The Structure of the Atom. 



affects the activity ot an atom tremendously. Hydrogen, when 

 deprived of an electron, will combine with many elements to form 

 acids. Hydrogen and nitrogen, when electrified, will combine at 

 once with potassium or phosphorus to form stable compounds. 

 Dr. Niels Bohr, of Copenhagen, has worked out a very simple 

 structure for the hydrogen atom as containing a nucleus with one 

 unit positive charge and a single electron. Two such atoms, he 

 has shewn, will combine to form the hydrogen molecule. Helium 

 similarly contains a nucleus with two unit positive charges and two 

 electrons. Such atoms will not combine, i.e., helium is monatomic, 

 as is well known from chemical considerations. 



When an electric discharge is passed through a gas at low 

 pressure in a glass tube the gas becomes luminous, giving a 

 spectrum characteristic of the gas present. Several considerations 

 point to the outer ring of electrons as the seat of such luminosity. 

 Firstly, from what is known of the stability of the outer ring it is 

 probable that the electrons composing it would vibrate when 

 disturbed, at such a rate as to give out visible light : indeed, 

 Nicholson and Bohr have devised atomic structures which give 

 the actual colours observed in such different places as the sun's 

 corona, certain nebulae, and a glowing tube containing hydrogen 

 or helium. 



Again, the spectra of compounds differ from those of their 

 constituent atoms : the inner electronic rings are not affected by 

 chemical combination, so that we must ascribe the spectra to 

 outer rings which become distorted when two or more atoms unite. 



So far we have not seen the central nucleus of the atom or 

 the inner rings play any part : chemical reactions and luminous 

 emissions leave the core of the atom unaffected. Indeed, until a 

 few years ago we possessed no weapons powerful enough to 

 penetrate into the atom and stir its hinterland to activity. 



Such a weapon was given to us by the discovery of X-rays. 

 These rays are now known to consist of light of extremely short 

 wave-length, beyond the power of the eye to see or the power of 

 the spectroscope to analyse. All radiations, whether manifesting 

 themselves as wireless electro-magnetic rays, heat, light, or X-rays, 



