RESEARCHES RELATIVE TO THE NEBULÆ. BY PROFESSOR GAUTIER he Smithsonian Institution from the Archives des Sciences Physiques et Naturelles, Geneva, 1862. no part of the vast field of the astronomy of observation which is at the object of persevering explorations. I propose on this occaa cursory view of those which relate to a widely extended and ous class of celestial objects, which was first made a subject of -y by the distinguished astronomers Herschel and Messier, and ord Ross, by Fathers De Vico and Secchi, and by MM. Lamont, Bond; a subject which presents peculiar difficulties, and respecting e remains much to be cleared up. I allude to the nebulæ, those sh patches, of feeble light, which the telescope reveals to us in great the heavens, and which powerful instruments enable us, for the zo recognize as assemblages of stars, situated at enormous distances rth. apid review I shall follow, in general, the order of dates, and I shall by saying a few words of a catalogue of the positions in the heavens ee nebulæ, the result of observations made at the observatory of M. Langier, principally in 1848 and 1849, and by him presented to my of Sciences of Paris at its sitting of December 12, 1853. This published in the Compte Rendu of that sitting, gives with the precision of a degree the right ascensions and mean declinations of the centre rilliant point of those nebula to January 1, 1850, as well as the s between these positions and those resulting from the catalogues of and Messier. It is a first attempt at precise determinations of the f a certain number of nebulæ, undertaken with a view of serving to the sequel, the question whether these bodies are really situated he fixed stars which are visible to us. RESEARCHES RELATIVE TO THE NEBULA OF ORION. -pounoff, director of the observatory of Kazan, in the beginning of 1856 to the Academy of Sciences of Petersburgh, through the medium of Struve, a memoir on the great nebula of Orion, being the result of ions made for four years with an equatorial telescope of the power of Dorpat and a meridian circle of Repsold.* He has applied himself ow this memoir only from a very succinct mention of it at the end of the number of thly Notices of the Astronomical Society of London for March 14, 1856, vol. xvi, As I shall frequently have to cite this compilation, as well as that published at by Dr. Peters under the title of Astronomische Nachrichten, I shall designate them wely by their initial letters, M. N. and A. N. observatory of Poulkova, the labors of t results of his researches in a commuesented to the Astronomical Society by I published in the seventeenth volume bing the variableness of the lustre of ula of Orion-a variableness which he f his observations with those of other as of his own.* "The existence of so so limited a space of the central part as must naturally lead to the supposition nnected with the mysterious nature of rapid changes of light observed in these Huygens or in that called Subnebulosa, bula, it might be presumed that changes rance of the nebula and in the distribuervations of this kind are subject to so sufficiently reserved in the conclusions at the course commonly pursued by es-the comparison, namely, with one nade at different epochs by different hich can be regarded as indubitable. ansparency of the atmosphere, varying of the observer's eye, the measure of esentations of the kind-all this, joined the observer, forms obstacles which it proceeding after this manner. It might method for centuries, to discover prose can never be thus verified which take the rapid variations of light in the stars d perhaps periodical, variations in the It is therefore to rapid changes of this ■ur attention, and we shall be better able observations on the degree of light and of the nebula than by representing it in t I endeavored to proceed during last -on me was a strong one that, at different within the short period of my observaegard them as positive facts until they by observers stationed in more favorable -umentalities sufficient for the purpose." e."t this work of M. O. Struve, in a Notice on the the numbers of the Bibliotheque Universelle ber and October, 1857. M. Otto Struve has of the great Russian observatory of Poulkova. ect has been published, I believe, in vol. ii of a t Astronomiques. of concentrated light about mi The twenty-second volume alternating with the more obs I cannot enter here into the Bond's memoir, and I shall c general aspect of the greater tufts or curvilinear pencils of Day, wich пав never been seen by Dir Jonn Merscnti. a nebulous bridge, which crosses the great straits, with a point 1 light about midway. M. Struve saw it in winter, sometimes as - Herschel, sometimes as by Liapounoff, with much greater conight, but always much more extended than in the representations nomers, and closely approaching the southern limit of the great faint traces of it are indicated by M. Lamont, while Professor see it at all. The third is a nebulosity surrounding star 75 of atalogue, which appeared to M. Struve to be subject to great ightness. Lastly, the fourth part is a sort of narrow canal, uniting ne the obscure space situated around the stars 76, 80, and 84, of atalogue, with the north side of the great strait, near the exterior I the bridge before mentioned. The canal, which has not been by any other observer, was distinctly seen by M. Struve March 24, on other occasions he has not perceived the least trace of it. onomer, in closing his communication, adds, that the general imulting from his observations is to the effect that the central part of of Orion is in a state of continual change of brightness as regards 3 portions. In those cases where the images were most distinct, rance did not seem entirely uniform from night to night. These the degree of light cannot, however, be perceived in the greater cases without instruments of considerable optical power; and he does hat achromatic telescopes of less than ten inches opening can serve nem, except under atmospheric conditions extraordinarily favorable. enty-second volume of the M. N. (pp. 203–207) contains the analysis memoir relating to the same nebula. It was communicated to the cal Society, May 10, 1861, by Professor George Bond, who has sucfather in the direction of the observatory of Harvard College, at e, near Boston. The paper bears for its title, On the spiral structure eat nebula of Orion. sor Bond the father, in a memoir published in 1848, had already that the light of this nebula seemed to present a radiated appearance uthern side, starting from the neighborhood of the trapezium of stars towards its middle. Professor G. Bond has undertaken, since 1857, catalogue of the stars comprised in a square of forty minutes to the ing 0 of Orion for its centre. He selected one hundred and twenty-one cars as guiding points to which to refer the smaller stars, of too feeble r the most part, to remain visible under a strong illumination of the etric threads. In a first sheet he has arranged two hundred and sixtyrs, and then subdivided the same surface into four charts, finally reunited ingle one. The form and arrangement of the elongated luminous tufts, ting with the more obscure spaces stretching from the neighborhood of pezium, have been determined by two independent procedures, the nebula irst delineated as a bright object on a dark ground, and then as a dark on a white ground. nnot enter here into the descriptive details given in the analysis of Prof. s memoir, and I shall confine myself to a report of its conclusion. The l aspect of the greater part of the nebula of Orion is an assemblage of or curvilinear pencils of luminous matter, emanating from bright masses 1 conformation, which had escaped both great number of cases, the masses of nebfrequently under the form of small tufts He cites two remarkable instances where ear stars of considerable brilliancy; the f, whose obscure centre has been remarked e star Iota of Orion. These peculiarities to the supposition of a physical associa he existence of an arrangement in a spiral ecords with the idea of a stellar constituresent this peculiarity of form are found - but masses of stars properly so called, s of stars of the constellation Hercules, y a curvilinear arrangement. TING TO THE NEBULE. observatory of Dr. Lee, at Hartwell, in læ, or mass of stars, No. 80 of the catastellation of the Scorpion, and very close the Scorpion, which have been observed th of May this nebulæ had its usual aspect, he 28th of the same month Mr. Pogson nagnitude, which has been also observed raud Auwers at Köningsberg, and which omething more than the 7th magnitude. magnifying power of 66, the stellar apt the nebule had a greater brilliancy than condensation. M. Pogson does not think a change in the nebulæ itself, but he restar, the third comprised in the same field uated between the earth and that nebulæ. in the twenty-first volume of the M. N., ecently, with M. Foucault's great reflectted as to procure a great degree of enlargeand he has ascertained that it is in reality stars, closely crowded together, the brights of the small diameter. This nebulæ, in sented to him the appearance of a hollow arallel to its axis; and its centre, as Lord ain of nebulous matter, which converts itlittle stars. M. Chacornac adds, in a comect, dated Paris, 9th June, 1862, and pubwhen the view is screened from all internultitude of luminous points, occupying a retina, produces a sort of giddiness which Dons of the nebu 16 feet focal length, the optic po M. d'Arrest, making his obse scarcely combine the observation the microscopic reading of the c new catalogue will not assign, w position of each object on the co the minute of a degree in right a are very carefully compared wi annular and thread micrometers taining with precision their prol constitutes one of the principal astronomer has published, in No 20th May, 1862, of his later 1 tails, tending to complete those læ, with a large achromatic telescope, of 11 inches opening anu ngth, the optic power of which he estimates to be intermediate Herschel's 20 feet reflecting telescope, and that of the telescope ad with which Lassell likewise has observed the nebulæ from The telescope of Copenhagen has enabled M. d'Arrest not ze all the nebula of Herschel, but to discover more than a hunamong 776 observed in eight months. He has been enabled also, e circumstances and with some difficulty, to see certain nebulæ assell. -, making his observations alone, soon perceived that he could ine the observation of celestial objects of very feeble light with ic reading of the circles of his instrument. It follows that his e will not assign, with all the precision attainable, the absolute ch object on the celestial sphere. This position is only given to a degree in right ascension and in declination; but as the nebulæ fully compared with the neighboring small,stars by the help of hread micrometers, we shall thus have competent means for ascerprecision their proper movements in respect to those stars, which me of the principal aims of the researches of M. d'Arrest. This has published, in No. 1366 of the A. N., an interesting notice, dated 1862, of his later labors; and from this I shall extract some deg to complete those which precede. VARIABILITY OF THE BRIGHTNESS OF THE NEBULE. est considers as well established one of the results of the great gelander, in which has originated his new catalogue of stars, namely, 000 stars already well recognized, there exists but a small number The brightness is periodically variable; and he believes the same rmed, though with less certainty, to be very nearly the case with Herschel had subdivided the nebulæ into three classes, with reference elative degree of brightness. M. d'Arrest has found a great many in which the nebulæ, as at first classed by Herschel, must now be asone or even two units a new place in the classification. Herschel ad, in the course of some years, changed several of his appreciations. ew of the great diversity of atmospheric influences in humid climates, pon observations of this kind, M. d'Arrest thinks, like M. Otto Struve, impossible to be too circumspect in regard to the conclusions to be deHe instances, however, a small numom variabilities of this nature. ases in which some degree of variability has been positively ascer rst of these cases is that resulting from the observations of M. O. Struve nebula of Orion before spoken of. The observations of this nebula made, at different times and in favorable nights, by M. d'Arrest, with telescope, have confirmed those of M. Struve, particularly as regards * See M. N., vol. xvii, p. 48.⚫ |