of the plate adjacent to these will alone move the air with concordant impulses. If now the card (or the plate) be rotated n' times a second, the intensity will show n' periods per second; if the amplitude of the original vibration of the plate be a, the amplitude corresponding to the rotation of the card be a', and the pitch of the tone of the plate n, we have a=a'sin 2n'at, and hence the original tone A a sin 2nat becomes a' a A a'sin 2n'at sin 2nat= cos2(n −n) t−, cos2(n+n), 2 that is two tones of pitch n-n' and n+n' (or a graver and a higher tone) will be heard instead of the primary tone of pitch n. Thus Stefan found that a plate giving the tone fis2, which according to Quincke's table (this Journal, Nov. 1866, p. 417) corresponds to 185 n vibrations, produces, when n'=10 rotations per second, the tones f21746 and g2=196, which are very nearly 185 10. L'Institut gives fis, etc., no doubt by a mistake in translating Stefan's German notation.-L'Institut, 1866, No. 1710, p. 327; Cosmos, 1866, vol. iv, pp. 458, 459. G. H. 14. Foucault's silvered objectives for observations of the sun.— -A very ingenious method for close observation of the solar disc was communicated by Foucault in September, 1866. Having noticed that no heat and very little light is transmitted through the thin bright silvering of his glasses, he coated the outer surface of the objective of a refracting telescope with such silvering, and found, as he expected, that all heatrays were reflected, as also the greater part of the light, so as to permit only a pale bluish-violet to pass through. LeVerrier reported, October, 1866, most favorably as to the results obtained by a 9-inch refractor (equatorial). No heat could be felt in the very focus of the objective directed toward the sun-thus freeing all solar observations of a very great cause of error. Furthermore only the ultra-red rays are really absorbed; all others are, as the prismatic spectrum shows, only diminished. in intensity so as to give a steady (calme) and pure image of the sun, showing all detail of outline and color with excellent definition, and permitting a magnifying power of 300.—L'Institut, 1866, pp. 281, 313; Cosmos, 1866, iv, 387, 430. G. H. 15. Lead-thallium glass has greater density and refracting power than common lead-flint glass; 300 pure sand, 200 minium, and 335 carbonate of thallium (instead of the usual 100 carbonate of potassa), give a glass of density 4.235, index of refraction 171, and only very slight yellowish tint. It has been made in England.-L'Institut, 1866, p. 320. G. H. 16. Expansion of water and mercury; A. MATTHIESSEN.-The results of this very elaborate investigation are the volume of water at any temperature t° C. is V-a-bi+ct2-dt3, the volume at 4° C. being 1 and the coefficients The coefficient of expansion for a volume of mercury he finds from five series of determinations (per degree C.) 0.0001812 Regnault found 0.0001815. -Poggendorff's Annalen, 1866, cxxviii, 512-540. G. H. 17. On the expansion of crystals.-FIZEAU has invented a method for. the exact determination of the coëfficient of expansion of small solids (only a few millimeters thick), and obtained important results thereby (Cosmos, 1865, xxvi, 641). The following is the substance of a later and more elaborate research of Fizeau. Let the coefficient of expansion in the direction of the three axes of elasticity of any crystal be represented by a, a', a", then the expansion D in any direction determined by the three angles &, d', d", will be Da cos2 8+a' cos2 d'+a" cos2 8", and the cubical expansion is c =α+a+a", which is the same as D for d=d′ =5" =54° 41', or in a direction at right angles to the surface of a regular octahedron whose axes coincide with the directions of a, a', a". Δα Fizeau determines a for three temperatures (viz., 20°, 40° and 60° C.) from which he deduces the value for a at any temperature 9, and also the variation of a for each degree, that is which is a constant quantity. ᎪᏭ He puts the crystal with one side on a platinum support, and places a polished glass plate above the upper surface so as to leave a small interval; by means of a telescope he counts the number of fringes passing beyond certain fixed points of the support, these Newtonian rings being produced by an alcohol flame with salt, and changed by heating the whole apparatus. For the detail of this method we must refer to the original paper-we can here only give a tabular view of the results obtained thereby. At 40° C: the coefficient of linear expansion in the direction of the axis is a, at right angles to the same a', cubical expansion ca+2a', A▲ the variation for each degree; t is the temperature at which the body has a maximum of density. The unit of a, a', c and ▲ is 0.00000001, or one hundred millionth of the unit of length or volume. It is evident that t is found by c-At=0; it thus appears that the maximum of density instead of being an exception may be the rule! Fizeau has cut a needle of beryl wherewith he proposes to verify it.— Poggendorff's Annalen, 1866, cxxviii, 564-589. G. H. 18. Expansion of a conductor due to the galvanic current; by ER. EDLUND (Swedish Academy, January, 1866).-When a current passes through a conductor, the latter is heated to a certain temperature, 1, above its surroundings and consequently expanded; but it may be questioned whether this expansion is due to the temperature of the conductor, or whether it is greater, so that the galvanic current itself produces a peculiar expansion of the conductor through which it flows. That this last is the case has been experimentally demonstrated by Edlund. This expansion might perhaps be called galvanic; the usual, caloric expansion. He very carefully measured the actual expansion, E, of the conductor (platinum, iron and brass were used) and the corresponding resistance R. Next he determined the expansion produced by heat alone in the same wire, so that he accurately can determine the temperature, T,, of the conductor from E, considering this expansion due to the temperature alone. Finally, he carefully determines the influence of temperature on the conducting power of the very same wire; so that he can calculate the temperature T2, which would correspond to the above resistance R—that is, he determines the actual temperature of the conductor while the current circulates by the resistance it offers. 1 Edlund found T invariably from 1° to 10° lower than T1—or the actual expansion, E, of the conductor is greater than would be produced by the actual heating, T2, of the same, this being calculated from the measured resistance, R, of the same conductor. The expansion was not due to a change in elasticity, for the tension of the wire varying from 2 to 3 pounds did not change the result. This galvanic expansion inereases rapidly with the intensity of the current-but according to what law is still unknown.-Poggendorff's Annalen, 1866, cxxix, 15-44. II. MINERALOGY AND GEOLOGY. G. H. 1. Note on the use of the name Hudson-river group: by F, B. MEEK. -In the Introduction to the Illinois Paleontology, just published, Mr. Worthen and the writer have some remarks on the impropriety of transferring the name Hudson-river group, from the older series of contorted slates and argillaceous sandstones to which it was originally applied (existing in great force along that stream above the Highlands), to the more modern group composed of the Lorraine shales, Frankfort slates, &c., with which the true Hudson-river rocks were subsequently confounded. Since these remarks were in print, I observe we were in error in sup posing that late investigations had brought to light facts casting doubt upon the occurrence of the later types of fossils along any part of the Hudson river, in other than the little isolated masses alluded to as occupying synclinal axes in the older rocks, or entangled amongst their contorted strata. The fact, however, that the more modern types of fossils are not known to occur under other eircumstances than those mentioned, along the part of that stream regarded as the typical localities of the Hudson-river group and lying mainly between the Highlands and the region of Albany, while the name, as originally used by Conrad and Mather, was expressly applied by them to this older series, which they regarded as belonging to the Cambrian of Sedgwick, is believed to be a sufficient reason for objecting to the transfer of the name to the later group. Hence if retained at all, it is believed this name should be applied exclusively to the group of rocks for which it was originally intended, and to which it must always carry the minds of those who may look into its origin and history. As it, however, subsequently became very generally also associated with the more recent series already alluded to, it probably could not now be restricted without much inconvenience, to the rocks to which it properly belongs. Consequently the surest, if not the only, way to avoid confusion, will be to strike it entirely from our nomenclature. The name applied to the more recent rocks, in Mr. Worthen's Report on Illinois, is the Cincinnati group, from the great development and highly fossiliferous character of these beds at the wellknown city of that name in Ohio.* 2. Note on Bellinurus Dance, from the Illinois Coal-measures; by F. B. MEEK. In the Proceedings of the Academy of Natural Sciences of Philadelphia for March, 1865, and again in the Illinois Paleontological Report, Mr. Worthen and the writer have described a new species of crustacean under the name Bellinurus Danæ. In both of these publications it is stated that we had not seen the original description published by the founder of the genus Bellinurus, nor a full description of it by any other author; but that our species, although closely allied to the forms figured by Prestwich and usually referred to this genus, differs from the characters assigned it by Portlock, Owen and some others, in having its body segments anchylosed, as well as in the position of the eyes. In the Quarterly Journal of the Geological Society of London, Nov. 1865, p. 490, I observe Mr. Henry Woodward, in speaking of the genus Bellinurus, says, "the segments of the abdomen, if not anchylosed in all, are so in most" of the species. In "The Reader" of Dec. 1866, containing an abstract of the Proceedings of the London Geological Society, it is stated that in a paper read by Mr. H. Woodward, Nov. 1866, "On some points in the structure of the Xiphosura," he remarked that this group is "divisible into three genera; 1st. Bellinurus, having 5 freely articulated thoracic segments, three anchylosed abdominal ones, and a telson; 2nd. Prestwichia, a new *It has been suggested that Prof. Safford's name, Nashville group, should be retained for this formation. To this I do not seriously object: the only reason for not using it is, that Prof. S. applied it to a group including along with the so-called Hudson river rocks, the upper part of the Trenton. Hence it cannot be conveniently used when we wish to speak with precision of the later so-called Hudson river rocks, as a distinct formation from the Trenton. genus, having the thoracic and abdominal segments anchylosed together; 3d. Limulus, Müller, having a head composed of 7 cephalic and one thoracic segments, followed by 5 coalesced thoracic somites bearing branchiæ, and one or more coalesced abdominal somites, to which is articulated the telson." From this I infer, that Mr. Woodward proposes to separate as a new genus under the name Prestwichia, those species formerly referred to Bellinurus, in which the body segments are anchylosed together. If so, our Illinois species would fall into the latter group, under the name Prestwichia Danæ.* 3. Section of the Rocks of Illinois, from Worthen's Geological Report, vol. II, p. viii. POST-TERTIARY. Feet. Drift, Loess, etc.--Clay, sand, pebbles, boulders, etc........ 150 Carboniferous period. Coal-measures and Millstone grit.--Coal, shale, clay, limestones, sandstones and conglomerate,.. Mountain Limestone or Subcarboniferous period. Chester group.--Limestone, sandstone and shale, St. Louis beds.--Limestone and shale, Keokuk group.-Limestone and shale,. Burlington group.--Coarse, subcrystalline limestone, Hamilton period. Genesee division.--"Black slate" and grayish shale,..... Oriskany period. Oriskany--upper bed.--Quartzose sandstone, Oriskany-lower beds, or Clear-creek group.-Highly siliceous, very Lower Helderberg period. Lower Helderberg group, (D. shaly limestone of Niagara period. Niagara group.-Magnesian and argillaceous limestones,... LOWER SILURIAN. 150 1200 800 200 150 200 150 100 120 25 40 200 200 200 Cincinnati period. Cincinnati group.-Limestones, shales and sandstone,... 140 Trenton period. Galena and Trenton beds.-Magnesian and more or less pure limestones, Potsdam or Primordial period. St. Peter's division.-Pure quartzose sandst., 150 Calciferous division.-Magnesian limestones and sandstones,.. 120 seen. Since the publication of the Illinois Report, I observe Quenstedt figures, on tab. 21, fig. 7, of his Handb. der Petref., under the name Gampsonyx fimbriatus, a little Crustacean from the Coal-measures of Germany, almost certainly congeneric with an imperfect specimen referred by us, provisionally, to our Palæocaris typus. (See Ill. Rep., ii, pl. xxxn, fig. 5a.) If Jordan's original figure, however, of the type of the genus Gampsonyx, as reproduced by Pictet, and that given by Bronn, are even nearly accurate, the typical specimen of our genus Palæocaris must be very distinct from Gampsonyx. |