AIR PUMPS AND APPARATUS. 



207 



Fig. 204. 



Guinea and Feather Experiment. (Fig. 204.) This in- 

 strument consists of a tall glass receiver, open at the bottom, 

 and having the top closed, so as to be air-tight, by a brass 

 cap or cover, through which passes a wire, fitting close, but 

 capable of being turned without admitting the air. The 

 lower end of the wire is made to support a small stage, the 

 two sides of which will fall and separate, when the wire is 

 turned in a transverse direction. Then, the stage being fixed, 

 a sovereign and a feather, or any two small bodies differing 

 greatly in their comparative weight, may be laid on the stage, 

 and the bell-glass, or, as it is called, receiver, being placed 

 on the plate of an air pump, must be 

 exhausted of the air it contained. This 

 being done, if the two bodies are 

 made to fall by turning the wire, it 

 will be found that they will both strike 

 the plate of the air pump beneath 

 them at the same point of time. 



Price, $10.00. 



Guinea and Feather Tube. This 

 piece of apparatus (Fig. 205) consists 

 of a strong glass tube, usually from 2 

 to 4 feet long, and 1 to 3 inches in 

 diameter, closed at the upper end, and 

 having a brass cap and stop-cock at 

 the lower end, with a screw plug, of 

 sufficient size for the introduction of a 

 guinea and feather. To use, turn the 

 tube up, and it will be observed that 

 the feather is several seconds longer 

 in falling than the guinea ; connect 

 the stop-cock with the air pump, and exhaust the 

 tube, and it will now be found that the guinea 

 and feather fall at the same instant. Air may 

 also be condensed within the tube by a con- 

 densing pump, and a greater difference shown 

 than in the first experiment. 



The apparatus described as the aurora tube is often used 

 for showing these experiments, though the ball and the 

 point, at times, interfere with the descent of the feather, and 

 piece of metal, which is not the case in the proper tube. 



Price, $4 and $6. 



