618 



RErouT — 1884. 



!r :: 



the motion will bpcnme sliorter and sliorter, and tlio amplitudes smaller and 

 smaller, and the motions will approach more and more nearly those of two perfectly 

 rigid groups of material point.'*, moving through space and rotating according to tlii^ 

 well-known mode of rotation of a rigid body having unoi. .fil moments of inertia 

 about its three principal axes. In one case the ideal i.early rigid connection 

 between the particles is produced by massless exceedingly still" springs ; in the o'^ivr 

 case it is produced by the exceedingly rapid rotation of the lly- wheels in a system 

 which, when the fly-wheels are deprived of their rotation, is perfectly limp. 



Tlie drawings (Figs. 1 and 2) l)efore you illustrate two such material systems.' 

 The directions of rotation of tiie flj'-wlieels in the gyrostatic .«ystem (lig. 2) aiv 

 indicated by directional ellipses, which show in perspective the direction of rotation 

 of the fly-wheel of each gyrostat. The gyrostatic system (fig. 2) might have been 

 constituted of two gyrostatic members, but four are shown for symmetry. Tliu 

 enclosing circle represents in each case in .section an enclosing spherical shell to 



prevent the interior from being seen. In the inside of one there are fly-wheels, in 

 the inside of the other a maissless .spring. The projecting hooked rods* seem as it' 

 they are connected by a spring in each case. If we' hang any one of the systems up 

 by the hook on one of its projecting rods, and hang a weight to the hook of tlif 

 other projectuig rod, the weight when iirst put on will oscillate up and down, and 

 will f, on doing so for ever if the .sy.'teiu be absolutely unfrictir.nul. If we check 



' In fig. 1 the two booked rods seen projecting from the sphere .-ire connected liy 

 an elastic coach spring. In fig. 2 the hooked rods are cnnnet^ted one to each of two 

 opposite corners of a four-sided jointed frame, eaeli nieinber of which carries a gyro- 

 stat so that the axis of rotation of the fly-wheel is in the axis of the member of tho 

 frame which bears it. Kach of the liooked rods in fig. 2 is connected to the frame- 

 work tlirough a swivel joint, so tha.. the wliolc gyrostatic framework may be rotatiii 

 about tlie axis of tlie hooked rods in order to annul tlie moment of momentum o[ 

 the framework about tliis axis due to rotation of the fly-wheels in the gj-rostats. 



^^ 



