304 



EFFLUX OF GASES 



rotate by rapidly unwinding a string wrapped round 

 the axis of the wheel. 



Cut a circular disc of very thin tin-plate, about 9 cm in diameter 

 make a hole in the middle, and make six incisions from the margii 



FIG. 201 (A., i real size ; B, C, D, real size). 



which do not quite reach to the centre, as in fig. 146 B, page 2<. 

 Bend the blades, as in fig. 146 A, and round off the corners ; if 1< 



