514 
POPULAR SCIENCE REVIEW. 
of great interest to the amateur astronomer, who, by constant practice, can 
bring his eye to detect very small fluctuations of brightness. As an example 
of the exactness with which their periods are determined, we might cite the 
case of the star S Cancri, the minimum of which was observed by M. Schmidt, 
at Athens, on April 16, 9h. 27'5m., or within one-third of an hour of the 
time foretold by Professor Argelander. Mr. Searle, of Cambridge (U.S.), 
proposes a very simple photometer, consisting of a plate of glass the faces of 
which are inclined to each other by a few minutes of arc. By covering 
the object-glass of a telescope with this, the image of a brighter star can be 
reduced to that of a fainter one seen with the full aperture, and comparing 
the areas' of the covered and uncovered parts of the object-glass, the real light 
of the two stars may be arrived at, taking into account the absorption and 
reflection of the plate. It is doubtful, however, whether the older and 
simpler plan be not more commodious and gives equally good results. 
Variable Nebula. — M. Schmidt points out that a small nebula, whose place 
for 1855 is llh. 16'5m. of B.A. and 90° 22' of N.P.D. (inserted in the Bonn 
Star Maps), and which should be visible with a two-foot telescope or comet- 
seeker, has become so faint that it is seen with the greatest difficulty with 
the large refractor of the Athens Observatory. There can be no doubt of its 
former lustre and its present faintness. As this object is no tv visible in the 
heavens, perhaps such observers as possess good telescopes may turn their 
attention to this interesting object. Sir J. Herschel, in a letter to Mr. Hind, 
furnishes another example of a missing nebula. This one was twice observed 
by Sir W. Herschel, who, in 1784 and 1787, saw two nebulre close together, 
the places of which were respectively 12h. 22m. 14s. and 12h. 22m. 29s., with 
N.P.D. 75° 33' and 75° 36', only one of which is now risible, although they 
are noted as being of nearly the same brightness. A telescope of four inches 
aperture should show both objects. 
Nebula of Orion. — M. Lassell has discovered a new star in the trapezium 
of Orion, situated near Theta, which appears to be a full magnitude less 
than that known as the sixth star. With his giant reflector, and under 
the transparent sky of Malta, he has obtained some excellent views of tins 
wonderful object, and intimates his intention of making it the subject of a 
fresh investigation. M. Struve has come to the conclusion, from numerous 
and careful observations, that the central regions of this nebula are subject to 
rapid changes of light, and is about to publish an extensive memoir on the 
subject. 
Saturn,— Between May 17 and August 12 the ring of Saturn is invisible. 
A fine opportunity is thus afforded of observing his satellites. These latter, 
with their eclipses and occultations, have been seen to great advantage 
during the present spring. M. Lassell, on one occasion, saw them all in the 
field at the same time, with the exception of Japetus. This distinguished 
observer is of opinion that if Uranus has more than four satellites, those 
which are undiscovered are very much fainter than those which are visible 
in his telescope. 
Miscellaneous. — Professor Littrow has discovered in the Vienna Times of 
April 27, 1820, a notice probably bearing on the intra-Mercurial Planet. A 
round, well-designed circular spot was seen by Mr. Steinheibel on February 
12, 1820, at 10.45 a.m., distinguished by its “equally circular atmosphere 
