SCIENCE. 



[N. S. Vol. XVI. No. 414. 



by any of his predecessors. The commer- 

 cial importance of the mercury pump had 

 but recently been greatly enhanced by the 

 introduction of vacuum bulbs for incandes- 

 cent electric lighting. In one of these a 

 vacuum of one millionth is sufficient. 

 Crookes had attained a vacuum of one 

 seventeen-millionth. Rood's improvements 

 added scarcely anything to the cost of the 

 piunp, but he attained a vacuum estimated 

 to be very nearly one four-hundred-mil- 

 lionth. 



The results of Professor Rood's extended 

 researches on color were collected by him 

 into a volume, entitled 'Modern Chro- 

 matics,' which was published in 1879. 

 This book at once became a standard, and 

 has continued to be so to the present time. 

 The author's style is so easy and clear as 

 to be readily intelligible to the non-profes- 

 sional reader, but without any sacrifice of 

 scientific truth. He frankly adopts the 

 theory of color-vision propounded by 

 Young and extended by Helmholtz, accept- 

 ing it as the best working theory, what- 

 ever may be the difficulties based on 

 purely psychological grounds. During the 

 twenty-three years that have elapsed since 

 the publication of this book the number of 

 theories of color-vision that have been 

 brought forward is so great that only pro- 

 fessional psj'chologists can be expected to 

 know them. If any one of them should 

 ever be established, its adoption will not 

 detract from the value of the present vol- 

 ume. Since 1890 the author has published 

 two noteworthy papers on physiological 

 optics, one on 'A Color System,' and the 

 other on 'A Photometric Method which is 

 Independent of Color. ' In his hands, and 

 also those of others, the 'flicker' photometer 

 invented by him has jdelded results quite 

 comparable in accuracy with what is at- 

 tainable by the use of instruments intended 

 exclusively for comparison of lights of the 

 same hue. 



One of the last researches published by 

 Professor Rood was on 'Regular or Spec- 

 ular Reflection of the Rontgen Rays from 

 Polished Metallic Surfaces.' The experi- 

 ments seemed to indicate that a small per- 

 centage of these rays may be reflected from 

 polished surfaces, and that they consist 

 probably of transverse waves like those of 

 ordinary light, but of shorter length. 



Professor Rood was essentially a student, 

 devoted to pure science, and not in sym- 

 pathy with the commercial spirit which has 

 so long tended to deter American students 

 from choosing science for a career. This 

 fact caiised him to appear to many as a 

 recluse. But he always had a welcome for 

 those who could understand his point of 

 view; and the present writer remembers 

 with keen pleasure the kindly words and 

 generous encouragement accorded by the 

 distinguished physicist to a young stranger 

 who, more than twenty years ago, formed 

 his acqiiaintance on the basis of two 

 articles, just published, on physiological 

 optics. The friendship thus started was 

 never broken. 



W. Le Conte Stevens. 



Washington and Lee Univeksitt. 



INTERNATIONAL CONGRESS OF AMERICAN- 

 ISTS AT NEW YORK. 



In accordance with the invitation of the 

 American j\Iuseiun of Natural History, ex- 

 tended throiigh its President, Mr. Morris K. 

 Jesup, and the Due de Loubat, the Thir- 

 teenth Session of the Congres International 

 des Amerieanistes met in New York during 

 the week from Monday to Saturday, October 

 20-25. The preparations for the meeting 

 were under the auspices of the Committee 

 on Organization, which consisted of Morris 

 K. Jesup (President), the Due de Loubat 

 (Vice-President), M. H. Saville (General 

 Secretary), Harlan I. Smith (Treasurer) 

 and the following members representing 

 learned and scientific institutions: Franz 



