

October i8, 1900] 



NA TURE 



597 



section deals with aberration ; it is supposed that the 

 ether in a moving body remains, so far as the motion of 

 the body is concerned, at rest. Thus another term has 

 to be added to the expression for the current ; the ions 

 are carried with the body, and give rise to a convection 

 current. 



This assumption appears, however, open to criticism. 

 Since the total charge in any element of volume is zero, 

 the total convection current due to the motion of that 

 element, as a whole, must also be zero. The case differs 

 from that in which the oppositely charged ions are set 

 in motion in opposite directions by electric force. The 

 fact that the axes to which we refer the relative motions 

 of the ions are themselves in motion, introduces new 

 terms into the equations which are sufficient to account 

 for aberration without assuming the existence of this 

 convection current. 



The consequences of this relative motion are ex- 

 amined, following H. A. Lorentz, to whose labour on 

 this subject so much of our knowledge is due, and an 

 explanation given of aberration and of Fizeau's celebrated 

 experiment on the effect of moving water on the velocity 

 of light. 



In all this work Prof. Drude has been most successful ; 

 the electromagnetic theory, supplemented by the one 

 additional hypothesis of the moving ions, serves to co- 

 ordinate in a satisfactory way very many of the phenomena 

 of light. 



Further knowledge may modify our views, but up to 

 the present Prof. Drude's book contains the most rational 

 account of the phenomena of optics which we possess ; 

 it is a book which should be read by all students, and 

 he is to be congratulated on having written it. 



And now having said this, in conclusion a grumble 

 and a suggestion may be permitted. There is no index, 

 and though the table of contents is a full one, this can 

 never replace an index. Again, the book would be more 

 interesting and more valuable, and would give a fairer 

 account of the subject, if the references to original papers, 

 especially papers published some time back and in other 

 countries besides Germany, were more complete. A 

 second edition will be called for before long. Will Prof. 

 Drude increase the gratitude due to him for his work by 

 remedying these two defects ? 



AGRICULTURAL EDUCATION IN THE 

 UNITED STATES. 

 Year-book of the United States Department of Agriculture, 

 1899. Pp. 880 ; 63 plates. (Washington: Government 

 Printing Office, 1900.) 



THE present volume is a special one, the Secretary of 

 Agriculture desiring ''that the Year-book for 1899, 

 the distribution of which will occur during the last year 

 of this century, shall present to the reader a picture of 

 the development of agriculture in the United States 

 during the nineteenth century, and of its condition at 

 the present time." The volume contains twenty-six 

 reports, from the various bureaux and divisions under 

 the Department of Agriculture. These reports are 

 followed by an appendix giving particulars respecting 

 the various agricultural organisations now at work in the 

 country. The whole is copiously illustrated. 

 The various reports on the development of knowledge 

 NO. 1616, VOL. 62] 



and of work during the past century are of course 

 written in a popular style, being primarily intended for 

 the information of the general community in the United 

 States ; we must not, therefore, expect to find in them 

 much exact science. They are, nevertheless, of great 

 permanent value, and should be carefully studied by all 

 those who desire that the agriculture and the agricul- 

 turist of Great Britain should exhibit the rapid progress 

 in improvement which this volume shows to be taking 

 place on the other side of the Atlantic. 



As the subject of agricultural education is now occupy- 

 ing the public mind in England, it will perhaps be of 

 service if we briefly mention what is at present being 

 done in America, as set forth in the volume now 

 before us. 



The Report dealing with education informs us that the 

 attempts to introduce instruction in agriculture into 

 elementary rural schools have failed. Now, however, a 

 hopeful movement has been started by the College of 

 Agriculture at Cornell University, and taken up by some 

 other State colleges, for the introduction of " nature 

 studies" into elementary schools. To accomplish this 

 object leaflets containing suitable matter for lessons have 

 been issued, and model lessons are given in the schools 

 by travelling inspectors. The first difficulty to be sur- 

 mounted is, in fact, the teaching of the teachers. Up to 

 the present time little has been done toward the estab- 

 lishment of second grade agricultural schools, and 

 agricultural subjects are not as yet taught in the High 

 Schools. 



In America, the State College or University, with 

 the Experiment Station attached to it, have been the 

 prime movers in agricultural education. The colleges 

 have by no means confined their work to their own 

 students, but have actively carried on a large amount of 

 external teaching of various kinds. Thus, besides the 

 full course of instruction, lasting two or four years, 

 provided for the members of the college, short winter 

 courses of twelve weeks' instruction are in many 

 cases provided for the special requirements of young 

 farmers, and in some States these short courses have 

 been very successful. The staff of the college and 

 experiment stations also do much good by lecturing at 

 farmers' institutes. These institutes will meet for a 

 session of three days in various places, the time being 

 occupied by a series of papers and discussions. It is 

 estimated that about 2000 of these meetings were held in 

 the United States during 1898, attended by half a million 

 farmers. In Wisconsin the best papers are issued as an 

 annual volume, 60,000 copies of which are distributed, 

 one being placed in the library of every elementary 

 school. The practical influence of these institutes has 

 been very great. Several State colleges have also com- 

 menced correspondence classes in agriculture, and have 

 enrolled a large number of readers who receive assistance 

 and advice from the college. The influence of the ex- 

 periment stations has also been very great ; their inves- 

 tigations have produced a local interest in the study of 

 agricultural problems, and afforded examples of the aid 

 which science can render to the farmer. Without the 

 v/ork of the station the teaching of the college would 

 have appeared academic and theoretical, and would have 

 failed to commend itself to the practical man. The 



