Evidence Of Progressive Change Research Articles

Discussions of Color Index and Spectral Type.

view Abstract Citations (9) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discussions of Color Index and Spectral Type. Seares, Frederick H. ; Joyner, Mary C. Abstract Color indices from the Mt. W. Polar Catalogue and numerous observations of spectral types made at Upsala, Harvard, Bergedorf, Yerkes, and Mount Wilson give the following results: 1. Information on the consistency of the color indices-For stars brighter than m = 9.0 and types earlier than GO the colors require a correction depending on the magnitude (Fig. 3). 2. A determination of the spectrum-color relation (Table 7, Fig. 4; international system for color, HD for spectra).-Freed from the effects of space absorption, C for A0 is -0.15 mag., in agreement with results from stars in unobscured regions. 3. A determination of the mean color excess E as afunction of distance (Table 11, Fig. 5).-To 400 parsecs (distance corrected for absorption) E increases at the rate of about 0.06 mag. per 100 parsecs. From 450 to about 700 parsecs it has an approximately constant value of 0.27 mag., as though the obscuring cloud ended a little beyond 400 parsecs. The corresponding absorptions for photographic and photovisual light (X' law) are 1.3 and 1.0 mag., respectively. The foregoing results leave for each star a residual (about 1350 in all) which includes the influence of deviations from the mean absorption E, of dispersion in color for stars of the same spectrum, and of ob- servational errors in color and in spectrum. The statistical relationships are such that these influences can be partially separated and estimated. Local zero-point errors (ME) in C for the Mt. W. Polar Catalogue are about ± 0.015 mag. (Table 12, relation [19]). Deviations from the mean E are appreciable but apparently local; the obscuring cloud extends over the polar cap north of +80° with little evidence of progressive change from side to side (Table 12, Figs. 6, 7). Except for types later than about K2, the dispersion in color for the same spectrum averages less than ± 0.035 mag. (Table 13, relation [25]). For late K and M giants it seems to be 0.1 mag. or more. Spectral-classification errors (Tables 14-14b) for early A's and for gK stars are generally smaller than for intermediate fypes. Slit spectrograms naturally show a higher precision than objective-prism plates; the errors for MW (only 53 stars available) average from 0.6 to 0.8 those for the HD in the polar re- gion, which for most types seem to be less than the average for the HD as a whole Publication: The Astrophysical Journal Pub Date: November 1943 DOI: 10.1086/144572 Bibcode: 1943ApJ....98..261S full text sources ADS | Related Materials (1) Reprint: 1943CMWCI.684....1S

Oscillations of Lake Levels and Changes of Climate

Theories of changing climate are fascinating to the student of history; seemingly conclusive on the surface, they are apt to prove inconclusive when subjected to a strict examination of facts. Cape Henlopen's famous wave of sand seemed clearly to point to a physiographic change of wind components; but an examination showed that it was due to destruction of timber and undergrowth which had held great dunes in situ. Similarly anyone who has seen the area covered by Golden Gate Park, San Francisco, with an interval of half a century between visits, would be justified in attributing the transformation to a change in the distribution of rainfall. But there was change neither of wind nor of rainfall. In every physiographic region there are species which live on the ragged edge of a precarious existence. A slight change in mean temperature or in the distribution of rainfall is the signal for their disappearance. The change may be temporary but the effects may be permanent and profound. Even within our own land the removal of protective shrubbery has been followed by destructive corrosion, leaving a given area in a condition which made reclamation impossible. A change in the efficiency of a people; a change in the demand for a commercial product of the soil; the invasion of a highly productive region by warlike intruders-all these are historical examples that have reduced fertile regions to conditions approaching those of a desert. The most productive areas in the world have been made so by irrigation. Irrigated lands are deficient in rainfall. The soil of such lands is usually very rich. It is rich because excessive rains have not leached the nutrition therefrom, thus reducing its producing power. When the cultivation of such lands ceases, they quickly revert to conditions apparently irreclamable. The foregoing does not apply to the changes in temperature which are indicated by geological data, such as the glacial periods. The evidence concerning these is fairly conclusive; in one instance it may be regarded as positive. The various glacial epochs, however, have no relation to the climatic changes which are alleged to have occurred in historic and near-historic times. Within the periods of written history there is no trustworthy evidence of progressive changes either in temperature or in rainfall occurring to productive lands. There are erratic changes, it is true, and it is probable that Bruckner has established evidence of an oscillatory period. These changes