Juniata sentinel and Republican. [volume] (Mifflintown, Juniata County, Pa.) 1873-1955, 1874-11-11
Scientific.

TwINKLING OF THE SrARs.-The SUBJ
ject of the twinkling of stars has en-
gagged good deal of attention of late
years, and some interesting results have
been obtained. A few years ago the
Italian astronomer, Respighi, announced
the discovery of the cause of scintilla-
ton, in certain dark bands which were
seen to traverse the spectrum of star,
indicating changes in the refrangibility
of our atmosphere, from hot and cold
strata, which produce something of the
effect of a passing mirage. A layer of
hot air would bend rays less than the
colder and denser air around. and thus
the stars light would not reach the OBJ
server, rays which traversed the hot
stratum passing over his head, and
those which traversed the cold air be-
low being bent so as to fall beneath his
feet. As the rays of different colors are
differently bent in their passage through
the air Cthe red rays being the least
refracted), different parts of a stars
spectrum would be thus cut off in sue
cession as the relative temperatures of
the layers of air varied. Arago's not
very lucid explanation of the pheno-
mena, as result of the interference of
light, is IN this way completely disposed
of.
NJ. Montignv, of Brussels, has been
Investigating the amount of scintillation
in different stars by the help of an in
genious contrivance, to which he gives
the name of scintillometer. His plan
is TO make use of the persistence of
Impressions on the retina, by causing a
thick plate of glass, mounted obliquely
on an axis, parallel to that of the tele-
scope used, and fixed Just in front of
the eyepiece to rotate rapidly: the
effect of this is to displace the stars
image, so that, owing to the varying
inclination of the glass plate, the star
appears to move in a circle, which, if
the rotation is rapid enough (three or
four times in a second), forms con-
tinuous circle of light, Just as in the
case of burning stick whirled rapidly.
The changes in the color of a star will
be seen on this circle, the successive
points of which give the appearance of
the object at successive small fractions
of second and in this way, by count
ing the alterations of color in the cir
cumference of this circle of light, NJ.
Montigny has succeeded in observing
nearly two hundred alterations of
color in a second of time.
The point sought to be established
was the connection between these
changes and the constitution of the
stellar light, for it is easy to see that
the rays which are deficient cannot be
acted on by undulations of the atmos-
phere, and there will therefore be fewer
changes of color the more dark bands
there are in stars spectrum. Now
Secchi has divided the stars of which
he has examined the spectra into four
types, and VI. Montigny has observed
the scintillations of stars belonging to
three of these types, VIZ blush white
stars exhibiting four black lines in their
spectrum somewhat resembling colon
made. As far as the results obtained
by NJ. MOntigny go, it seems that the
greatest amount of twinkling is to be
found in the first type (white stars, and
the least in the third type (orange stars)
and that the mere brightness of the star
has no influence on the phenomena.
But the principle of combining obser-
vations of different nights without any
further correction, on which NJ. Mon
tigny has acted, is highly Objectionable
and destroys our confidence In his con-
clusions. The proper way of treating
such measures Is to arrange the stars In
sequences representing the order of
scintillation, just as Sir John Herschel
formed sequences of brightness as
basis for his standard magnitude of
stars.