Bumstead — Heating Effects produced oy Rontgen Bays. 7 



eter of its spherical portion was lY cm and the electrodes were 

 big euongh to bear a very heavy discharge. The anti-cathode 

 was sealed into the bottom of the water tube so that it was in 

 direct contact with the water, and I have frequently caused 

 the water in the tube to boil without seriously heating the rest 

 of the tube. It was provided with an automatic vacuum 

 adjuster which worked well ; the focus was sharp and the 

 Rontgen rays obtained were very powerful and fairly steady 

 in intensity and " hardness." The bulb was driven by an 18- 

 inch Apps coil and a rotating mercury- jet interrupter. The 

 coil was in an adjoining room and about 6 meters from the 

 radiometer ; its orientation was adjusted so that it produced 

 very little effect upon the magnetic " torsion head " of the 

 instrument — less than 4 mm with the largest currents used ; this 

 was always in one direction aud could be applied as a correc- 

 tion. The secondary leads were gutta-percha covered and 

 supported by silk ribbons ; where they passed from one room 

 to the other, through the wooden frame over a door, they were 

 enclosed in long glass tubes. As the rays used were not very 

 hard, there was little difficulty with the insulation, though 

 there was often a good deal of brush discharge from the leads. 

 The earthed metallic case of the radiometer protected it com- 

 pletely from any electrostatic disturbance. . A lead screen, 2 mm 

 thick, which hung by a quadrifilar suspension from the ceiling 

 about 2 cm in front of the aluminium window, permitted both 

 strips to be exposed to the Rontgen rays, or both screened, or 

 either exposed while the other was screened. A large card- 

 board screen was kept between the Rontgen bulb and the radi- 

 ometer to diminish the effects upon the instrument due to 

 the heating of the bulb. 



Measurements of the absorption of the lead and zinc were 

 carried on simultaneously with the radiometer observations. 

 For this purpose an electroscope was set up 270 cm from the 

 bulb ; it had an aluminium window 2 cm in diameter and the 

 remainder was covered with sheet lead 2 mm thick. As this did 

 not sufficiently protect it from the rays, a lead wall was built 

 up of blocks two inches thick between the electroscope and 

 bulb, with a hole opposite the window ; this gave satisfactory 

 protection, when the window was screened. Observations 

 were made with a micrometer microscope and stop-watch in 

 the usual manner. 



Experiments. 



The experimental method was based upon the following 

 considerations : the Rckitgen rays absorbed in the strips will 

 generate heat throughout the mass of the metals and a steady 

 state of temperature will be reached when the heat generated 



