Chemistry and Physics. 447 



the bulb and of the angle between the reflecting surface and the 

 axis of the incident beam of molecules. As yet no satisfactory 

 explanation of the cause of the superior limit of the angles of 

 reflection has been published. — Phil. Mag., xxx, p. 300, August, 

 1915. h. s. cr. 



6. The Stark Effect for Solids. — The question as to whether 

 excitation by canal-ray bombardment is a necessary condition for 

 the electric resolution of spectral lines is suggested by the fact 

 that in the single case where a different mode of excitation was 

 emjjlojed, the Stark effect could not be detected. During the 

 past year this problem has been attacked by C. E. Mendenhall 

 and R. W. Wood, and negative results were invariably obtained. 

 This fact is of no little importance at the present time and hence 

 a brief account of the experimental conditions may be of general 

 interest. 



Most of the data were obtained photographically with grating 

 spectrographs, and the electric fields were applied by means of a 

 motor-driven Wimshurst machine. In order to have the spectral 

 lines as narrow as possible the solids studied were usually main- 

 tained at the temperature of liquid air. The strong, sharp fluor- 

 escent line at X 5736, which was radiated by a certain specimen 

 of Weardale fluorite, was the first to be examined. A gradient 

 of about 50,000 volts per cm. produced no sensible change in the 

 line which was excited (at room temperature) by the light from a 

 heavy spark between magnesium electrodes. Also this field did 

 not alter the amount of polarization of the light which was 

 emitted at right angles to the lines of force. An attempt to 

 detect the longitudinal Zeeman effect, at liquid-air temperature 

 and with a field of 22,000 gauss, met with no success. Negative 

 results were likewise obtained when the line was examined for 

 selective absorption of its own wave-length, both with and with- 

 out fluorescent excitation. 



The next lines studied were the brilliant red fluorescent 

 pair of the ruby (XX 6932 and 6946), which are stimulated 

 by a wide range of visible and ultra-violet radiations, but most 

 strongly by the yellow-green. A field of 45,000 volts per cm. did 

 not produce the slightest change in these lines. In this case 

 there is a sharp absorption doublet of the same wave-lengths, but 

 this too was quite uninfluenced by the electric field. When the 

 temperature of the ruby was changed from 23° C. to —180° C. 

 the lines became much sharper and each one shifted toward the 

 violet by 12 A. A number of interesting phenomena were pre- 

 sented by the eighteen lines of the fluorescent spectrum when 

 examined in magnetic fields, but lack of space and diagrams will 

 necessitate reference to the original paper. With regard to the 

 resonance radiation of the ruby the authors make the following 

 remarks. " Careful tests, using sunlight dispersed by a mono- 

 chromatic illuminator to excite with, showed that the strong red 

 emission lines are excited by light of their own wave-length. 

 This, or a similar effect in the case of a solid or liquid, has not 



Am. Jour. Sci.— Fourth Series, Vol. XL, No. 238. — October, 1915. 

 29 



