Chapter IV: Part I: I (2)

"When papa comes home," said Jessie, "I'm going to get him to tell me about the 'inclined plane' as well as the ropes and pulleys."

The two timbers were rolled into the river and floated to the boat house, where one end of each was raised to the floor level at the doorway and made fast; the other end sank to the bottom, where Nick dug down and made a bed for it to rest in. These beds were made deep enough to bury the ends, and large stones were then thrown in to keep them from moving, but these were not allowed to reach within 18 inches of the surface of the water, which was then at its lowest mark. The timbers were kept about three feet apart, ample space to admit of any ordinary launch or row boat being taken into the boat house.

"Oh, Fred," said Jessie, "do you think those two sticks will be strong enough to hold the boat while you are pulling it up?" "Why, yes; strong enough to hold a dozen boats no larger than the one we intend having made. I don't know how much weight these timbers will support, nor how heavy our boat will be with the engine in it, but I'm sure the timbers are strong enough."

Jessie's question, however, caused Fred to think over the matter, and he set to work to find out how to tell the strength of timber beams. He discovered that to be able to determine the strength of beams and wooden pillars under all sorts of conditions required considerable training in mechanics and mathematics, but that the case before him was comparatively easy. A general rule for finding the safe carrying capacity of wooden beams of any dimensions, for uniformly distributed loads, is to multiply the area of section in square inches, by the depth in inches, and divide their product by the length of the beam in feet. If the beam is of hemlock, this result is to be multiplied by seventy, ninety for spruce and white pine, one hundred and twenty for oak, and one hundred and forty for yellow pine. The product will be the number of pounds each beam will support. For short-span beams, the load may be increased considerably. Fred, who had some knowledge on the subject, acquired at the training school, determined to pursue his studies in this direction.

In talking over the matter of nails with his father, their holding power was mentioned, and Mr. Gregg told Fred of a test that had been made some time ago by the U. S. Ordnance Department, where cut and wire nails had been tested respectively, showing a decided superiority for the former, both in spruce, pine, and hemlock. Thus in spruce stock nine series of tests were made, comprising nine sizes of common nails, longest 6 inches, shortest 1-3/8 inches; the cut nails showed an average superiority of 47.51 per cent.; in the same wood six series of tests, comprising six sizes of light common nails, the longest 6 inches and the shortest 1-1/8 inches, showed an average superiority for cut nails of 47.40 per cent.; in 15 series of tests, comprising 15 sizes of finishing nails, longest 4 inches and shortest 1-1/8 inches, a superiority of 72.22 per cent. average was exhibited by the cut nails; in another six series of tests, comprising six sizes of box nails, longest 4 inches and shortest 1-1/4 inches, the cut nails showed an average superiority of 50.88 per cent.; in four series of tests, comprising four sizes of floor nails, longest 4 inches and shortest 2, an average superiority of 80.03 per cent. was shown by the cut nails. In the 40 series of tests, comprising 40 sizes of nails, longest 6 inches and shortest 1-1/8 inches the cut nails showed an average superiority of 60.50.

Speaking of the ropes used in blocks, while taking down the old barn timbers, Mr. Gregg suggested that it would not be a bad idea if the boys were taught a few general items concerning hempen ropes; so he asked them to memorize the following: A rope 1/4 inch in diameter will carry 450 pounds, and 50 feet of it will weigh one pound. If 5/8 inch in diameter, it will carry 3,000 pounds and 7 feet will weigh one pound. When a rope is 3/4 inch in diameter, it will carry 3,900 pounds, and 6 feet will weigh 1 pound. A rope one inch in diameter, the same as we have in our blocks, will carry 7,000 pounds, and 3 feet 6 inches will weigh one pound. "It is not likely that sizes greater than these will ever be used by you. If they are, you can obtain a fair knowledge of their strength by finding their areas, and comparing them with the areas of the ropes given, taking the rope having one inch in diameter, as a constant example."

Wire ropes are much stronger than hempen ones, whether made of steel, brass, or bronze. The care and preservation of ropes is deserving of consideration, particularly in localities where the atmosphere is destructive to hemp fibre. Such ropes should be dipped when dry into a bath containing 20 grains of sulphate of copper per gallon of water, and kept soaking in this solution some four days, before they are dried. The ropes will thus have absorbed a certain quantity of sulphate of copper, which will preserve them for some time, both from the attacks of animal parasites and from rot. The copper salt may be fixed in the fibres by a coating of tar or by soapy water. In order to do this the rope is passed through a hot bath of boiled tar, drawn through a ring to press back the excess of tar, and suspended afterwards on a staging to dry and harden.

The figures given are intended for new manila ropes, and do not hold good for ropes made of inferior hemp. It is always safer never to load a rope to more than 60 per cent. of its capacity, and not even this much when it is old and weathered.

Jessie reminded her father of his promise to give them some information regarding the power of blocks and tackle and the qualities of the inclined plane. Accordingly, Fred, George, and Jessie joined their father in his den after supper, and George placed his blackboard in a convenient place with chalk, rule, and other requisites.

When all were seated, the father said: "Some time ago I tried to explain to you the uses of the lever in quite a number of different situations; to-night I'm going to show you how the various ropes and pulley blocks are made to do service for mankind. These devices are used very generally, especially in building operations, where heavy beams, girders, or blocks of stone have to be raised. On board ship, it is the favourite mechanical power by which rigging is raised, cords and ropes tightened, and goods lifted from or lowered into the hold.

"The pulley, the main feature of the third mechanical power, may be explained almost on the same principle as the lever, as you will see upon examining the sketch (Fig. 11) I now make on the blackboard.

"The pulleys seen in the blocks around which the rope runs may be considered so many levers whose arms are equal, and whose centres are fulcrums.

"In describing this power, it will perhaps be better to begin with the first and simplest form of the combination. The pulley, weight, and rope I show now (Fig. 12) is the simplest form of making use of this power. It is called a snatch-block and often employed for drawing water from wells, or for hoisting light weights. It is very handy, but we do not get any additional power from it, though we get a change of direction and quick movement. From its portable form, its low cost, and the handiness with which it can be applied, this arrangement is one of the most useful of our mechanical contrivances.

"When pulleys are adjusted, as I show you in this sketch (Fig. 13), the block which carries the weight is called a movable pulley, and the whole, as shown, a system of pulleys.

"In this illustration, suppose the weight is 20 pounds. It is supported by two cords, A and B; that is, the two sections of the cord support 10 pounds each. Now, the cord being continuous, the power must be 10 pounds.

"We leave out of consideration the weight of pulley and the friction of the various parts.

"We have seen that the weight is sustained by two cords; if, therefore, it has been raised two feet, each cord must be shortened two feet. To do this, the power P must run down four feet. To get the full value of this machine the cords must be parallel.

"If we increase the number of movable pulleys, as sketched at Fig. 14, to three, the relation of P to W will be as 1 to 8 and the distance through which P will travel will be eight times that through which W is raised.

"If we apply this principle to the sketch (Fig. 11), which illustrates the blocks you used to-day in lifting the large timbers, and which is the usual form of pulley employed to lift heavy weights, you will notice that there is a four-sheave block at the top, and a three-sheave block at the bottom, with the end of the rope fixed from the top block. The three-sheave block is movable. A power of 10 pounds will, with this form of pulley, balance a weight of 60 pounds.

"Suppose a block of stone weighing 8,000 lbs. is to be raised to the top of a wall and we use a system of pulleys where each of the two blocks has four pulleys; we shall find that it will require a power of 1,000 pounds to raise it.

"Now, as to the inclined plane: this is called the fourth mechanical power, and it is not in any way related to the lever, but is a distinct principle. Some writers on the subject reduce the number of mechanical powers to two, namely, the lever and the inclined plane. The advantages gained by this are many for just so much as the length of the plane exceeds its perpendicular height is an advantage gained. Suppose A B C (Fig. 15), I make in the sketch, is a plane standing on the table. If length A B is three times greater than the perpendicular height C B then a cylinder at R P may be supported upon the plane A B by a power equal to a third of its own weight. That is, a block of that weight would prevent the roller or cylinder from going farther. From this we gather that one third of the force required to lift any given weight in a perpendicular direction will be quite sufficient to raise it the same height on the plane; allowance, of course, must be made for overcoming the friction, but then, you see, you will have three times the space to pass over, so that what you gain in power, you will lose in time. We see the use of the inclined plane every day we pass a building under construction, where the workmen wheel bricks, mortar, and other materials from the street to the floors above, using long planks for the plane or tramway. Merchants, too, often make use of an inclined plane when rolling heavy boxes and packages from the street to the floors of their warehouses.

"An excellent, practical illustration was given you to-day when Nick and Fred built the ways on which the proposed boat is to be slid into the new house. It would require five or six strong persons to lift the boat bodily into the new house; but I expect two or three will easily slide it up into the building on the ways; and by arranging a winch--another mechanical contrivance--at one end of the boat house, Fred, or George, for that matter, will be able to haul the boat up. The winch for this purpose will be a very simple affair, merely a ready adaptation of the wheel and axle, as I will show you later. Now, however, we are talking about inclined planes, and to illustrate its early application to the building arts, it is only necessary to tell a few things we know regarding the moving and raising of the great stones used in building the Pyramids. For centuries it was a mystery how the heavy stones in these structures had been placed in their present positions. Recent investigations have led many scientific men to believe the stones were taken up inclined planes, on rollers, and then put in place by the workmen, who moved them to the different sides of the building on strong timber platforms, where rollers, or rolling trucks, carried the load. According to one authority, there are the remains of the approach to an inclined plane near the Great Pyramid, which, if continued at the angle, as now seen, would rise to the apex. According to this writer, the foot of the plane was more than a mile from the building, fifty or sixty feet wide, and had been one huge embankment, formed of earth, sand, and the clippings and waste of stone made by the workmen. This, of course, would be an expensive and a tedious method, but in those days time and labour went for little. Every time a course of stones was laid and completed, the plane was raised another step, to the height of the next tier of stones. The same angle of incline was probably maintained during the whole period of erection, and this angle, you may rest assured, was made as low and easy as possible; for the Egyptian engineers were not slow in adapting the easiest and quickest methods available.

"This method of conveying the heavy stones to their places in the Pyramids was simple and effective, with no engineering difficulties that could not be readily overcome. Moreover, it was really the very best method considering the narrow limits of their appliances.

"You may ask, 'How were these big stones carried to the foot of the inclined plane?' The quarries, in some cases, were five hundred miles distant, and most of the stones had to be brought across the Nile to the works. We know from the monuments, and from the papyrii that have come down to us from remote periods, that many of the stones were brought down the river on large rafts or floats, and on barge-like vessels; and we also know that many of the larger ones were hauled or dragged down from the quarries at Assowan to Memphis, alongside the river, a distance of 580 miles. This is particularly true of the obelisks, for all along an old travelled road evidences have lately been found that these stones had been taken that way, and that resting places for the labourers had been provided at stations about twelve miles apart, along the whole distance. It has been estimated that a gang of men--say forty--well provided with rollers, timbers, ropes, and necessary tools, could easily roll an obelisk like that in Central Park, New York, twelve miles in twelve hours; and doubtless this was the system employed in conveying those immense stones that great distance.

"A large number of obelisks were erected near Memphis, though there are none there now, for the Greek and Roman engineers, at the command of the rulers, took a number down and carried them to the city of Alexandria; but we have less knowledge of how these later engineers transferred the stones to the newer city, than we have of the methods of the older. The beautiful column known as Pompey's Pillar was once an obelisk, and was transformed into a pillar, by either Greek or Roman artisans, it is not clear which. The work of putting those huge stones in place was not easy, as Commander Gorringe discovered when he stood the New York obelisk in the place it now occupies.

"But let us get back to our inclined plane.

"I have shown you how a weight or roller acts on the incline, but I did not explain it clearly, nor in a scientific way, as I do not want to puzzle or confuse you with terms and problems you cannot understand. I will, however, give you another illustration or two on the subject, in which another factor plays a part, namely--gravitation. Let us suppose you have two golf balls laid on a table that is perfectly horizontal or level in every direction; they will remain at rest wherever placed, but if we elevate the table so that the raised end is half the length of the top higher than the lower end, the balls will require a force half their weight to sustain them in any position on the table. But suppose they are on a plane perpendicular to the table top, the balls would descend with their whole weight, for the plane would not contribute in any respect to support them; consequently they would require a power equal to their whole weight to hold them back. It is by the velocity with which a body falls that we can estimate the force acted upon it, for the effect is estimated by the cause. Suppose an inclined plane is thirty-two feet long, and its perpendicular height sixteen feet, what time should a ball take to roll down the plane, and also to fall from the top to the ground by the force of gravity alone? We know that by the force of attraction or gravitation, a body will be one second in falling sixteen feet perpendicularly, and as our plane in length is double its height at the upper end, it will require two seconds for the ball to roll down from top to bottom. Suppose a plane sixty-four feet in perpendicular height, and three times sixty-four feet, or one hundred and ninety-two feet long; the time it will require a ball to fall to the earth by the attraction of gravitation will be two seconds. The first it falls sixteen feet, and the next forty-eight feet will be travelled in the same time, for the velocity of falling bodies increases as they descend. It has been found by accurate experiments that a body descending from a considerable height by the force of gravitation, falls sixteen feet in the first second, three times sixteen feet in the next; five times sixteen feet in the third; seven times sixteen feet in the fourth second of time; and so on, continually increasing according to the odd numbers, 1, 3, 5, 7, 9, 11, etc. Usually, the increase of velocity is somewhat greater than this, as it varies a trifle in different latitudes. In the example before us we find that the plane is three times as long as it is high on a perpendicular line; so that it will take the ball to roll down that distance (192 ft.) three times as many seconds as it took to descend freely by the force of gravity, that is to say, six seconds.

"The principle of the inclined plane is made use of in the manufacture of tools of many kinds, as in the bevelled sides of hatchets, axes, chisels and other similar tools, the examples of which are in a great measure related to this power, though many of them partake largely of the wedge, of which we shall now have something to say.

"The wedge may be a block of wood, iron, or other material, tapered to a thin edge, forming a sort of double inclined plane, =A P B=, (Fig. 16) where their bases are joined, making =A B= the whole thickness of the wedge at the top. In splitting wood as is shown in the illustration, =R R= being the wood, the wedge must be driven in with a large hammer or heavy mallet which impels it down and forces the fibres of the wood to separate and open up. The wedge is of great importance in a vast variety of cases where the other mechanical powers are of no avail, and this arises from the momentum of the blow given it; which is greater beyond comparison than the application of any dead weight or pressure employed by the other mechanical powers. Hence, it is used in splitting wood, rocks, and many other things. Even the largest ships may be raised somewhat by driving wedges below them. Often, in launching a vessel, wedges are used to start it on its way. And they are also used for raising beams or floors of houses where they have given way by reason of having too much weight laid upon them. In quarrying large stones, it is customary to wedge or break off the rock by first drilling a number of holes on the line of cleavage. Wooden wedges are then driven tightly into these and left there until they get wet, when they expand and split off the rock as required. This method of quarrying large stones was well known to the old Egyptians, and employed by them in quarrying their famous obelisks.

"Owing to the fact that the power applied to force a wedge is not continuous, but a series of impulses, the theory of the wedge is less exact than that of the other mechanical powers. Considering the power and the resistance on each side, however, as three forces in equilibrium, it may be demonstrated that the

Resistance (R) equals P × Length of equal side/Back of wedge

Then the mechanical advantage will be--

R/P equals Length of equal side/Back of wedge

So that by diminishing the size of the back and increasing the length of the side--that is, diminishing the angle of penetration--the mechanical power of the wedge is increased. While I did not intend to inflict you with arithmetical or algebraical formulæ, I have been compelled to give you that simple example which I know you can all work out, as it is concise, and the same would be long and tedious if rendered in text."

Next morning, as Fred and his father were out on the new place early, looking over the boat house, the slide for the boat, and some other matters, Mr. Gregg suggested that a winch be placed at the upper end of the house, to haul the boat out of the water. He also suggested that Fred prepare for work on the boat at once, and provide himself with all the tools and materials necessary. He promised to call on a friend of his in the city, who is a noted boat builder, and ask him the best method to adopt in building the craft.

"Perhaps," said the father, "it might be a good plan to buy a full set of shapes or patterns from some one of the professional boat builders who advertise such. They are sold at a very low rate--being made of paper--and many firms sell all the material that is required to build a boat complete; with the sweeps, ribs, and curved stuff cut out to the required shape and numbered all ready to set up.

"What we want, Fred," continued the father, "is a boat sixteen or eighteen feet long, just the size of the one belonging to your friend, Walter Scott; that is plenty large enough for all our purposes. His boat can stand as a kind of a model for you to work after in case you do not thoroughly understand the patterns you are to get, or the manner of arrangement. The gasolene motor we'll order from some manufacturer, with whom we'll arrange to install it, with a suitable propeller and necessary attachments."

Fred was quite satisfied with all his father had said and started to get ready. Jessie began to question him about several things she did not fully understand in her father's talk the night previous. Fred explained matters, made them quite clear to her, and then asked her to get her memorandum book and write down the following, which he said, she would often find useful: "There are six mechanical powers, two of which father has not told us about, but will no doubt do so, before long. These are called, the Lever, Pulley, Wheel and Axle, Inclined Plane, Wedge, and Screw. The Screw and the Wheel and Axle, you have yet to hear about. Now, study carefully the following rules:

"_The Lever._--Rule: The power required is to the weight as the distance of the weight from the fulcrum is to the distance of the power from the fulcrum.

"_The Pulley._--A fixed pulley gives no increase of power. With a single movable pulley the power required will equal half the weight, and will move through twice the distance. Increasing the number of pulleys, diminishes the power required. Rule: The power is equal to the weight, divided by the number of folds of rope passing between the pulleys.

"_The Wheel and Axle._--Rule: The power is to the weight as the radius of the axle is to the length of the crank or radius of the wheel.

"_The Inclined Plane._--Rule: The power is to the weight as the height of the plane is to the length.

"_Wedge._--Rule: Half the thickness of the head of the wedge is to the length of one of its sides as the power which acts against its head is to the effect produced on its side.

"_The Screw._--Rule: As the distance between the threads is to the circumference of the circle described by the power, so is the power required to the weight."

Fred told George also to copy the foregoing in his memorandum book, so that he would be able to work out any problems for himself.

III

BRIDGE AND BOAT WORK

The next day Fred and his father talked over the proposed boat, the result being that Walter Scott was asked over the telephone if he would come down in his launch to the Gregg property in the evening, as Mr. Gregg and Fred would like to see the craft, hear all about it, and find out if it had any defects that might be avoided in the building of another one. Walter said he'd be glad to sail down, and would take his sister to see Jessie. In the meantime some addresses of boat builders were handed to Fred, with instructions to write and ask for catalogues, prices of materials, and the other information usually sent out to prospective customers. Fred immediately wrote to a number of firms, including several who manufactured motors and other requisites for small launches.

A little after the city clock struck four, Jessie, who was home from school, saw _The Mocking-Bird_ sailing down the river at good speed, with Walter, his sister Grace, and their mother on board. Fred went down to the water's edge, and helped Walter haul the boat to the unfinished landing place, where Mrs. Scott and Grace were safely landed.

Fred and Walter soon became deep in "boat talk," and kept it up until the arrival of Mr. Gregg, who began to make inquiries regarding the speed, capacity, and safety of _The Mocking-Bird_. All his questions were intelligently and favourably answered by Walter, a bright and earnest little fellow. He was some months the senior of Fred, but was not so strong or robust looking.

"She's just 18 feet long over all," said he, "with a 5-foot beam, a draft aft of about 18 inches, and a forward draft of 1 foot. She is fitted with a 6-horse-power gasolene engine, and her speed is from 8 to 9 miles an hour."

An illustration of her, as she appeared when partly built, is shown in Fig. 17, where a plan and a section of her length may be seen. The manner of her construction is also shown, also the lines of ribs, portion of inside lining, position of motor, rudder, and propeller.

Mr. Gregg also ascertained from Walter that his father had sent to a firm who made a business of preparing the complete wood-work for many kinds of boats on the "knockdown" system, selling the whole material ready to set up without the aid of an expert. Printed instructions came along with each boat, so that the buyer would have but little difficulty in setting up the wood-work and making it ready for use. An expert workman had been engaged by Walter's father to install the engine, line up the propeller shaft, and connect the wheel and shaft to the engine. On the arrival of the materials--within a week after the order was sent--Walter had gone to work; and inside of fourteen days, _The Mocking-Bird_ took to the water.

So fully and so satisfactorily did Walter explain to Mr. Gregg all that he asked about, that Fred was able at once to order the material for a similar launch, to be sent on immediately. In order to hurry matters, a cheque was inclosed with the order, and Fred, Walter, and George walked over to the postoffice with the letter, so that it went by the night mail.

On returning, it was suggested that the boys, Grace, and Jessie go for a sail on the river, and all were soon at the landing. Walter adjusted his engine and made all ready as George and the girls got on board, while Fred cast off the rope which held the boat to the dock, then stepped after them. The engine was started, Fred took the tiller, and they were soon afloat, sailing with the tide in their favour at a rapid speed, and returning to the landing place inside of an hour, well pleased with their little outing. Fred showed Walter his new boat-house and workshop, explained to him how Nick and he, with the help of George and the advice of his father, had completed the work and the building. He also pointed out other work he was going to do as soon as his boat was finished.

Though not yet dark, it was getting rather late, and Walter's mother advised that they start for home as soon as he was ready. So wishing Fred every success in the building of his boat, Mrs. Scott, her daughter, and Walter left for home.

"Well, Fred," said Mr. Gregg, when his family were all seated in the living room, "you are now in for quite a job, one that will test your working qualities; but I am sure you will come out with flying colours. You will meet difficulties, but you must overcome them, and when the boat is finished, painted, and ready to name, you can have some of your friends up for the launching. Mother will have a special tea for you all, and we'll christen the new craft. Meantime we must think over the matter of a name, and decide upon one we shall all like."

Next morning, Fred and his father went down to the river's edge to examine the little ravine that had been cut out by the spring and fall freshets. It was a small affair, only about six feet deep and ten or twelve feet wide. At present, the opposite side was reached by crossing a couple of planks, safe enough while the land had been in a measure unoccupied. To leave it so now would be a different matter, as Jessie or her mother, attempting to cross, might easily fall over; so it was decided to have a foot-bridge built over the creek, which was nearly dry the greater part of the year. There was plenty of material on the ground for the purpose, and Fred was asked by his father to get Nick to help, so that the bridge might be ready as soon as possible.

Fred felt he was getting to be quite an important person when his father trusted him with work which must necessarily entail considerable expense, but he accepted the responsibility with pleasure, and promised to commence at once, so as to have it finished by the time the material for the boat arrived. So, when Nick arrived, operations began immediately.

Taking a tape line, Fred sent the Italian to the other end of it, and they picked out a favourable location to measure across, making it over 11 feet at the narrowest spot from one edge to the other. Allowance was then made for bearings five feet on either side of the span, so that timbers 21 feet long would be required to cross the chasm. This width would require three string-pieces, or chords, to run across, one on each side, and one in the centre. These, covered with three-inch plank from end to end, would make a good, solid deck sufficient for all purposes. The planks were cut off seven feet long, to have the deck of the bridge, over all, exactly seven feet wide.

Among the timbers taken from the old barn were nine pieces, measuring 22 feet in length, 8 × 10 inches in section, so Fred decided to make use of three of these just as they were, without cutting, and to place them on their edges to get the most strength out of them. He then had six posts cut off the old cedar fence posts, about two feet long, which were sunk into the ground their whole length, as shown in Fig. 18, three on each side of the creek, and the tops made level, so that a flat timber or plank would rest on them, touching each one. This plank was made nine feet long, so as to project over the posts about a foot at each end. This was, of course, the same at each end of the bridge. After the flat timbers had been laid on the ends of the posts and fastened with spikes, there were laid the three long timbers spanning the gully. The spaces between were equally divided, and then covered with three-inch planks taken from the floor of the old barn. The boards were cut off to the proper length and fastened down on the three timbers with spikes five inches long, the planks not laid close together, but kept about three-eighths of an inch apart, in order to let the water run off after a rain, as well as to allow air to circulate underneath and between the joints to prevent the planks from decay.

In order to make the bridge safe, it was necessary to build a rail on each side. Two pieces of timber about 20 feet long and 6 × 6 inches square were used for the rails, while posts and braces were made of timber of about the same dimensions. The bottoms of the posts were halved, so that they could be spiked or nailed to the long outside string-pieces, as shown in the illustration. Tenons were made on the top of these posts, and these fitted into mortises made in the top rails, and all were then put together and fastened with wooden pins.

Nick dug away the surplus earth from the approaches to the bridge, and made an easy grade to its deck. This completed the work all but the painting, which was left to be done some other day.

Mr. Gregg inspected the bridge, pronounced it all right, and congratulated Fred on his workmanship, at the same time saying a good word to Nick and George, both of whom had helped very much to make the effort a success.

In the evening Mr. Gregg told Fred and George that a friend of his had given him a copy of the rules to be observed when running a launch, so he asked the boys to get their note-books, and take these down as he read them out. Even Jessie, too, he thought, ought to be acquainted with the rules, as she might be called upon some time to make use of them, so three pencils were soon at work, as the father read out the following:

"1. When at the wheel, remember as a first consideration, that you
cannot entertain the boat's occupants as well as steer.

"2. Keep your course, and know what that course is.

"3. Regulate your speed to the company you are in. Marine motors
are, as a rule, very flexible.

"4. Do not cut corners.

"5. When approaching a landing, learn to judge exactly the distance
your boat will travel after your propeller has stopped, so as to
run alongside without using your reverse gear. This requires some
practice, but is amply rewarded by time saved, in the long run,
and decrease of wear and tear on engine, gear, and propeller. Any
one can get to a landing in time by alternately running full speed
ahead and then astern.

"6. When aboard your boat, and facing the bow your right hand is
starboard, your left, port. Keep to the right. Should you be
overtaking any one, it is your duty to pass clear on their left.
The above applies only to narrow waters.

"7. When going up or down stream, should you wish to cross over to
the other side and return, and another boat is overtaking you on
your left, don't attempt to cross its bow; slow down until it has
passed.

"8. Keep clear of non-engined crafts. You have greater freedom
of action than they; it costs you nothing, and their occupants
appreciate your courtesy.

"9. Do not tow canoes or skiffs alongside. If towed at all, they
should be right aft with as short a towline as possible.

"10. Finally; remember the rules of the road--

"'Green to green or red to red
Perfect safety--go ahead
If to starboard red appear
'Tis your duty to keep clear.
When upon your port is seen
A steamer's starboard light of green,
There's not so much for you to do
As green to port keeps clear of you.'"

The children all promised to memorize these rules.

As the stuff for the boat was not expected for some days, Fred and Nick kept at work about the new boat house, and building up the landing dock. The former fitted up a work bench, and put his little shop in readiness for actual use. Fred also hunted for a nice stick of timber among the old barn ruins, on which to set up the boat. A good piece found, he cut it to a length of 20 feet, and then he and Nick got it into the boat house, where Fred planed it off a little with a rough jack plane, keeping a sharp lookout for nails, sand, or gravel. Nothing destroys the cutting edges of tools more than nails, bits of iron, glass, sand, or small pebbles, which sometimes escape the vigilance of the workman. Especially is this true of saws, which Fred knew quite well since he had once run a good sharp saw against a nail, while cutting a piece of timber in two. This taught him a lesson he never forgot, and whenever he had to cut up old material, he was always careful to examine it all round, and to scrape or brush off all the dirt and sand from the parts through which the saw teeth had to travel. In planing, or "dressing" the stick of timber, the same precautions were taken, and the surface of the wood was made as clean and free from dirt and sand as it possibly could be. Notwithstanding all this, Fred found it almost impossible to keep the cutting iron of his jack plane sharp enough to take off shavings. He had to sharpen it every few minutes. This is nearly always the case when working up wood which has previously been used. However, he managed to "dress" his stick very nicely, and after finishing it, laid it down along the middle of the floor of the shop, putting blocks of wood under it here and there to raise it up from the floor five or six inches. It was then made level on top and fastened down so that it would not move or get out of line. This was about all they could do on the boat until the materials arrived. Nick had managed to fill in the space between the two walls of the little pier with heavy bowlders, and had strengthened the whole with coarse rubble-stone work in such a manner that there was little danger of injury from floating ice or flood tides; and he had covered the whole over with small stones, gravel, and a good thick layer of cement concrete, which made it correspond with the cement walk.

The question of a winch was then taken up with Mr. Gregg and it was decided to construct a simple affair at the end of the boat-house opposite the large doors, where the boat would have to enter.

Mr. Gregg suggested, in order to make the end of the building strong enough, that two upright posts be set up, well braced by being fastened to both floor and ceiling, and that the winch be attached to them in a way that would be easy to work, as shown in Fig. 19, room enough being left between the posts and the wall for the crank to turn without the hand of the operator striking the boards. The cylinder around which the rope should wind ought to be about six inches in diameter, and the crank or handle on the end, not less than fifteen or sixteen inches long. The longer the crank, the less force it would require to haul in the boat. If desired, a crank could be fitted to the other end of the cylinder so that two persons could work at one time, pulling in the weight.

In the evening Mr. Gregg asked the boys and Jessie to visit his room, and he would try to explain the principle and advantages of the wheel and axle, as the winch they were to make was in a measure related to that principle. Mr. Gregg began by saying: "The wheel and axle is merely a modification of the lever and consists of a couple of cylinders turning on a common axis, the larger cylinder is usually called the wheel, the lesser one the axle. This arrangement, which I draw on the blackboard herewith, forms a kind of lever of the first or second class. Considered as a lever, the fulcrum is at the common axis, while the arms of the lever are the radii of the wheel and of the axle.

"The fulcrum is at C, the centre. The arm of the weight is W W, and the arm of the power is A C. In Fig. 20 the arm of the power is the spoke of the wheel, while the arm of the weight is the radius of the axle. Fig. 19 shows the ordinary winch, often used in well-digging for hauling up dirt and rock, and also for raising planks, shingles, rafters, and other light stuff, to the roofs and upper floors of buildings. Often it is made more powerful by adding spur or geared wheels to the end of the shaft, consisting of a pinion and a larger spurred wheel. The crank or handle is attached to the pinion, and the power is increased according to the difference in diameters of the spur wheels. The machine is then called a 'crab' and it is often used for lifting safes and other heavy weights to elevated situations. In Fig. 20 the length of the crank (in a straight line) is the arm of the power.

"The mechanical advantage of the wheel and axle equals the ratio between the diameter of the wheel and of the axle.

"It is not necessary that an entire wheel be present. In the case of the windlass and the capstan (Fig. 21), the power may be applied to a single arm or to a number of arms placed in the holes shown. The cable or rope on the barrel of the capstan is hauled in by turning the capstan on its axis, with handspikes or bars. The capstan is prevented from turning back by a pawl attached to its lower part, working in a circular ratchet on the base.

"As an illustration of the lever action, and of work put into and got out of a machine, there is no better illustration than the ingenious contrivance termed the fusee (Fig. 22). In good watches and clocks, where the elastic force of a coiled spring is used to drive the works, the fusee compensates the gradually diminishing pull of the uncoiling spring. The driving of the works at a constant rate is the object for which a watch or clock is designed. This usually entails a constant resistance to be overcome, but since one of the most compact and convenient forms of mechanism into which mechanical force can be stored is that of the coiled spring, and since the very nature of the spring is such that its force decreases as it uncoils, we must employ some compensating device between this variable driving force and the constant resistance. The fusee does this in a most accurate and complete manner. As the fusee to the right is to compensate for the loss of force of the spring as it uncoils itself, the chain is on the small diameter of the fusee when the watch is wound up, as the spring has then the greatest force.

"In the differential, or Chinese windlass (Fig. 23), different parts of the cylinder have different diameters, the rope winding upon the larger and unwinding from the smaller. By one revolution the load is lifted a distance equal to the difference between the circumference of the two parts.

"There are many other contrivances and appliances of the wheel and axle for performing various services, but I think the examples I have shown you will be sufficient to enable you to make use of the device to perform any duty you may be called upon to attempt in ordinary life, but, should you enter professional life as civil, mechanical, naval, or mining engineer or architect, you will be obliged to pursue the study of these subjects further.

"Before closing I may add a few problems for you to solve at your leisure by the application of the rules I have given you when describing the other mechanical powers.

"The pilot wheel of a boat is 3 feet in diameter; the axle is 6 inches; the resistance of the rudder is 240 pounds. What power applied to the wheel will move the rudder? Here the difference between the axle and wheel is 18 inches.

"Four men are hoisting an anchor of 3,000 pounds' weight; the barrel of the capstan is 8 inches in diameter; the circle described by the handspikes is 7 feet 6 inches in diameter. How great a pressure must each of the men exert?

"With a capstan four men are raising a 1000-pound anchor; the barrel of the capstan is a foot in diameter; the handspikes used are 5 feet long; friction equals 10 per cent. of the weight. How much force must each man exert to raise the anchor?

"The circumference of a wheel is 8 feet; that of its axle is 16 inches; the weight, including friction, is 85 pounds. How great a power will be required to raise it?

"A power of 70 pounds on a wheel whose diameter is 10 feet balances 300 pounds on the axle. Give the diameter of the axle.

"An axle 10 inches in diameter fitted with a winch 18 inches long is used to draw water from a well. How great a power will it require to raise a cubic foot of water, which weighs 62-1/2 pounds?"

The first mail in the morning brought word that the whole of the partly prepared stuff for the boat had been shipped by "fast freight," and that it would reach its destination in the course of a few days. The paper patterns, directions, and all necessary instructions for building would be mailed at once.

IV

MAKING A GASOLENE LAUNCH

Two or three days after Mr. Gregg had talked over the principles of the wheel and axle, with the children, Fred received notice that a consignment of wood-work was at the station awaiting his orders. Mr. Gregg made immediate arrangements with the railway people, and by the time he got home from his office, the stuff was being unloaded by the boys, who carried it piece by piece into the workshop, each section being laid by itself in the order in which it was to be put in place in the boat. Printed instructions were in the equipment for laying the keel, setting up the frames, and even for taking the stuff out of the packages and putting it in heaps, so that it could be readily picked out when wanted for use.

Each rib was numbered, and marked or stamped "right" or "left," and all the pieces were cut off to the right length and to the right bevel or angle to suit the positions they were to occupy, as specified in the printed instructions. This made the setting up an easy matter, requiring only care, patience, and a fair knowledge of the use of wood-working tools. That Fred possessed these qualities, was partly due to the training he had received in the technical school, and partly to his natural aptitude for picking up methods, ideas, and new applications.

Fred, George, and Mr. Gregg himself, were much interested in the selection of the various materials, and when the plank that was to form the keel had been unpacked, George was anxious that it should be laid down on the bed that had been prepared for its reception. He was quite disappointed when he found it considerably shorter than he had expected the boat to be. It was explained to him, however, that the overhanging of the stern, and therefore shortening of the forefoot, or stem, necessitated the keel being shorter than the boat would be when measured over all on top. The keel was found to be a fine piece of tough oak, nicely dressed, made the proper shape at each end, bored and gained to receive the stern post, the stern ribs, and side stanchions. Everything was marked, and each timber was sized so that it would fit in place snugly without using a tool on it, except a hammer or mallet.

At tea time George felt it difficult to keep reasonably quiet, he was so enthusiastic about the boat--much to the amusement of his father, who knew exactly how the boy felt.

After tea, all walked to the boat house, and the father assisted Fred to set up the keel, which was in two pieces, halved together midway and well fastened with screws. The joint was painted with a heavy coat of white lead and linseed oil paint, before being put together and screwed up. The keel is the lowest timber in a boat or ship, and it runs nearly the length of the craft. Sometimes there is a keelson placed on the top of the keel, and the ribs of the boat, or stanchions, are made fast to that timber, as shown in the illustration, (Fig. 24,) in which the gains for the ribs or moulds are made. This portion of the boat was put together temporarily, so Fred had no difficulty in assembling the various pieces. The stem, keel, keelson, and deadwood were all made of oak, and looked strong. The keel and keelson were properly laid and adjusted, and after some explanations by Mr. Gregg the manner of setting up the ribs was thoroughly understood. Fred decided to telephone Walter Scott to come down next day, as it was Saturday, and help him to set up the skeleton.

As the weather was getting warm, the whole family spent the evening on the veranda and George introduced the question of naming the boat. He suggested _Red Bird_, but this did not seem to take well, and several others were proposed but none seemed to suit everybody. Jessie sat quietly on the steps till asked by Fred what her choice would be.

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

"That's a good idea, Jessie," said her father, "and if the boys or your mother don't object, I think we'll settle on _Caroline_."

Early next morning the boys were out watching for _The Mocking-Bird_, which very soon made its appearance. Fred and Walter tied the boat up to the new dock and went into the boat house, where the latter began to examine the boat stuff, and to explain the manner of setting it up and fastening it in place.

Nick, who was on hand to help, did the heavy work, and helped to put up the stanchions. Walter seemed quite familiar with the work, and he and Fred soon had the boat so well in hand that it seemed to grow under their fingers. The ribs were easily selected, as they were tied together in pairs and numbered. They were then set in their places according to their numbers and were fastened to the keelson with the strong copper nails. All the nails required for the boat were of copper, because that metal is less likely to corrode than iron or steel.