Marc# 1, 1901.] 
rected chromatic aberration has been devised by 
Mr. Ritchie of the Yerkes Observatory. He 
employs a yellow collodion film in front of the 
photographic plate at the eye end of the instru- 
ment, by which the blue rays are cut off. Suit- 
able isochromatic plates, such as can be found 
on the market, are used. This is a very inex- 
pensive means of using the telescope for pho- 
tography. A special form of guiding apparatus 
to keep the star image at the same point of the 
plate has to be employed. On account of the 
unavoidable flexure of the large telescope tube, 
an auxiliary telescope placed parallel to the 
telescope tube cannot be used. The image of 
another star just outside the photographic plate 
is made use of. By means of a little eye- 
piece with a fine pair of cross-hairs, attached to 
the plate holder which is adjustable in two di- 
rections at right angles to each other, the image 
of the guide star is kept on the intersection of 
the cross-hairs during the entire time of the ex- 
posure. The photographs taken at the Yerkes 
Observatory in this manner by Mr. Ritchie are 
much finer than those taken at Potsdam with a 
photographic telescope. 
A most important application of photography 
with this telescope will be the determination of 
the parallax of stars, which has not yet been 
done to any extent by photographic means. 
Photographs of the small planetary nebulz 
taken with this telescope show more than can 
be actually seen with our eyes, as in some cases 
a radial structure. 
The instrument can also be used to study 
stellar spectra and stellar evolution. We can 
pass by gradations from the type of hot and 
white stars like Sirius, to the more developed 
and colder ones like our sun, and then to the 
red stars. There are two types of red stars, 
and by the aid of their spectra photographed 
with this telescope, we have detected a relation- 
ship between the two types, through the pres- 
ence of carbon bands. Even in the atmosphere 
of the sun there is a very thin layer of carbon 
vapor and above this the gases of the chro- 
mosphere. In thered stars we have this carbon 
vapor, which is very dense in one of the types. 
Another important line of work is that of 
measuring the motion of stars in the line of 
sight. Professor Frost uses the titanium line 
SCIENCE. 
O47 
for this purpose, and has just had a new spec- 
trograph constructed for the work. 
In photographing the spectrum of Saturn 
with its rings, we find a faint band in the red 
indicating the presence of a comparatively 
dense absorbing atmosphere on the planet 
which is absent from the rings. 
With the help of a spectroheliograph we are 
able to photograph solar phenomena. ‘These 
photographs show that the mottling of the 
sun’s surface persists throughout the minimum 
period of sun spots as well as through the 
maximum. Prominences can be photographed 
nearly as well with it as at times of total solar 
eclipse. 
Mr. W. G. Levison presented a ‘ Note on a 
Cause of the Deterioration of Gelatin Photo- 
graphic Dry Plates.’ The author suggests that 
there is some emanation, probably Becquerel 
rays, from the pasteboard of the boxes in 
which the plates are packed for the market, 
which causes their deterioration. He found 
that if he cut a star from the pasteboard of a 
plate box and laid it on the sensitive side of a 
plate, the whole then being enclosed in a box 
for a week, when he developed the plate he 
obtained an image of the star. This would ex- 
plain the deterioration at the edges of plates 
where they come nearly in contact with the box, 
or the deterioration due to the pasteboard sepa- 
rators at the edges of the plates. The author’s 
experiments led him to the suggestion that 
metal boxes would be better for the plates than 
the pasteboard boxes. Wrapping with paraf- 
fine paper might also have the same effect. 
WILLIAM 8. Day, 
Secretary. 
TORREY BOTANICAL CLUB. 
Av the annual meeting, January 8, 1901, the 
Secretary, Professor E. S. Burgess, reported 15 
meetings held during the year, with an average 
attendance of 38; 19 active members were 
elected. The active membership is now 238, the 
total membership 383 ; 20 papers have been pre- 
sented, with addition of 26 brief notes of col- 
lections or of botanical progress. 
The editor, Professor L. M. Underwood, re- 
ported a continued increase in the number of 
pages and of plates in the Club’s publications, 
