288 



BODIES FALLING IN VACUO 



of the air-pump ; or a similar tube, with a well-groui 

 edge at one end, may be simply placed upon the plate, tl 

 other end being provided with a cap of a peculiar coi 

 st ruction, shown in fig. 192. Inside this cap there is 

 small plate j?, which moves about a hinge c. Throiu 

 a so-called ' stuffing-box ' s, passes a moveable bi 

 rod carrying a small bracket a, which supports 

 plate p until the exhaustion is complete; two obje< 

 differing considerably in weight, as for example a coin 

 and a feather (hence the apparatus is often called the 

 'guinea and feather apparatus'), are placed upon the 

 plate before the experiment commences. As soon as the 

 air is exhausted the bracket a is turned into the positioi 

 indicated by dots, the plate drops, and both bodies fal 

 with equal velocities. The apparatus has the disad vantag< 



FIG. 192 (an. pro}. $ real size). . 



that it must be taken off the plate, set up again, an 

 exhausted every time that a repetition of the experirnei 

 is desired an operation which is rather tedious, but 

 demonstrates the fact in a very beautiful manner. 



