BINARY STAR a@ CENTAURI. 449 
I have inserted here the observation of MAsKELYNE in 1761, with which, pro- 
bably, Sir J. HerscurL was unacquainted; it makes an apparently bad figure 
among the rest, but is by no means to be left out on that account merely, seeing 
the care and the superior means for that day with which the measures were made. 
‘“‘Mr Fattowss’ determinations,” continues Sir Joun, “in this series, are open 
to objection, from the decidedly inadequate instrumental means by which they 
were furnished (a small altitude and azimuth circle). Mr Tayuor’s results also 
rest on so few observations, as to entitle them to little weight. 
“ Though it is obviously impracticable to deduce any elliptic elements from 
such a series, there are some features which it is impossible not to recognise. 
There can be no doubt that the distance has gone on decreasing since 1822 at 
least ; and the comparison of the measures least open to objection leads us to con- 
clude that, for the ten years previous to 1838, the rate of decrease was j4, or a 
little more than half a second per annum, which, if continued, will bring on an 
occultation, or exceedingly close appulse, about the year 1867. The small amount 
of variation in the angle of position shews that the plane of orbitual motion passes 
nearly, but not quite through our system, while its actual tendency to increase 
exemplifies the general law of increase of angular velocity, with diminution of 
distance. Mr Fattowes’ distance is probably too great by 3” or 4’; but in the 
long interval between 1750 and 1822 (at the former of which epochs the distance 
must have been on the increase), there is room for a very much greater excursion 
of the small star towards its apparent aphelion, so that, although we are sure that 
the major axis of the real orbit must materially exceed 24”, it is impossible to say 
how much it may exceed that limit. Taking, therefore, the co-efficient of parallax 
for a Centauri, as determined by Professor HENDERSON, at 1”, it will follow from 
what has been said, that the real orbit of one star about the other cannot be so 
small as that of the orbit of Saturn about the sun, and exceeds, in all probability, 
that of the orbit of Uranus. 
“ The plane of the orbit in the case of a Centauri, passing nearly through our 
system, my method of approximating to the elliptic elements becomes inapplicable, 
and for their determination, measures of the distance of the stars from each other 
can alone be relied on. No subject more worthy of continued and diligent inquiry 
can possibly be urged on the attention of southern astronomers.” 
Thus the result arrived at, both by Professor HENDERSON and by Sir J. HERSCHEL, 
and which, though proved since to be erroneous, would have been probably con- 
cluded by any one else from the same data, seems to be, that the smaller star 
had been employed during the last century in gaining its aphelion, without any 
sensible change of angle of position; what the aphelion distance, the diameter 
of the orbit, and the period of revolution, might be, no guess could be at- 
tempted: but in his address, on the occasion of giving the gold medal to 
Besset for his discovery of the parallax of 6 Cygni, Sir Joun HeErscHet stated, 
VOL. XVI. PART IV. DY 
