PHYSICAL ANt) LITERARY. 197 



of the atmofphere, made the mean di- 

 ftance of the moon lefs by 4 femidiame* 

 ters of the earth than it really is. It is 

 true, Mr Caflini's obfervation in 1655, 

 compared with late ones, raiakes it vary 

 at the rate of SS'^ in 79 years. Let us 

 therefore fee, if a variation, fuch as that 

 arifes from MeflT. Caflini's and Goden's 

 obfervations, be not a confequence of 

 principles already eftabliflied in the folar 

 fyftem ; and offer fome hints of a method 

 by which it may be afcertained whether 

 this be the jufl folution of this queflion, 

 and how, from a proper feries of obfer- 

 vations, made with great exadlnefs, an 

 improvement and corredlion in geogra- 

 phy and navigation may be deduced fromi 

 this inquiry, by bringing the theory of 

 the earth's motion in her orbit, and 

 particularly what relates to the declina- 

 tion of the lun, to greater perfedlion. 

 This will be the more ufeful, that the u- 

 fual methods of taking the latitude of 

 places by the fun's meridian altitudes, 

 fuppofes the tables of his declination to 



be 



