Astronomical and Nautical Collections. 109 



For those who are acquainted with the Greenwich observations, 

 and who compare them with the critic's remarks, every further ex- 

 planation would be superfluous ; but since it may be supposed 

 that these remarks will fall into the hands of many persons not 

 deeply versed in astronomy, I readily comply with the request 

 Which you made, that I would commit to writing our common view 

 of the subject. I feel, as well as yourself, the propriety of doing 

 my best on the occasion, in order that too great importance may 

 not be attached to this censure of an establishment, to which 

 astronomy is indebted for a great proportion of its advancement; 

 and that its importance cannot be very great, is sufficiently shown 

 by the facility with which Mr. Olufsen has computed the declina- 

 tions of the fundamental stars, as published in the Nachrichten, 

 No. 73, from the Greenwich observations for 1822. 



The greater number of the errors which have been pointed out by 

 the censor, are merely accidental errors of the pen. Errors of this 

 kind are certainly disagreeable, and it would be better if they 

 could be entirely avoided ; but since all collections of observations 

 in existence do contain such errors, they clearly appear to be una- 

 voidable. 



The first class of errors mentioned in the Philosophical Maga* 

 tine contains the cases in which the mean deduced from the read- 

 ings of the two microscopes A and B differs from the column in 

 which that mean is assigned. Since there must be some manifest 

 oversight in all these cases, it may sometimes be difficult to de- 

 termine whether it is in the readings or in the mean assigned ; but 

 it will, in general, be easy to distinguish, from the preceding or 

 following observations of the same star, where the error lies. 



The second class contains the differences between different 

 records of the same observation. These must be errors in the 

 copies sent to the press, and not in the readings of the microscopes ; 

 and they may generally be corrected by a comparison of the two 

 passages : they sometimes extend to whole degrees, or to the tens 

 of the minutes, and are then of no importance ; for example, in the 

 observations of Procyon the 23d Feb. 1821, and of $ Cephei the 

 8th Dec. where there are errors of 30° and 5° respectively. 



