A YEAE IN SCIENCE 



67 



stop-cock. Try to separate the hemispheres. What 

 do you find? Open the stop-cock and try to separate 

 the hemispheres. How does this result compare with 

 the result obtained in the first instance? How do you 

 explain these r.esults? 



B. Fill the tin can with water to a depth of two 

 inches. With the aperture open, place the apparatus 

 over the Bunseii flame and heat until the water boils. 

 Tightly close the aperture and remove the apparatus. 

 Let it cool and note what happens. How do you 

 explain the result? 



Exercise 40. Barometer. (Demonstration.) 

 Object: To study a means of measuring atmospheric 

 pressure. 



Apparatus 



If! 



Mercury 

 Glass dish 

 Torricellian tube 



Barometer 

 Meter stick 



Directions: Fill the Torricellian 

 tube with mercury. Carefully close 

 the open end with the thumb and 

 invert the tube into a basin of mer- 

 cury. Remove the thumb from the 

 open end of the tube under the 

 mercury in the .basin. Measure the 

 height of the column of mercury in 

 the tube above the surface of the mercury in the 

 basin. What keeps the mercury in the tube? Would 

 the same results be obtained if both ends of the tube 

 \\cre open? 



Fig. 24. 



