130 THE NEW KNOWLEDGE. 



intervals of 48 hours and during this interval no perceptible 

 weakening of the radiation has been observed. A varia- 

 tion of one one-hundredth thousandth of its activity would 

 have been apparent a singular example of the constancy 

 of radio-activity and the powers of radio-active methods. 



POLONIUM. 



Polonium was first extracted from the mineral pitchblende 

 by Mde. Curie and named in honour of her native country, 

 Poland. It is chemically a sister to bismuth, from which it 

 has never been satisfactorily separated. A most minute 

 quantity, only, has been obtained for experimentation. Po- 

 lonium is intensely active but differs from other radio-active 

 elements in giving rise to alpha-rays only. Furthermore, 

 its activity seems to decrease with time, a result quite out 

 of concord with the activity of the other elements. 



Prof. Markwald has recently succeeded in extracting 

 what seems to be the same substance by another method. 

 The " polonium " obtained by him is intensely active. A 

 minute trace on the end of a rod will cause a diamond to 

 phosphoresce brightly and, indeed, may be used to distinguish 

 the diamond from imitations. The activity of polonium is 

 so great that an electric bell will ring at its mere approach for 

 it renders the air in its neighbourhood a strong conductor of 

 electricity. Owing to the minute traces as yet isolated, 

 knowledge of polonium is in a chaotic condition ; but since 

 its activity seems greater even than radium it bids fair to 

 be an important factor in future research. 



ACTINIUM. , 



Another radio-active element discovered/in Prof. Curie's 

 laboratory has been called actinium. Chemically it re- 

 sembles thorium but its activity is many thousands of times 



