20 



Introduction to the Sixth Section 



The differences of the results obtained in the different po- 

 sitions of the circle and in both passages are commonly small, 

 and easily to be reconciled with the probable errors above 

 given. Differences amounting to a second of a great circle 

 are, notwithstanding the frequently small number of observa- 

 tions, rare, and occur only about once in nineteen times at 

 those altitudes where the proximity of the horizon has no in- 

 fluence on the observations : usually the differences go on 

 without any regularity ; but sometimes they appear to follow 

 some law, e. g. from 60° to 80° declination, in the upper pas- 

 sage and eastern position of the circle. Its small amount, 

 however, would render any further conclusions very difficult, 

 especially as it can hardly be doubted that the errors arising 

 from the instrument itself are mixed with others which are as 

 yet unknown. I believe, therefore, that the severe test to which 

 this instrument has been subjected, warrants the conclusion 

 that the deviation of the line of collimation from a circle, if 

 any exists, is too small to be determined by observations. 



As a transit, this beautiful instrument completely fulfills 

 every thing that can be required. It gives the right ascen- 

 sions, whether the stars are observed above or below the 

 pole, whether the circle is in its eastern or western position, 

 by a comparison with the fundamental catalogue, with such a 

 near agreement that no decided difference can be assigned. 



7. Place of the Meridian Mark. 



The same equations which were employed for determining 



the collimation, likewise give 15A« or the eastern deviation 



of the mark from the meridian. I have determined it so as 



to compare every period with the preceding and following 



The 



