SCIENCE 



Editorial Committee : S. Newcomb, Mathematics ; R. S. Woodward, Mechanics ; E. C. Pickering, As- 

 tronomy ; T. C. Mendbnhall, Physics ; R. H. Thdrston, Engineering ; Ira Remsen, Chemistry ; 

 J. Le Conte, Geology; W. M. Davis, Physiography; 0. C. Marsh, Paleontology; W. K. Brooks, 

 Invertehrate Zoology ; C. Hart Mereiam, Vertebrate Zoology ; S. H. Scudder, Entomology ; 

 N. L. Britton, Botany ; Henry F. Osborn, General Biology ; H. P. Bowditch, 

 Physiology ; J. S. Billings, Hygiene ; J. McKebn Cattell, Psychology ; 

 Daniel G. Brinton, J. W. Powell, Anthropology. 



Friday, Septembee 20, 1895. 



CONTENTS: 



Springfield Meeting of the American Association for 



the Advancement of Science : — 349 



Section B. Physics: William Hallock. Sec- 

 tion C. Chemistry : W. A. NoYES, A. H. Gill, 

 Francis C. Phillips. Section D. Mechanical 

 Science and Engineering. 



Development of Vegetable Physiology: J. C. Ar- 

 thur 360 



Current Notes on Physiography {XVI.): — 373 



National Geographic Monographs; The Composite 

 Origin of Topographic Forms; Tidal Streams 

 about the British Isles ; Meteorological Charts of 

 the Bed Sea : W. M. Davis. 



Preliminary Note on a Contagious Insect Disease: 

 S. A. Forbes 375 



Scientific Notes and News: 376 



University and Educational Neios 378 



Correspondence: — 379 



Are Consequences Ever a Test of Truth ? JOSEPH 

 Le Conte. Tlie Katydid's Orchestra : George 

 M. Gould. 



Scientific Literature : — 381 



Foster's Physiology : W. T. Porter. Nehrling's 

 North American Birds : C. H. M. 



Scientific Journals: 383 



The American Geologist; Ihe Astrophysical 

 Journal. 



New Books 384 



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

 for review should be sent to the responsible editor, Prof. J. 

 McKeen Cattell, Garrison on Hudson, N. Y. 



Subscriptions and advertisements should be sent to Science, 

 41 N. Queen St., Lancaster, Fa., or 41 East 49th St., New York. 



SPRINGFIELD MEETING OF THE AMERICAN 

 ASSOCIATION FOR THE ADVANCE- 

 MENT OF SCIENCE. 

 SECTION B. PHYSICS. 



The address of the Vice-President, Prof. 

 W. Le Conte Stevens, was upon ' Eecent 



Progress in Optics.' He introduced the 

 subject by referring to the impossibility of 

 summarizing all of the work, even of a 

 meritorious order, that has been accom- 

 lished, and preferred to discuss certain in- 

 vestigations of special merit. First among 

 these was the standardizing of the metre in 

 terms of a wave-length of light, an investi- 

 gation begun by Michelson and Morley 

 eight years ago, and recently completed by 

 Michelson at the observatory of the Inter- 

 national Bureau of Weights and Measures 

 near Paris. A brief description was given 

 of the construction and use of the interfer- 

 ential comparer, and the difficulties encoun- 

 tered in securing a perfectly homogeneous 

 spectrum tint. Spectral lines that had 

 been supposed to be single, and hence due 

 to approximately homogeneous light, were 

 found to be multiple, presenting the phe- 

 nomenon of optical beats, or maxima and 

 minima of brightness in the interference 

 fringes that pass across the field of view in 

 the observing telescope. So delicate is the 

 method that it is possible to detect a varia- 

 tion of wave-length corresponding to as little 

 as one-thousandth of the interval between the 

 two main components of what is commonly 

 known as the sodium line. The red line of 

 cadmium was found the most nearly simple 

 of all those examined, and the length of 

 the standard meter was determined to be 

 1,553,163.5 wave-lengths of cadmium light. 

 This was the mean of two independent 



