THE ORBIT OF URANUS. 



Ill 



"VVhcre no declination has been observed the observed corrections in right ascen- 

 sion have been clianged to corrections in longitude on the hypothesis that tlie 

 theoretical latitude is correct. The approximate formula is 



, , ^a cos f> . 

 cl = . — rr , where 

 sni Ij 



cos E =z sin e cos a, e being the obliquity. 



DISCUSSION OF THE MODERN OBSERVATIONS. 



Rednctinn of the PuhlLshed liesidts of Observations to a Uniform Si/siem. 



We have now to discuss the great mass of observations made at the principal 

 observatories of the world since tlie discovery of the planet by Herschel, in 1781. 

 To make all the data of reduction rigorously homogeneous and uniform, it would 

 be necessary to completely re-reduce the greater part of the observations made 

 before 1850, using the modern values of the constants of reduction, and to com- 

 pare each observation separately with the geocentric place deduced from the pro- 

 visional theory. Such a reduction and comparison would be extremely desirable. 

 Their execution would, however, involve an amount of labor far greater than it is 

 now possible for the author to bestow upon the problem. We must, therefore, 

 adopt the reductions which have been already made, applying such systematic 

 corrections for reduction to a uniform system of star places as we have the means 

 readily to determine. No reduced places are employed unless Ave can find data 

 for some more or less accurate determination of these corrections, a rule which 

 necessitates the rejection of a great mass of observations made at the minor obser- 

 vatories of the European continent, and published in the Astrovomi'ichcn Nach- 

 richten. We still have the following rich collection of materials at our disposal : 



