GEEAT EEFRACTING TELESCOPE AT ELCHIES, IN MORAYSHIRE. 375 



Hence considerable confusion has crept in, where a mere number-reference is 

 employed, and great loss of time is experienced in tracing the measures of any 

 one star, through the catalogues of different observers arranged and indexed 

 merely according to their own separate independent and peculiar numbers, which 

 numbers too, in no case indicate the precise point of the sky to which a telescope 

 should be directed in order to find the star. Some natural method therefore 

 should evidently be made to over-ride all these artificial systems ; and none seems 

 better than a statement of the Right Ascension and Declination at a given epoch : 

 I have therefore been much more particular in designating each of the stars in 

 the Elchies list by that method, than by reference to any name or catalogue 

 number. One of these is, indeed, usually given as an approximate step to begin 

 with, but is always followed by the place for 1862, as brought up from the 

 " Cycle," the chief book of reference employed. 



Identification, however, thus by place and epoch, has its limits when stars 

 are very close together ; especially as the pointing of an equatorial may often be 

 in error, from an accumulation of causes, to the extent of 1, 2, or 3 minutes of 

 space. In such case, recourse must evidently be had to such further natural 

 features as may be presented by the objects in the field of view ; and which 

 features do indeed form the chief portion of an equatorial's work to ascertain and 

 record, viz.,— 



Magnitude, or brightness. 



Colour. 



Relative position angle, when more than one star is concerned ; and 



Distance, under the same circumstances. 



This consideration is evidently not new, though it has not been by any means 

 so generally employed as it might have been with advantage to science ; for with 

 stars, at first thought nearly similar, most manifold physical peculiarities have 

 been found on closer study. I have endeavoured, therefore, to take more account 

 than has usually been the case, of all the prominent characteristics of every star 

 observed ; and have not only arranged all my own results in that manner, but 

 those of other observers referred to for comparison, as well ; setting down each 

 person's work in order of date, to the end that any large cosmical progressive 

 change in any of the elements may be instantly manifested. 



When the cosmical change, however, is small, or the previous authorities 

 scanty, and the Elchies observation simply shows a difference from what had 

 been expected, then comes the all-important question, as to within what limits 

 can we depend on an Elchies observation ; for on the answer given thereto will 

 it rest, whether the difference noted may most probably be put down to mere 

 error of observation ; or, quite certainly assumed as showing a cosmical change 

 in the objects obsei^ved. A formal inquiry into these conditions will be all the 



VOL. XXIII. PAET II. 5 K 



