that general attention which its intrinsic brilliancy deserved; nor was the analysis of its light as instructive as might have been expected.

However, something has been done since last we adverted to the subject, which ought to find place in these pages, as giving additional information with regard to the Rings of Saturn, the most astonishing and incomprehensible feature of the planetary system. It was suggested, in our number for March last, that discovery was not at an end in that quarter, and the planet, though too near the horizon to admit of satisfactory scrutiny in England, has been more advantageously situated for observation in America. The oppo1tunity has not been thrown away. Mr. Trouvelot, an astronomer attached to the observatory of Harvard College, Cambridge, U.S, has been making a careful study of the planet with several excellent telescopes, including the great 26-inch achromatic of the Washington Observatory, the largest as yet constructed; and has arrived at some interesting results. For the satisfaction of those who may not have given much attention to the subject, we shall mention that irregularities of a perplexing character have been long noticed in the outline of the shadow of the ball where it falls across the rings. The laws which determine the form and perspective appearance of shadows are so well known in all cases as to admit of no doubt as to the operation of some unexplained cause for such deviations, supposing their existence to be established by adequate evidence. And of this, notwithstanding their minuteness, no doubt can be entertained. Traces of such abnormal forms were noticed by Schröter as far back as 1792, and by Sir W. Herschel in 1806: after a long interval the suspicion is renewed, and assumes the form of certainty in 1850, and the following six years, during the investigations of such observers as Lassell, Dawes, De la Rue, Secchi, Jacob, and Bond with his staff; the latter having given us no less than forty drawings of these peculiarities, made with the great 15inch achromatic of Harvard College. A considerable proportion of the deviations might indeed be accounted for on the supposition of a ring-system thick enough to admit of a very irregular and undulating surface; but some of the observed phenomena would still be outstanding; and the explanation is rendered after all wholly inapplicable by the edgeways presentation of the rings every fifteen

years, which proves their extreme tenuity: at those epochs they almost if not entirely disappear. It is interesting at the present time to find that Mr. Trouvelot has, after a considerable interval, confirmed the existence of these mysterious phenomena, by finding that the outline of the shadow of the globe upon the rings, especially the outer one, is in a state of constant change. Whatever explanation may be attempted, the fact is now beyond controversy.

The same observer has also found that the inner edge of the exterior ring is not perfectly regular, a phenomenon which is probably connected with the varying aspect, long ago and repeatedly noted, of the form and breadth of the dark opening, termed Ball's division from its discoverers in 1665, which separates the two principal rings. He remarks, also, a spotted and cloudy aspect of the brighter part of the rings during the last four years, and has satisfied himself that the innermost dusky ring, or "crape veil," as it has been called, which in 1852 was sufficiently transparent to permit the outline of the ball behind it to be traced across its whole breadth, now corresponds to that description only in its inner portion-the exterior half having become opaque enough to intercept what lies beyond it. It deserves, however, to be borne in mind, in connection with this observation, that various astronomers between 1850 and 1856 had noticed a diminution of brightness inwards in the breadth of this ring, naturally pointing to an increase of transparency. The total inference from this recent most careful scrutiny is the confirmation of what might have been previously inferred a degree of mystery, as well as a tendency to instability, in the arrangements of this magnificent object. When we consider that the total breadth of the ring-system is upwards of 37,000 miles, with a thickness variously estimated from 100 down to 40 miles, we shall be better prepared to admit the probability of marvels, as yet perhaps unsuspected, in this region. We have no intention of speculating upon the subject; it is sufficient to revert to the fact, mentioned on a former occasion, that on mathematical grounds the idea of its continuous structure, either solid or fluid, is considered untenable; and no other hypothesis seems to remain excepting Proctor's ingenious idea of streams of innumerable satellites, or a wide-extended plane of vapour, or possibly unknown matter in some viscous condition, of unequal and varying density.

The sole phenomenon of exceptional character, to which we have already alluded as marking the close of the year, has been the wholly unexpected appearance of a new star in the constellation Cygnus. This was first perceived by Schmidt, at Athens, on November 24, of the third magnitude, after a scrutiny of the vicinity on November 20, in which it was imperceptible. It had by December 15 become invisible to the naked eye, but is still conspicuous, and only slowly decreasing, in the telescope. The discoverer considered its light always a deep yellow; to M. Paul Henry it seemed, when of fifth magnitude, greenish, almost blue. On December 5 M. Cornu succeeded in examining its spectrum satisfactorily with the great equatorial at Paris, and found it extremely remarkable, containing eight bright lines on a less luminous background, which was almost entirely interrupted by darkness between the green and the blue. Three of the lines coincided with those of hydrogen, one with magnesium, one with either sodium, or more probably one of the unknown bright lines in the solar chromosphere; the latter also is the case with the two remaining lines in the star's light. So that we find a striking correspondence between some at least of the materials of this sudden outburst, and those of our own sun-a remarkable and suggestive fact, paralleled to a certain extent by the spectrum of the last new star T Coronæ, discovered by Birmingham in 1867. It is much to be regretted that the great new stars of former days-that of Tycho in 1572, which was visible even at noon-day, and that of Kepler in 1604, which surpassed the lustre of Jupiter-preceded the invention of the spectroscope; in such intense developments of light we have every reason to suppose that its composition and origin would have been very distinctly revealed. Yet, wonderful and fascinating as these investigations are, the curiosity of man soon finds its limit. We scarcely, after all the aids of modern science, know what it is that we are gazing at. We can better estimate what it is not. It is not a conflagration, natural as such an impression might be. The outbreak is not one of combustion, such as that of an ordinary fire. There is no destruction, or more properly rearrangement, of material. The original elements do not disappear by assuming fresh chemical forms, as in the flames of earth. There is only a greatly exalted incandescence, a vehemently intensified glow, of certain gaseous

elements. We can in part imitate this in our laboratory experiments, but under conditions involving great uncertainties as to heat and pressure, as well as the very embarrassing complication of electro-polar influence. At present, therefore, it is preferable to be very cautious in our inferences. It is, at any rate, sufficiently evident that so great an increase of luminosity must have been accompanied by a corresponding evolution of heat-such heat, that had our earth been a planet circulating round that distant sun, it must inevitably have met its final doom. This well deserves our serious thought. And in the meantime the little that we can see of such phenomena, renewed as they are from time to time, is abundantly sufficient to disprove the old cavil of the sceptic, that" all things continue as they were from the beginning of the creation."

BIOLOGY.-BY PROFESSOR W. R. MCNAB, M.D.

N such a report as the present it is obviously impossible to do

literature of Biology is very extensive, and some idea of its extent in one department only, namely that of Botany, may be got by consulting that admirable work the "Botanischer Jahresbericht," edited by Dr. L. Just. The selection of one or two papers from the works of over a thousand botanical writers is a difficult task, and only such as are of some general interest, and have special bearings on the progress of science, can be noticed. In the present paper three or four papers will be noticed, while scores of others of equal interest and scientific importance must be passed over.

Naturalists have long devoted attention to the study of the animal and vegetable cell, indeed ever since the days of Schleiden and Schwann, and gradually our knowledge of the subject has been increasing, and becoming more accurate as it became more extensive. At first, attention was chiefly directed to the study of the cell-wall, with its markings and characteristic sculpturing. Then it was discovered that the protoplasm was the important part of the cell: and accordingly that marvellous substance was carefully scrutinised. Now-a-days the little rounded bodies in the protoplasm called nuclei are being studied with great care, and all the refinements of microchemical research brought to bear on them.

Professor Auerbach of Breslau describes the nuclei of cells as being flexible and elastic vesicles surrounded by a doubly-contoured membrane. Within are small more or less rounded smooth bodies called nucleoli, and numerous exceedingly minute granules. According to Auerbach, the nuclei first appear as clear spaces in the granular protoplasm, as vacuoles filled with a clear tenacious fluid mass, and possessing no distinct wall. After a time each vacuole becomes enveloped by a wall which is formed by the inmost layer of the protoplasm of the cell, but forming a definite investing wall not separable from the nucleus. In his researches Auerbach chiefly studied the ova of two small parasitic worms. The little egg shortly after it has been fertilised, and before the wonderful process of segmentation has begun, consists merely of a mass of protoplasm and yolk-granules, the nucleus or germinal vesicle having entirely disappeared, although it was present nearly up to the time the little egg arrived at maturity. The substance of the nucleus seems to have become distributed through the protoplasm of the cell. When the egg begins to divide into two it is noticed that at each end of the mass of protoplasm a clear ill-defined space, somewhat star-like in form, begins to appear. These grow large and change their form, while little spots or nucleoli form in the interior. The two new structures or pronuclei now begin to move inwards towards the centre of the cell, leaving a clear track behind them: when the centre is reached the two pronuclei touch, elongation occurs, and the two pronuclei fuse together to form the true nucleus. Elongation of the nucleus now begins; radiating lines are seen to form, so that the nucleus now looks like two stars united by a central band. The mass of protoplasm next separates into two. Two vacuoles form in the band uniting

the stars. The vacuoles increase in size, and form nuclei, one in each segment, and the star-like figure gradually disappears. The star-like figures are described by Auerbach as Karyolytic figures.

Similar researches have been made by Professor Strasburger of Jena on the nuclei and modes of cell formation in plants. Other observations have been made on animal cells, by Dr. Buetschli, Dr. Oscar Hertwig, and Professor Van Beneden of Liége. The general result of these researches is to show a wonderful similarity in the details of the process of cell-division in animals and in plants. It is, however, somewhat curious that there are several methods of cell