744 Mr. & Mrs. Soddy and Mr. A. S. Russell on the 



Table II. 

 Pb and Zn Hemispheres (Initial Parts). 

 Pa and UrX 7-Pays. (See PI. XII. figs. 4, 10, and 11.) 





Fig. 4. 







Fig. 11. 





Fig. 10. 



Fig. 11. 

 29/6/09. 



Pb. 



18/6/09. 



Pb. 



19/6/09. 



21/6/09. 



Zn. 



30/6/09. 



T (cm.). 



•47 mg. Ea. 



T (cm.). 



UrX. 



UrX. 



T (cm.). 



•47 mg. Ea. 



UrX. 

 642 



•0316 



253 





295 



245 



•0375 



317 



•0632 



209 





81 



70-8 



•075 



224 



107-6 



•0947 



191 





65 



55-5 



•112 



203 



79-3 



•1261 



181 





5fr3 



47-3 



•150 





711 



•1573 



172 





50-6 



42-4 



•184 



190-5 



65-2 



•1893 



165 



a 



48-8 



40-4 



•222 



183-5 



61-5 



•3155 



139 



3 



35-4 



30-6 



•260 



181 



57-6 



•4418 



121 





 



31-4 



2365 



•331 



175-5 



49-6 



•5674 



106-7 





24-0 



19-8 



•369 





47-9 



•6914 



93-7 





20-3 



16-7 



•406 



165-5 



46-2 



•8156 



84-4 



CO 



<1 



176 



14-6 



•478 



159-5 



42-5 



•9419 



74-5 





15-3 



12-4 



•553 



156-9 



393 



1-066 



66-4 





13-6 



11-02 



•625 



151-9 



36-7 



1190 



61-4 





11-8 



9-35 



•700 



146-9 



34-5 



1-314 



55-4 

 69-5 



•543 



10-2 



24-8 



8-35 

 21-7 



•772 

 •847 



141-9 

 137-4 



32-5 

 30-7 



•994 



1494 



48-7 



1-041 



13-0 



10-9 



•919 



133-4 



29-6 



1-987 



35-4 

 50-2 



1-527 

 2037 



8-15 

 5-5 



6-95 

 4-62 



•994 

 1066 



129-4 

 125-4 



28-1 

 26-6 



1-434 



1-558 



472 









1-360 



113-4 



220 



1-682 



409 









1-654 



97-9 



1905 



1-806 



36-2 









2097 



83-4 



15-50 















2-977 



635 



10-50 



Pakt III. — The Variations in the Value of the Absorption 

 Coefficient of Radium *y-Rays. 



In the former paper the absorption of the 7-rays of radium 

 by lead over a range of thickness of 1 cm. to 9 cm. was 

 examined. The absorption was found to be strictly expo- 

 nential, the value of X being 0*495 (cm.) -1 . This investi- 

 gation has now been pushed further by employing much 

 larger quantities of radium than before, to see if the 

 exponential absorption held over as large a range as could be 

 investigated accurately. 



In the first of the new experiments the same 7-ray lead 

 electroscope was used and the same method of measurement 

 employed as had been used previously. 6*7 mg. of radium 

 bromide was placed immediately below the electroscope at a 

 distance of 21*5 cm. from the upper surface of the base. 

 The lead used for absorbing the rays was in the form of 

 circular plates 12'5 cm. in diameter and about 1*25 cm. thick. 



