THEORY AND PRACTICE OF ENGINEERING.
1000
Book If.
destination; he also informs us that the temple, consisting of one solid stone, was a cube,the length of whose side was 40 cubits.
AVe can scarcely imagine it possible to move so vast a block, the original weight ofwhich would be upwards of 100,000 tons; but supposing that four-fifths were cut awaypreviously to removal, to produce the cha-racter of an Egyptian temple, there would -
still remain 25,000 tons to transport by the aidof levers, capstans, pulleys, and inclined planes.
The interposition of rollers or balls in theabove arrangement of Count Carbury bearssome resemblance to the application of fluids :supposing surfaces to be flat and parallel, aroller will move between them without muchfriction; but it will have to overcome the re-
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Fig. 1501.
END VIEW.
sistance occasioned by the depression whichit produces in the substance on which it moves,and which is greater or less according toits softness or want of elasticity : if perfectlyelastic, the depression would be productive oflittle resistance, because the tendency to rise
Fig. 1502. 'i'HE bed, balls, and axles.
behind the roller would be equivalent to theforce opposing its progress, the actual re-sistance arising from a want of elasticity in thematerials made use of. In this case, by layingdown rails in front of the mass to be moved,upon which the balls could turn, the objectionusually made to their introduction was ob-viated ; but had they been placed betweentwo cylinders, one convex and the otherconcave, much of the friction would have beenavoided; it is always materially diminishedby lessening the velocity of the parts whichslide on each other, as is proved by reducingthe diameter of an axis on which a wheel turns.
Combinations of wheels are generally used where heavy weights are to be moved, orwhen, by the application of great power, a higher velocity is required: for the first thepower must be applied to the circumference of the first wheel, and its pinion must transmitthe motion to the teeth of the second wheel, and so on, in order that the weight may be