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A dynamo in an electric light plant.

       Fig. 118. The magneto in an automobile is a small dynamo.

       Fig. 119. Electricity flows through the coin.

       Fig. 120. Will electricity go through the glass?

       Fig. 121. Electrical apparatus: A , plug fuse; B , cartridge fuse; C , knife switch; D , snap switch; E , socket with nail plug in it; F , fuse gap; G , flush switch; H , lamp socket; I , J , K , resistance wire.

       Fig. 122. Which should he choose to connect the broken wires?

       Fig. 123. Electricity flows around a completed circuit somewhat as water might be made to flow around this trough.

       Fig. 124. Diagram of the complete circuit through the laboratory switches.

       Fig. 125. Parallel circuits.

       Fig. 126. How should he connect them?

       Fig. 127. The ground can be used in place of a wire to complete the circuit.

       Fig. 128. Grounding the circuit. The faucet and water pipe lead the electricity to the ground.

       Fig. 129. How the lamp and wire are held to ground the circuit.

       Fig. 130. How can the electric iron be used after one wire has been cut?

       Fig. 131. Feeling one live wire does not give her a shock, but what would happen if she touched the gas pipe with her other hand?

       Fig. 132. Pencils ready for making an arc light.

       Fig. 133. The pencil points are touched together and immediately drawn apart.

       Fig. 134. A brilliant arc light is the result.

       Fig. 135. An arc lamp. The carbons are much larger than the carbons in the pencils, and the arc gives an intense light.

       Fig. 136. A , the "fuse gap" and B , the "nail plug."

       Fig. 137. What will happen when the pin is thrust through the cords and the electricity turned on?

       Fig. 138. The magnetized bolt picks up the iron filings.

       Fig. 139. Sending a message with a cigar-box telegraph.

       Fig. 140. Connecting up a real telegraph instrument.

       Fig. 141. Diagram showing how to connect up two telegraph instruments. The circles on the tables represent the binding posts of the instruments.

       Fig. 142. Telegraphing across the room.

       Fig. 143. The bell is rung by electromagnets.

       Fig. 144. A toy electric motor that goes.

       Fig. 145. An electric motor of commercial size.

       CHAPTER NINE

       MINGLING OF MOLECULES

       Fig. 146. Will heating the water make more salt dissolve?

       Fig. 147. Will the volume be doubled when the alcohol and water are poured together?

       Fig. 148. Alum crystals.

       Fig. 149. Filling a test tube with gas.

       Fig. 150. The lower test tube is full of air; the upper, of gas. What will happen when the cardboard is withdrawn?

       Fig. 151. Pouring the syrup into the "osmosis tube."

       Fig. 152. Filling the barometer tube with mercury.

       Fig. 153. Inverting the filled tube in the cup of mercury.

       Fig. 154. Finding the pressure of the air by measuring the height of the mercury in the tube.

       Fig. 155. The kind of mercury barometer that you buy.

       Fig. 156. An aneroid barometer is more convenient than one made with mercury. The walls are forced in or spring back out according to the pressure of the air. This movement of the walls forces the hand around.

       Fig. 157. Different forms of snowflakes. Each snowflake is a collection of small ice crystals.

       Fig. 158. If you blow gently over ice, you can see your breath.

       Fig. 159. The glass does not leak; the moisture on it comes from the air.

       CHAPTER TEN

       CHEMICAL

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