224 Mr. South on the Eclipses of [March, 



should the emersion be seen earlier ; a little allowance being 

 made for error of observation : let us see if it were so. 



6 h 43' 50-46" = Emersion at Bushey. 

 + 59*17 = Difference of longitude. 



6 44 49*63 = Blackman-street time when the emersion was 



observed at Bushey. 

 6 43 11*89 = Emersion at Blackman-street. 



— 1 37*74 = the time that the satellite was seen earlier at 

 Blackman-street than at Bushey. 



Hence it appears that the emersion was seen earlier in Black- 

 man-street than at Bushey ; and by an interval of time agreeing 

 with that by which the immersion was observed later, to 1 1 hun- 

 dredths of a second. 



Let us now see how far the results can be converted to prac- 

 tical utility — to what degree of accuracy then, will they enable 

 us to determine the difference between the meridians of the two 

 observatories. 



Im. at Blackman-street = 4 h 35' 3-89" 

 Bushey = 4 32 27*09 



Hence diff. of longitude = 2 36*80 Bushey to the W. 



Em. at Blackman-street = 6 h 43' 11-89" 

 Bushev = 6 43 50-46 



Hence diff. of longitude = 38*57 Bushey to the E. 



Now + 2' 36*80" or W. 

 - 38-57 or E. 



2)+ 1 58-23 W. 



Difference of longitude =0 59*11 Bushey being to W. 



But known difference =0 59- 1 7 



Error of observation = 0-06 at the two Stations. 



Consequently the difference of longitude, between the two 

 observatories of Blackman-street and Bushey, is ascertained to 

 six-hit ndredt lis of a second ; a quantity therefore which we must 

 consider, as the error of observation at the two stations. 



But some time since, the difference of the two meridians was 

 found by the same observers, with the same instruments, and the 

 results will be shown in the following table : — 



