INTRA-ATOMIC ENERGY. 287 



never toueli eueh othei-, and are only kept together by a special force 

 called cohesion. It is this which pcM-niits bodies to retain their form. 

 If it were possible to annul it by a niaoic wand, or more simply ])y an 

 antagonistic force, we would instantaneously .reduce into an atomic 

 dust a block of metal, a rock, or a living })eino-. ^^"e could not even 

 perceive this dust, for atoms do not seem to possess any properties 

 that could render them visible to our e3"es. 



If atoms are simply a condensation of energy we might say that the 

 matter most rigid in appearance — a block of steel, for example — simph" 

 represents a state of mobile equilibrium between the condensed energy 

 that constitutes it and the various energies, heat, pressure, etc., that 

 surround it. Matter 34elds to their influence as an elastic thread 

 obeys tractions to which it may be subjected, yet resumes its form as 

 soon as the traction ceases. 



The mobility of matter is one of its most easily- demonstrated 

 characteristics, since it is only necessary to place the hand near a 

 thermometer bulb to cause the column of li(|uid to become at once 

 displaced. Its molecules are then separated from each other under 

 the influence of slight heat. When we place the hand upon a l)lock of 

 metal the movements of rotation and oscillation of its atoms are like- 

 wise moditied, but so sligiitly that we fail to perceive it, which is 

 precisely the reason ^vhy matter appears to us to possess very slight 

 mobility. 



The general belief in its stability seems likewise cotitirmed by the 

 observation that in order to cause considerable modifications in a body — 

 for example, to melt it or to reduce it to vapor — it is necessary to 

 employ very powerful means. 



Sufficiently precise methods of investigation show, on the contrary, 

 that not only is matter extremely mobile, l>ut also that it possesses a 

 sensitiveness that no living being has ever approached. 



Physiologists measure, as is well known, the sensitiveness of a being 

 by the degree of excitation necessar}- in order to obtain from it a 

 reaction. The being is considered as very sensitive wlien it reacts 

 under slight stimuli. Applying similai- tests to brute matter we can 

 show that the most rigid su})stance and the least sensitive in appear- 

 ance, a bar of metal, for example, is really incredibly sensitive. The 

 matter of the bolometer, formed essentially of a thin thread of plat- 

 inum, is so sensitive that it reacts — l)y a variation of electric conducti- 

 bility — when it is sti'uck by a rav of light having an intensity so t'eebl(> 

 that it t-an produce an elevation of temperature amounting to onl^- 

 one hundred millionth of a degree. 



With imi)rov('nient in oui' means of investigation this extreme sen- 

 sitiveness of matter and the niol)ility that necessarilv accompanies it 

 become more and moi-c nianifest. M. II. Steele latelv showed that it 



