Manchester Memoirs, Vol. xlvi. {igo2), No. \i^. 9 



but a small percentage of their number would have an 

 intellectual perception of this simple astronomical truth. 

 Hence the sporadic attempts that are made at different 

 times to disprove the truth of the moon's axial rotation 

 as well as the diurnal rotation of the earth.* Now the 

 gyroscope affords another demonstration in addition to 

 those already given, and is valuable in presenting negative, 

 as well as positive, proof of the rotation of the moon by 

 showing its synodical revolution without axial rotation. 



Let a small globe or other symmetrical object be placed 

 in the centre of a table, and let the gyroscope, at rest, 

 with its stand, be moved horizontally in a circle round 

 the globe, so that the same face of the disc and one side of 

 the stand are always presented to the central globe, in like 

 manner as the moon does to the earth. A spectator 

 outside the circle, will then see every part of the disc in 

 succession just as if he were placed outside the moon's 

 orbit. Now if the disc be rapidly rotated, to preserve 

 the fixity of its vertical plane of rotation, it will 

 revolve round the central body without rotating on its 

 axis ; the relative positions of the bodies will now be 

 reversed, as every part of the disc will present itself in 

 succession to the central globe, while the same face of the 

 disc will always present itself to a spectator outside the 

 circular orbit. Moreover, the stand on which the vertical 

 spindle of the gyroscope is supported will make one 

 revolution round the stationary vertical spindle during 

 its orbital motion round the globe, thereby affording, 

 simultaneously, positive and negative proof of the moon's 

 axial rotation during its synodical revolution. 



In few departments of knowledge has the antagonism 

 between the simianism of the race and natural truth been 

 * De Morgan's Budget of Paradoxes. 



