THE CEBIT OF NEPTUNE. 



51 



The maximum value of &v being less than 30", the first term will be entirely 

 neglected. The value of &r sometimes amounts to .018, so that the correction 

 arising from the second term may sometimes amount to 0".ll. We shall, there- 

 fore, take account of it in a few cases. 



The ephemeris which will be compared with observation in order to deduce 

 normal places of the planet will be the same with which the Greenwich obser- 

 vations are compared, namely, "Walker's ephemeris until the year 1854, and 

 Kowalski's ephemeris in subsequent years. It will be remembered, however, 

 that these ephemerides are used only for the purpose of obtaining normal places, 

 and in order to save the trouble of comparing every individual observation with 

 the provisional theory. 



25. Mean corrections of the Ephemeris of Neptune given by observations at the 

 different observatories, without correction for systematic differences. 



