certain conditions: the atmospheric temperature, and the

altitude the pump is to be fixed above the sea-water level. The higher

the temperature, and the greater the altitude, the less distance the

height of the pump can be above the water. The height to which water can

be drawn from the source to the top of the bucket, or under side of a

piston or plunger, when at the top of the stroke, or what is termed the

'height of suction,' cannot reach more than about 33 feet when the pump

is at the sea level. If a tube about 34 feet long is immersed in a well,

and the air is extracted by means of an air pump at the upper so that a

vacuum is formed, the water will not rise in the tube until the air is

expelled, when it will not rise more than 33 feet, even though there is a

complete vacuum formed in the upper end of the tube. The reason why the

water will not rise in the tube higher than this, is that the height of

the water counterbalances the pressure of the atmosphere. This height is

the theoretically greatest height that water will rise in a suction pipe.

For the pump to discharge water, it is necessary for the water to be in

motion, and to set and keep it in motion a portion of the water will rise,

due to the atmospheric pressure. The shorter the suction pipe, the more

certain the pump is of being completely filled at every stroke of the pump

handle.

"The action of the pump is as follows: The bucket on moving upward

attracts the air, so that the atmospheric pressure on the surface of the

water in the well causes the water to follow the bucket up the suction

pipe, through the suction valve, into the working barrel. On the return

stroke, the suction valve will close, the valve in the bucket will open,

and the water which before was under the bucket will pass through it to

the top side. When the bucket is again raised, the water will be lifted

through the delivery valve into the delivery pipe. There is practically

no limit to the height of lift, which may be any height consistent with

the strength of the pump and the available power. The ordinary pump used

for raising water to the level of the top of the bucket, is termed a lift

pump; for raising water above this, a force pump or a plunger pump must

be used, when the water is displaced by a solid plunger on its downward

stroke, when the quantity of water raised will be equal to the volume of

the plunger. This system may be repeated when water is to be lifted more

than ordinary heights."

X

WALL MAKING AND PLUMBING

A few evenings later, Mr. Gregg and his little family were gathered

together on the river's bank, watching the movements of a number of

pleasure boats and launches, when a good-sized tugboat came along and made

quite a "wash" as she steamed past the Gregg domain. Mr. Gregg noticed

that this had actually carried down a portion of the bank near the new

pier, and he called Fred's attention to it. The two, followed by George,

walked to the pier, and, to their alarm, found that quite a piece of the

bank had been carried away by the current, the tides, and the frequent

wash of passing steamers.

"This will never do," said Mr. Gregg. "We must protect the bank at this

point, or the water will soon undermine and demolish our pier, for you see

it is only near the landing where the bank shows signs of injury, and it

is as badly damaged on one side as the other. This is caused by projection

of the pier into the river, which prevents the water from flowing in

its regular course, and causes it to rush into the angle formed by the

junction of the pier with the bank, thus cutting away the latter."

"Perhaps it will be best to build a sort of retaining wall against the

bank for ten or twelve feet each side of the pier to prevent this rush

of water from cutting away the earth. If we had field stones enough on

the ground, it would be cheaper to use them, though they would not make

as good a 'job' as either cut stones or concrete; since we haven't the

stones, we'll build it of concrete, as you have some knowledge of that

material, and I will engage Nick to help you."

[Illustration: Fig. 72_a_. Retaining wall]

The next day Mr. Gregg ordered Portland cement and all the other materials

required to build the wall, and engaged Nick, who promised to come the

following morning. In the evening, Mr. Gregg had the boys in his den, and

explained to them how to go about constructing the wall. He decided to

have it built of concrete blocks about 12 × 24 × 12 inches, to be faced

with good, strong, cement mortar on the face and ends, which would give

the exposed wall a nice, smooth appearance. Mr. Gregg explained that there

must be a foundation of stone under the concrete, formed by large bowlders

or "fielders," laid as closely together as possible, the joints filled in

with smaller stones and, when possible, cement mortar, to bind the whole

into a solid mass--as shown by dotted lines in the illustration which he

made on the blackboard. The blocks for the work were to be cast in wooden

moulds or forms, which Fred and George could easily make out of boards

taken from the dismantled barn. At the points where the wall was wanted,

the bank was about 8 feet high from the bottom of the river, and it was

determined to make the wall 8 feet high, 2 feet wide at the top and 3 feet

at the bottom, with the batter on the water side, the weight of the wall

being 140 pounds per cubic foot. It is always best to have the inclined

surface on the side of the wall where the water will be. The water at high

tide rises to a level of 6 feet above the base C D.

"In designing such a retaining wall," said the father, "for water one

side, and earth the other, or determining its stability, the principles

generally followed may easily be worked out by Fred, or even by George.

"Taking the earth side first, as shown in diagram Fig. 72_a_, W C X, angle

of repose of earth to be retained--30 degrees; G C, the line of rupture;

G C A, the wedge of earth at 112 pounds per cubic foot to be accounted

for, the weight of which equals--

(GA × AC)/2 × 112 lb. = (4' 7" × 8')/2 × 112 lb. = 2,053 lb.

"This will act at a point one-third the height of the wall H. From H erect

a perpendicular H I equal to 2,053 lb. Set out the angle H I J equal to

angle of repose, 30 degrees. From H erect a perpendicular to A C, cutting

I J in J. Then J H equals the direction and magnitude of the weight of

the earth acting on the wall.

"Produce J H through the wall toward the water side. Find centre

of gravity of wall in K and the weight of the wall, which in this

illustration equals--

(AB + CD)/2 × AC × 140 lb. = (2 + 3)/2 × 8/1 × 140 lb. = 2,800 lb.

"From where J H produced meets a vertical line drawn through the centre

of gravity, K, in L set of L N equal to 2,800 lb.; make L M equal to J

H; complete parallelogram L M O N, when L O equals resultant of earth and

wall.

"The magnitude and direction of P R can be found as in the first part

of this article. Produce R P through the wall, and from where it cuts

the resultant L O in S make S T equal R P. Let the diagonal L O now be

produced so as to make S V equal to L O. Complete the parallelogram S T U

V, when the resultant S U equals the combined resultant of earth, water,

and wall, and as it passes within the middle third it can be considered

safe.

"Now, boys," said Mr. Gregg, "I have not only told you how to build

a retaining wall, I have also told you how to make all the necessary

calculations for designing it, as the same figuring and diagraming, on

this principle, will answer for any sea wall requiring like conditions.

"I know you both understand figures and geometry enough to make such

calculations, if you are ever called upon to do so."

The next morning, before the boys had finished their breakfast, Nick was

on hand ready to go to work, equipped with a pair of hip rubber boots

which would enable him to wade in water two feet deep and remain dry.

Fred and George were soon ready and Mr. Gregg went out to tell them the

proper way to commence. The foundation was the first consideration, so

an examination of the site and was made, the length of the proposed walls

measured off. While waiting for the tide to ebb to its lowest point, Nick

and the boys busied themselves gathering up stones for the foundation and

wheeling them to the point nearest where they were to be used.

After gathering all the stones thought necessary, the question of making

the moulds for the concrete blocks was considered, and, as the greatest

bulk of the blocks would be simply blocks with square ends and square

faces, the moulds for these would be a box having inside dimensions of 12

inches deep, 12 inches wide, and 24 inches long. These dimensions would

then allow of blocks being made in the moulds that will contain exactly 2

cubic feet. The mixed concrete was dropped gently in the mould and lightly

tamped so as to make it solid. The mixture consisted of not less than 3

of cement, 5 of sand, and 7 of very fine gravel or broken stone, no piece

being larger than a white bean. It was mixed in the same manner and in

accordance with the rules given for making concrete for the sidewalk in