790 
thousand revolutions it is probably very 
accurate. 
The Annular Nebula in Lyra. 
A number of the Planetary Nebule have 
been observed and measured. The position 
of the nucleus of the annular Nebula of 
Lyra (M 57) was carefully measured in 
1898 and 1899. These, compared with Mr. 
Burnham’s measures in 1891 with the 36- 
inch of the Lick Observatory, seem to show 
a sensible proper motion for the whole of 
about 0.13 annually. This can be verified 
with certainty by measures four or five 
years hence. 
The small stars near this nebula meas- 
ured by Professor Hall at Washington in 
1877, have been remeasured and the obser- 
vations show that one of these stars (f of 
Hall’s list) of the 15th magnitude seems to 
have a considerable proper motion. 
Difference of Declination of Atlas and Pleione. 
The summers and winters of Williams 
Bay subject the 40-inch to extreme ranges 
of temperature. Micrometer measures were 
made in all temperatures between + 80° F. 
and — 26° F. These observations showed 
that the focus of the great objective changed 
to the extent of about 0.7 inch—shortening 
with the cold weather. To test these 
changes, a great number of measures of 
the difference of declination of Atlas and 
Pleione of the Pleiades, had been made in 
1897, 1898 and 1899. These measures 
besides showing considerable temperature 
changes, also show some peculiarities not 
satisfactorily accounted for and which do 
not show in similar measures of Electra and 
Caeleno, and which could be explained by 
a slight oscillation in the position of one of 
the stars. It is intended to further con- 
tinue these measures. 
Ormonp Stone: On the Motion of Hyperion. 
If, in the first approximation the motion 
of the perisaturnium of Hyperion be as- 
SCIENCE, 
[N. S. Vou. X. No. 257. 
sumed to be 4n’—38n, in which n and n’ are 
the instantaneous mean motions in longi- 
tude of Titan and Hyperion, the perturba- 
tive function will contain an expression of 
the form 
C, fe, + e [1 + cos (4 —31—7’)]?, (1) 
in which C is a function of the mass of 
Titan and the mean distances from Saturn 
of Titan and Hyperion, e, is the quasi-eccen- 
tricity of the orbit of Hyperion introduced 
by the erroneous assumption in regard to 
the mean motion of the perisaturnium, e’ 
and =’ are the eccentricity and longitude of 
perisaturnium properly so-called, and /’ and 
! are the longitudes in orbit of Hyperion 
and Titan, the motions of the two bodies 
being considered co-planar. 
Integration, assuming the values of the 
coefficients given by Newcomb in his ‘Astro- 
nomical Papers,’ Vol. III., and comparison 
with Eichelberger’s value of the inequality 
in mean longitude detected by Hermann 
Struve, result in two solutions, giving rise 
to two sets of values for m, the mass of 
Titan, and e’: 
m = saa e’ = 0.0224; 
m= pn e’ = 0.0195. 
As neither of these values of m differs 
greatly from the more reliable values found 
hitherto, it is uncertain which of the solu- 
tions is the correct one, and we can only 
say, at present, that the true value of the 
eccentricity of the orbit of Hyperion prob- 
ably does not differ greatly from 0.02. | 
W. W. Camppett: The Variable Velocity 
of Polaris in the Line of Sight. 
Polaris furnishes an interesting case of 
variable velocity in the line of sight. Six 
spectrograms were obtained in 1896, as 
follows: 
