OF CAMBRIDGE OBSERVATORY. 279 



for the single correction, of the co-latitude ; and the co-latitude thus 

 corrected is 37° . 47' . 8",24, or the latitude 52°. 12'. 51",76. This result 

 I conceive to be correct within a small fraction of a second. The 

 number of circumpolar stars used for this determination is 10, and 

 the whole number of observations 917. 



In describing the process by which I have arrived at the above 

 result, it has been my wish to present to the Society not only a 

 determination possessing considerable local interest, but also an account 

 of instrumental anomalies which are of general scientific importance. 

 In further illustration of the latter point I will allude to the dis- 

 cordances in the determinations of the obliquity of the ecliptic. It 

 is well known that most astronomers have found the obliquity smaller 

 from observations at the winter solstice than from those at the 

 summer solstice. Now if I had used only the latitude found from 

 direct observations of circumpolar stars, and had applied no correction 

 to the observations of the Sun, I should also have found two values 

 for the obliquity discordant by about 5", the winter obliquity being 

 the smaller. With the corrections above described, (and which were 

 formed entirely from observations of stars, and before I had even 

 examined my sun observations) the two values of the obliquity 

 agree within 1". I might have altered the corrections so as to re- 

 move part of this discordance, but I prefer leaving them in 

 the shape in which they were given by independent considerations. 

 Indeed if I had confined myself to the January observations for the 

 winter solstice, and omitted those of December when the correction is 

 less certain, the discordance would wholly have disappeared. A very 

 small alteration of the constant of refraction (such as would not alter 

 the latitude much more than 0",1), or a very small alteration in the 

 law of refraction (which would not be sensible in the latitude) would 

 remove this difference. But I hardly venture to assume that obser- 

 vations of the Sun, near the winter solstice, can be relied on to this 

 degree of accuracy. 



I will only add, in conclusion, that I believe the method which 

 I have used to be the only one of those in practice from which a 



