in the relative Situation of double Stars. 
359 
I shall now proceed to a continuation of my account of the 
changes that have happened in the relative situation of double 
stars, either in their position or their mutual distance ; and, in 
the following list of them, it will be seen that, of 50 changeable 
double stars which are given, 28 have undergone only moderate 
alterations, such as do not amount to an angle of 10 degrees. 
None of them however have been admitted, except where the 
change was at least so considerable, that the micrometer which 
was used on this occasion could ascertain the change with 
a proper degree of accuracy. Two of the stars, indeed, have 
hardly suffered any alteration in the angle of position; but, 
with them it will be found, that a change in their distance has 
been so ascertained as not to admit of any doubt. Thirteen of the 
stars have altered their situation above 10 degrees, but less than 
20. Three stars have undergone a change in the angle of posi- 
tion, of more than 20, and as far as 30 degrees. The six 
remaining stars afford instances of a still greater change, which, 
in the angle of position of some of them, amounts to more than 
30 degrees; in others, to near 40, 50, 60, and upwards, to 130 
degrees. 
a Herculis. II, 2.* 
The two stars of this double star have undergone a consi- 
derable change in their angle of position. By a measure taken 
May 20, 1781, it was 21 0 28' south-following.-f April 3, 1783, 
two measures gave 2 5 0 29'. A mean of two measures, taken 
* The numbers after the name of the star, refer to my Catalogues of double Stars, 
published in tho Philosophical Transactions. For instance, II, z, denotes that 
a. Herculis is the 2d star in the 2d class. 
+ By mistake, the first angle of position in my Catalogue is given 30 0 35', instead 
of 21 0 28', and should be corrected. See Phil. Trans. Vol. LXXII. Part l. p. ltz> 
3 A 
MDCCC 1 V. 
