SCIENCE 



A WEEKLY JOURNAL DEVOTED TO THE ADVANCEMENT OF SCIENCE, PUBLISHING THE 



OFFICIAL NOTICES AND PROCEEDINGS OF THE AMERICAN ASSOCIATION 



FOR THE ADVANCEMENT OF SCIENCE. 



EditoeIjJL Committee : S. Newcomb, Mathematics ; E. S. "Woodward, Mechanics ; E. C. Piokeeing, 

 Astronomy ; T. C. Mendenhall, Physics ; R, H. Thurston, Engineering ; Ira Eemskn, Chemistry ; 

 Charles D. Waloott, Geology ; W. M. Davis, Physiography ; Heney F. Osboen, Paleon- 

 tology ; W. K. Brooks, C. Hart Mbrkiam, Zoology ; S. H. Scudder, Entomology ; C. E. 

 Bkssey, N. L. Brixton, Botany ; C. S. Minot, Embryology, Histology ; H. P. Bow- 

 ditch, Physiology ; J. S. Billings, Hygiene ; William H. Welch, Pathol- 

 ogy ; J. McKeen Cattell, Psychology ; J. W. Powell, Anthropology. 



Friday, July 18, 1902. 



coy TEN T8: 



The American Association for the Advance- 

 ment of Science: — 

 The Ch-oup-velooity and the Wave-velocity 



of Light : Professor D. B. Brace 81 



Prehistoric Porto Rico : De. J. Walter 



Eewkes 94 



Remarks of the Retiring President and of 



the President-elect 109 



Report of the Permanent Secretary 110 



Scientific Books: — 



Ortmann's Reports of the Princeton Uni- 

 versity Expedition to Patagonia. Sacha- 

 roff's Das Eisen als das thatige Prinzip der 

 Enzyme und der lebendigen Suistanz: Pro- 

 fessor Lafayette B. Mendel. Dickson's 

 Linear Groups with an Exposition of the 

 Galois Field Theory: Dr. G. A. Miller. . . Ill 



Scientific Journals and Articles 114 



Discussion and Correspondence : — 



A Method of Fixing the Type in Certain 

 Genera 114 



Shorter Articles: — 



The Prevention of Molds on Cigars: Rod- 

 ney H. Tetie 115 



The Graduate School of Agriculture . 116 



Scientific Notes and News 116 



University and Educational News 120 



MSS. intended for publication and books, etc., intended 

 for review should be sent to ttie responsible editor, Pro- 

 fessor J. McKeen Cattell, Garrison-on-Hudson, N. Y. 



THE GROUP-VELOCITY AND TEE WAVE- 

 VELOCITY OF LIGHT* 



Although the determination of the im- 

 portant constant of nature — the velocity 

 of light— has occupied the attention of sci- 

 entists from the time of Galileo, and while 

 astronomical and terrestrial methods have 

 been so carefully refined that individual 

 observers have obtained values differing 

 by less than one part in 3,000, it is a sig- 

 nificant fact that no terrestrial method thus 

 far used gives the absolute velocity of 

 light under all conditions. If a group 

 of periodic disturbances are radiated out 

 into any medium the velocity of the indi- 

 vidual elements will in general be different 

 from that of the mean of the group. Only 

 in the one instance, the propagation in 

 vacuo, is it likely that these two velocities 

 are the same; and here physical methods, 

 thus far, have not put the question to a 

 test. In the case of ponderable media im- 

 portant data are to be expected. The 

 astronomical method used by Eomer in 

 1675 and founded on the observation of 

 the eclipse of Jupiter's satellites gives the 

 so-called group-velocity of light in vacuo. 

 The observation of the fixed stars discov- 

 ered by Bradley in 1727 gives the wave- 



* Address of the retiring President and Chair- 

 man of Section B — Physics — of the American 

 Association for the Advancement of Science, 

 Pittsburgh meeting, June 28 to July 3^ 1902. 



