Characteristic X-Rays from Boron and Carbon. 145 



by screwing the lid up or down by a small amount. In 

 practice it was found to be quite impossible so to arrange 

 matters that there was equilibrium on charging the vane, 

 but no matter how finely the adjustment was made it was 

 found that the behaviour of the vane at this sensibility 

 was quite independent of the sign of the charge upon it up 

 to a potential of 1000 volts. 



It should be mentioned that had any difference in beha- 

 viour been observable it was intended to isolate a circular 

 portion (c) of the bottom of the box, adjust the opposite 

 vane, as above, for temporary equilibrium when it was 

 charged, say, positively. On switching over to the nega- 

 tive let us suppose that this vane experienced a smnll 

 downward force, this force could now be counterbalanced 

 by putting a small potential simultaneously on the isolated 

 portion of the bottom of the box. However, as no difference 

 in behaviour between the vane being charged positively or 

 negatively was observed, this portion of the apparatus was 

 not used but was kept screwed down flush with the bottom. 



Having regard to the dimensions of the vane and its 

 distance from the top and bottom of the box, the quantity 

 of electricity upon it when charged to 1000 volts was 

 approximately 41 e.s.u. Now a deflexion for a mass of 

 1*5 x 10 ~ 7 gm. on the centre of a vane could have been 

 observed, and therefore there was no observable difference in 

 the force on +41 e.s.u. of charge in the gravitational field 

 greater than 1*5 x 10 _7 x 980 dyne, or in other words there 

 was no observable resultant gravitational electrostatic field 

 greater than approximately 1*8 x 10" 6 dyne/e.s.u. 



June 3rd, 1921. 



XIII. Characteristic X-Rays from Boron and Carbon. By 

 A. Ll. Hughes, JD.Sc, Research Professor of Physics^ 

 Queen's University, Kingston, Canada *. 



THE purpose of this investigation was to see if some 

 progress could be made towards rilling up the gap 

 between the shortest ultra-violet waves hitherto produced 

 and the longest X-ray waves known. The Ka emission-line 

 of sodium, X 11*8, and the La emission-line of zinc, \12*3, 

 are the longest wave-lengths which have been identified in 

 the X-ray region. There is no reason to believe that X-rays 

 of still longer wave-length cannot be produced, but no 

 crystal has been found, or is likely to be found, with 



* Communicated by the Author. 

 Phil. Mag. S. 6. Vol. 43. No. 253. Jan. 1922. L 



