Page:Popular Science Monthly Volume 58.djvu/675

Rh Observatory photographs of the spectrum were obtained on February 22 and February 23. On these dates the spectrum was not the typical one which we have learned to expect for Nova?, but instead was of the Orion type, consisting of a strong, continuous spectrum crossed by dark lines. Between February 23 and February 24, however, a wonderful transformation took place. Since the latter date the spectrum has consisted in large part of the bright and dark bands which are characteristic of the spectra of Novæ.

first new star of which there is authentic record appeared 134 B. C. During the two thousand years which have since elapsed, nineteen more have been noted, making about one per century. This can by no means represent the true number of such stars which have appeared during that time. Doubtless only a few of the brightest have been seen. Of the twenty on record, thirteen belong to the century just ended, and six to the last decade, five of which were found on Harvard photographs. Of all the stars visible in the largest telescopes, not more than one in ten thousand can be seen by the naked eye. Thirteen of the Novæ were bright enough to be seen by the unaided vision. At the same rate for the fainter stars, if we may assume that the number of Novæ corresponds in some degree to the whole number of stars for the different magnitudes, several thousand new stars must have escaped observation during each century. No entirely satisfactory explanation has yet been given of these remarkable objects. From dark, or at least from extremely faint bodies, they suddenly blaze up and slowly fade away. Any theory which aims to explain the phenomena must at least account for certain leading facts. The increase of light is very sudden and very great. The decrease is slower and sometimes irregular, but no collision can have occurred such as would change a solid body into a gaseous, otherwise ages, not weeks, would be required for the cooling. The spectrum is generally composite, composed of bright and dark lines or bands. The bright bands are displaced toward the red, the dark bands toward the violet. If this separation is due to the relative motions of two gaseous masses, the velocities concerned appear to exceed those found elsewhere in the universe. The Nova sometimes remains as a permanent telescopic object with the spectrum of a planetary nebula. The problem might be somewhat simplified if the broadening of the lines could be due to the Zeeman effect from the presence of a strong magnetic field. It appears probable that the phenomena are due either to some outburst in the dark world itself, or else to the collisions of a solid dark world passing through a dense meteor swarm. It is to be hoped that a discussion of all the materials, which will be obtained at the different observatories during the next few weeks, may serve to formulate a theory of new stars which will receive the general approval of the scientific world.

investigations on agricultural soils which are being conducted in this country are probably unsurpassed in quality and extent by those of any country, unless it be Russia, where a very systematic and extensive line of investigations, including a survey and classification of the soils of the whole country has been in progress for a number of years. The work in this country has been carried on mainly by a number of the agricultural experiment stations and the Division of Soils of the National Department of Agriculture. The report of the Field Operations of the Division of Soils for 1899, by Prof. Milton Whitney and a number of his assistants, lately issued, is a report of progress in surveying the soils of the United States. During the year areas aggregating about 720,000 acres were studied in the field and mapped. This work has been largely confined to localities in New Mexico, Utah and Colorado, and a special feature made of studies on the