Methods of correcting Lunar Observations. 371 



, The process, with and without these corrections, will stand 

 thus : — 



true dist. 32 25 13 137665 137468 



It appears, therefore, that the neglect of these corrections, 

 especially of that which depends on the density of the atmo- 

 sphere, may easily produce an error of more than a minute in 

 the moon's distance, which corresponds to half a degree of lon- 

 gitude ; and it must be highly worthy of the attention of a 

 practical navigator to enable himself to avoid errors of such 

 magnitude in extreme cases. The errors independent of the 

 density amount, in this example, to about 20", which is double 

 the supposed greatest error of the existing tables of the moon's 

 motion ; so that the habitual correction of these errors is in 

 factof greater practical importance than the attainment of abso- 

 lute perfection in the lunar motions without this attention. 



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