1918] on The Spinning-Top in Harness 287 



si rixji est, ubi tu pulsas, ego vapulo taut am " ("A fight where I 

 hold out my head, for von to whack it.") 



Grasp the stalk, and brandish it, with the wheel at rest. Xo 

 gyroscopic effect is felt : the wheel is inert. But give it a spin first, 

 gently at a start with the novice, as the result will take him by 

 surprise when the stalk is brandished. It flies to one side or the 

 other. 



I avail myself here of the priviletje of addressing a learned 

 audience, and so employ some of the technical jargon of our science. 

 Represent the angular velocity and momentum of the spinning-wheel 

 by a right-handed screw vector, as also the axis of an applied couple. 

 By a vector that is right-handed we mean one such that the direction 

 of the vector is the advance with a right-handed screw propeller. 



Then if the wheel is swung | j^^^,^^^^. .A an angular momentum 



is communicated about an axis drawn to the < i^., >, and the axle 



swerves the same way Vl^r^ [ unless prevented by a couple 



given by the hands, represented by an axis drawn jfiQtvnwardr 



Swuncr to the VIK^ i, ansfular momentum is communicated about a 

 ° ( left y ^ 



(downward) • ^ ^^ ^ (down ) -^ • <- v.^ 



< 1 > axis, and the axle swerves < >, and reuuires to be 



( upward j ' ( up i' ^ 



held < T \ ( by a couple with axis to the < i°,., >. 



With two screws on a ship or flying-machine they are generally spun 

 opposite ways, so one of them will be left-handed. On a left-handed 

 screw these directions are reversed, and we should get into confusion. 

 Better, then, keep to the right-handed screw of ordinary practice, 

 in any popular explanation. These are influences felt in a flying- 

 machine, especially if provided with a Gnome revolving motor — 

 a spinning-top in harness. The name Gnome seems to have been 

 anticipated by Pope, in his lines 



" Know, then, unnumbered Gnomes around thee fly, 

 The light militia of the lower sky," 



in the poem of the " Rape of the Lock." 



Putting the helm (joy-stick the airman calls it) of the flying 

 machine to port, as a sailor would say, a couple is called up from the 

 rudder tending to turn the head to starboard, and the couple axis is 

 downward, and the nose of the machine dips. To ascend, the helm 



must be put to starboard. But to turn the machine to < „ ' ' i 



by utilizing the gyroscopic domination, a horizontal rudder must be 



used, and its helm put < > vertically. 



