280 PROFESSOR AIRY ON THE LATITUDE OF CAMBRIDGE OBSERVATORY. 



good result can be obtained. Had I determined my zenith points 

 by a floating collimator, the result of observations on Polaris and 

 ^ U. Minoris would have given the latitude more than a second 

 wrong, and the polar distance of every southern body more than 

 two seconds wrong : the result of observations on the Sun would have 

 given nearly the same error in the latitude but with the opposite 

 sign. If a circle reversible round a vertical axis had been used 

 (as at Dublin, Palermo, &;c.) its errors would (supposing the mere 

 circle exactly as good,) have been just as great as if a collimator 

 were employed. The method adopted above appears most valuable, 

 not only because it gives numerical conclusions more accurate than 

 any other, but also because it enables us to observe discordances and 

 to suspect faults which, though they confused our results, might 

 otherwise have wholly eluded our discovery. 



G. B. AIRY 



Obskkvatouy, 



March 23, 1834. 



