264 Mr. Ivory's Remarks on a late Article 



shall say nothing, as they are not contained in my paper; and . 

 I have not had time to examine the calculations. 



There next follows, in the same article, what is called a 

 table of comparative results. Whatever purpose this was 

 intended to serve, it is certain that, as it now stands, it can 

 only mislead. The column, headed 52°, and of course that 

 of differences, should be both struck out. The mean tem- 

 perature of my table is 50° ; and I know no reason why it 

 should be compared with refractions at 52°, rather than any 

 other temperature. 



The column of M. Bessel's refractions is liable to be mis- 

 apprehended, from the omission of a very important remark. 

 The numbers in the column, when we refer to the table in 

 F. A., appear to be the refractions at 48f °, 30 B ; whereas 

 they should stand at 50°, 30 B, in order to make them com- 

 parable with the other columns. But M. Bessel has very lately 

 discovered that no error existed in Bradley's thermometer, as 

 he formerly supposed ; and that the temperature of the table 

 in F. A., which is marked at 48f °, should really be 50°. It 

 is indeed extremely improbable that Bradley, whose mind 

 was, for so long a time, intensely occupied with the deter- 

 mination of minute quantities, should allow any inaccuracy in 

 one of his principal instruments to escape his notice. 



Very important consequences follow from this change in 

 the temperature of M. Bessel's mean refractions. Above 

 10° of apparent altitude, his table is now very little different 

 from that of the French astronomers ; and it approximates in 

 a still greater degree to my table as far as 88° from the zenith. 

 Thus at the altitude of 45°, the refraction (50°, 30 B) is 

 58"'36 according to the French table and mine ; and, accord- 

 ing to M. Bessel, the same refraction is 58"'27, the difference 

 being no more than 0"*09. And this leads me to observe that 

 the writer in the Journal is very careless of accuracy in his 

 strictures. He remarks that, at' the altitude of 45°, it appears 

 highly improbable that the refraction at the temperature 50°, 

 or even 48°, can be so much as 58"*36. Yet this quantity 

 has the authority of the French table, known for so many 

 years, and so much approved of by astronomers. It is the 

 result of almost innumerable observations and experiments 

 by Delambre, Biot, Arago, Dr. Brinkley; and to these we 

 have now to add M. Bessel. 



The relation of my table to those of best authority ; which 

 I take to be that of the French astronomers, and M. Bessel's 

 when the temperature, according to his late correction, is 

 taken at 50° instead of48f°; is thus exhibited: 



Alt. 



