128 



Art. XVII. ASTRONOMICAL AND NAUTICAL 

 COLLECTIONS. 



No. XIII. 



i. Empirical Elements of a Table q/" Refraction : computed 

 from Observations communicated and reduced by Stephen 

 Groombridge, Esq., F.R.S. 



Professor Schumacher has lately published a very useful 

 little volume of Permanent Auxiliary Tables. But with regard 

 to the subject of Astronomical Refraction, he has left it entirely 

 undecided, by which of the many systems a computer will be most 

 justified in correcting his observations ; so that it is probable that 

 almost every unprejudiced and diligent astronomer will prefer 

 those which appear to be the most elaborate, or of which the 

 author or authors have acquired the highest mathematical repu- 

 tation; a reputation which but too often tempts its professor to 

 look down with contempt on physical truth. 



The mode of examination, exemplified by the Editor, in the 

 former numbers of these Collections, appearing to him to be the 

 only unexceptionable mode of obtaining a fair determination of 

 this complicated question, he has prevailed on the kindness of 

 Mr. Groombridge to add a number of later and more extensive 

 observations to those which he had before communicated ; and 

 their ultimate results are here exhibited, with the addition of 

 some further steps towards an immediate application to prac- 

 tice, or at least to a more satisfactory comparison of the merits 

 of the diflferent tables actually existing: and these results are 

 not made public with the less readiness, because they appear, in 

 some respects, not to agree quite so well with the Editor's own 

 theory, as the former ; but confirm the suspicion, which he for- 

 merly entertained, that the corrections of his table are some- 

 what more strictly appropriate to the different mean tempera- 



