PHILOSOPHICAL TRANSACTIONS. 



503 



VOL. LI.J 



to the sun, and consequently his latitude and declination, which are both 

 south, must be less in the former case than in the latter ; and therefore, as he 

 passes north of the zenith at the Cape of Good Hope, his zenith distance 

 must be greater in the former season than in the latter, as the observations in- 

 dicated: but, in March and April, when Sirius is in quadrature with the sun, 

 and equally distant from the sun and earth, his apparent latitude and zenith 

 disance must be the same as the true, or that which would obtain, if the earth 

 was translated to the sun, and consequently, a mean between the zenith dis- 

 tances in July and December, agreeably to the observations. 



Mr. M. then lays down the observations themselves, with the calculations 

 which he made of of the values of the parallax for each, the maximum being 

 assumed Qf\ which he found would best reconcile the observations with one 

 another. 



The first column shows the year and day of the observations ; the 2d the 

 zenith distances of Sirius at the Cape of Good Hope, as delivered in Abbd de 

 la Caille's recital ; the 3d contains the computed values of the parallax at dif- 

 ferent times, taking that of the maximum of'; the 4th column gives the observa- 

 tions reduced to the mean, by applying the parallax computed in the 3d column 

 to the observations in the 2d ; which quantities ought all to agree together, if 

 the observations were liable to no error, and the parallax was rightly assumed : 

 but, taking a mean of them all, the last column shows how much each of them 

 differs from that mean, which in general is very small, and scarcely exceeds 2", 



