50 E. S. Holden—Note on the satellite Tethys. 
just before analy appeared to the naked eye; and that Tethys 
ost at the same time, or a very little after this. 
When Ssintin: was just appearing or Ss Titan was as 
bright in the telescope as Dione when no clouds were present. — 
Dione was always a little brighter shat Tethys. The southern 
edge of the belt in the southern hemisphere of Saturn vanished — 
about at the same time as Hnceladus. ‘This observation is, how- 
ever, not so precise as those on Ttthy : 
As many appearances and dita ppeupiiced as possible were — 
observed and the result of them all is that Zethys was as bright — 
to my eye in the telescope as Saturn was to Anderson’s unas: — 
sisted eye. It may be mentioned that Anderson under good — 
circumstances can see Uranus with the naked eye, and by — 
experience I have learned that my eye is weil suited to seeing — 
faint satellites like those of Uranus and Neptune. I believe 
that our he used as in this experiment were as nearly equal 
as any co 
The a became rina) cloudy before I could measure the 
the posttio of Tethys. From Prof. Ne ee MS. tables the ; 
both bail and rip 
rom the table given by Zéllner in Photometrische Unler- 
eas p. 200, it follows that if Saturn had been without his 
ring, the light from the ball alone would have been 0:9356 
(log. 9°9711) of the light of ball and rings combined. Hence 
if H, is the light from the ball alone, the light received from 
‘1 H, 
Tethys was 75 18,900 * 0-98 9356 = 000006323. H, (log. 58009 H,} 
H = aes 
1s 
TPs 
At another time, H, = A.d?. (5 1 ‘) and 
i 
A: ee 3 = rt p2: rtp. 
* See Stampfer: Sitzungsber. der k. Acad. d. Wiss. Berlin, vol. vii, 1851, p. 760 
