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Transactions. 



AA^as continued for half an hour. After another interval (the same for all 

 the waters tested, ten minutes) the gases so collected were passed on into 

 an airtight electroscope which had previously been exhausted to about 

 half an atmosphere. The partial vacuum so formed was never filled to 

 atmospheric pressure by the gases collected from the water, as the volume 

 of these was never sufficient. To make up for this deficiency, the necessary 

 amount of air was allowed to pass through the whole apparatus to the 

 electroscope, which acted as a further safeguard against any radio-active 

 gas remaining in the tubes. Between the collecting-vessel and the elec- 

 troscope two drying-tubes (the first containing calcium-chloride, and the 

 second sulphuric acid) were placed. Previous experience had shown that 

 these were sufficient to thoroughly dry the gas if (as was the case) 

 it was passed so slowly through them that ten minutes was taken over 

 the operation. The electroscope was charged to a potential of 220 volts, 

 and the rate of motion of the leaf was exaijained by a reading-microscope 

 with a micrometer eyepiece. The electroscope was standardised by per- 

 forming the same experiment with a standard solution of radium, kindly 

 given to us by Professor Rutherford. The solution used contained 3-925 

 X 10~^° grammes of radium, and before boiling was allowed to stand 

 securely corked for at least three weeks, so that the equihbrium amount of 

 radium emanation might be generated. 



Residts. — All the wells examined were found to contain radium emana- 

 tion, though in none of them could any radium in solution be detected. 

 For the standard solution of radium with the equilibrium amount of emana- 

 tion the rate of leak of the electroscope was 64 micrometer-divisions per 

 minute. The leaks per litre of the various wells examined were as follows : — 



Museum 



Boys' High School . . . . 



Ward's brewery 



West Christchurch School 



W^harenui . , 



Holly Lea . . 



Waltham School 



New well (Aikman's Road) 



New well (Chemical Laboratory) 



No. 1 well (Gardens) . . 



No. 2 well 



No. 3 well 



Well-supply to aquarium in Exhibition , 



Dr. Moorhouse's well 



San Marola Well, Papanui Road 



Exhibition well . . 



River Avon . . 



Whilst these figures indicate that there is a considerable amount of 

 radium emanation in the water of all the wells tested, they do not apparently 

 show that there is any simple relation between the amount contained and the 

 depth ; it is possible that some of the depths given may be wrong, though 

 there is reason to believe that the distribution of the water-bearing strata is 

 'very irregular as regards depth. Thus we think, from consideration of near- 

 ness and radio-activity, it might be inferred that the same stratum supplied 



Well. 



