JUNE 138, 1884.] 
And besides, the effect of changes of temperature 
upon the spectroscopic portion of his apparatus, and 
the difficulty of securing nights on which the atmos- 
phere would not cut off the actinic rays to an unusual 
degree, not to mention the fact that the observatory 
was more than two miles distant from his residence, 
— these and many other conditions hindered the prog- 
ress Of the work. Spectrographic operations are, as 
Professor Young well says, much more sensitive to 
atmospheric conditions than are visual observations. 
As regards the spectroscopic apparatus, a great 
many forms were employed, the first of which has 
already been mentioned. Later, direct-vision prisms 
were used in the same way, and spectroscopes made 
up of such prisms, some with a slit, some without, 
and some with a cylindrical lens to give necessary 
width to the spectrum. In the definitive arrange- 
ment of the apparatus, with which all the plates 
measured by Professor Pickering were made, a re- 
modelled form of Browning’s star-spectroscope formed 
the basis of the instrument; the telescope and colli- 
mator each having a focal length of six inches, and 
an aperture of 0.75 of an inch. The eye-piece and 
micrometer being removed, a block of hard wood was 
fitted on in such a way as to carry the photographic 
plate (a small piece of glass about an inch square); 
and a small positive eye-piece was mounted on the 
block, so that the yellow and red portions of the spec- 
trum, projected beyond the sensitive plate into the 
field of view, could be examined at pleasure. It was 
thus possible to be sure that the driving-clock was 
running properly, and that all the adjustments re- 
mained correct. The whole apparatus weighed less 
than five pounds, and could be screwed on the eye- 
end of whichever telescope it was desirable to use it 
with. The development of the plates was usually 
by ferrous oxalate, though the alkaline development 
and pyrogallic acid were both used on some occa- 
sions. The pictures were about half an inch long, 
and one-sixteenth of an inch in width, extending 
from a point between the Fraunhofer lines F and G 
to a point near M. 
Professor Pickering divides his work on these plates 
into three parts: first, the determination of the rel- 
ative positions of the lines in the various spectra in 
terms of any convenient unit of length; second, from 
the known spectra of the moon and Jupiter, a deter- 
mination of the relation of these measures to wave- 
lengths; third, a reduction of the measures of the 
stellar spectra to wave-lengths, and a discussion of 
the results. The stars whose spectra have been meas- 
ured are a Aquilae, a Lyrae, a Aurigae, a Bootis, and 
aScorpii. The spectrum of the first of these stars is 
remarkable for containing, in addition to the intense 
broad hydrogen-bands which characterize the spec- 
trum of a Lyrae and similar stars, a multitude of very 
fine lines, which are easily seen between G and H in 
several of the plates, but are too delicate to be satis- 
factorily measured. Dr. Draper considered these fine 
lines very important as showing that Altair should 
be regarded as a sort of intermediate link between 
a Lyrae and Sirius on the one side, and Capella and 
the sun on the other. 
SCIENCE. 
127 
On the plates of the spectra of a Aurigae and 
a Bootis, not only do the lines appear to ceincide in 
position with those of the sun, but their relative in- 
tensity seems to be nearly the same. Of the twelve 
lines seen in at least seven of the nine spectra of the 
moon and Jupiter, every one is contained in the spec- 
tra of both a Aurigae and @ Bootis. Of the fifteen 
lines which are so faint as to be contained in but one 
or two of the spectra of the moon or Jupiter, only 
four are contained in the spectrum of a Bootis, and 
but one in that of a Aurigae. There is therefore no 
room for doubt of the correctness of Professor Pick- 
ering’s conclusion that the evidence afforded by these 
photographs is very strong indication of the same- 
ness of their constitution with that of our sun. 
Professor Pickering’s method of deriving his results 
from these plates is worthy of note here, as indicat- 
ing the great degree of confidence to which they are 
entitled. To secure entire independence in the re- 
sults, the measures were completed before the reduc- 
tions were begun. ‘The lines in each plate were 
measured without comparison with any map, and no 
search was made for lines which appeared to be want- 
ing. When two similar spectra were photographed 
side by side, care was taken to cover one when meas- 
uring the other. Under these circumstances, the 
agreement in the measures of several plates is strong 
evidence of the identity of the spectra. 
Appended to this monograph are three of the pa- 
pers of Dr. Draper, reprinted from the American jour- 
nal of science: 1°, On photographing the spectra of 
the stars and planets (December, 1879); 2°, On pho- 
tographs of the spectrum of the nebula in Orion (May, 
1882); and, 3°, Note on photographs of the spectrum 
of comet b 1881 (August, 1881). The first of these 
papers gives, in brief form, a very lucid statement 
of the conditions of the problem of celestial spec- 
trum-photography, as well as the obstacles which he 
had, up to that time, overcome in solving it. 
DAvip P. Topp. 
THE GEOLOGY OF THE ASTURIAS AND 
GALICIA. 
Recherches sur les terrains anciens des Asturies et de 
la Galice. Par CHARLES Barrots, docteur és- 
sciences. Lille, Six-Heremans, 1882. 630 p., 20 
pl. 4°. 
Ir was the good fortune of one of the writers 
of this review to see this work in process of 
evolution in the workshop and study of its 
hospitable author in Lille; but much as he 
admired the indomitable energy and patience 
which were presiding at its birth, as well as 
the copious notes and experience which were 
being assimilated into this monograph, the re- 
sult is a surprise. How much more must it 
surprise those who are unacquainted with Dr. 
Barrois, to learn that he is but little past his 
thirtieth year; that this is but one of several 
important memoirs which he has begun and 
