RADIOACTIVE SUBSTANCES IN THE EARTH 



133 



free from erratic variations. The whole apparatus was placed within 

 a wood-lined lead-covered box on the ground. The wood lining was 

 2 cm. thick, and the lead covering 6-5 mm., so that the walls were 

 equivalent to al^out • 73 cm. lead. It was found that the walls cut down 

 the T rays from 14 mg. radium bromide, passing through 4-5 cm. of 

 lead, from 100 to 66, whence ju = -56. 



Figure 2 



The readings were taken from 4 p.m. to 9 a.m. and the results are 

 shown in figure 3. There was clear evidence of fluctuations opposed 

 to the barometer, the range being from q=9-2 to q = 10-l; difference 

 0-9. 



The readings were extended over a fortnight excellent for obser- 

 vations, as there was continuous frost, with no risk of error due to rain, 

 thaw, snow, or fog. 



