92 THE POPULAR SCIENCE MONTHLY. 



tendencies, and of the habits with which mental states seem directly 

 associated. 



It is, we believe, probable, perhaps certain, that the disposition in 

 some animals to destroy their weak associates has come down from a 

 former undomesticated condition of their kind, in which its correlative 

 habits were essential to safety and life. 



If this view be correct, our friend's birds may not be obnoxious to 

 the charge of being specially cruel ; and, seeing how persistent in- 

 stinctive habits may become in some of the higher animals and in 

 man, it is not strange that they continue in the turkey, a species re- 

 cently domesticated, and by no means remarkable for intelligence. 



•♦•»- 



THE PEIMAKY CONCEPTS OF MODERN PHYSICAL 



SCIENCE. 



By J. B. STALLO. 

 II. — The Atomic Constitution of Matter as a Postulate of Thought. 



MY inquiry thus far has touched the assertion according to which 

 the atomic hypothesis is the necessary basis of the theories 

 which constitute the sciences of physics and chemistry. I propose 

 now to consider the claim that this hypothesis is an essential pre- 

 requisite of the realization of material existence in thought. 



To show how pointedly this claim is made, it will be sufficient to 

 extract a passage from a recent lecture of Prof. John Tyndall, before 

 the British Association at Liverpool, " On the Scientific Use of the 

 Imagination" ("Fragments of Science," American edition, p. 135). 

 The words of Prof. Tyndall, whose opinions, by reason of his eminence 

 among physicists, may be taken instar omnium, are these : 



" Many chemists of the present day refuse to speak of atoms and 

 molecules as real things. Their caution leads them to stop short of 

 the clear, sharp, mechanically-intelligible atomic theory enunciated 

 by Dalton, or any form of that theory, and to make the doctrine of 

 multiple proportions their intellectual bourn. I respect the caution, 

 though I think it is here misplaced. The chemists who recoil from 

 these notions of atoms and molecules, accept without hesitation the 

 undulatory theory of light. Like you and me, they one and all be- 

 lieve in an ether and its light-producing waves. Let us consider what 

 this belief involves. Bring your imagination once more into play, 

 and figure a series of sound-waves passing through air. Follow them 

 up to their origin, and what do you there find ? A definite, tangible, 

 vibrating body. It maybe the vocal chords of a human being, it may 

 be an organ-pipe, or it may be a stretched string. Follow in the same 



