362 SCIENCE PROGRESS 



(5) An investigation of the spectra of stars belonging to 



class R of the Draper classification. 



(6) A study of ft Cephei. 



(7) The spectrum and radial velocity of p Leonis. 



PHYSICS. By James Rice, M.A., University, Liverpool. 



In the Proc. Roy. Soc, June 191 8, Professor Strutt gives an 

 account of experiments to test if light is scattered by dust-free 

 air, and finds that by proper arrangement of experimental 

 conditions it is possible to observe the scattering by pure air, 

 free of dust, in a small-scale laboratory experiment. Other 

 gases also scatter, hydrogen much less than air, oxygen about 

 the same, carbon dioxide decidedly more. The scattered light 

 is in all cases blue and is almost completely polarised, illustra- 

 ting directly the well-known theory of the blue sky. In the 

 Phil. Mag. for September last, Prof. Wood, criticising Strutt 's 

 research from the point of view of some earlier, unpublished 

 work of his own, suggests that the effect was due to a cloud 

 resulting from the action of the ultra-violet rays in the light 

 on the air. In the October number of the Phil. Mag. Strutt 

 replies to the effect that he was aware of the necessity of guard- 

 ing against spurious results such as Wood suggests, and that 

 the intensity of the light which he used, and the fact that it 

 could not have been rich in ultra-violet rays, were such as to 

 guarantee the soundness of his conclusion. He promises the 

 publication of further results in a forthcoming number of the 

 Proc. Roy. Soc. 



In the Phil. Mag. for September G. A. Hemsalech gives 

 an account of a research on the comparison of the flame and 

 furnace spectra of iron. He summarises his work in the state- 

 ment that the spectra of iron as given by an electric-tube 

 resistance furnace at atmospheric pressure and up to a tem- 

 perature of about 2,400° C. are caused by the action of heat on 

 a chemical compound of the metal and not on the free metal 

 itself. Hence .these spectra are not of purely thermal origin. 

 An iron spectrum observed at as low a temperature as 1,500° C. 

 is the same as that given by an air flame burning in coal gas. 

 The spectra emitted by iron compounds in flames are identical 

 with those given by the furnace at corresponding temperatures 

 up to about 2,400° C. From this and other considerations the 

 author concludes that the mode of excitation is the same in 



