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POPULAR SCIENCE MONTHLY. 



of morality itself becomes, therefore, 

 the guarantee of their existence. Prac- 

 tise thus gives what speculation fails 

 to give. So after all the theologian could 

 take courage from the Kantian phi- 

 losophy, and the pragmatism of to-day 

 could find a basis in the searching 

 criticism of the Konigsberg professor. 

 The significance of Kant for modern 

 philosophy has thus been wide and 

 varied. He has been at once an inspira- 

 tion and a check to free speculation, 

 and also a source of renewed progress 

 in moral and religious inquiry. Yet, 

 it must be admitted that his impor- 

 tance has waned considerably in re- 

 cent years. His central idea that there 

 are necessities of thought and practise 

 which of themselves significantly de- 

 termine the content of our knowledge 

 and belief has come to lack its author- 

 itative tone. This has been brought 

 about not so much by direct refutation 

 as by the steady advance in stability 

 of scientific knowledge, which insists 

 that we can be really compelled only 

 by the exigencies of the things with 

 which we deal. Kant in his early 

 years was no mean scientist. Indeed 

 he thought that his philosophy could 

 give to science its only stable basis and 

 its only correct interpretation. The 

 result is in striking contrast with his 

 conviction. 



RECENT PROGRESS IN THE STUDY 

 OF RADIOACTIVITY. 



The dream of the alchemists had 

 without doubt a strong philosophical 

 foundation, and although the desire to 

 accomplish transmutations of the ele- 

 ments has lost all power as an incen- 

 tive to the study of natural phenomena, 

 one can not help noticing the small 

 amount of reverence modern physics 

 has for the identity of the atom of a 

 chemical element. The electronic 

 theory of matter, well set forth by Sir 

 Oliver Lodge in his Romanes lecture 

 at Oxford, which was published in this 

 magazine last August, holds that there 

 is no more difTerence between the atoms 

 of the different elements than between 



houses of different shapes and sizes, 

 but built of the same kind of bricks, 

 the little electrons being the bricks of 

 which the atoms are built, although 

 the structure of an atom is more like 

 that of a planetary system than that 

 of a house. Confidence in the stability 

 of this structure in the case of ordinary 

 atoms has not been shown to be mis- 

 placed, but in the case of the radio- 

 active substances — elements they are by 

 the usual tests — evidence of atomic dis- 

 integration continues to accumulate. 

 Their radiations consist chiefly of pro- 

 jected particles, far smaller than the 

 atoms of the radioactive elements, and, 

 as Professor Rutherford and Mr. Soddy 

 have shown, the radioactive matter 

 passes successively through a series of 

 unstable forms. The final product of 

 this atomic disintegration must be 

 stable and therefore not radioactive, 

 and since the gas helivim is found in 

 all radioactive minerals it is suggested 

 that helium is one of the stable resi- 

 dues left by the heavy and unstable 

 radioactive atoms. 



During the past summer Professor 

 Ramsay, the discoverer of terrestrial 

 helium, and Mr. Soddy followed up 

 this suggestion with experiments and 

 came to the conclusion that helium is 

 continuously produced by radium. The 

 experiments consisted in examining in 

 a spark tube the spectrum of the radio- 

 active gas, or emanation, given on dis- 

 solving in water fifty milligrams of 

 nearly pure radium bromide that had 

 been in the solid state for some time. 

 This radioactive gas is not stable, but 

 decays in a geometrical progression 

 with the time, the rate being about 

 half in four days. Of course the most 

 careful precautions were taken to free 

 the spark tube from foreign gases, es- 

 pecially hydrogen, oxygen and carbon 

 dioxide. When first prepared the tube 

 gave a new and hitherto unknown 

 spectrum, probably that of the radio- 

 active gas. After four days the lines 

 of the helium spectrum began to ap- 

 pear, growing brighter for several days, 

 while the new spectrum observed at 



