112 THE NATURE STUDY COURSE. 



Other Object Lessons. — Lessons similar to those on water 

 and glass may be based on a great variety of objects, natural 

 and artificial, such as coal, salt, paper, iron, stoves, wire, 

 wood, chairs, pails, wool, hats, umbrellas, rubber, sulphur, 

 soap, sugar, &c. 



Method.— Seize occasion of interest as opportunity for 

 introducing the topic. Appeal to observation. Leave pupils 

 to make inferences or hypotheses. Use experiments for 

 illustration or for proof or refutation of inferences. Search 

 for practical applications of the truth inferred. Express 

 in suitable modes. 



Heating and Ventilation of Living Rooms.— Refer to 



known examples of different methods of heating — open fire- 

 places, stoves, furnaces, steam, hot water. Heat from the 

 fireplace like that from the sun comes in rays, radiates, or is 

 radiant. Such heat passes through the air without much 

 decrease and is absorbed or reflected by denser bodies. It is 

 a healthful mode of heating because the objects, including the 

 people in the room, are heated more than the surrounding air. 

 It is best to feel comfortably warm in a cool atmosphere. 



Air heated in a furnace in the basement conveys the heat to 

 the living room. It feels comfortable but it is not stimulating. 



Heat is mostly radiant but partly conveyed where stoves, 

 steam pipes and hot water radiators are in the room. 



Ventilation. — In school-rooms it is very important that fresh 

 air be supplied in large quantities. Count how many times 

 you breathe in a minute. Fill a bottle with water, invert it 

 into a basin of water. Expire a breath through a rubber 

 tube into the bottle. Measure the displacement of water to 

 find how many cubic inches you expire with each breath. 

 Four per cent, of that is vitiated product, mostly carbon 

 dioxide, in place of the oxygen you used in your lungs. Find 



