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36. Why doesn't the water spill out?

       Fig. 37. An automobile race. Notice how the track is banked to keep the cars from overturning on the curves.

       Fig. 38. The horse goes forward by pushing backward on the earth with his feet.

       Fig. 39. As he starts to toss the ball up, will he weigh more or less?

       Fig. 40. Action and reaction are equal; when he pushes forward on the ropes, he pushes backward with equal force on the seat.

       CHAPTER FOUR

       HEAT

       Fig. 41. A thermometer.

       Fig. 42. A thermometer made of a flask of water. It does not show the exact degree of heat of the water, but it does show whether the water is hot or cold.

       Fig. 43. Will the hot ball go through the ring?

       Fig. 44. When the wire is cold, it is fairly tight.

       Fig. 45. But notice how it sags when it is hot.

       Fig. 46. The expansion of the compressed gas freezes the moisture on the tube.

       Fig. 47. Why did the bottle break when the water in it turned to ice?

       Fig. 48. An evaporating dish.

       Fig. 49. Diagram illustrating how in the evaporation of water some of the molecules shoot off into the air.

       Fig. 50. A view of the Dead Sea.

       Fig. 51. In a minute the cork will fly out.

       Fig. 52. A toy balloon has been slipped over the mouth of a flask that is filled with steam.

       Fig. 53. As the steam condenses and leaves a vacuum, the air pressure forces the balloon into the flask.

       Fig. 54. Will boiling water get hotter if you make it boil harder?

       Fig. 55. By distillation clear alcohol can be separated from the water and red ink with which it was mixed.

       Fig. 56. The metal balls are fastened to the iron and glass rods with drops of wax.

       Fig. 57. Does the heat travel faster through the iron or through the glass?

       Fig. 58. Convection currents carrying the heat of the stove about the room.

       Fig. 59. Diagram of a hot-water heater. What makes the water circulate?

       CHAPTER FIVE

       RADIANT HEAT AND LIGHT

       Fig. 60. It is by radiation that we get all our heat and light from the sun.

       Fig. 61. How a thermos bottle is made. Notice the double layer of glass in the broken one.

       Fig. 62. The ball bounces from one boy to the other, but it does not return to the one who threw it.

       Fig. 63. In the same way, the light bounces (reflects) from one boy to the other. It does not return to the point from which it started and neither boy can see himself.

       Fig. 64. How should the mirror be placed?

       Fig. 65. In passing through the prism the light is bent so that an object at b appears to be at c .

       Fig. 66. The pencil is not bent, but the light that comes from it is.

       Fig. 67. The bending of the light by the water in the glass causes the pencil to look broken.

       Fig. 68. The light is bent when it enters a window pane and is bent again in the opposite direction when it leaves it.

       Fig. 69. When the light from one point goes through the lens, it is bent and comes together at another point called the focus.

       Fig. 70. The light from each point of the candle flame goes out in all directions.

       Fig. 71. The reading glass is a lens which focuses the light from the candle flame and forms an image.

       Fig. 72. The light from the tip of the candle flame is focused at one point.

       Fig. 73. And the light from the base of the flame is focused at another point.

       Fig. 74. The light from the tip and base (and from every other point) of the flame is, of course, focused at the same time. In this way an image of the flame is formed.

       Fig. 75. The light spreads out again beyond the focus.

       Fig. 76. So if the light comes to a focus before

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