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reaches the paper, the image will be blurred.

       Fig. 77. Or if the light reaches the paper before it comes to a focus, the image will be blurred.

       Fig. 78. Lenses of different kinds.

       Fig. 79. A section of the eye.

       Fig. 80. How an image is formed on the retina of the eye.

       Fig. 81. A simpler diagram showing how an image is formed in the eye.

       Fig. 82. A diagram showing how a reading glass causes things to look larger by making the image on the retina larger.

       Fig. 83. Diagram showing how a reading glass enlarges the image on the retina. More lines are drawn in than in Figure 82.

       Fig. 84. Diagram of a microscope.

       Fig. 85. This is the way a concave mirror forms a magnified image.

       Fig. 86. The concave mirror forms an image of the burning candle.

       Fig. 87. The great telescope of the Yerkes Observatory at Lake Geneva, Wisconsin.

       Fig. 88. The sunlight is scattered (diffused) by the clouds. The photograph shows in the foreground the Parliament Buildings, London, England.

       Fig. 89. How the droplets in a cloud scatter the rays of light.

       Fig. 90. Making a rainbow on the wall.

       Fig. 91. The prism separates the white light into the rainbow colors.

       Fig. 92. When the wheel is rapidly whirled the colors blend to make white.

       Fig. 93. Which color is warmest in the sunlight?

       Fig. 94. A mercury-vapor lamp.

       Fig. 95. Explain why the breakers are white and the sea green or blue.

       CHAPTER SIX

       SOUND

       Fig. 96. An interesting experiment in sound.

       Fig. 97. When the air is pumped out of the jar, you cannot hear the bell ring.

       Fig. 98. Making a phonograph record on an old-fashioned phonograph.

       Fig. 99. A modern dictaphone.

       Fig. 100. How the apparatus is set up.

       Fig. 101. When the tuning fork vibrates, the glass needle makes a wavy line on the smoked paper on the drum.

       Fig. 102. When the wave reaches the end of the sink, it is reflected back. Sound waves are reflected in the same way.

       Fig. 103. When the prongs of the tuning fork are made longer or shorter, the pitch of the sound is changed.

       CHAPTER SEVEN

       MAGNETISM AND ELECTRICITY

       Fig. 104. The compass needle follows the magnet.

       Fig. 105. Magnetizing a needle.

       Fig. 106. A compass made of a needle and a piece of cardboard.

       Fig. 107. Diagram of molecules in unmagnetized iron. The north and south poles of the molecules are supposed to be pointing in all directions.

       Fig. 108. Diagram of magnetized iron. The north and south poles of the molecules are all supposed to point in the same direction.

       Fig. 109. When the comb is rubbed on the coat, it becomes charged with electricity.

       Fig. 110. The charged comb picks up pieces of paper.

       CHAPTER EIGHT

       ELECTRICITY

       Fig. 111. A wet battery of three cells connected to ring a bell.

       Fig. 112. A battery of three dry cells.

       Fig. 113. A storage battery.

       Fig. 114. Spinning loops of wire between the poles of a magnet causes a current of electricity to flow through the wire.

       Fig. 115. The more loops there are, the stronger the current.

       Fig. 116. If the electricity passes through a lamp on its way around the circuit the filament of the lamp glows.

       Fig. 117.

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