Apeu, 10, 1908] 



SCIENCE 



565 



Velocity of the Negative Ions produced 

 hy the Ultra-violet Bays. Alois F. 

 KovAEfs, University of Minnesota. 

 Rutherford, adopting the alternation of 

 the field method, found the velocity of the 

 negative ion produced in air at atmospheric 

 pressure by the ultra-violet rays to be 1.41 

 cm. per sec. for a potential gradient of 1 

 volt per cm. Lenard, adopting Zeleny's 

 method of driving a current of air against 

 the motion of the ions found the velocity 

 to be 3.13 cm. per sec. In the present ex- 

 periments the former method was used, 

 making the alternations of the potential of 

 the field by means of a sechom meter. With 

 rates of alternations differing by more 

 than 100 per cent, the values of the velocity 

 of the negative ion in air at atmospheric 

 pressure were found concordant within 

 limits of experimental error and the aver- 

 age of the values obtained is 2.05 cm. per 

 sec. for a potential gradient of 1 volt per 

 cm. Reducing the pressure from 76 cm. 

 to less than 2 mm., the velocities were 

 measured. The products of the velocities 

 by the ratio of their corresponding pres- 

 sures to 76 gives uniform values whose 

 average is 2.09 cm. per second. The 

 velocity in moist air at atmospheric pres- 

 sure is found 10 to 15 per cent, less than in 

 dry air. Experiments will be carried on 

 with different gases, pressures, and also 

 temperatures. 



Absorption Spectra of Eontgen Rays, 

 measured iy a Badiomicrometer : J. M. 

 Adams, Harvard University. 

 It has previously been shown photo- 

 graphically that the Rontgen rays from an 

 ordinary focus tube are heterogeneous, that 

 metals show selective absorption toward the 

 different kinds of rays, and that this 

 selective absorption follows different laws 

 with the various metals. The spectrum 

 used in the present paper was obtained by 

 the same method that was used in making 



the photographs above mentioned, and nar- 

 row slits taken from different parts of the 

 spectrum were examined by the radio- 

 micrometer. It was usually found that the 

 beam proceeding from any one of these 

 slits consisted chiefly of rays of one kind, 

 upon which was superposed a small quan- 

 tity of rays of other kinds. The latter 

 rays were easily removed from the beam 

 by transmission through a metallic sheet of 

 proper thickness, and the beam thus puri- 

 fied satisfied a test for homogeneity, in that 

 its quality, judged by its penetrating power 

 for various substances, was not changed by 

 further transmission through metallic 

 sheets. A beam of rays direct from an 

 ordinary focus tube, on the contrary, shows 

 a decided change of quality after each 

 transmission. 



Absorption spectra for metallic sheets of 

 different materials and thicknesses were 

 obtained by placing the radiomicrometer 

 in various regions of the spectrum, and 

 plotting its deflections, reduced by the in- 

 terposition of the metallic sheet, as ordi- 

 nates against the distance from one end of 

 the spectrum as abscissse. The resulting 

 curves in some cases were practically 

 straight lines, indicating by their slope that 

 the rays produced by the swiftest cathode 

 particles had the greatest penetrating 

 power ; while in other eases there were well^ 

 marked maxima and minima of absorption 

 in going along the spectrum. 



A Mechanical Effect accompanying Mag- 

 netization: 0. W. Richardson, Prince- 

 ton University. 



On the view that the magnetic proper- 

 ties of bodies are due to the motion of 

 electrons in closed orbits, magnetization is 

 accompanied by the acquirement by the re- 

 volving electrons of a resultant moment of 

 momentum about the direction of magneti- 

 zation. The magnitude of this moment of 

 momentum is calculated, and it is shown. 



