1876.] 
Sidereal Astronomy. 
5i 
are far from accurate determinations. As a methodical divi- 
sion to determine generally the number and separation of 
systems, the preceding is not valueless, but it is defective as 
the basis of a catalogue ; also there is already difficulty in 
finding the stars when they are looked for. Thus, for ex- 
ample, the binary system of 7 Virginis is not placed in the 
first class of Struve, because in 1836 the angular distance 
of its components was inferior to 1", and it is found in the 
catalogue of P. Secchi (i860), p. 41, amongst the stars of 
from o'' to T', although its distance in i860 was already 
above 3". At the present time, in 1875, it is 4*8 // . We 
should thus have to place it, in 1830 in the second class, 
in 1836 in the first, in 1842 again in the second, in 1850 in 
the third, in 1870 in the fourth. Many other groups would 
offer analogous examples. As a system of cataloguing, one 
by right ascension, or even by constellation, would be 
evidently preferable. 
After the observations of William Struve, we may mention 
those which Sir John Herschel made during his stay of four 
years at the Cape of Good Hope, at Feldhausen, where he 
examined and measured 2100 double stars of the southern 
hemisphere, of which a few only were before known. 
A brilliant series of observations is due to the English 
astronomer Dawes, who, from 1831 to 1867, made no less 
than 2762 observations on double stars. 
We may finally give a description, in chronological order, 
of Otto Struve’s observations, son of the celebrated William 
Struve in Russia ; of Madler, in Prussia and in Germany ; 
of Admiral Smyth and Lord Wriottesley, in England ; of 
Captain Jacob, in the Southern hemisphere; of Kayser, at 
Leyden ; of P. Secchi, at Rome ; of Powell, in the Southern 
hemisphere ; of Fletcher, in England ; of Dembowski, at 
Gallarate, near Milan ; of Brunnow, at Dublin ; of Knott 
and Wilson, in England ; of Winlock, at Harvard College 
(United States); and of Burnham, at Chicago — who, by 
their researches, their observations, their micrometrical 
measurements, and their discoveries, have successively en- 
dowed astronomy with accumulated riches. 
Such are the principal astronomers who have specially 
devoted themselves to the observation of double stars. Others 
have been occupied with calculations of the orbits of binary 
systems. The French astronomer Savary was the first who, 
in 1830, applied a method of calculation to these determina- 
tions. Encke afterwards proposed a method much more 
complicated than that of Savary, which appeared to him to 
lead to more accurate results. Sir John Herschel, on the 
