432 M. Bessel on the Declination of the Stars. 



Your idea, that a new catalogue of declinations ought al- 

 ways to be accompanied with a detail of oui" own investiga- 

 tions on refraction, perfectly accords with my own; but 

 Dr. Brinkley as well as myself have actually caused such in- 

 vestigations to accompany our papers ; and I therefore cannot 

 conceive how the author of the paper in Tilloch's Magazine 

 can still apprehend any considerable error from this circum- 

 stance. 



I certainly am not so fully acquainted with Dr. Brinkley's 

 investigations on refraction as with my own : nevertheless it 

 appears to me, that, in case both instruments really indicate 

 exactly equal zenith distances, an error of l",2 in one of the 

 two determinations for 45° cannot be allowed : but if it be al- 

 lowed for the sake of reconciling both catalogues, then it 

 proves plainly, that both instruments do not indicate equal 

 zenith-distances. — I have examined my own very particularly, 

 as you will see from the seventh section of my Observations, 

 with regard to the absolute correctness of the reading {Atigabe), 

 and have indeed discovered a trifling bend in the telescope, on 

 account of which there must be added to the direct reading 

 {Angabe) u of the circle, + ]",11 sin. {u + 1° 33') -f-0",26. 

 Cos. {ti+l° 33'); if this correction be omitted, my polar- 

 distances would also thereby become smaller, and approach 

 nearer to those of Dr. Brinkley's : but this is quite contrary to 

 my observations, which do not allow the application of a par- 

 tial alteration, without destroying the accordance in some other 

 part. 



The apprehension of the author of the account in the Phi- 

 losophical Magazine, that there might arise, from the faults of 

 meteorological instruments, a difference in the determination of 

 the constant of refraction, is undoubtedly well grounded : but 

 he observes very properly, that even this would not explain 

 the difference of declinations, inasmuch as each observer ap- 

 plies his own refraction. However, as far as concerns my own 

 meteorological instruments, the barometer is undoubtedly cor- 

 rect to a very minute quantity, both according to its construc- 

 tion and as to its being compared with other good instruments. 

 The thermometer I have examined most minutely, agreeably 

 to a method peculiar to myself, as described in the 7th section 

 of my Observations; which does not leave an error of 0**,! 

 Fahr. undiscoveretl. I could wish that every observer would 

 make use of this method ; and at the same time desist from the 

 disadvantageous practice of computing the tables of refraction 

 for the position of the interim- thermometer : by these means 

 the different determinations of refraction could be correctly 

 compared, and a new trial of the correspondence of the ob- 

 servations 



