EVIDENCE OF INORGANIC EVOLUTION 5S9 



This statement is now known to be too broad, but is true in general 

 principle. 17 Again, 



The embryos of the most distinct species belonging to the same class are 

 closely similar, but become, when fully developed, widely dissimilar. 18 



To cite a few examples: The human embryo, at one stage of its 

 development, possesses the rudiments of gill arches and gill clefts. 

 The larva? of most insects, no matter how diverse, pass through a worm- 

 like stage. 



The larva? of most crustaceans, at corresponding stages of development, 

 closely resemble each other, however different the adults may become, and so it 

 is with very many other animals. 19 



It is with the latter of the two embryological peculiarities mentioned 

 above, viz., the resemblances between the embryos of different related 

 species, that we are at present concernd. 



In the radioactive transformations, we have not the advantage of 

 witnessing a building up of elements from simple to complex forms, as 

 in the process of embryology we observe the formation of complicated 

 organisms from the egg. But, what is almost as good, we observe a 

 devolution of elements, from complex forms to simpler. In the course 

 of their disintegration, the three distinct elements, radium, thorium and 

 actinium give rise to products (i. e., elements) which have very similar 

 properties. 



The substances thorium, radium and actinium exhibit many interesting 

 points of similarity in the course of their transformation. Each gives rise to an 

 emanation whose life is short compared with that of the primary element itself. 

 Such experiments as have yet been made, indicate that these emanations have no 

 definite .combining properties, but belong apparently to the helium-argon group 

 of inert gases. In each case, the emanation gives rise to a non-volatile substance 

 which is deposited on the surface of bodies and is concentrated on the negative 

 electrode in an electric field. The changes in these active deposits are also very 

 similar, for each gives rise to a rayless product, followed by a product which 

 emits all three types of rays. In each case, also, the rayless product has a longer 

 period, or, in other words, is a more stable substance than the ray product which 

 results from its transformation. 



The disintegration of the corresponding products, thorium B, actinium B 

 and radium C is of a more violent character than is observed in the other 

 products, for not only is an a particle expelled at a greater speed, but a 

 j3 particle is also thrown off at great velocity. After this violent explosion 

 within the atom, the resulting atomic system sinks into a more permanent state 

 of equilibrium, for the succeeding products thorium C and actinium C have not 

 so far been detected by radioactive methods, while radium B is transformed at 

 a very slow rate. 



This similarity in the properties of the various families of products is too 

 marked to be considered a mere coincidence, and indicates that there is some 

 underlying law which governs the successive stages of the disintegration of all 

 the radioelements. 20 



17 Cf . Spencer, loc. cit. 



18 "Origin of Species," Tol. II., Ch. XIV. 



19 Loc. cit. 



20 Eutherf ord, ' ' Eadioactive Transformations," pp. 169-170. 



