NOVEMBEB 20, 1908] 



SCIENCE 



em 



stood; for the difficulties to be overcome 

 are coBsiderable, and the precautions to be 

 taken many. The quantities dealt with are 

 astoundingly minute, and to extract with 

 completeness a total of a few billionths of 

 a cubic millimeter of the radio-active gas — 

 the emanation— from perhaps half a liter 

 or more of a solution rich in dissolved sub- 

 stances can not be regarded as an opera- 

 tion exempt from possibility of error; and 

 errors of deficiency are accordingly fre- 

 quently met with. 



Special difficulties, too, arise when dealing 

 with certain classes of rocks. For in some 

 rocks the radium is not uniformly diffused, 

 but is concentrated in radio-active sub- 

 stances. "We are in these cases assailed with 

 all the troubles which beset the assayer of 

 gold who is at a loss to determine the aver- 

 age yield of a rock wherein the ore is 

 sporadically distributed. In the case of 

 radium determinations this difficulty may 

 be so much the more intensified as the 

 isolated quantities involved are the more 

 minute and yet the more potent to affect 

 the result of any one experiment. There is 

 here a source of discrepancy in successive 

 experiments upon those rocks in which, 

 from metamorphic or other actions, a segre- 

 gation of the uranium has taken place. 

 With such rocks the divergences between 

 successive results are often considerable, 

 and only by multiplying the number of ex- 

 periments can we hope to obtain fair in- 

 dications of the average radio-activity. It 

 is noteworthy that these variations do not, 

 so far as my observations extend, present 

 themselves when we deal with a recent 

 marine sediment or with certain unaltered 

 deposits wherein there has been no read- 

 justment of the original fine state of sub- 

 division, and even distribution, which at- 

 tended the precipitation of the uranium in 

 the process of sedimentation. 



But the difficulties attending the estima- 

 tion of radium in rocks and other materials 



leave still a large balance of certainty — so 

 far as the word is allowable when applied 

 to the ever-widening views of science — 

 upon which to base our deductions. The 

 emanation of radium is most charactertistic 

 in behavicjr; knowledge of its peculiarities 

 enables us to distinguish its presence in the 

 electroscope not only from the emanation 

 of other radio-active elements, but from 

 any accidental leakage or inductive dis- 

 turbance of the instrument. The method 

 of measurement is purely comparative. 

 The cardinal facts upon the strength of 

 which we associate radium with geological 

 dynamics, its development of heat and its 

 association with uranium, are founded in 

 the first case directly on observation, and, 

 in the second, on evidence so strong as to be 

 equally convincing. Recent work on the 

 question of the influence of conditions of 

 extreme pressures and temperatures on the 

 radio-active properties of radium appear to 

 show that, as would be anticipated, the 

 effect is small, if indeed existent. As ob- 

 served by Makower and Rutherford, the 

 small diminution noticed under very ex- 

 treme conditions in the y radiation possibly 

 admits of explanation on indirect effects. 

 These observations appear to leave us a free 

 hand as regards radio-thermal effects un- 

 less when we pursue speculations into the 

 remoter depths of the earth, and even there 

 while they remain as a reservation, they 

 by no means forbid us to go on. 



The precise quantity of heat to which 

 radium gives rise, or, rather, which its pres- 

 ence entails, can not be said to be known to 

 within a small percentage, for the thermal 

 equivalent of the radio-active energy of 

 uranium, actinium and ionium, and of 

 those members of the radium family which 

 are slow in changing, has not been measured 

 directly. Professor Rutherford has sup- 

 plied me, however, with the calculated 

 amount of the aggregate heat energy liber- 

 ated per second by all these bodies. In 



