S Y N' 



from astronomical observation ; since the best instruments could not 

 have given the zenith distances nearer than about one second, answer- 

 ing in these parts to lul feet on the, surface of the earth. 



TABLE 



Qftho fli-f.n-jit I -> norths of a degree, as measured in various parts of the 

 earth, (,\ fane of its measurement, the latitude of Us middle point, fyc. 

 (Bar 



SYNODIC A L revolution of the planets. 



1. If two planets revolve in circular orbits, to find the time from con- 

 junction to conjunction. 



Let P = periodic time of the earth, p that of the planet, suppose an 

 inferior, t tlie time required j then 



- 



V-p 



For a superior planef, 



t = - 

 290 



