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space at great speed, show a difference from a discussion of measurements of in velocity of 200 km. per second. 299 plates taken with 13 different telThis apparently indicates a rapid ro-escopes with apertures ranging from tation of the nebula. He further suspects a rotation of the great Andromeda nebula. Wolf announces that he has found evidence of the rotation of the nebula M81 Ursa Majoris at a velocity of the order of 300 km. per second. Lalande 1966 is found to have a radial velocity of 325 km. per second, the largest so far observed among the stars.

Photometry. By careful experimentation (A. N., 4720) Wilsing finds that the ratio of the intensity of a ray emerging from a system of Nicol prisms to the intensity of the incident ray is independent of wavelength (between λ 4250 and X 6300), and that within an interval of 3.5 magnitudes the ratio is given by Malus' law.

Capon (M. N., April, 1914) and Zurhellen (A. N., 4729) independently discuss the effect of the motion of the source on the velocity of light from the evidence furnished by the observation of spectroscopic binaries, and conclude that any such effect is very small. The Ritz emission theory calls for a constant velocity of the center of the light wave, equal to the velocity of the source at the instant of emission.

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Kron (Potsdam Publ. No. 67) has carried out an elaborate investigation of the law of blackening of photographic plates. He finds that in the formula: blackening function of (brightness of source X exposure time), the exponent p is a variable, having the value 1 (hence reducing to the old reciprocity law) for the "optimale Intensität," the light which produces the greatest effect upon the plate in the shortest time. Each kind | of plate has its peculiar law, which is altered by altering the manner of development.

Great industry is being shown in establishing a reliable foundation for the photographic photometry of the sky. The Harvard sequence of stars near the North Pole has been extended by Seares, working with the 60-in. reflector on Mt. Wilson, and a comparison of the two scales made. The complete sequence now contains 96 stars whose magnitudes have been derived

0.5 to 60 in. (Harv. Ann. lxxi, No. 3). Several wholly independent methods for determining absolute magnitudes have been used. Errors from order of exposure and distance from center of plate have been fully investigated. The so-called "color equation" of the individual instrumental equipment proves a very important factor. The observed difference between visual and photographic brightness for different spectral types varies with the absorption of the lenses, the sensitiveness of the plate and the observer's eye, the character of the photometer used, etc. The "color equation" of a catalogue of photometric results can be determined quite closely. It is now proposed to enlarge the international definition of photographic magnitudes to read as follows: "Photographic magnitudes coincide with visual magnitudes on the Harvard system for stars having spectra of class A, between the magnitudes 5.5 and 6.5, and are fainter than the visual magnitudes by 1.00 magnitude for stars having spectra of class K, between the same limits." Seares concludes that a photographic magnitude can be determined with a probable error of ±0.11 magnitudes. catalogue of the photographic magnitudes of all stars brighter than the ninth magnitude and within 15° of the North Pole has been made at the Greenwich Observatory. The probable error of a single observation is stated to be 0.064 magnitude. The catalogue is based on the Harvard sequence. Halm, at the Cape Observatory, has determined the photographic magnitudes of a sequence of stars near the South Pole (M. N., lxxiv, 600). Martin and Plummer have published (ibid., 225) a photographic light-curve of the variable XZ Cygni.

A

The variation of this star is of the Cephei type. The probable error of a single measurement, ±0.02 to ±0.03 mag., obtained by Martin, is remarkably small.

If the Andromeda nebula consists of a central star involved in nebulous matter which is illumined by the star, as Reynolds believes, then the lightcurve along the major axis of the nebula should be the inverse square

curve x*y constant. Reynolds finds | with great variation in density; an by observation a curve very similar almost complete absence in the Milky but flattened at the apex.

Bright stars are more variable than faint ones, according to D'Esterre, who finds from a study of 34,000 stars that while one in every 277 stars brighter than the ninth magnitude is a variable, the ratio among the fainter stars is but one in 16,900.

Radiation and Color.-A successful attempt to measure the heat radiation from the stars was reported by Coblentz at the Evanston meeting of the American Astronomical Society. With the Crossley reflector of the Lick Observatory, stars of the fourth magnitude gave measurable deflections. The reddest stars, such as a Herculis and ß Pegasi, radiate very much more heat in proportion to their light than the white stars.

The faint stars were found to be redder than the bright stars in two fields where Seares compared the photographic with the visual brightness (Ap. J., xxxix, 361). Tikhoff obtains a similar result in the Pleiades. Evidence to this effect has been accumulating for some time.

Number and Distribution of Stars. -Henie publishes (Lund Obs. Publ., ser. ii, no. 10) a chart showing the distribution of the stars to the eleventh magnitude, as derived from a count of selected areas of the 55 glass negatives of the Harvard Map. The Milky Way is well defined, and the total number of stars to the eleventh magnitude is found to be 1,013,328.

A count of the stars in each photographic magnitude to the eighteenth, made by Chapman and Melotte, leads to the conclusions that the condensation to the galaxy is the same for all magnitudes; that the rate of increase of the number of stars diminishes steadily from the sixth magnitude downward; that one-half of all the stars are fainter than the 23d or 24th magnitude; and that the total number of stars is not less than one billion (Royal Astron. Soc. Memoirs, lx, pt. 4).

The number of nebulæ down to the limit of one-hour plates taken with the Mt. Wilson 60-in. is estimated by Fath from selected counts at 160,000. The nebula show a striking condensation toward the galactic poles but

Way; and no systematic orientation of their planes. The "white" nebulæ are much the more numerous.

Parallax and Proper Motion.-The accumulation of accurate stellar parallaxes is, from the nature of the problem, slow, but is likely to become more rapid, as many of the great observatories are at work on the problem by photographic methods.

A fairly reliable estimate of the distance of stars too far away to be measured directly can be obtained by general reasoning, based on known statistics, from their radial velocities, proper motions, stream motions, apparent magnitudes and color indices. Certain assumptions are necessarily involved. These methods are exemplified in a remarkable manner by Kapteyn in a determination of the individual parallaxes of the brighter helium stars in the southern hemisphere, between galactic latitudes 30° and galactic longitudes 216°-360° (Ap. J., xl, 43). Three hundred and nineteen stars brighter than the sixth magnitude were discussed. All but four per cent. of the helium stars within the limits chosen are shown to belong to one stream directed toward right ascension 18h 18m, declination +42, and moving at a velocity of 18.3 km. per second. The parallaxes are found by the method previously used for the Hyades and Ursa Major groups. It is shown that the helium group is quite sharply limited in distance as well as in longitude and latitude. About onehalf of these stars are more than 100 times as bright as our sun and several, such as ẞ Centauri and κ and X Scorpii, are 1,000 to 2,500 times as bright.

K

From a discussion along general lines based on the proper motions shown by 3,700 Carrington stars around the North Pole from 1855 to 1900, Dyson (Nature, xliii, 574) draws many interesting conclusions concerning the distribution of the stars. The stars thin out very materially at great distances-80 per cent. of the stars discussed lie between 100 and 500 "parsecs." The yellow stars average the nearest, the red stars the farthest and most luminous. Ninety to 95 per cent. of all the stars discussed are brighter than the sun.

Gyllenberg and Wicksell have determined the axes and orientation in space of the ellipsoids which represent the direction and amount of the velocities of radial and proper motion of the stars. For the radial velocities an ellipsoid is found whose longest and shortest axes are in the plane of the Milky Way. Proper motions give a more oblate ellipsoid with the shortest axis directed toward the pole of the Milky Way.

Stellar Evolution.-Russell, writing in Nature and the Observatory during the year, has brought together much evidence with which to champion the view that the accepted interpretation of the classification of stellar spectra does not represent the complete history of stellar development. According to his opinion, and that of some others, the observable order of evolution begins with large diffuse bodies of low temperature but bright on account of their great surface area. As the star contracts its temperature rises, counteracting the effects of diminished size and leaving the star still bright. When the density reaches about one-tenth that of the sun, the temperature is at a maximum. After this the temperature falls and the brightness rapidly decreases. The "giant stars" of great luminosity are thus regarded as in an early stage of evolution, particularly the reddest ones, while the relatively faint "dwarf stars" represent the later stages. Only the most massive stars should reach the highest temperatures. The stars of spectrum B are almost certainly the hottest and also the most massive.

Dynamics. -Jeans (Phil. Trans., 213) arrives at the conclusion that the ideal incompressible mass, whose stability has been discussed by Darwin, Poincaré and others, supplies a surprisingly good model by which to study the behavior of compressible, heterogeneous masses, at least in the spheroidal form. He finds that the most "dangerous" modes of vibration are common to both classes and that they leave the symmetrical figure at about the same velocity of rotation.

Absorption of Light in Space.— The problem of determining a possible absorption of light as it travels through space has received considerable attention during the year. Several independent researches show that the apparently faint stars are, on the average, redder than the brighter ones. If the faint stars are farther away than the bright ones, then the color of stars of the same spectrum is affected by distance. One of the possible causes is the absorption of light in space. Adams has recently compared the spectra of pairs of stars of the same spectral type, one known to be near, the other assumed from its small proper motion to be more distant (Ap. J., xxxix, 89). In a few cases the spectrum of the nearer star was found to be distinctly more intense in the violet, and in no case was the opposite condition observed. More recently, however (Ap. J., xl, 67) he and Kohlschütter have discussed a large number of radial velocity spectrograms and have found that the continuous spectra of the small proper motion stars are decidedly less intense in the violet region relatively to the red than the spectra of the nearer and smaller stars, but that this effect must be ascribed in large part to conditions in the stellar atmospheres, since it varies with the spectral type. A considerable number of the small proper motion stars show hydrogen lines of abnormally great intensity, which radial velocity measurements show to be produced almost entirely in the stars themselves. Further, these authors find that certain lines are usually strong in the small proper motion stars and other lines strong in the large proper motion stars. The intensities of these lines in pairs are found to serve as a measure of the absolute magnitudes of the stars, giv ing results in good agreement with those found from parallax and proper motion. Hnatek (A. N., 4731) finds no difference in the temperature of near and distant stars of the same type. Tikhoff finds evidence of a selective absorption in the ultraviolet, disappearing very quickly toward the longer wave-lengths.

XXIII. GEOLOGY, METEOROLOGY, AND GEOGRAPHY

GEOLOGY

DYNAMIC AND STRUCTURAL GEOLOGY

J. B. WOODWORTH

Geophysics: Isostasy. The experimental investigation of the condition of the earth's interior has been notably advanced recently by Michelson (Jour. of Geol., xxii, 97-130) in a novel manner (see XXII, Astronomy), confirming the deduction previously demonstrated by the seismographic record of the rate of propagation of vibrations through the earth, that its inner mass possesses a coefficient of rigidity as great as or greater than that of steel. Michelson interprets his observations as meaning that the coefficient of viscosity of the earth's interior has also the same high value. In the matter of isostatic compensation Gilbert (U. S. Geol. Surv., Prof. Paper 85) reviews the work of Hayford and Bowie on gravity anomalies, discusses several suggested interpretations, and is led to discard the assumption of uncompensated excesses and deficiencies in mass in the earth-crust in favor of the view that the anomalies of gravity "express chiefly an effect of heterogeneity in the nucleus and an effect of irregularity in the vertical distribution of densities in the crust." On the more strictly geological side which takes account of the known structure of the crust, T. C. Chamberlain and Joseph Barrell (Jour. of Geol., xxi and xxii) discuss at length the rôle of isostasy as a factor in crustal deformation and accord it a minor part. Hobbs analyzes the structures and folding movements in great arcuate mountain ranges of Tertiary time (ibid., xxii).

Geological Climate: Glacial Periods. -The recognition of glacial deposits

in the geologic section prior to the well-known surface moraines of the "glacial period" goes on by leaps and bounds. Atwood announced in December, 1913, the discovery by the U. S. Geological Survey of a typical bed of tillite in the San Juan Mountains of southwestern Colorado, either of late Cretaceous or early Eocene age. Schuchert (Carnegie Inst., Publ. 192) reviews the evidence, including ancient glaciation, bearing on "Climates of Geologic Time." The distribution of volcanic dust in the air, suggested by W. J. Humphreys (Bull. Mt. Weather Obs., Wash., vi, pt. i, 1-34), Schuchert finds does not appear to be a primary factor in bringing in glacial climates. He concludes that the markedly varying climates of the past seem to be due primarily to periodic changes in the form of the earth's surface, accompanied by variations in the amount of heat stored by the oceans. M. L. Fuller (U. S. Geol. Surv., Prof. Paper 82) has presented a compendious and detailed account of the geology of Long Island, N. Y., including the terminal moraine and older glacial deposits. Evidence of four glacial epochs are found, represented by till or by outwash gravels and separated by three interglacial episodes characterized by erosion, deposition of clay or the formation of peat deposits. The excavation of the Hudson submarine channel is referred to the Pleistocene period. In the same report the Cretaceous deposits of the island are subdivided and mapped in the light of the most recent survey. J. W. Goldthwaite (Geol. Surv. of Canada, Summary Rept., 1914, 357) reports on the marine shore lines in southeastern Quebec. H. L. Fairchild (Bull. Geol. Soc. Am., xxv, 219-242)

argues that the terraces and plains in the Connecticut Valley were deposited in waters at sea level at the close of the glacial period. G. D. Hubbard (Am. Jour. Sci., May, 1914) finds evidence of tilted glacial lake shore lines in Ashland and Wayne counties, Ohio. The tilt rate is given as four feet per mile rise to the north. W. C. Alden and E. Stebinger (Bull. Geol. Soc. Am., xxiv, 529-572) describe in greater detail than heretofore the extension of pre-Wisconsin glacial drift in the region of the Glacier National Park in Montana.

Transportation of Débris by Running Water. The Italian hydrographers Guglielmini and Frisi laid the foundations of the subject which Gilbert (U. S. Geol. Surv., Prof. Paper 86) has subjected to critical experiment and vigorous mathematical treatment in the most notable contribution to the advance of geological science during the past year (see also Physical Geography of Land Areas, infra). In the matter of sediments, Grabau (Bull. Geol. Soc. Am., xxiv, 711-713) gives a classification of marine deposits. On the interpretation of the peneplain of the northern Appalachian region, Barrell (ibid., xxiv, 688) offers the explanation that this ancient land surface consists in reality of a series of piedmont terraces cut by marine action. Barrell correlates these terraces with coastal plain deposits varying in age from the Lower Cretaceous (Comanchean epoch) to the Pliocene.

Geological Time-Table for North America. - Schuchert and Barrell (Am. Jour. Sci., xxxviii, July, 1914) have published a "Revised Geologic Time-Table for North America." The term Waucobian is employed for the Lower Cambrian, Croixian for the Upper Cambrian. Chamberlain and Salisbury are followed in the use of Comanchean for the Lower Cretace

ous.

Origin of Coal. The origin of coal in all its aspects has received notable attention in recent publications. David White (U. S. Geol. Surv., Prof. Paper 85 E) points out the occurrence of resins in Cretaceous and Tertiary coals, and argues for the origin of high-grade coal in peat. In a report "The Origin of Coal" (U. S. Bu

reau of Mines, Bull. 38) White and Thiessen discuss at length the conditions attending the formation of coal, refuting the algae hypothesis and holding that all coal was laid down in beds analogous to the peat beds of to-day. All kinds of plants went into the deposit. Coal is chiefly composed of the residue of plants, resins, resin waxes, waxes, and higher fats or derivatives therefrom. The various grades of coal result from decomposition, elimination, maceration, and chemical reduction begun in peat, modified by biochemical agencies in the peat stage and dynamochemical agencies during the coal stages. C. A. Davis contributes to the work a chapter (pp. 165-186) on the "Origin and Formation of Peat." E. C. Jeffrey (Bull. Geol. Soc. Am., xxiv, 715-716) finds that the "mother of coal," otherwise known as fusain, faserkohle, etc., is the charred or partly charred vestige of woody structures. Coals containing mother of coal are ascribed to deposition of vegetable matter in open lakes and not to the growth of peat bogs. (See also Economic Geology, infra.)

Progress of Geological Surveys.— The national and state surveys continue to publish geological maps and accompanying descriptive texts of extensive areas. In the eastern United States these maps represent resurveys called for by advance in the classification of formations or by the development of new industries demanding a closer discrimination between rocks of economic use. The geological map of New Jersey, 1914, by Lewis and Kummel is a conspicuous example of such work revised from time to time. Much of the work in the Rocky Mountains and westward covers hitherto unmapped areas. (See also X, Mineral Resources.)

L. F. Noble (U. S. Geol. Surv., Bull. 549) gives a detailed description of the structure of the Grand Cañon District in Arizona west of the railroad approach at Grand Cañon. D. F. MacDonald (Bull. Geol. Soc. Am., xxiv, 707-711) gives an account of the rock succession on the Isthmus of Panama. L. V. Pirsson (Am. Jour. Sci., Sept., 1914) gives the record of the deep Princess Hotel boring (1,413 ft.) on Bermuda Island.

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