Ce iy Bent, a 0 
and the Absolute Size of the Fixed Stars. 309 
gives about 2 square seconds for the amount described annu- 
ally. This quantity being carried back to 1750, it cannot be 
fitted even approximately into any ellipse whatever, 80 as to 
give a distance not exceeding 25’, and a position in the S.P. 
quadrant ; it will be impossible, unless a revolution be allowed 
to intervene. The period is therefore limited at the widest 
to between 75 and 80 years (two revolutions cannot be ad- 
mitted) ; and this again limits the area of the apparent el- 
lipse to 150” or 160’. The section being fitted into an ellipse 
of that area, the greatest possible value of minimum distance 
is found to be about 2”5 ; and the latest possible time of near- 
est approach about 1854. If I could have got a decent mea- 
sure within the last six months, I might have got closer limits. 
With regard to the mass, the least possible value of the 
major-semi axis (true) is about 115, which corresponds to 
a mass of 0-325; the upper limit is not so easy to fix, be- 
cause the excentricity may be almost anything above 0-9, and 
consequently, the inclination and major axis may be very 
great ; but it appears highly improbable that ¢ is above ‘975, 
in which case a might be about 1:98 and m = 1:73; so that 
the mass cannot differ very widely from the solar. 
I have also been able to arrive at same result with regard 
to the quantity of light emitted by a Centauri, as compared 
with our Sun, through means of some results arrived at on 
the intensity of solar light and the absorption of the atmo- 
sphere, during my employment on the Trigonometrical Survey 
of India. 
On commencing work with heliotropes in 1837, I soon 
found that for long distances it was necessary to enlarge the 
aperture more than in the simple ratio of the distance, though 
such was Colonel Everest’s practice ; and before the end of 
the first season, I had found a scale of apertures for corre- 
sponding distances which afterwards needed very little alter- 
ations ; but when finally corrected by subsequent years’ ob- 
servation stood as follows :— 
Aperture. Inches. 0:5. 1:0 2:0 4:0 8:0 
Max. distance. Miles). 15 23 33 45 60 
Our heliotropes were circular glass mirrors, 8 inches dia- 
meter, and for the smaller apertures, diaphragms were used 
