186 RECORDS. 



For sodium light where the wave-length, I, is 0.0005893 mm., 



( 0.2929 — 

 / o.ooo5893A^\ 



(^0.2929 pi-j 



o.ooo5893A^\^ 

 0.5 + (^0.2929 j 



This method has been extended to the measurement of 

 doubly refracting plates, such as mica. The plate crystalline 

 must contain in its plane at least one of the axes of the so-called 

 ellipsoid of elasticity, and must be mounted with this axis 

 vertical. The bands may be observed through a Nicol prism 

 having its shorter diagonal vertical. 



Dr. G. B. Warring detailed the results of some interesting ex- 

 periments with the gyroscope. The paper led to an interesting 

 discussion. 



S. A. Mitchell, 



Sccretaiy. 



SECTION OF BIOLOGY. 



May II, 1903. 



A regular monthly meeting was held at the American Mu- 

 seum of Natural History on May i i, Professor Bashford Dean 

 presiding. 



The following papers were presented and read : 



H. F. Osborn, On Recent Models and Restorations of a 

 Number of Extinct Animals, with a Discussion of their 

 Probable Habits and Modes of Life. 



E. L. Thorndike, Natural Selection and Fertility in 

 Man. 



C. T. Brues, The Internal Factors of Regejsieration and 

 Reversal of Asymmetry in the Crustacean Alpheus. 



Summary of Papers. 



Professor Osborn's paper was based upon models and restora- 

 tions from the Department of Vertebrate Paleontology of the 

 American Museum of Natural History, prepared by Charles 



