Chapter I.

The mould should rest on a smooth block of stone, wood, or other suitable material, while being filled and tamped, and when full the surplus should be levelled off, by a straight-edge--wood or iron--drawn over the top of the mould, until all the surplus is removed. The mould is then allowed to stand a little while until the concrete "sets" fairly hard, when the mould may be removed. To make it easy to take the block out of the mould, the inside should be well sprinkled with neat cement before the concrete is put in, and the box itself might be made slightly tapering to permit the block to move out easy. This method, however, is not to be recommended, as the blocks do not fit so well in a wall as when left perfectly square. There are a number of devices for making moulds so that delivery of blocks may be easy. One of the best is to hinge one corner of the mould with heavy hinges, while the opposite diagonal corner is left loose but held in place by a strong hasp and staple. When the box or mould is full and the block ready to remove, the hasp is loosened, the mould opens across at the two corners and frees the block. Should there be any holes or defects on the face of the blocks, they can be filled with cement mortar made with 2 of cement and 3 of clean sand. Blocks of this size should season not less than 4 or 5 days, to set hard before being used.

A portion of these blocks must have a bevel face on them to form the batter on the front of the wall. There must also be a proper proportion of them having their ends bevelled to the batter of the wall, to use as "headers." A header in brick, stone, or concrete, is a unit, or piece, that is laid in the wall with its ends showing through on the face, while a "stretcher" shows its whole length on the face of the wall. Other portions of brick or stone, when built in a wall, are called "closers."

The batter on the blocks is formed by making one side of the mould lower than the other. In this case, the difference in the width of the sides of the mould would be 1-1/2 inches; because the height of the wall being 8 feet, the blocks 1 foot thick, and the batter 1 foot, there would be a falling off on each block of 1-1/2 inches in order to have the top front of the wall 12 inches back from the bottom front. The ends of the header blocks may be battered by placing in the ends of the mould a piece of wood 12 inches wide, and the lower edge 1-1/2 inches thick, and the top edge planed to a thin wire edge. The end or section of the plank will then have the appearance of a wedge 12 inches long, 1-1/2 inches thick on one end, and tapered to nothing at the other end. When the block is taken from the mould, and the wedge piece removed, the block will show the same batter on its end as the stretchers do on their face, and they can be built in together without showing any difference in the slope, if the work is carefully done.

Nick, who had had some experience in this kind of work, found no difficulty in understanding the whole process.

At low tide he set to work to make a solid bed for the foundation, while the boys handed him the stone and the prepared mortar as he required it, so that before the tide rose one side of the stone foundation was ready to receive the concrete blocks. During the interim between tides, Nick and the boys made the moulds, prepared for mixing the concrete, and got old timbers and lumber for a temporary scaffolding. After the moulds were made and some concrete mixed, Nick began on the blocks. It was not long before he had a sample, which seemed all right, and before he stopped quite a number of them were ranged on boards "setting."

On the sixth day after it had been commenced, the job was entirely finished. The joints in the wall had been nicely "pointed" up with cement mortar by aid of a fine-pointed trowel. The back, or ground side of the wall was filled in with earth, and danger to the pier was entirely removed.

That night Mr. Gregg told the boys and Jessie--who had watched closely the growth of the wall--quite a lot about Portland cement and concrete, which interested them very much. Portland cement as we have it now was unknown a hundred years ago, but an Englishman invented the method of making it and properly proportioning the various materials used. Fifty years ago there was scarcely any made in this country, the little that was used being imported from England, and later from Belgium; but now more of it is made and used in the United States than anywhere else in the world. He pointed out that the building of the Panama Canal was made much easier and less costly because of cement, and that the largest dam ever built had just been suggested, to dam the Mississippi near Keokuk, Iowa. This would be over 5,800 feet long and nearly 40 feet high and from 25 to 35 feet thick. He told of the various big storage dams being built and contemplated by the United States, in Montana, Arkansas, Nebraska, Wyoming, New Mexico, Dakota, Texas, and many other places, at a cost of hundreds of millions of dollars--which never would have been attempted if concrete had not been available. He also made mention of the great wall that now protects Galveston from the ravages of the sea. It is not many years since Galveston was almost destroyed by tidal waves that caused an enormous loss of life, and destruction of property amounting to over $17,000,000. The wall was built to prevent a recurrence of similar disasters. It is 17,503 feet long, 17 feet high, and 16 feet thick at the base. Another recent work is the enormous dam built by English engineers across the river Nile at Assiout, about 250 miles above Cairo in Egypt, which increases the area of good land some 300,000 acres. Ancient Babylon is again to blossom and become a beautiful country to live in, for British engineers are laying out plans for building storage dams and irrigating canals in these now sandy and barren lands. All, or nearly all, of these works and proposed works would never have been thought of, if Portland cement had not been in existence.

Mr. Gregg, after finishing his talk on concrete, noticed that George had two fingers on his right hand tied up, and on inquiry was told that George had his fingers hurt by a concrete block falling on them just as the retaining wall was being finished. The father insisted on seeing the bruised fingers and found they were not badly hurt, though the skin in one place was broken. George explained that his mother had washed his hand, dressed the wound, and applied an antiseptic to it, so that it was all right now and did not pain him.

"You were wise to go to your mother and have your bruise attended to immediately, otherwise you might have had something serious happen to you, as lockjaw frequently comes from wounds of that kind, if deep enough and not attended to immediately. It is often said that lockjaw or tetanus is caused by a wound made by a rusty nail. It is certainly bad to be wounded with a rusty nail--or any other rusty iron--and tetanus may follow; but it does not follow because the nail is rusty, but because the tetanus microbe that may be on the nail, or on the skin when the wound is made, is carried into a favourable place for development.

"This tetanus microbe, which has a long name, is very plentiful and is scattered broadcast by every gust of wind. It is a microbe of dirt, and the ground and street abound with it. Its first home and breeding place is in the intestines of horses and other domestic animals, but its greatest danger to the human family is when it gets into the blood by way of a wound. Cleanliness, in this as in many other cases, is both a preventive and a cure."

"Father," said Jessie, "I saw a very funny thing to-day while watching Nick and the boys finish the wall. The train across the river came to a standstill for some reason or other, and, as I was watching it, I saw three puffs of steam go out of its boiler, and a short time after I heard three loud whistles. This seemed to me quite curious, but while I was thinking over it, there were three more jets of steam, followed by three more 'toots.' How was it that I saw the toots before I heard them?"

"This is a question, my dear, that will require some little time and thought to answer properly. In the first place, you must understand that light travels very much faster than sound and that sounds do not reach you until some time has elapsed, if you are a little distance away. You see a flash of lightning, and a little while after you hear the thunder; and if you count 1, 2, 3, in the ordinary way, between seeing the flash and hearing the thunder, you may be fairly satisfied the source of the thunder is well on to three miles away. This, of course, is not exactly correct, but approximately so. Every time you count one, it stands for a mile. According to science, light travels 186,000 miles a second, while sound only travels at the rate of 1,090 feet per second at a temperature of 32 degrees Fahrenheit, or freezing, its velocity being increased at the rate of one and one tenth feet per second for every degree above this temperature. So you see light travels nearly a million times faster than sound, and this accounts for your seeing the puffs quite a little while before you heard the 'toots', as you call them. There are many curious and interesting things about light and sound which I'd like to describe to you sometime.

"Sound travels in dry air at 32 degrees, 1,090 feet per second, or about 170 miles per hour; in water, 4,900 feet per second; in iron, 17,500 feet; in copper, 10,378 feet; and in wood, from 12,000 to 16,000 feet per second. In water, a bell heard at 45,000 feet, could be heard in the air out of the water but 656 feet. In a balloon, the barking of dogs can be heard on the ground at an elevation of four miles. Divers on the wreck of the Hussar frigate, 100 feet under the water, at Hell Gate, near New York, heard the paddle wheel of distant steamers hours before they hove in sight. The report of a rifle on a still day may be heard at 5,300 yards; a military band at 5,200 yards. The fire of the English, on landing in Egypt, was distinctly heard 130 miles. Dr. Jamieson says he heard, during calm weather, every word of a sermon at a distance of two miles. The length of the sound waves in the air is sometimes many feet, while the length of the longest light wave is not more than .0000266 of an inch; it is no longer a mystery why we can hear, but cannot see, around a corner."

The children were greatly interested by these familiar marvels and made their father promise that he would resume the talk some other evening and tell them about thermometers and barometers.

The late afternoon next day was taken up with an excursion on the _Caroline_ down the river to Newark, where Fred induced his father to purchase a full soldering outfit, as the boys wanted to try some plumbing and soldering work. There had been a plumber at the Gregg home nearly all that day doing repair work of various kinds, and Fred, who had watched the workman, concluded he could have made the repairs himself if he had had the proper tools.

An hour or two in the city, then a pleasant sail home, proved a fine ending for a day's labour.

The next day, after school, George and Jessie assisted their mother "making garden," planting flowers, trimming bushes, and destroying weeds, while Fred gave the _Caroline_ another coat of varnish, and finished painting his little workshop, which now looked very snug and tidy. He soldered up all the leaks in every kitchen utensil he found defective, much to the delight of his mother and the maid. Fred found many things about the house wanting more or less attention, so he determined to try to put them in order. He discovered that to make a good job of soldering, he must first make the metal to be fastened together, perfectly clean and free from rust, dirt, or grease, the parts around the leak being scraped bright and smooth. He found some little difficulty in getting the solder to the exact place he wanted. In the outfit his father bought him, was not only a soldering iron,--which is not iron but copper--but a scraper, a lump of solder, a box of rosin, a piece of chamois leather, a bottle of muriatic acid, and a piece of sal-ammoniac, to be crushed fine and dusted over any surface that is to be finished bright. Fred had no trouble in soldering holes of small size in teakettles, tins, or such things as he could handle easily, for the impaired portions could be placed in a horizontal position before him and the solder applied readily. A leak in an upright water pipe in the shed, however, gave him a hard time, for he could not get the solder either to run up hill or to stay on the place where it was put. He got over this difficulty, however, by making a clay dam, a "tinker's dam"--mixing clay until it was soft, then winding a strip of it around the pipe just below the leak and applying the solder until the hole or crack was entirely covered, when a good solid job resulted. Of course, before applying any solder, all the water was drained from the pipe, and the defective part was thoroughly scraped. When the work was done, there was an edge of solder left projecting from the pipe, which Fred rasped away with a course rasp, leaving just enough solder to cover the leak properly. He then sandpapered the work and it looked almost as "good as new."

It is easy enough to solder across the work when level, even if the article being soldered is round, because the metal can be worked across the top and down the sides; but on the under side, it may be necessary to make use of a clay dam. A plumber's work covers a lot of things, among which may be mentioned metal roofing, wall flashings, water-pipes of all kinds, drain connections, hot water and steam fittings, hot-air and ventilation fittings, stove and range settings, and many other things connected in some way or another with the foregoing. Many times an offensive odour is noticeable in the cellar, or near the line of drainage, and it is often difficult to locate the source, so that expensive excavations are made before the trouble is remedied. Plumbers and drainage men often use what is termed "the peppermint test," to find where the leakage exists, and this is particularly suitable for the examination of existing soil pipes and drainage fittings. This test consists in pouring a small quantity of oil of peppermint or other substance possessing a pungent, penetrating, and distinctive odour, into the pipe or drain. The defective pipe or joint is then located by the escaping odour.

It is very important that defects of this kind should be located and repaired immediately, for odours emanating from drains or soil pipes carry with them germs of the kind most dangerous to human health and life.

Some taps in the bath room and over the kitchen sink were not working freely, and others were "dropping" a little. Fred, after cutting off the water from the main, unscrewed these and put new rubber washers in some, wound cotton twine around the plugs of others, and made the tight ones work easy by removing worn out washers and cut strings. He also fixed the hydrants on the lawn in the same manner, and made all the taps in and about the house work tightly and smoothly.

When Mr. Gregg arrived home, Fred told him all he had done, showing the tin pans and the leaky pipe he had soldered, and he straightened up with pride at being told that he was already "quite a plumber."

After tea, the family went down to the river's bank and chatted awhile on home matters; then shortly after the sun went down, they adjourned to "the lion's den."

"Now," said George, "father will tell us about barometers and thermometers, as he promised."

"Well," said Mr. Gregg, "I'm pleased to know you are so ready to listen to my talks, and I hope you'll remember some of the facts I've been telling you.

"There are many kinds of barometers, but all are constructed about on the same principle, and on the old theory that 'nature abhors a vacuum'. There may have been some kind of an instrument that did service as a barometer in the early ages, but we have no knowledge of it. The instrument as we now know it had its beginning with Galileo, Torricelli, and Pascal, but was not perfected until about 1650. Good barometers require the greatest possible care in their construction, and there ought to be two or more standing together as checks on one another in order to obtain correct results. The mercury used must be pure and good, free from all other substances and from air bubbles or films of air on the sides of the bulb. Simple barometers, suitable for ordinary purposes, can be easily made. I will describe one, and make a sketch of it on the blackboard.

"This simply consists of a wide-mouthed glass bottle filled with ordinary drinking water up to the point indicated by the letter A (Fig. 73); in this is dipped an inverted glass flask, or an incandescent light bulb, the extremity of the neck being allowed to dip just below the surface of the water.

"The flask should be inverted quite empty during wet weather, and as long as the atmosphere remains in a stormy condition, no change in the water takes place; but immediately the weather becomes finer, the water will rise in the neck of the inverted flask, and, if a continuance of fine weather be probable, will rise to the point indicated by letter B.

"I have found this simple contrivance to give sure and early warning of the approach of rain, and I need hardly remark that the principle upon which this little weather glass acts is exactly similar to that of the ordinary mercury barometer, for the rise and fall of the water is due to the respective increase or decrease of atmospheric pressure.

"By dividing the neck A B into six or eight divisions, with the aid of a diamond or piece of flint, and then marking the lines so cut, with ink, an approximate graduation of degrees of pressure may easily be obtained.

"I show you a water barometer here, (Fig. 74) that is somewhat less hard to construct than the one I have already described, as the parts are easier to obtain.

"It consists of a bottle, containing water, inverted and suspended with its mouth in the jar of the same fluid. It is capable of roughly indicating atmospheric changes in a similar way to the mercurial barometer. When the atmosphere becomes denser, the greater pressure on the surface of the water in the jar causes it to rise in the bottle; while with a lesser density it falls. As with the mercurial barometer, temperature makes a slight difference, which, strictly speaking, should be allowed for; but, as the arrangement is of such a simple character, this may be ignored. Water, also, is more subject to evaporation than mercury, besides going stagnant, and will require occasional changing and replenishing.

"A barometer of a more scientific character, and more presentable, is, I think, within your range of skill, and it may be made as follows: Obtain a glass tube, closed at one end, about two feet ten inches long and three eighths of an inch thick, with a bore of about three sixteenth inch. A circular turned wood box, one and one half inches in diameter and one and one fourth inches deep, is required for the cistern. Cut out the bottom and glue on instead a piece of leather, sagging loosely. Then cut the lid in two, and make an opening in the centre to receive the tube.

"The mahogany base, shown in two halves by A and B (Fig. 75), is 3 feet 1 inch long, 3-3/4 inches at its greatest width, 2 inches at its least width, and 3/4 inch thick. Make a groove down the centre to admit the tube, and cut an opening 2 inches square right through the wood at the round end. Glue at the back of this a circular piece of pine or cedar, 3 inches in diameter and 1/2 inch thick, and screw a semicircular piece of the same thickness at the other end, with a ring for hanging.

"Fill the tube by degrees with pure mercury, boiling each portion, as introduced, by holding the tube in a nearly horizontal position over a spirit lamp, taking care not to crack it by too sudden heating. Half fill the wooden cistern with mercury, and when the tube is full, place a finger over the end, carefully raise it to a vertical position, and lower the open end below the surface of the mercury in the cistern. While some one holds the tube, glue on the two halves of the box lid and seal up the opening round the tube with wax or cement. Then fasten the tube to the base with brass clips and screws, and secure the cistern from shifting by gluing in wedges of wood. A thumb screw, with washer, for regulating the height of the mercury, is fixed at the bottom; this presses on a cork washer glued to the leather of the cistern.

"A hollowed hardwood boss is screwed over the top end of the tube, and a hollowed circular turned boss of mahogany, C, is glued over the bottom. The ivory or cardboard scale D, is of inches and tenths, from twenty-six and one half inches to thirty-one inches, the distance being measured approximately from the surface of the mercury in the cistern. A vernier having a scale of eleven-tenths of an inch, divided into ten parts, works in a slot on the scale and should be attached as shown at D.

"Before screwing on the scale, fix its correct position by comparison with the standard barometer. It is usual to place a small thermometer on the other side.

"With regard to the thermometers, it would be quite out of place here to discuss them at length, or to offer you a scientific explanation of the principles governing their construction. I may say however, that, as the barometer is intended to measure the different degrees of density of the atmosphere, so the thermometer is designed to mark the changes in its temperature, with regard to heat and cold. The first thermometers, so far as we know, were made less than three hundred years ago, and water, spirits of wine, or alcohol, and oil were used to fill the bulbs, in the order given. It was the great Halley, of 'Halley's Comet' fame, who first made use of mercury or quicksilver in these instruments, because of its being highly susceptible to expansion and contraction, and capable of showing a more extensive scale of heat. It is owing to this quality of expansion and contraction that the degrees of heat and cold can be measured. If you put your thumb on the bulb, you will notice the quicksilver in the little tube gradually rise until it reaches the limit of the thumb's heat. Thermometers, in this and nearly all English-speaking countries, make use of the Fahrenheit scale, which is different from those used in some other places; and this often causes trouble and annoyance.

"The scale of Reamur prevails in Germany. He divides the space between the freezing and boiling points into 80 degrees. France uses that of Celsius, who graduated his scale on the decimal system. The most peculiar scale of all, however, is that of Fahrenheit, the renowned German physicist, who, in 1714 or 1715, composed his scale, having ascertained that water could be cooled under the freezing point without congealing. He, therefore, did not take the congealing point of water, which is uncertain, but composed a mixture of equal parts of snow and sal-ammoniac, about fourteen degrees R. This scale is preferable to both those of Reamur and Celsius, or, as it is called, Centigrade, because: (1) The regular temperature of the moderate zone moves within its two zeros and can, therefore, be written without + or -. (2) The scale is divided so finely that it is not necessary to use fractions whenever careful observations are to be made. These advantages, although questioned by some, have been considered so weighty that both Great Britain and America have retained this scale, while nations on the Continent of Europe use the other two. The conversion of any one of these scales into another is very simple. (1) To change a Fahrenheit temperature into the same given by the Centigrade scale, subtract 32 degrees from Fahrenheit's degrees and multiply the remainder by 5/9. The product will be the temperature in Centigrade degree. (2) To change from Fahrenheit to Reamur's scale, subtract 32 degrees from Fahrenheit's degrees and multiply the remainder by 4/9. The product will be the temperature in Reamur's degrees. (3) To change a temperature given by the Centigrade scale into the same given by Fahrenheit, multiply the Centigrade degrees by 9/5 and add 32 degrees to the product. The sum will be the temperature by Fahrenheit's scale. (4) To change from Reamur's to Fahrenheit's scale, multiply the degree on Reamur's scale by 9/4 and add 32 degrees to the product. The sum will be the temperature by Fahrenheit's scale. A handy table can easily be figured out from the data given."

Mr. Gregg concluded his conversation for the night at this point, but promised to take it up again the first available evening.

Two or three nights afterward it was very wet and dreary. The boys and Jessie were called into the den by Mr. Gregg, where a brisk fire, made of limbs and branches gathered by the boys, was burning in the little fireplace, and the room looked bright and cheerful. The young folks all drew up around the fire to listen.

"I have so many things to talk to you about," said he, "that I scarcely know where to begin; however, I promised to tell you something concerning springs, so I will make these useful contrivances my theme to-night."

"There are many kinds of springs, but I will only talk of steel or other metal springs; and even then must limit myself to a few. The carriage or laminated spring is probably the most in use, as it is an important factor in the construction of all classes of railway trucks and carriages, locomotives, automobiles, road carriages and light wagons of all kinds. These are also much used in the manufacture of invalids' chairs, children's perambulators, and many other things. The springs used in the construction of the largest locomotives are big affairs and often weigh over 500 pounds. These are bearing springs and carry the whole weight of engine and boiler. There are, of course, a number of these springs to each engine. Springs on the coaches and carriages are somewhat lighter and more flexible than those on the heavier trucks. The double spring, shown at Fig. 76, is known in railroad parlance as a 'draw-spring.' One of these is secured at each end of the car, and used to attach or couple the cars together, or to attach the engine to the train, the object being to lessen the bump or impact of the blow when the engine and cars come together. The effect is the same when the engine starts a train; the springs in the first car draw out, then the springs on the second car do likewise, and this causes the load of the whole train to fall on the engine gradually, a matter of great importance in railway economy. If it were not for bearing springs on the trucks and carriages, it would be almost impossible to use railroads for passenger traffic or for carrying fine goods, as the jolting and pounding on the iron rails would shake things to pieces, destroy the carriages, and pound the roadbed and bridges to bits in a very short time. Now, by the aid of steel springs, you ride in a Pullman as smoothly almost as in a boat, so you see how useful springs are to mankind.

"There are many kinds of bearing springs, but all are built in the same manner, of steel leaves, made of different dimensions to suit conditions. As you will see in the diagram, the sheets of steel are laid over each other, like the scales of a fish, and made shorter as they approach the top. All the leaves are fastened together by having an iron buckle driven onto the middle, as shown, while hot, and when this cools, it shrinks and clasps the whole so tight it cannot be taken off until heated or cut. I could tell you of many other kinds of springs--watch springs, gun springs, trap springs, spiral springs--used for various purposes, but I will end this subject by describing to you something you can make for yourself, if you wish; namely, a cross-bow, which is very simple. I make on the blackboard a diagram, (Fig. 77), with A representing the stock, 5 feet long; B, the bender, 6 feet long, which should be made in four pieces. The front piece should be 3/4 inch thick, the three inner pieces 1/2 inch thick. C are brass ferrules to keep the leaves of the bender from shifting; D the string, which should be very strong. The bender should be cut out of straight well-seasoned ash, rock elm, or hickory. Instead of brass ferrules, strong brass or copper wire can be used, properly twisted at the joints.

"The gyroscope has become quite famous of late, because of its having been employed as a steadier for the monorail car, and proposed as a regulator or governor for aeroplanes, so that I think it will not be amiss to tell you that a study of this toy is well worth any time and labour you may spend on it. There are great possibilities within this little instrument and its applications. I do not intend dealing with its principles, or with rotation problems generally, as they would, I fear, be beyond your present comprehension, but I will confine myself to describing the toy and showing you how it can be made, though it would be much cheaper to buy one from a dealer. The instrument consists of a ring of brass or other metal, like a curtain ring, and a smaller brass ring attached to a thick disc of white metal, or a metal disc with a thickened rim, as shown in Fig. 78. This disc is securely fixed to a metal pin, which is passed through two holes in the outer brass ring, and at one side a small rounded nut or ball of brass is screwed on the outer ring. The metal disc is at right angles to the outer ring. If a cord is wound several times round the metal pin, the outer ring held in the left hand, the pin and metal disc will revolve at a very high speed, while the outer ring remains stationary. The gyroscope can be placed on the knob, and while the disc is revolving the outer ring can be placed at any angle, and will remain stationary. It is also possible to balance it at any angle on the top of a support, such as the tip of a stick."