Currents of Air. 



The movements of the air due to heating portions of it may be illus- 

 trated in many ways. To detect the currents of air some substance 

 which will burn slowly giving oflf smoke without flame is very useful, 

 such as cotton rags or strings twisted together. Paper may be pre- 

 pared by soaking strips of blotting paper, or carpet paper in a solution 

 of potassium nitrate (salt petre). The strips are then dried. On light- 

 ing they will burn without flame. The little sticks used to light fire- 

 crackers with will answer. Now with the lighted smoke-paper, the cur- 

 rents of air ascending from a candle flame or lighted lamp, and those 

 approaching the flame from the sides may be detected. The currents 

 above a stove, register or radiator may be studied. Even those about 

 the body of a pupil sitting still may be seen. The different places 

 about the room may be examined to learn just where the air is coming 

 into the room, such as open doors, windows, cracks about these, or 

 openings of ventilators. A thorough going over the room exploring 

 the air for currents will give a good foundation for future lessons on the 

 larger operations occurring outside of the room, that is, the winds; and 

 will also be the basis for lessons on ventilation to follow in time. 



The hot air balloon shows how masses of warm air may rise to great 

 heights. The children will take great delight in making a tissue paper 

 balloon. It can be filled with air in the schoolroom by holding it over 

 the stove or a lamp. It will rise to the ceiling and on cooling will 

 slowly descend. If, when it is filled, it be suddenly inverted the warm 

 air can be felt rushing up, while the cool air will crowd the sides 

 together with considerable force. 



The sending up of such a balloon with cotton soaked with some com- 

 bustible fluid is somewhat dangerous in a city as it may catch fire. It is 

 very dangerous in the dry season in the country where there is standing 

 grain. Still the balloon may be sufi&ciently filled with hot air by hold- 

 ing it over a stove to send it up quite a distance. 



The coverings of animals are adaptations to the conditions of their 

 life, and are all interesting objects of study. Hair, scales, thick epider- 

 mis, bony plates, spines, and feathers of various forms are in endless 

 varieties. 



Feathers are characteristic of birds and are very interesting when 

 their true meaning is seen. For a lesson on feathers, a bird freshly 

 killed, e. g., a duck or fowl from the market, and a quantity of feathers 

 sufficient to allow each pupil to have examples of each kind in hand 

 during the lesson. If the question were asked: "What is the use of 

 feathers?" the answer that will usually come is: "To keep the animal 

 warm." This is one use of feathers, but the lesson is to show that this 

 is by no means the only one, perhaps not the most important one. (The 

 uses are not to be told, but if possible to be brought out by the observa- 

 tion of the pupils.) 



