PHYSICS — WHITEHEAD, WOOD. 255 



Whitehead, John B., Johns Hopkins University, Baltimore, Mary- 

 land. Grant No. 178. Study of the ?nag?ietic effect of electric 

 displacemc?it. (Continuation of Grant No. 59.) $1,200. 



Abstract of Report. — Alternating displacement currents were set up 

 in a cylinder of paraffin by means of an alternating electromotive 

 force impressed on electrodes on the two faces of the cylinder. The 

 cylinder was surrounded by a magnetic circuit of soft iron lamina- 

 tions which was wound with many turns of fine wire. If the displace- 

 ment currents have a magnetic effect, an alternating electromotive 

 force should be set up in the secondary winding. The calculation 

 of the magnitude of the effect from Maxwell's equation necessitated 

 a large size for the apparatus, a high value of the impressed electro- 

 motive force, and an instrument for measuring alternating currents 

 of the order of magnitude io~ fi amperes. In the experiments these 

 conditions were met and results in good agreement with the values 

 as calculated from Maxwell's assumptions were obtained. 



A method for observing the analogous electric effect of magnetic dis- 

 placement has been suggested by Kolacek in discussing the writer's 

 former work. The results indicate that the various factors and quan- 

 tities involved can not be increased to values necessary to give results 

 which may be observed by experimental methods now at our disposal. 



Wood, Robert W., Johns Hopkins University, Baltimore, Md. Grant 

 No. 248. Researches on the theory of light. (For previous reports see 

 Year Book No. 2, p. xxxix, and Year Book No. 3, p. 128.) $1,000. 



The fltwrescence of sodium vapor and the resonance radiation of elec- 

 trons. — The work begun on this subject two years ago has been con- 

 tinued, and the results have been published in the Philosophical 

 Magazine for November. 



The fluorescence spectrum of the vapor of metallic sodium has 

 been photographed, the vapor being illuminated with highly homo- 

 geneous light of varying wave-length. It has been found that cer- 

 tain lines in the fluorescence spectrum are associated, indicating that 

 the molecule contains a number of groups of electrons, the stimula- 

 tion of any one of which by light of the same period as that of the 

 electron sets the entire group in vibration, without, however, disturb- 

 ing any of the other groups. 



If the wave-length of the exciting light is gradually changed, the 

 lines in the fluorescent spectrum appear to dance about with a rippling 

 motion, an illusion due to their periodic disappearance and reappear- 

 ance. Very remarkable changes in the distribution of intensity in 

 the fluorescent spectrum have been observed to accompany changes 

 in the wave-length of the exciting light. 



