



31] INCREASING ERRORS OF HANSEN'S LUNAR TABLES. 263 



Whereas, according to Mr Stone's theory, this ratio should be 



n 



It has been already remarked that it is convenient practically to deter- 

 mine the mean solar time from the sidereal time, but in order to do this 

 correctly, it is of course necessary to employ the correct value of the Sun's 

 mean longitude. At the present time Bessel's value of the Sun's mean 

 longitude is about S- 6 in error, and therefore the mean solar time 

 inferred by means of it from the sidereal time would be in error to the 

 same amount. The mean longitude found from Le Verrier's Tables is much 

 nearer to the truth, and therefore the mean solar time found from the 

 sidereal time by using this value would be much more nearly correct. 



It must not be forgotten however that, as we have already stated, 

 the mean solar time may be derived from observations of the transit of 

 the Sun over the meridian, without employing the sidereal time at all. 

 Apparent solar time, which is found directly from observation of the Sun 

 is converted into mean solar time by applying the equation of time, which 

 is known from the solar theory, without reference to the sidereal time. 



