the end of the lever under the stone, and O the power. The weight thrown on the lever by the man at O, raises the stone so that it can be blocked up, the lever and fulcrum arranged for another lift, and the process repeated. This can be continued until the stone is raised to the height required, or until it is turned over. This method applies to the raising of any sort of weight, engine, boiler, heater, etc.

"In this sketch the distance from B to C shows the short arm of the lever, and the distance from C to O shows the length of the long arm.

Fig. 5. Lever as a mechanical power

"A lever, used in this way, is called a lever of the first kind, because of its simplicity and easy adaptation to many purposes. I saw George digging in the garden the other day, making a flower bed for his mother. The spade he used formed an excellent lever. He forced it into the ground to its full depth, pried the handle toward him, and broke loose the soil, after which he turned over the earth in the bed. Now, in this case, the top of the blade or foot-plate of the spade, rested on the hard ground, which was the fulcrum; the soil dug up was the weight, and George's hand at the top of the spade handle, furnished the power. I am sure you all understand the working of a lever of this kind, but I will give you another illustration.

Fig. 6. Double lever as scales

"Here's another sketch (Fig. 5), in which A,B,C, together show the lever, also the power A, the fulcrum B, and the weight C. If I should place the fulcrum B so that it would be in the middle between the ends A C, there would be what is termed an equilibrium between the weight and the power, and if they are equal there will be a perfect balance maintained. It is on this principle that scales for druggists are made, the lever being suspended in the centre of its length, as I show in the sketch (Fig. 6). These scales are very nicely adjusted, and the chains and receivers are made as nearly alike in weight as possible. The arms of the lever being of equal length from the centre, or pivot, permit the lever to stand in a perfectly horizontal position, unless disturbed by having a weight placed in either one or other of the receivers. In this case, the pivoted point P is the fulcrum, and the two points O and X may be taken as the power and the weight. If one pound is placed in the receiver at O, it will tip the scale down, and that will become the weight, while any commodity placed in the receiver at X, until the lever is again brought level, or horizontal, may be called the power. As another illustration I'll tell you of something that took place the other day. In the vacant lot are several piles of bricks, stones, and planks. George, seeing this, took one of the planks and threw it across several others, making a 'Teeter Tauter,' or, as some children call it, a 'Seesaw.' He balanced the plank nicely, and then invited Jessie and her cousin to sit on it, one at each end. The two girls were about the same weight, and George held the plank until both were seated. It remained level and balanced, until George got on the top of it, and stood on the centre of its length, placing his feet so that one was on one side of the centre, or fulcrum, and the other on the other. By causing his weight to rest on his right foot, the right end of the plank would dip downward; then by throwing his weight on his left foot, the movement of the plank would be reversed, and the motion continued until George ceased to exert any extra pressure on either of his feet. What do you call the boy or girl who stands on the plank?"

"Sometimes," said Jessie "we call him a 'candlestick' and sometimes 'the balancer'."

"This teeter tauter and the explanation of the druggist scales," said the father, "show you that many of our conveniences are due to the lever in one way or another. These are but a few of the thousands of instances I could name. Take a nut-cracker, for instance. There we have a sort of double lever, the joint being the fulcrum, the nut the weight, and the two handles the combined power or lever. By pressing the handles or levers, we crack the nut or overcome the weight, by crushing it. We owe many of our amusements to the lever in one form or another. Even our pianos would be impossible were it not for the combination of levers in the adjustment of the keys. Machinery and all kinds of moving instruments, including watches, clocks, and other fine mechanism, could not be perfected without the lever. The common every-day wheelbarrow is a good illustration of the use of the lever combined with the wheel. George fills up his barrow with stones or other materials that weigh two or three times the amount he could lift easily. Yet he gets away with the load, apparently with very little trouble. The handles form the lever or power, the wheel the fulcrum, and the stones the weight. George raises the handles, and throws the greater part of the weight on the fulcrum, which is the wheel, and this latter, acting as a roller, is easily moved around its own axle, thus enabling George to move his threefold load with ease.

"This example shows you how, by a simple combination of mechanical devices, labour may be reduced. The roller is related to the wheel and axle class—another of the mechanical powers.

"In your bicycles you have a fine illustration of the application of the roller principle, in the ball-bearings. The little round balls, over which the axle of the wheel runs, are simply rollers rounded in every direction, and placed there to destroy friction, which they do almost entirely.

"Another excellent illustration of the use of the roller is seen in the hanging of the grindstone we have in our back shed. The axle passing through the stone rests on two pairs of wheels or rollers, one pair at each side of the stone. If you turn the stone on its axis, you will notice the wheels turn also, and the effort required to turn the stone is hardly noticeable. If the grindstone were well balanced and true, and the little wheels the same, so that they could be run without friction on their bearings, the stone, by giving it one good turn with the hand, would keep revolving a very long time. So you see how much we are indebted to the mechanical powers for our present state of civilization."

Next morning being Saturday, George was up early, put on a pair of overalls his mother had bought, and, when breakfast was over, all but the mother went out to the new property. They found Nick helping a teamster to unload gravel, also a load of cement, which was placed in a dry and convenient place, for once damp or wet in the least it becomes of little use, unless worked up immediately. George was full of glee. He got his wheelbarrow and wanted to commence work without delay. The father took Fred and Nick to the trench and explained what was to be done and the way to do it. "The trench is now eight inches deep," he said, "and you must wheel gravel, broken bricks, hard mortar, or cinders into it so that there will be about five inches of it in the trench from one end to the other.