Astronomical and Nautical Collections. Ill 



Nachrichten, NO. 73 ; the differences between the latter days of 

 July and the beginning of August, 1821, depending on a change 

 of this kind, so that they cannot be considered as accidental errors 

 of observation, nor are they of material importance, as they may 

 be readily determined by a series of observations of the pole star, 

 so complete as those which are made at Greenwich. The acci- 

 dental irregularities of the polar distances, which remain after the 

 correction of the place of the pole, can be as little considered as an 

 imputation on the accuracy of the observer, as those of the inter- 

 vals of the micrometer wires. The truth of this remark is illus- 

 trated in the Nachrichten, No. 73. 



The fourth class contains the differences between the times of 

 transits observed with the transit telescope, and the mural circle. 

 The latter instrument, however, not being intended for the obser- 

 vation of transits, nor being ever actually so employed, it would 

 have been of no manner of use to seek for greater accuracy in the 

 memorandums which are made merely with a view of determining 

 its place with respect to the meridian. We ought to acknowledge 

 the occasional insertion of these memorandums with gratitude, as 

 they assure us that the instrument never deviates so much from 

 the meridian as to aft'ect the polar distances ; but they are not in- 

 tended for any other purpose. Neither Bradley nor Maskelyne 

 have ever noted the times of the transits by their mural quadrant, 

 although it was more liable to variation than the mural circle. But 

 to correct the place of the axis of this circle continually, so as to 

 bring it perfectly into the plane of the meridian, would certainly be 

 of no advantage to the Greenwich observations. 



Other errors which are criticized, for example, those of the 

 names of the stars, of the hour or minute of their transits, and so 

 forth, are of no material importance whatever ; and how difficult 

 it is to avoid errors of this kind, may be inferred from the circum- 

 stance of my having found about 1400 such errors in Bradley's 

 observations. [The catalogue of these errors is already printed at 

 the expense of the Board of Longitude, and is to be annexed to 

 the publication of Mayer's original observations, which is nearly 

 completed.] 



