IV. 



■THE THERMOMETER. 



This expansion of bodies when heated gives iis a means of finding 

 how hot anything is, that is, finding its temperature. For instance, 

 to find whether it is hotter ont of doors than in a room, you might 

 talvB a Ijottle with a very narrow neck and fill it up to the middle of 

 the neck with water. Xow let it stand in the room for half an hour 

 and mark where the surface of the water stands in the neck; then put 

 it out in the sun and let it stand for another half hour, and see whether 

 the water has risen or fallen. This will tell yon whether the tempera- 

 ture is higher or lower indoors than outddors. But if it should happen 

 to be a))out as warm outdnors as indoors there would only be a very 

 small rise or fall of the water in the neck. You can easily understand 

 that the change of level would be much greater if you used a bottle 

 with a much narrower neck: but then the neck would need to be very 

 much longer to prevent it running over altogether. ("\\'hy not try it 

 with two bottles, one with a broad, short neck and the other with a 

 long, narrow neck?) And now you know what a thermometer is, for 

 it is merely a very small bottle with a very long and very narrow neck. 

 There is, however, one other_ difference — it does not contain water, 

 but mei'cury. One reason for not using water you will see if you think 

 what would happen to a thermometer containing water on a very cold 

 day in Avinter. There is also a scale marked on the thermometer or 

 attached to it, so that it can tell you different degrees of temperature. 

 If you can get a thermometer to use, trv some temperatures with it. 

 For instance, note the tem))erature when the thermometer is in the 

 air, and then bury the lower end of it in a small hole in the groitnd 

 and find whether the soil is warmer or cooler than the air. Do this 

 at difl'erent times of the day and of the vear and keep your results in 

 a notebook, and you may make some iuteresting discoveries. If vou are 

 near a river or lake, make notes of its temjierature in the same way. 

 If your thermometer is one with degrees marked on the glass, put the 

 bulb of it in your mouth and find how hot you are; see whether you are 

 warmer on a hot day than on a cold day, or at noon than at nio-ht. 

 8ei> also whether working makes you any warmer. You may try the 

 temperature of the cat and the ilog also, if yon can coax them to be 

 quiet enough. You will be able to think of many other interesting 

 things to try with a thermometer. 



V. 



HOW HEAT TRAVELS. 



Heat being invisible, it is somewhat more difficult to find how it 

 travels than it is to see how something visible, like water, travels, and 



