Practical Education, Volume II. Edgeworth Maria

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this skeleton-pulley be used horizontally, instead of perpendicularly, the circumstances which have been mentioned, will appear more obvious.

      Upon the wooden road lay down a piece of girth-web; nail one end of it to the road; place the pulley upon the web at the other end of the board, and, bringing the web over the radii, let the boy, taking hold of it, draw the loaded sledge fastened to the hook at the centre of the pulley: he will draw nearly twice as much in this manner as he could without the pulley.24

      Here the web lying on the road, shows more distinctly, that it is quiescent where the lowest radius touches it; and if the radii, as they tread upon it, are observed, their points will appear at rest, whilst the centre of the pulley will go as fast as the sledge, and the top of each radius successively (and the boy's hand which unfolds the web) will move twice as fast as the centre of the pulley and the sledge.

      If a person, holding a stick in his hand, observes the relative motions of the top, and the middle, and the bottom of the stick, whilst he inclines it, he will see that the bottom of the stick has no motion on the ground, and that the middle has only half the motion of the top. This property of the pulley has been dwelt upon, because it elucidates the motion of a wheel rolling upon the ground; and it explains a common paradox, which appears at first inexplicable. "The bottom of a rolling wheel never moves upon the road." This is asserted only of a wheel moving over hard ground, which, in fact, may be considered rather as laying down its circumference upon the road, than as moving upon it.

The inclined Plane and the Wedge

      The inclined plane is to be next considered. When a heavy body is to be raised, it is often convenient to lay a sloping artificial road of planks, up which it may be pushed or drawn. This mechanical power, however, is but of little service without the assistance of wheels or rollers; we shall, therefore, speak of it as it is applied in another manner, under the name of the wedge, which is, in fact, a moving inclined plane; but if it is required to explain the properties of the inclined plane by the panorganon, the wooden road may be raised and set to any inclination that is required, and the sledge may be drawn upon it as in the former experiments.

      Let one end of a lever, N. Plate 2. Fig. 7. with a wheel at one end of it, be hinged to the post of the frame, by means of a gudgeon driven or screwed into the post. To prevent this lever from deviating sideways, let a slip of wood be connected with it by a nail, which shall be fast in the lever, but which moves freely in a hole in the rail. The other end of this slip must be fastened to a stake driven into the ground at three or four feet from the lever, at one side of it, and towards the end in which the wheel is fixed (Plate 2. Fig 10. which is a vue d'oiseau) in the same manner as the treadle of a common lathe is managed, and as the treadle of a loom is sometimes guided.25

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      1

      Garretson's Exercises, the tenth edition.

      2

      V. Chapter on Attention.

      3

      Mrs. Piozzi.

      4

      V. Blair.

      5

      V. Plutarch.

1

Garretson's Exercises, the tenth edition.

2

V. Chapter on Attention.

3

Mrs. Piozzi.

4

V. Blair.

5

V. Plutarch.

6

Valpy's Exercises.

7

V. Darwin's Poetry.

8

Since the above was written, we have seen a letter from Dr. Aikin to his son on the morality and poetic merit of the fable of Circe, which convinces us that the observations that we have hazarded are not premature.

9

Chapter on Imagination.

10

We speak of these engravings as beautiful, for the times in which they were done; modern artists have arrived at higher perfection.

11

Darwin. V. Botanic Garden.

12

V. Gray's Memoria Technica, and the Critic.

13

Instead of

William the conqueror long did reign,And William his son by an arrow was slain.

Read,

William the Consau long did reign,And Rufkoi his son by an arrow was slain.

And so on from Gray's Memoria Technica to the end of the chapter.

14

Page 24.

15

V. A strange instance quoted by Mr. Stewart, "On the Human Mind," page 152.

16

NOTE.

17

The word calculate is derived from the Latin calculus, a pebble.

18

This method is recommended in the Cours de Math, par Camus, p. 38.

19

Plutarch. – Life of Dion.

20

V. Rivuletta, a little story written entirely by her in 1786.

21

When this question was sometime afterwards repeated to S – , he observed, that the feather would throw down the castle, if its swiftness were so great as to make up for its want of weight.

22

Were it thought necessary to make these experiments perfectly accurate, a segment of a pulley, the radius of which is half the length of the scale-beam, should be attached to the end of the beam; upon which the cord may apply itself, and the pulley (P 3) should be raised or lowered, to bring the rope horizontally from the man's shoulder when in the attitude of drawing.

23

The word power is here used in a popular sense, to denote the strength or efficacy that is employed to produce an effect by means of any engine.

24

In all these experiments with the skeleton-pulley, somebody must keep it in its proper direction; as from its structure, which is

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