7. (Pg. 55) When and why do the scales balance each other, and where is their centre of gravity? (fig. 1. plate 4.) 8. (Pg. 55) Why would they not balance with unequal weights? 9. (Pg. 55) Were the fulcrum removed from the middle of the beam what would result? 10. (Pg. 55) What do we mean by the arms of a lever? 11. (Pg. 56) How may a pair of scales be false, and yet appear to be true? 12. (Pg. 56) If the fulcrum be removed from the centre of gravity, how may the equilibrium be restored? 13. (Pg. 56) How is this exemplified by fig. 3. plate 4? 14. (Pg. 56) What proportion must the weights bear to the lengths of the arms? 15. (Pg. 57) On what principle do we weigh with a pair of steelyards, and what will be the difference in the motion of the extremities of such a lever? 16. (Pg. 58) How is this exemplified by fig. 4. plate 4? 17. (Pg. 58) What line is described by the ends of a lever? fig. 4. plate 4. 18. (Pg. 58) How many kinds are there; and in the first how is the fulcrum situated? 19. (Pg. 58) When may the fulcrum be so situated that this lever is not a mechanical power, and why? 20. (Pg. 59) What is represented by fig. 5. plate 4? 21. (Pg. 59) Give a familiar example of the use of a lever of the first kind. 22. (Pg. 59) In what instruments are two such levers combined? 23. (Pg. 59) How may two horses of unequal strength, be advantageously coupled in a carriage? 24. (Pg. 60) Describe a lever of the second kind. (Fig. 6. plate 4.) 25. (Pg. 60) What is represented in fig. 7. plate 4, and in what proportion does this lever gain power? 26. (Pg. 60) What is said respecting a door? 27. (Pg. 60) Describe a lever of the third kind. 28. (Pg. 60) In what instance do we use this? 29. (Pg. 61) What remarks are made on its employment in the limbs of animals? 30. (Pg. 61) What are the conditions of equilibrium in every lever? CONVERSATION V. CONTINUED. ON THE MECHANICAL POWERS. OF THE PULLEY. OF THE WHEEL AND AXLE. OF THE INCLINED PLANE. OF THE WEDGE. OF THE SCREW. MRS. B. The pulley is the second mechanical power we are to examine. You both, I suppose, have seen a pulley? _Caroline._ Yes, frequently: it is a circular, and flat piece of wood or metal, with a string which runs in a groove round it: by means of which, a weight may be pulled up; thus pulleys are used for drawing up curtains. _Mrs. B._ Yes; but in that instance the pulleys are fixed; that is, they retain their places, and merely turn round on their axis; these do not increase the power to raise the weights, as you will perceive by this figure. (plate 5. fig. 1.) Observe that the fixed pulley is on the same principle as the lever of a pair of scales, in which the fulcrum F being in the centre of gravity, the power P and the weight W, are equally distant from it, and no advantage is gained.