FOR THE USE OF TEACHERS. 



No. 12. 



Leaflet 



On Nature Study. 



Especially Adapted to the Use of Children in Schools 

 IN Rural Districts. 



PREPARED BY THE 



FACULTY OF PURDUE UNIVERSITY. 



A TALK ABOUT WATER-DROPS. 



By Prof. A. Wilmer Duff. 



What is a water-drop? To experiment is to try for yourself, and 

 as that is the surest way of learning anything, we shall begin with an 

 experiment. Dip your finger into water and withdraw it, and you will 

 be able to see the shape of the drop that forms at its end. It is 

 round like a glass bead except just where it hangs to your finger, and 

 if you watch it carefully you will see that, just when it gets free from 

 your finger, it is nearly perfectly round. If you let it fall on a piece 

 of glass it will form a circle. If you could see it while it is falling 

 you would find that it is nearly a perfect sphere. If I let water from 

 the end of a stick gather and form a drop, while the end is in a glass 

 of parafiin oil, you will be able to see a much larger drop hanging 

 from the stick and you will find that it is nearly quite round. 



Such, too, is the shape of a rain-drop while it is falling. You may 

 try this the next time it is raining by holding a sheet of paper so as 

 to catch some of the drops. We can, however, learn still more from 

 the drops formed at the end of the finger. Watch a few and you will 

 see that each drop seems to have some difficulty in tearing itself away 

 from the water that remains. The drop has to grow quite large and 

 heavy before it can by its weight pull itself free. It is evident, thea, 

 that water holds together with considerable force. It is, in fact, this 

 force which causes the drops to become round, for it makes the parti- 



NOTE.— This leaflet will furnish material for several short lessans. 



