lobes, a furrow passes quite across the glabella, being curved backward in the middle. Behind this is another nearly parallel furrow, and in front is a pair of faint furrows situated nearly opposite the anterior extremity of the palpebral lobe, and each traceable about one-third the distance across the glabella. Another glabella, very similar to this, shows three transverse furrows, besides the anterior interrupted furrow. A finely preserved pygidium presents a strong convexity, especially in the middle lobe. Aside from the marginal flap, the external outline is nearly semicircular, with the anterior margin considerably curved. The lateral lobes are strongly convex, becoming less so nearer the border, and abruptly joining the cau dal flap, at an inclination of about 45°. The pleuræ are furrowed in such a manner that there seems to be an accessory pleura between each two principal ones. The articulations are seven in number in both the axial and side lobes, and extend nearly to the terminal apex of the middle lobe. The caudal flap is flat, and about as wide as the middle lobe at its anterior end, and marked uniformly through its whole length by eight or more rigid concentric striæ. No indications of caudal spines. This pygidium was originally referred to this species on such information as was accessible, amongst which was Hall's figure in the Wisconsin Report (p. 22, fig. 4), showing indications of a similar striated caudal flap. I am not able by the help of Prof. Hall's last memoir to change the reference, although I perceive the pygidium does not fully agree with the complete characters now published. I am inclined to think this pygidium has not previously been described. PTYCHASPIS BARABUENSIS, n. sp. The collection embraces some fragments of the cephalic and caudal shields of a large trilobite, which, while its generic relations are somewhat indeterminate, has a certain expression which. is peculiar. The head is about 24 inches broad, and rather convex; the thickened and convex margin of the border is separated from the glabella by a narrow, concave furrow, giving the border a width of three-tenths of an inch. Posteriorly, the border is continued in genal points which attain a length not less than three times the length of the glabella. The movable cheek is swollen and separated by a deep transverse furrow from the posterior borders of the cheek. The surface is feebly scrobiculate-wrinkled; though with oblique light it is seen to be distinctly so, and the character is even better shown with a low magnifier, though the cast is preserved in sandstone. The pygidium which undoubtedly belongs to the same species is 2.9 inches across, and three-fourths of an inch in height. The middle lobe is nine-tenths of an inch across, and is quite prominent, with its posterior portion inarticulate and broadly rounded. There is no limiting furrow separating it from the, lateral lobes; and posteriorly it fades insensibly into the terminal border. The lateral lobes are but faintly articulate, and, meeting behind the axis, form a border three-fourths of an inch broad, which is strongly curved downward on all sides, and presents a circularly curved outline, without any indications of caudal appendages. The foregoing was written before seeing Prof. Hall's memoir; and I had referred the specimens to Dicellocephalus, with a query. I could scarcely doubt of their generic distinctness, but felt reluctant to engage in genus-making without ampler materials. I am happy now to recognize Prof. Hall's new genus as exactly meeting my want. This species differs from P. Miniscaënsis Hall, in its broader and fuller movable cheek and broader margin, and much longer genal points. II. The University has for many years been in possession of some fucoidal remains from the red sandstone of the south shore of Lake Superior. As it is so uncertain when any further paleontological data will be obtained from that region, I do not deem it necessary to defer longer a brief notice of these fossil Algæ. There are two methods of frond-arrangement noticeable among these remains. One exhibits a rudimentary symmetry, while the other is totally destitute of it. There is little difficulty in deciding that neither form falls under any description that has been published; but it is nearly or quite impossible to determine whether these differences are of generic, specific, or still inferior value. The great variation exhibited in the arrangement of the different portions of the fronds of recent marine algae, shows how little dependence can be placed upon descriptions founded on detached fragments of these fossil fucoids. Those differences which have been sometimes recognized as marking the bounds between distinct genera, may easily have co-existed upon the same frond. There was great plausibility in the method pursued by the older writers in referring all these remains to the single genus Fucoides. There seems, nevertheless, some prospect of utility in making such distinctions as we are able; and while I cannot vouch for the generic characters of the fossils under consideration, I shall refer them provisionally to a Paleozoic genus established by Prof. Hall to receive some fucoids from the Calciferous sandrock of New York. PALEOPHYCUS ARTICULATUS, n. sp. Consisting of large, straight or geniculated, compressed-cylindrical, irregularly articulated, branching stems. The largest stems are an inch and a quarter in diameter; the transverse section oblong, rounded at the ends, or, in other cases, more nearly a circle. The branches are uniformly much smaller than the main stem, and leave it at an angle of about 30°. One of the most marked peculiarities of the species is the somewhat regular transverse constrictions, which occur at intervals of about half an inch, in most of the specimens. At these constrictions the fucoid has shown a disposition to separate, so that most of the fragments present sharply truncate extremities. Surface smooth. This fucoid is found abundantly scattered over the surfaces of slabs of dark red, fine-grained sandstone, from the north flank of the Porcupine mountains, Lake Superior. Collected by Dr. Douglass Houghton, in 1840. PALEOPHYCUS INFORMIS, n. sp. Fucoid apparently consisting of fleshy, leaf-like masses, having an irregularly triangular, elongate, or variously amorphous outline. In some instances it would seem that a hollow, conical piece had been compressed so as to present two opposite edges. Sometimes an irregularly elongate piece presents occasional enlargements and tuberculous eminences. There are some indications that the plant was branched, some of which consist in the close approximation of co-adapted edges without complete junction. The surfaces are smooth and shining. The fragments vary from half an inch to two inches in width. Abundant in dark red sandstone from Montreal river, Lake Superior-a region where Col. Whittlesey estimates the formation to attain the enormous thickness of 15,000 feet. (Proc. Bost. Soc. Nat. Hist., ix, July, 1863.) Collected by Dr. Houghton, in 1840. Similar but thinner and more ill defined fucoids occur in red sandstone three miles west of Eagle river; and again in white sandstone near Carp river, on the south shore of Lake Superior. In associating these remains with others from the Potsdam sandstone of Wisconsin, I do not intend to express any opinion whether the Lake Superior sandstone is of Mesozoic age, as argued by Jackson and Marcou; or of the age of the Chazy formation, as recently concluded by the Canadian geologists (at least in reference to the St. Mary's sandstone); or the prolongation of the lowest fossiliferous sandstones of Wisconsin, as thought by Messrs. Foster and Whitney, and formerly by Hall, and still earlier intimated in the unpublished notes of Dr. Houghton; or finally, as now intimated by Hall, a formation ranging from a horizon below the fossiliferous sandstones of Wisconsin to the top of the Chazy formation or St. Peter's sandstone. University of Michigan, Dec. 11th, 1863. ART. XXIII.-On the Orbits of Binary Stars; by Prof. DANIEL KIRKWOOD, Bloomington, Indiana. THE whole number of double stars hitherto observed is rather more than 6000. The proportion of these in which the duplicity is merely optical cannot now be determined: the number, however, in which a change of relative position had been detected, was, at the middle of the present century no less than 650. In the motions of these bodies, so far as observed, we find one general and striking characteristic; the orbits are much more elliptical than those of our planetary system. In Sir John Herschel's Table (1850) of fourteen double stars whose orbits had been calculated, the eccentricity in seven cases is greater than that of Faye's comet (0.5559); while in the case of Alpha Centauri it is nearly equal to that of Halley's. We propose to inquire whether this remarkable fact in regard to the sidereal orbits is susceptible of explanation by the nebular hypothesis. In a former number of this Journal' it was stated that the theory of Laplace, which so beautifully accounts for so many otherwise unexplained phenomena of the solar system, might be extended to the binary and multiple systems among the so-called fixed stars. But how, it may be asked, can the same theory explain the almost circular orbits of the planets and also the extremely elliptic motions of the sidereal systems? The correllation between the members of a binary system is different from that between the sun and a planet. In the former, both are large, self-luminous bodies; on the other hand, our solar system has resulted from the concentration of the whole mass of a primitive nebula about a single nucleus. Now if a mass of nebulous matter, in which the process of condensa tion has commenced, have a very slow rotation, and if, instead of a single center of attraction, two distinct nuclei be formed, the consequence may be its complete separation into two bodies while the rotation is yet so slow that the centrifugal force as compared with the centripetal is too feeble to produce a nearly circular motion. While, therefore, orbits of small eccentricity must characterize planets formed from the abandoned equatorial rings of a condensing nebula, orbits highly elliptical may be regarded as the probable consequence of a separation in the earlier stages of its physical history. 1 The components being less than 32" asunder. 2 The eccentricity of the former is 0.95; that of the latter, 0-9674. ART. XXIV.-On the best Mode of presenting, in a popular form, the Theory of the Tides, with suggestions for constructing illustra tive apparatus; by WILLIAM DENNIS, Philadelphia, Pa. It is remarked by Sir J. Herschel that "many persons find a strange difficulty in conceiving how they (the tides) are produced;" and Mrs. Somerville goes so far as to say (Physical Sciences, C. 13), that among those classed as astronomical problems this "is by far the most difficult and its explanation the least satisfactory." This latter statement is perhaps rather broad as it stands, but if it were limited somewhat, so that the singularity of the phenomenon and the importance and familiar interest that attach to it and to its effects should be taken into account, it would scarcely require further qualification. It can hardly be denied that an intelligent comprehension of this subject is rare even among those to whom the causes of most natural phenomena are familiar, while to the great majority of intelligent people it is altogether a mystery. It seems, therefore, worth while to enquire whether the difficulties complained of have been reduced to a minimum, or whether they be not in part owing to defects or errors in the usual mode of presenting the explanation. Having had occasion, in the preparation of a new elementary treatise on astronomy, to consider this subject attentively, as well as to examine the explanations commonly given, I have been compelled to conclude that no small portion of the obscurity and perplexity commonly supposed to belong to this subject arises from the want of a proper consideration and statement of the conditions and circumstances under which the causes producing the phenomenon act. If a learner be told, (and for whom are explanations intended if not for learners?) that the waters of the ocean are raised by the moon's attraction, his first idea, in many cases, will be that they are lifted up by main strength, as it were, the force of gravity being overcome,' and having no where observed any similar effect of the moon's attraction, he cannot conceive how this can be. Nor will it tend in any degree to lessen his perplexity if he shall see it stated, (as he may,) that according to Newton's calculations, the disturbing power of the moon's attraction on the surface of the earth is less than a ten-millionth part of the force of gravity, and that of the sun's attraction not even half as great as it. It is therefore important to show, by a preliminary explanation, that the waters of the 'An idea akin to this must exist, it would seem, in the minds of those authors who speak of the lateral attraction of the moon at a given place after or before its passing the meridian of that place; as if this disturbing force, so minute at its greatest, and in respect of this lateral action, so greatly reduced by its very oblique direction, or else by the near approach of the place in question to the mean distance could ever produce any appreciable effect whatever in that way. |
