138 jNIii. E. Hunt on certain Phenomena connected tvilh 



perhaps inclined downwards, at an angle of about 45 °. In the gyroscope, 

 however, the weight is actually carried round horizontally : — the expla- 

 nation is therefore still incomplete. In proceeding to carry it a step 

 farther, I must first observe, that as the application of a downward 

 pressure on the end of the spindle A a gives it a tendency to turn round 

 horizontally towards c c, if this movement is prevented — by making the 

 spindle end move in a vertical groove, for example — a pressure correspond- 

 ing to the weight, or to the horizontal or precessional motion it tends 

 to produce, will obviously be exerted against the side of this groove — as 

 may also be proved by experiment. The weight also moves down the 

 groove, in consequence of the supporting power not being called into 

 play, and carries tlie spindle of the gyroscope with it. Now, the action 

 of the centrifugal resultant akeady pointed out, as tending to turn the 

 spindle round horizontally, is precisely that of a separate external pressure, 

 tending to turn the already rotating wheel about a vertical axis, and conse- 

 quently, according to the principle of the composition of rotatory motion, 

 the wheel will tend to turn about a new axis, lying between its original 

 horizontal axis and the vertical axis. As in the case already considered, 

 in which the weight constituted the external pressure, the spindle will 

 tend to move towards this new axis — that is, the end of the spindle to 

 which the weight is applied will tend to turn upwards. Now, if this 

 upward motion were prevented by a horizontal groove, an upward pres- 

 sure would be exerted against the groove, and the spindle would move 

 horizontally. The weight itself obviously acts the part of the horizontal 

 groove, and its downward pressure obviously meets or sustains the 

 upward pressure, whilst the spindle consequently moves horizontally. 

 Instead of saying that the weight sustains the upward pressure, we 

 ought of course rather to say that the upward pressure derived from 

 the unbalanced centrifugal force, or the centrifugal resultant called 

 into play by the weight, sustains that weight, or prevents it from oscil- 

 lating vertically as in the case of the perfect sphere. 



The upward pressure due to the horizontal or precessional motion of 

 the spindle is in proportion to that motion ; and if an attempt is made 

 to accelerate that motion, the upward pressure will be increased, and 

 becoming greater than that of the weight, will lift the latter. If, 

 on the other hand, the horizontal or precessional motion is retarded, the 

 upward pressure will be diminished, and becoming less than the weight, 

 the latter will fall. These results may be easily verified on the Bohnen- 

 berger instrument. The friction of the pivots of the outer ring retards 

 the horizontal or precessional motion, and the weight gradually descends. 

 It is not, as might be supposed, the diminution of the rotatory velocity 

 of the wheel which causes the weight to gradually descend. The pre- 



