324 Prof. E. Rutherford and Mr. H. Robinson on the 



that under ordinary experimental conditions, radium B 

 provides about 11 per cent, of the 7-ray effect due to the 

 emanation, and radium C 89 per cent. We have seen 

 earlier that radium C contributes about 40 per cent, of the 

 heating effect of the emanation. Taking these factors into 



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account, it can be deduced that the heating effect of the 

 emanation which gives a 7-ray effect equal to that of one gram 

 of radium is about 0*54 per cent, less than corresponds to one 

 curie of emanation in equilibrium with radium. 



The heat emission of one curie of emanation thus reduces 

 to 98*5 gram calories per hour in terms of the laboratory 

 standard. By the kindness of Professor Stefan Meyer of 

 Vienna, the laboratory standard has been compared in terms 

 of the pure radium salt prepared by Honigschmid. Ex- 

 pressed in terms of the Vienna standard, the heat emission 

 of one curie of emanation is equal to 103*5 gram calories 

 per hour. In the experimental arrangement the ft rays 

 traversed a thickness of glass, copper, &c., equivalent to a 

 weight of *354 gram per square cm. More than 90 per 

 cent, of the energy of the ft rays was absorbed and added 

 its heating effect to that of the a rays. 



Heating Effect of the ft and 7 Raya. 



Before comparing the observed heating effect with the 

 calculated value, it is necessary to determine how much of 

 the heating effect observed is to be ascribed to ft and 7 rays. 

 A number of experiments were made to form an estimate 

 of the magnitude of these effects. In the experimental 

 arrangement described the greater part of the ft rays was 

 absorbed in the glass tubes, heating-coil, and copper tube 

 surrounding it. The heating effect under these conditions 

 will be taken as 1. Experiments were first made to de- 

 termine the alteration of the heating effect when a lead 

 cylinder 12 mm. thick, which completely absorbed the 

 ft rays and some of the soft y rays, was substituted for the 

 copper cylinder. As a result of a series of measurements, 

 the heating effect was found to be 1*02. 



A series of measurements were then made to determine 

 the heating effect of the 7 rays. For this purpose about 

 4 metres of platinum wire were wound on the outside of two 

 similar thin-walled test-tubes of 1*5 cm. diameter. Each of 

 these was inside a metal cylinder of 6*5 cm. diameter, closed 

 at one end and immersed in a water- bath (fig. 5). Each of the 

 test-tubes was filled with mercury so that the mercury extended 

 about 5 mm. above and below the platinum coil. After the 

 balance had been obtained the emanation-tube, surrounded 

 by its heating-coil, as in previous experiments, was fixed in 



