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contributes to the formation of the tails of comets.
actual existence of this force is established by the accurate
observations that have been made. He examines successive-
ly the various theories that have been put forth-the elec-
trical theory as proposed by Zöllner, the molecular theory
of Zenker, and the theory of Faye that repulsion is exerted
by all incandescent surfaces, and that thereby the gaseous
matters attending the comets are repelled from the surface
of the solid nucleus. The latter does not seem to Schiaparelli
to afford any material explanation of the phenomena. The
electric theory was first suggested by Olbers, but has been
in general terms objected to by Herschel, Lamont, etc. Zöll
ner's views have been elaborated more minutely, and he has
endeavored to show that the free electricity existing upon
the surface of the earth is sufficient to produce an effect sim-
ilar to that found in comets; but his conclusions are in too
many respects at variance with actual observations to allow
the author to consider them as affording a reasonable expla-
nation as to the nature of comets. Zenker's views are rejected
by him for the reason that the evaporation of fluids from the
surface of the nucleus should give rise to several phenomena
not seen in comets, while, on the other hand, it does not ex-
plain the multiple tails which have frequently been observed.
In conclusion, Schiaparelli thinks that we are forced to be-
lieve that the repulsive force acting upon comets is a force
exterior to the comet itself, and since this force evidently
operates in the direction of the radius drawn from the comet
to the sun, therefore we must regard it as having for its
origin the sun or some medium surrounding the sun, and he
adds that this is about all we at present know upon the
subject.-3 B, XXXV., 263.

WINNECKE'S COMET.

The comet known as Winnecke's comet is a very faint telescopic comet, whose recent appearance was observable by only a few of the largest telescopes in the world. It was first observed in 1819, but attracted no notice until in 1858 it was again observed by Winnecke. From the observations made at that time, Winnecke showed that it accomplished its revolution in its orbit in about 2400 days, and that it was identical with the comet of 1819, having made seven

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revolutions about the sun since that time without having been observed. Its short period of revolution gives it an additional interest; its movement seems to have experienced no disturbance in the course of the two revolutions that it has made during the past fifteen years.-13 B, III., 174.

ON THE REPULSIVE FORCES OF COMETS.

Schiaparelli has recently published his views upon the cause of the peculiar phenomena exhibited by comets, views which he has entertained and in part published since 1862, during which time, on the other hand, he has taken so prominent a part in the development of our knowledge of shooting-stars. According to Schiaparelli, there actually exists a repulsive force, not only between the sun and the tail, but also between the particles composing the nucleus and the tail of a comet; and the phenomena exhibited by these bodies can not be explained without assuming these repulsive forces. In fact, if we consider, first, the formation of the tail itself, we shall find that the solar gravitation and the movement of the comet do not suffice to explain it, as has been abundantly testified to by all who have minutely examined the observations that have been made. Again, too, if we consider the tail itself, and its path in space, we shall find, as has been shown by Bessel in reference to Halley's comet, and by Pape and Bond in reference to Donati's comet, the existence of a repulsive force repelling the comet from the sun results with as much certainty as the movements of the earth prove the existence of an attracting force toward the sun. The third comet of 1862, on the other hand, whose tail was not projected in a direction opposite to the sun, but continually approached this direction as the comet moved away from the sun, shows that the repulsive force acts upon the particles of the tail as well as upon the nucleus of the comet; that, in fact, the tail was first sensibly brought under the influence of the sun after it had been projected from the nucleus of the comet by a force residing therein. Under a minute examination, the head of a comet sometimes shows beams of light projected from the nucleus, but subsequently turning back and forming portions of the tail, so that here, also, the existence of the repulsive force is apparent. Finally, the increase in the breadth of the tail as it separates from the

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nucleus shows that the repulsive force is exerted, not only between the sun and the tail, but also between the separate atoms of which the tail is formed. Since, thus, repulsion is proved, and even apparent as we may say, we must attach some value to the determinations that have been made by Bessel, Pape, and Bond, who were obliged to make certain hypotheses as to the development of the tail, while, on the other hand, the third comet of 1862, like many others, seems to have developed its tail in such a manner that we have at present no safe foundation for computing the amount of the repulsive force existing therein.-19 C, VIII., 109.

PECULIAR AURORAL PHENOMENA.

The nature of the auroral light is the subject of a communication by Lemström, who concludes that the white flaming appearances occasionally seen on the summits of mountains in Spitzbergen and in Lapland are of the same nature as the northern lights. Similar appearances have also been seen in other parts of the world. Electrical currents that develop themselves in the earth when the auroras are present are not induction phenomena caused by the atmospheric auroral currents, at least not in northern regions.—19 C, VII., 383.

THE SPECTRUM OF THE AURORA BOREALIS.

The late Professor Angström, who at no time accepted the theory that the spectra of gases varied with the pressure and temperature and chemical process, advanced the opinion that the spectrum of the aurora borealis is composed of two dif ferent superposed spectra, the one consisting of extremely feeble bands of light, belonging to the spectrum of the negative pole, the other consisting of a single strong yellow line, which is characteristic of the aurora, and which, Angström believed, owes its origin to fluorescence or phosphorescence. -12 A, X., 211.

THE GEOGRAPHICAL DISTRILUTION OF AURORAS.

In a recent paper in Petermann's geographical notices, Professor Fritz, of Berne, gives the results of his researches into the geographical distribution of auroras. Having as far as possible eliminated the sources of error arising from the

fact that few observers preserve complete records of the aurora, and that few records which continue over a number of years have a uniform degree of completeness at all times; having also eliminated the periodic changes, both the diurnal and the annual, and after making allowance for the relative cloudiness of the different stations, Fritz presents a map compiled from the records for upward of two hundred places in Europe, Asia, and America. He discusses with great care. the probable value of the observations, and then draws lines of equal frequency of auroral display, or isochasms.

The zone of maximum frequency is a narrow belt passing just north of the North Cape and the Siberian coast, through the northern part of Spitzbergen, and near Point Barrow, Great Bear Lake and Nain on the coast of Labrador. According as we go from this zone northward or southward, we come to regions of gradually diminishing frequency and diminishing intensity of auroral display; and it is important to observe that, while south of this zone of maximum frequency the auroral arches are generally seen north of the observer, they appear to stations on the north of it to be south of the observer's zenith, while to those upon the zone they appear indifferently to the north or south. The whole system of belts deduced by Dr. Fritz has very great similarity to, and almost coincides with, those given by Muncke in 1820, and by Loomis in 1856. The curves of equal frequency generally cut the magnetic meridians at right angles, and apparently follow the borders of the continents and the limits of perpetual ice; upon which fact Professor Fritz seems inclined to dwell with special attention, and to conclude therefrom that the atmospheric electricity produced by the friction of winds blowing over ice-fields has something to do with the exhibition of the aurora. It has been suggested, in carrying out the same idea, that it may not be unlikely that the aurora varies with the increase and decrease of the ice, whence, by analogy, it may be concluded that the neighborhood of the Alps may influence the frequent displays of aurora seen in Northern Italy.—12 A, XI., 14.

GROUND CURRENTS AND THE AURORA,

In some remarks on the auroras of February 4, 1871, and 1872, Mr. Tarry states that it appears from the observations

made at the telegraph bureau at Brest that magnetic and telegraphic disturbances preceded, accompanied, and fol lowed the apparition, which was a visible but, in fact, only secondary part of the phenomena. The aurora borealis is in reality a magnetic storm, as defined by Humboldt, and it is only by the study of the changes experienced by terrestrial magnetism during these apparitions that we shall come upon the true cause of the phenomenon; moreover, inasmuch as the magnetic disturbances are always recognizable long before the appearance of the aurora, we can easily predict the latter. The disturbances of terrestrial magnetism have probably a cosmical cause, and it is impossible to study them properly except throughout the whole world simultaneously.-Nouvelles Meteorologiques, p. 36.

THE CELESTIAL INDICATOR

Is the name of a pretty piece of apparatus, patented, we believe, by Mauperin, of Paris. It is designed to enable one to determine instantly the name of any star or constellation by simply pointing in its direction with the indicator of the instrument. The apparatus consists essentially of a tripod stand supporting a circular table, which may be inclined at any angle to the horizon. On this table is engraved a map of the stars, and its circumference is divided into degrees and the divisions of the year. From its centre there stands up a column which revolves about its axis, and supports at its top a pointer. This pointer is movable about its centre in a plane perpendicular to the table, while in a horizontal direction it carries a second pointer, fixed at the base of the column, and therefore in close contact with the map of the stars. It of course follows that when the upper pointer is directed toward any stars, and the star map is properly oriented for the day and the hour, the lower pointer will then cover the star in question, and its name may be read on the chart. A lantern attached to the table illuminates the chart sufficiently, so that the whole stand may be carried out of doors and used there with convenience. The indicator may also be used for the inverse process; that is, for making charts, and, perhaps with advantage, may be employed by observers of shooting-stars and auroras, might also, at least in principle, be extremely convenient

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