THE ORBIT OF, NEPTUNE. 47 



The above places were reduced to the dates of observation with the constants 

 of the Tabulae Regiomontange. 



The apparent positions of/? Virginia and a Virginis are derived from the same 

 work, correcting the Declination of the latter by + 0".60. The former is not used 

 for index error, owing to its distance from the zone of Neptune. 



Intervals of wires. 







On attempting to test the wire intervals of Lalande, H. C., p. 576, the interval 

 of the third wire was found to exhibit well-marked systematic discrepancies. The 

 observations of May 10 concur very well in indicating a diminution of OMO; and 

 this correction has been applied to Lalande's intervals. The interval for wire 1 has 

 not been changed. 



Deviation of- instrument. 



The next quantity required is the deviation of the instrument from the circle 

 of Eight ascension of the planet. On using Lalande's value of this correction, 

 stars of different altitudes, even in the zone of observation, gave inadmissible dis- 

 crepancies. It is found necessary to reduce the value to less than half. This 

 will be readily seen from the table below. 



Clock error, &c. 



The following tables give, for each star and each date 



The number of wires observed, ^ meaning a doubtful observation. 



The concluded time of transit over the middle wire. 



Lalande's correction to this time for deviation of the middle wire, this deviation 

 being supposed to vanish at the circle reading for Neptune, viz.: 60 7'. 



The correction for deviation actually applied, derived from the comparison of 

 clock corrections given by {$ Virginis and 8 Corvi. 



Seconds of apparent R. A. of star. 



The clock correction, using Lalande's deviation. 



The clock correction, using the concluded deviation. 



The weight assigned to the result for clock correction, depending on the number 

 of wires, and the proximity of the star to the planet. 



For the second observation the deviation is of less importance than for the 

 first, the planet being near the middle of the zone, and the mean of the cor- 

 rections, therefore, very small. 



