Feb. 2, 1882 | ; 
NATURE 327 
o 
work. With the former, sixty-four eclipses of Jupiter’s satellites 
were obseryed photometrically, an improvement having been in- 
troduced by which the number of settings is largely increased. 
A single obseiver, it was found, could make but three settings 
in a minute, or one in twenty seconds. With an assistant to 
record, the time is reduced to about nine seconds, while by the 
employment of two assistants, one of whom reads the photometer 
circle, while the other records and observes the time by the 
chronometer, the time is reduced to five seconds. It is probable 
that, as the observer does not remove his eye from the eyepiece, 
the accuracy of the observations is increased, and the satellite 
followed nearer to the point of disappearance. The search for 
objects having singular spectra, which only admits of being 
carried on in perfectly clear, moonless nights, had been much 
interrupted by other current work. The most notable result was 
the discovery of the peculiar spectrum of the star Lalande 13412, 
a seventh magnitude ; two of the lines appear to be coincident 
with two in the spectrum of the great comet of 1881, as described 
by Dr. Konkoly ; ‘‘accordingly, while other comets have a 
spectrum identical with that of the stars of Secchi’s fourth type, 
this comet contains a substance as yet unknown, which one star 
only is as yet known to contain.” The star L? Puppis was found 
to have a banded spectrum ; its declination is more than forty- 
four degrees south of the equator, and at the time of Prof. 
Pickering’s examination it was less than two degrees above the 
horizon. Its variability was pointed out by Dr. Gould (U7vano- 
metria Argentina, p. 279) ; he inferred a period of about 135 
days ; maxima occurred in 1874 on Feb. 8 and June 25; the 
star is stated to be red in all its stages and remarkably so about 
minimum, limits of variation 3°6 and 6°3. The position for 
1875‘0 is inR.A. 7h. gm. 43s., N.P.D. 134° 26’. 2. The spectra 
of all the stars north of — 4o°", marked as red or coloured in 
Dr. Gould’s work have been examined at Harvard College, no 
peculiarity of spectrum being detected in the majority. Algol 
and the star D. M. 81°, 25 were assiduously studied photometrically. 
The meridian-circle had been in use on 250 days. The work 
originally proposed for the meridian-photometer, viz., the 
measuring on three nights the light of each of the naked eye stars 
visible in the latitude of the Observatory, was essentially com- 
pleted on August 25, 1881, but it is intended to continue the 
observations for another year, as the necessary delay in reduction 
and publication will not be greatly increased thereby. With the 
view to a more complete comparison of the photometric observa- 
tions with those made by the naked eye, which the Uvanometria 
Argentina affords the means of doing as far as 10° north, all the 
stars in the dias Celestis Novus of Heis north of the equator and 
brighter than the sixth magnitude, are being measured by the 
eye, aided by an opera-glass when necessary. It is intended that 
each star shall be measured by three observers, who are to com- 
pare it with two stars in the vicinity of the pole, one a little 
brighter, the other a little fainter ; the interval between the two 
stars is supposed to be divided into ten parts, and the brightness 
of the star under comparison is estimated on terms of this in- 
terval, Prof. Pickering mentions that out of about nine thousand 
comparisons required for this work, nearly a quarter have been 
already made. 
Vol. xiii. of the ‘* Annals” now in process of publication will 
contain results of work with the large equatorial, under the direc- 
tion of the late Prof. Winlock, and micrometrical measures up to 
the present time. These include measurements of double stars, 
observations of nebulz and their spectra, satellites of Saturn, 
Uranus, and Neptune, satellites of Mars during the oppositions 
of 1877 and 1879, &c. Vol xiv. will contain the measures made 
with the meridian-photometer. 
An important and much-wanted bibliographical work has been 
undertaken by Mr. Chandler, viz., the collecting of references to 
observations of stars of known or suspected variability, those of 
each star being brought together ; on the completion of this work 
it is intended to measure the comparison-stars photometrically, 
and to effect a reduction on a uniform system of all the observa- 
tions of the variable-stars of long period. 
The staff of computers employed upon the ordinary reduc- 
tions of observations with all three instruments includes several 
ladies. We suspect that those who are competent and have had 
opportunity of judging of the work of the lady-computer (who 
is to be found elsewhere than at Harvard Observatory) will be of 
opinion that she is well able to hold her own against even the 
practised computer of the other sex. If proper opportunities 
and encouragement were afforded, we might hear of Madame 
Lepautes in our own day. 
| 
BIOLOGICAL NOTES 
DELICATE TEST FOR OXYGEN.—T, W. Engelmann proposes» 
in the Botanische Zeitung, a new test, of an extremely delicate 
nature, for determining the presence of very minute quantities 
of oxygen, namely, its power of exciting the motility of bacteria. 
If any of the smaller species, especially Bacterium termo, are 
brought to rest, and then introduced into a fluid in which there 
is the minutest trace of free oxygen, they will immediately begin 
to move about freely ; and if the oxygen is gradually introduced, 
their motion will be set up only in those parts of the drop which 
the oxygen reaches. In this way Engelmann was able to deter- 
mine the evolution of oxygen by Zuglena and by chlorophyll- 
granules, 
PROTHALLIUM AND EMBRYO OF AZOLLA.—The development 
of the prothaliium and embryo of Azolla, hitherto but imperfectly 
known, have been followed out by Prof. Berggren (Lunds 
Univ. Arsskrift) in the case of A. caroliniana, and found closely 
to follow the phenomena in Salvinia. The endospore splits, on 
germination, along its three edges ; and the prothallium, on 
escaping, has the form of a slightly convex disk, consisting in 
the middle of several layers of cells, at the margin of only one, 
and separated below by a thin hyaline membrane from the large 
protoplasmic spore-cavity. Shortly afterwards an archegonium 
is formed, con-isting of four cells inclosing the oospore, and of 
four neck-cells. When quite mature, the part of the prothallium 
which projects outside the spore is nearly hemispherical, and 
three obscure wings are produced by three longitudinal furrows. 
After fertilisation the oospore is divided by the first oblique 
division-wall into a smaller upper cell facing the neck of the 
archegonium, and a somewhat larger lower cell filled with coarse- 
grained protoplasm. By successive walls vertical to one another 
and to the first division-wall, and parallel to its longitudinal 
axis, the embryo is then divided into octants. In each octant a 
wall next appears parallel to the first division-wall, and the 
entire embryo then consists of sixteen cells arranged in four 
parallel rows. After fertilisation the embryo breaks through 
the prothallium near the archegonium, and the prothallium then 
surrounds the foot of the embryo like a cup, carrying the 
withered archegonium on its dorsal side behind the scutellum. 
‘o prepare for fertilisation the massulz of the macrosporangia, 
with their anchor-shaped glochidia, fix themselves in large num- 
bers to the epispore of the macrospores which are floating on 
the surface of the water. The central fibrous portion of the 
floating apparatus is perforated by a narrow canal, through 
which the antherozoids probably reach the archegonium. By 
their subsequent growth the prothallium, and later also the 
embryo, force themselves into this canal and increase its size. 
By this means the three floating bodies are displaced from their 
original position, and finally stand at a right angle from the macro- 
spore. The indusium which covers the floating apparatus in 
the form of a brown cap is at the same time pushed upwards, 
and finally forced against the embryo, The hood-like fibrous 
layer which is closely applied to the floating apparatus is turned 
over, and surrounds the foot of the embryo like a collar. Shortly 
afterwards the embryo detaches itself from the macrospore, the 
margins of the scutellum become broader, and then lie on the 
surface of the water in the form of cups or scales. 
PHYLLOMIC NECTAR GLANDS IN POPLARS.—In a very in- 
teresting memoir on this subject, Mr. Wm. Trelease calls atten- 
tion to the fact that these glands have been very generally 
overlooked, and that they have been considered of little value 
by the systematic botanist. He accounts for this by their being 
occasionally suppressed, and of their limitation to the earlier- 
formed leaves. Still most of the American botanists refer to 
them, and Michaux figures them in his monograph of the genus. 
In May, 1880, Mr. Trelease’s attention was drawn to examine 
the leaves of a small aspen by the action of some bees. The 
tree was covered with its newly expanded foliage, and the bees 
were flying from leaf to leaf; they were seen to be collecting 
nectar which was poured out from a double gland at the base 
of each leaf. These glands were placed on the upper surface 
of the petiole at its union with the blade. On section and 
microscopical examination they showed the usual structure. They 
were found not to occur on all leaves, but as a rule only on the 
first half dozen or less which appear on each branch in the early 
spring ; and later on in the season, when these have fallen off, 
one may sometimes examine all the leaves without detecting a 
single glanduliferous one, and this on a species which produced 
