196 ' ' MEASURING APPARATUS OF THE 



discussed with his governor what lie was to be taught, but that author 

 must be left to speak for himself, for it is impossible to improve upon his 

 delicate irony by any description. 



" Mais qu' apprendra-t-il done ? Car encore faut-il qu'il sache 

 quelque chose; ne pourroit-on pas lui montrer un peu de geographie? 

 A quoi cela lui servira-t-il ? repondit le gouverneur — quand Monsieur le 

 Marquis ira dans ses terres, les postilions ne sauront ils pas les chemins ? 

 ils ne r egareront certainement pas." 



We are all acquainted with what is called the precession of the equi- 

 noxes. The mean annual precession is the joint effect of the Sun and 

 Moon, acting on the protuberant portion of matter about the equator, and 

 is determined by iinding how much any particular star has retrograded 

 in right ascension, by a comparison of observations made by the older 

 astronomers with those made in recent days. 



But Bradley never would have been able to separate the inequalities 

 wliich he detected only in heaps and parcels into the atoms of aberration. 

 Solar and Lunar nutation, and inequality of precession, unless he had 

 had an approximate value for the excess of matter at the equator, and 

 it cannot be doubted for a moment that the nearer we approach to the 

 real value of this astronomical datum, the more truly we shall be able 

 to assign the amount of the effects which are produced by it. 



Not to tarry too long at this part of the subject it will suffice to notice, 

 that on account of the ellipticity of the earth's meridians, the direction 

 of gravity is not towards the centre, and that in the determination of 

 Lunar parallaxes it is necessary to compute the angle, which the normal 

 makes with the diameter drawn to any point on the surface, but this 



