162 NATURE STUDY 



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the time is sent out in the same way over regions assigned to each 

 center. 



The story of the discovery of the properties of the pendulum 

 and the effect of its application to time keeping, could be made 

 interesting and profitable. (See Encyclopedia, etc.) 



The relation of the pendulum to falling bodies; the 

 effect on the pendulum if the earth were heavier or lighter or if 

 the pendulum were near or farther away from the center of the 

 earth, are subjects which might be taken up in some of the grades 

 under certain conditions, but would perhaps better be deferred at 

 present. 



Soap Bubbles. 



Blowing soap bubbles is a fascinating exercise for almost 

 any grade, and may be repeated without fear of tiring. They 

 are so familiar to every one that how to make them and what to 

 do with them need hardly be told. It might be worth while to 

 say that for making very tenacious bubbles that will become very 

 large and stand rough handling, use very good soap and rain- 

 water or distilled water. Slice the soap into shavings and make 

 a very strong solution, and mix with this a good quality ot 

 glycerine or molasses; the latter is better. It is wonderful what 

 may be done with these bubbles. 



Bubbles show the tenacity of liquids (try pure water, alco- 

 hol, glycerine, or molasses alone). As the bubbles grow older they 

 become very thin in their upper parts, showing brilliant colors, 

 due to interference of light (see text-books on Physics). They 

 may be made to contain different gases, e. g., air, carbonic acid, 

 illuminating gas, hydrogen, and thus used to show which is lighter 

 than air. To blow bubbles with these gases is somewhat trouble- 

 some, as gas bags or reservoirs filled with the gas under pressure are 

 necessary. The clay pipe is connected with a tube from the reservoir, 

 and the gas turned on as required to fill out sufficiently the bubble. 

 One may be fortunate enough to have the gas come off from the 



