88 



NATURE STUDY 



from the lighted strip produces currents in the air. This makes 

 it necessary to manage the smoke paper so that the smoke at 

 some distance from the burning part is allowed to fall in the way 

 of the currents to be tested. The condition of the air about a 

 stove, a radiator, or a register is next to be explored. The same 

 tests may. be applied to the air about a person sitting quietly in a 

 room. These experiments will reveal the fact that in a closed 

 room where all else is quiet, the air in all parts is in constant mo- 

 tion, the motion being caused by some of it being heated more 

 than the rest. 



Next allow the pupils to open the windows at the top and at 

 the bottom and find out at which points the air is entering and at 

 which it is escaping from the room. Various combinations of 

 opening and closing of the different windows may be studied as 

 well as the conditious with doors partially or wholly open, also with 

 other openings which may be in the room. These experiences 

 making familiar the movements of air and their cause form a 

 good basis for study of both ventilation of rooms and of means 

 of the greater movements of air outside in thephenomenaof winds. 



Fig. 57. Ventilation in a miniature room. 



Beside the study of a real room in reference to its ventilation, 

 which of course is the best subject, the matter can be further 



