MOVEMENTS OF IRRITATION. 



465 



from possibly dried up oil (the apparatus must be kept in a place 

 as free from dust as possible). Petroleum is very good for the 

 purpose. 



To the shaft is now fixed the metal disc Mscli, which is 

 about 17 cm. in diameter. This disc, seen from above in Fig. 156, 

 is provided in the neighbourhood of its periphery with three slots, 

 in which the three flower-pot supports can move. Each of these 



FIG. 155. Centrifugal apparatus. 



supports consists of a vertical rod, which at the base, as indicated 

 in Fig. 156, carries a metal plate ; a screw situated below the 

 disc (the three screws are lettered q, r, s), and serving as a 

 clamp ; and a sliding piece (the three sliders are lettered #, 

 ft, and r), to fix the flower-pot after it has been placed on the 

 disc. If the rotation is required to be in the vertical, instead of 

 in the horizontal plane, so as to eliminate the influence of gravity, 

 the shaft must be fixed horizontally. This is managed by loosen- 

 ing the set screw Sch, removing the pin St, turning the shaft 

 P.P. H H 



