THE THEORY OF DIABOLO 567 



other method, makes the direction of spin a matter of perfect 

 indifference. 



I have already referred to the fact that it is necessary for the 

 player to make a half-turn if he would face the spool between 

 every reversal. This is merely another way of saying that the 

 spool maintains its direction in space — that is, it does so if it is 

 perfectly balanced. It is impossible in that case, and provided 

 that it is kept level, to get the spool to veer round to any appre- 

 ciable extent. If the disturbances were a good deal less than 

 they are, it would in this country appear to follow the sun, but 

 at the reduced rate of nearly 12 per hour, in consequence of the 

 rotation of the earth. Though such accuracy is beyond practical 

 attainment, the persistence of direction is very marked. If while 

 spinning the diabolo a person walks round the garden, he will 

 soon find he is getting his arms involved with one another, as the 

 spool will not turn and the sticks must not either. Or if while 

 travelling in the railway along a curve a passenger is spinning 

 a diabolo and maintaining it level, the apparent turning of the 

 spool will indicate the actual turning of the carriage in the 

 opposite direction. A good place to try this is in the " Bakerloo" 

 tube where it enters the Regent's Park in its northward journey, 

 or in the Hampstead tube in the Euston district. 



I have insisted upon the necessity of keeping the spool level 

 when making this experiment. Suppose, for instance, that the 

 far end is down a little and that the usual right-hand spin is 

 being applied, then, as the far end is down to a certain extent, 

 the centre of gravity, instead of being above the string, is on the 

 far side of this position, and gravity tends to topple the spool 

 over on the far side — i.e. to turn the spinning axis so that the 

 far end moves downwards. Just as the tendency of the string 

 support to turn the far end to the right makes it actually rise, as 

 already explained, so this tendency of gravity to make the far 

 end move downwards causes it, in consequence of its rotation, 

 to go sideways, and the particular sideways in this case is to 

 the right. If, then, a player desires to work the spool round he 

 has merely, by thrusting one hand forward, to make one end dip 

 somewhat, and then to keep spinning it in that position, when 

 it will veer round — more quickly if the spin is slow — and then, 

 when it has the required direction, to bring the low end up 

 again by drawing the same hand towards himself. It does not 

 matter whether the spin is right or left handed ; if the right hand 



