426 



THE POPULAR SCIENCE MONTHLY. 



take up and continue the circulation com- 

 menced 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 tem- 

 perature or of specific gravity is insignificant, 

 though no doubt these play their part, espe- 

 cially in causing slow under circulations, and 

 in a larger degree the vertical mixing of the 

 lower waters. 



Progress in Indexing Chemiral Litera- 

 tnret The Committee of the American As- 

 sociation on Indexing Chemical Literature 

 reports the printing during the past year of 

 A. C. Langmuir's Index to the Liteiature of 

 Didymium, and the second volume of Mr. 

 Trjmble's Bibliography of the Tannins. 

 Reports have been received by the com- 

 mittee 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 pro- 

 ductions 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 Interna- 

 tional Conference of Geologists at Washing- 

 ton appointed a committee to prepare a list 

 of the geologic bibliographies now in exist- 

 ence. A committee of the Torrey Botanical 

 Club is publishing an index to recent lit- 

 erature relating to American botany. The 

 Smithsonian Institution is publishing a series 

 of bibliographies of aboriginal languages. 



Seenlar Magnetic Clianges. In discuss- 

 ing the problems and conclusions suggested 

 by the Magnetic Survey of the United King- 

 dom, Prof. A. W. Riicker observed that the 

 question of the cause of the magnetic varia- 

 tions 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 ex- 

 plained 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 pro- 

 ducing or profoundly modifying the influ- 

 ences 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 varia- 

 tions in the state of magnetized matter. 

 We need not now consider the sudden jerks 

 that disturb the diurnal sweeps of the mag- 

 net, which are simultaneous at places far 

 apart, and probably originate in causes out- 

 side our globe. But the slower secular 

 change, of which the small part that has 

 been observed has taken centuries to ac- 

 complish, 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 im- 

 portance 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 im- 

 proved, and are now more complete than at 

 any previous time, and the increased circu- 

 lation that these bulletins have attained am- 

 ply attests their value. It is believed that 

 there is no other class of information to 

 which so much space is devoted in the pub- 

 lic press to-day. A file of these bulletins 

 for all the States for a year will form the 

 most complete history of the weather condi- 

 tions 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 organi- 



