_Mrs. B._ I shall defer the explanation of the motion of the moon till our next interview, as it would prolong our present lesson too much. Questions 1. (Pg. 71) What revolution does the earth perform in a year? 2. (Pg. 71) Had the earth received a projectile force only, at the time of its creation, how would it have moved? 3. (Pg. 72) What do the lines A B, and A C, represent in fig. 1. plate 6? 4. (Pg. 72) What have you been taught respecting a body acted upon by two forces at right angles with each other? 5. (Pg. 72) How does the force of gravity change the diagonal into a curved line? 6. (Pg. 72) Describe the operation of the forces of projection and of gravity as illustrated by the parallelograms in the figure? 7. (Pg. 72) What is the law respecting the time required for motion in the diagonal? 8. (Pg. 73) What portion of a year is represented by the three diagonals in the figure? 9. (Pg. 73) How will what you have learned respecting motion in a curve, apply to the earth's motion? 10. (Pg. 73) In what form are you directed to cut a piece of card to aid in illustrating the two forces acting upon the earth? 11. (Pg. 73) How must you apply it to this purpose? (fig. 2. plate 6.) 12. (Pg. 73) If these two forces did not exactly balance each other, what would result? 13. (Pg. 73) Does the earth revolve in a circular orbit? 14. (Pg. 73) What results from its motion in an ellipsis? 15. (Pg. 74) What is represented by the lines A C, A B, in fig. 3. plate 6? 16. (Pg. 74) Were the projectile force to carry the earth from B to D, (fig. 3.) what would result? 17. (Pg. 74) When it has arrived at E, what angle will be formed by the lines representing the two forces? 18. (Pg. 74) What effect will the accelerated motion then produce? 19. (Pg. 75) What is the form of the earth's orbit, and what circumstances produce this form? 20. (Pg. 75) What is the consequence as regards the regularity of the earth's motion? 21. (Pg. 75) What law governs as regards the spaces passed over, and how is this explained by fig. 4. plate 6? 22. (Pg. 75) What is meant by _perihelion_, and by _aphelion_? 23. (Pg. 75) What is the difference of the distance of the earth from the sun, in these two points? 24. (Pg. 76) At what season of the year is it nearest to, and at what furthest from the sun? 25. (Pg. 76) What is the mean distance of the earth from the sun? 26. (Pg. 76) Why is but little effect produced, as regards temperature, by the change of distance? 27. (Pg. 76) Has it any influence on the sun's apparent size? 28. (Pg. 76) Are the summer and winter, half years, of the same length; what is their difference, and what is the cause? 29. (Pg. 76) What are the planets? 30. (Pg. 77) What circumstances render it probable that they are habitable globes? 31. (Pg. 77) What is believed respecting the fixed stars? 32. (Pg. 77) What discoveries have been made in the moon?