512 JAMES CLERK MAXWELL. 



by inserting it in a hole in one of the spokes of that wheel. 

 There is also a handle H, which is in one piece with the wheel 

 T, and serves to turn the axle. 



Now suppose the pin P taken out, so as to allow the 

 cranked axle to turn, and the pin Q inserted in its hole so as to 

 prevent the wheel R from revolving ; then if the crank C be 

 turned by means of the handle H, the wheel T will have its 

 centre carried round in a vertical circle, but will remain parallel 

 to itself during the whole motion, so that every point in its 

 plane will describe an equal circle, and all the cranks K will be 

 made to revolve exactly as the large crank C does. Each 

 satellite will therefore revolve in a small circular orbit in the 

 same time with the handle H, but the position of each satellite 

 in that orbit may be arranged as we please, according as we 

 turn the wire which supports it in the end of the crank. 



In Fig. 8, which . gives a front view of the instrument, the 

 satellites are so placed that each is turned 60 farther round in 

 its socket than the one behind it. As there are thirty-six satel- 

 lites, this process will bring us back to our starting-point after 

 six revolutions of the direction of the arm of the satellite ; and 

 therefore, as we have gone round the ring once in the same 

 direction, the arm of the satellite will have overtaken the radius 

 of the ring five times. 



Hence there will be five 

 places where the satellites 

 are beyond their mean dis- 

 tance from the centre of the 

 ring, and five where they are 

 within it, so that we have 

 here a series of five undula- 

 tions round the circumfer- 

 ence of the ring. In this case 

 the satellites are crowded 

 together when nearest to the 

 centre. . . . 



Now suppose the cranked 

 axle C to be turned, and all 

 the small cranks K to turn 

 with it, as before explained, 



every satellite will then be carried round on its arm and in the same 

 direction; but, since the direction of the arms of different satel- 

 lites is different, their phases of revolution will preserve the same 

 difference, and the system of satellites will still be arranged in 

 five undulations, only the undulations will be propagated round 



