Page:Popular Science Monthly Volume 46.djvu/440

426 take up and continue the circulation commenced by the trade winds; in others they originate extensive movements of the water. Compared with the great circulation from this source the effect of differences of temperature or of specific gravity is insignificant, though no doubt these play their part, especially in causing slow under circulations, and in a larger degree the vertical mixing of the lower waters.

Progress in Indexing Chemical Literature.—The Committee of the American Association on Indexing Chemical Literature reports the printing during the past year of A. C. Langmuir's Index to the Literature of Didymium, and the second volume of Mr. Trjmble's Bibliography of the Tannins. Reports have been received by the committee of progress from several chemists on other works in this line upon which they are engaged. While the annual reports of this committee are properly confined to the productions of Americans, attention is directed to indications of a growing appreciation of the value of special bibliographies on the part of European chemists, confirming by their recent and proposed activities the work begun in America at Prof. Bolton's suggestion more than twelve years ago. The bibliographical work is extending to other branches of science. The International Conference of Geologists at Washington appointed a committee to prepare a list of the geologic bibliographies now in existence. A committee of the Torrey Botanical Club is publishing an index to recent literature relating to American botany. The Smithsonian Institution is publishing a series of bibliographies of aboriginal languages.

Secular Magnetic Changes.—In discussing the problems and conclusions suggested by the Magnetic Survey of the United Kingdom, Prof. A. W. Rücker observed that the question of the cause of the magnetic variations in the earth has entered upon a new stage. It has long been recognized that the earth is not a simple magnet, but that there are in each hemisphere one pole or point at which the dip needle is vertical, and two foci of maximum intensity. A comparison of earlier with later magnetic observations leads to the conclusion that one or both of the foci in each hemisphere is in motion, and that to this motion the secular change in the values of the magnetic elements is due. The observed changes can not be explained by any simple theory of a rotating or oscillating pair of poles; they suggest that secular change is due to waxing and waning of forces apparently exerted by secondary lines or points of attraction or repulsion. New facts lead us to look upon the earth not as magnetically inert, but as itself—at the equator as well as at the poles—producing or profoundly modifying the influences which give rise to secular change. And then, when we push our inquiry further, experience tells the same tale. The earth seems, as it were, alive with magnetic forces, be they due to electric currents or to variations in the state of magnetized matter. We need not now consider the sudden jerks that disturb the diurnal sweeps of the magnet, which are simultaneous at places far apart, and probably originate in causes outside our globe. But the slower secular change, of which the small part that has been observed has taken centuries to accomplish, is apparently also interfered with by some still slower agency, the action of which is confined within narrow limits of space.

The Weather Crop Service.—According to Major H. H. C. Dunwoody, of the National Weather Service, the weather crop service of the national bureau ranks next in importance to the work of making forecasts. The system of gathering reports upon which the weather crop bulletins are based has been greatly perfected in recent years. The crop bulletins of the States have been improved, and are now more complete than at any previous time, and the increased circulation that these bulletins have attained amply attests their value. It is believed that there is no other class of information to which so much space is devoted in the public press to-day. A file of these bulletins for all the States for a year will form the most complete history of the weather conditions attending the growth and development of the several crops throughout the country. More than ten thousand crop correspondents are to-day co-operating with the National Weather Service through the State