The Library of Work and Play: Mechanics, Indoors and Out

by Fred. T. Hodgson

Fig. 15

"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.