206 Captain W. S. Jacob on the 



A recent Revision of a Portion of the Catalogue of Stars 

 published by the British Association in 1845. By Captain 

 W. S. Jacob, H.E.I.C. Astronomer at Madras. Commu- 

 nicated by Professor C. Piazzi Smyth. 



Notes by Professor C. Piazzi Smyth at the time of communication 

 of this Paper to the Royal Society. 



This paper is short, but important ; yet, though important, 

 it can hardly but be somewhat dry and uninteresting to those 

 not immediately engaged in the pursuit of exact astronomy, 

 and not conversant with the foundations on which it rests. 



With our earth turning on its axis, and revolving about the 

 Sun in an orbit continually changing in every element, and 

 with the Sun itself describing a similar orbit about some other 

 sun or suns, there may well be difficulty in finding any truly 

 fixed and immoveable objects from which our measurements of 

 the moving ones may be reckoned. 



The so-called fixed stars are not fixed, and the nearer are 

 sensibly displaced by the amount of the Sun's movement, as 

 well as by having proper motions of their own. Hence, 

 though the larger stars are a very convenient system of mile- 

 stones whereupon to begin our measurement of celestial arcs, 

 yet they are not to be implicitly depended on. They 

 can only be looked on as intermediate, and must have their 

 reputed fixity tested by comparison with the more distant 

 stars, and especially with the mean of an immense multitude 

 of them, whose varying aberrations may, on the whole, tend 

 to balance each other, and to exhibit a constancy of which no 

 single star is capable. 



To this end, accordingly, the efforts of most of our public 

 and many of our private astronomers have long been directed ; 

 and an exceedingly important step was taken by the British 

 Association a few years ago, in the publication of their large 

 Catalogue of 8377 stars. Some persons, indeed, were inclined 

 to think it rather premature, as many of the stars rested on 

 old and rather scanty and apocryphal observations ; but others 

 contended that the publication of a catalogue so made up, and 

 duly pointing out the good and the bad material, would incite 



