4 6 



SCIENTIFIC RECREATIONS. 



which I turn upside down (fig. 40). What follows ? The water rises in 

 the glass. Why ? Because the burning of the paper having absorbed a part 

 of the oxygen, and the volume of confined gas being diminished, the pressure 

 of the outer air has driven back the fluid. I next fill a goblet with water up to- 

 the brim, and cover it with a sheet of paper which touches both the edge of the 

 glass and the surface of the water. I turn the glass upside down, and the sheet 

 of paper prevents the water running out, because it is held in place by atmo- 

 spheric pressure (fig. 41). It sometimes happens that this experiment does not 

 succeed till after a few attempts on the part of the operator; thus it is prudent 

 to turn the glass over a basin, so that, in case of failure, the water is not 



Fig. 40. Pressure of the air. 



spilt. Having obtained a vase and a bottle, both quite full of water, take the 

 bottle, holding it round the neck so that the thumb can be used as a stopper, 

 then turn it upside down, and pass the neck into the water in the vase. 

 Remove your thumb, or stopper, keeping the bottle in a vertical position, 

 and you will see that the water it contains does not escape, but remains in 

 suspension. It is atmospheric pressure which produces this phenomenon. If, 

 instead of water, we put milk in the bottle, or some other fluid denser than 

 water, we shall see that the milk also remains suspended in the bottle, only 

 there is a movement of the fluid in the neck of the bottle, and on careful 

 examination we perceive very plainly that the milk descends to the bottom 

 of the vase, and the water rises into the bottle. Here, again, it is atmo- 



