612 



SCIENCE 



[N. S. Vol. XXVII. No. 694 



by the components of the electric and mag- 

 netic forces which lie perpendicular to the 

 direction of motion of the system. This is 

 a highly general result and is obtained by 

 a method involving the generalized con- 

 straints of the system. 



When the second order of the ratio v/V 

 may be neglected, Wy is equal to two thirds 

 the total electromagnetic energy (W) of 

 the system (because of the average sym- 

 metry before mentioned), and hence we 



have 



Mass = 4/3 l/V W. 



This gives the electromagnetic mass of 

 the system in terms of its total energy 

 content. 



If the electrical theory of matter be ac- 

 cepted this result applies to the mass of 

 any piece of matter and we have the mass 

 proportional to the total contained energy. 



It is shown that if this hypothesis is 

 accepted the irregularities which exist in 

 the table of atomic weights ax'e in har- 

 mony with the evolutionary theory of the 

 elements. 



Also on this basis gravitation must be 

 considered as acting between quantities of 

 confined energy and not between masses in 

 any other sense. 



Method of Determining the Modulus of 

 Bending of a Flat Spring: E. S. Wood- 

 WAED, Carnegie Institution of Washing- 

 ton. , (Read by title.) 

 The inethod applies especially to a iini- 

 form flat spring held rigidly and horizon- 

 tally at one end but otherwise free to as- 

 sume the shape due to its weight. The 

 exact theory of this shape shows that meas- 

 urements (1) of the vertical sag of the 

 spring at any point of its length, (2) of 

 its weight per unit length, and (3) the 

 total length of its free part will give the 

 modulus of bending. 



An Investigation of the Optical Properties 



of Films of Magnetic Metals: C. A. 



Skinnee and A. Q. Tool, University of 



Nebraska. 



This paper deals with the magnetic rota- 

 tion and ellipticity produced by films of 

 iron, cobalt and nickel of definite thick- 

 nesses together with the refractive indices, 

 reflection and transmission of the same. 



It appears that two distinct types of 

 films may be produced by cathode deposit 

 in vacuo, one a metallic the other a dark 

 film. The difference does not arise from 

 the gas in which the films are produced, for 

 they are alike, whether hydrogen, nitrogen 

 or helium be used as gas filling. 



The optical properties of these different 

 types are quite different, and they also 

 differ from those obtained by electrolytic 

 deposition. Both iron and cobalt in the 

 metallic type possess magnetic rotary power 

 four times as large as the electrolytic films, 

 while the dark types exhibit a rotary power 

 remarkably smaller than the electrolytic. 

 The ellipticity imparted to the transmitted 

 ray is affected to an equal degree. 



Dark films of iron have an absorption 

 region in the blue and in this region the 

 magnetic rotation and ellipticity reverse 

 their directions, as might be predicted from 

 the characteristics exhibited by other sub- 

 stances possessing an absorption region in 

 the visible spectrum. Dark films of cobalt 

 show also interesting results in the visible 

 spectrum, which duplicate in a sense the 

 results from the iron. 



Only metallic films of nickel could be 

 obtained and these exhibited effects almost 

 too small to measure. 



The Electric Double Refraction of Carhon 

 Bisulphide: Chaeles F. Hagenow, Ar- 

 mour Institute. 



In insulating media subjected to an elec- 

 tric field, light waves vibrating in the direc- 

 tion of the field are propagated at a veloc- 



