NATURE OF LIFE AND LIVING MATERIAL 7 



energy. To do so requires that the imagination be projected to 

 consider the structure and behavior o£ particles that are almost 

 infinitesimally small, and that one visualize the behavior of the 

 units of w^hich they are composed, an order that is as complex as 

 the relations between the sun and the planets. 



According to the modern theory of the nature of all matter, all 

 substances are made up of exceedingly small particles, termed 

 ATOMS. The atomic theory is in reality a very old one; in its earliest 

 form it was based upon pure speculation, but modern Science by 

 experimental methods has substantiated the essentials of this early 

 theory and has greatly enlarged it. When a material is composed of 

 atoms of the same kind it is known as an element. There are 

 known to be ninety-two elements. Some are solids at ordinary tem- 

 peratures, as gold, iron, carbon, lead; others are gases, oxygen, 

 nitrogen, hydrogen, and others; one, mercury, is a liquid. For con- 

 venience the elements are designated by symbols: C is carbon, 

 O is oxygen, Na is sodium, Cl is chlorine, K is potassium, S is sul- 

 phur, and so on. The atoms of the various ninety-two elements dif- 

 fer greatly in size. The hydrogen atom is the smallest; one gram 

 of the hydrogen gas contains 660,000 times a million billion hydro- 

 gen atoms. The heaviest element is uranium, an atom of which 

 weighs as much as 238 hydrogen atoms. The atoms of all the ele- 

 ments are so very minute that they are utterly beyond the range of 

 vision of the highest power of the microscope; their existence, struc- 

 ture, and behavior, are known from indirect evidence. 



The structure of the atom has been one of the chief problems of 

 modern science; it is now generally regarded as being composed 

 of two types of electrical charges, electrons, which are negative, 

 and PROTONS, which are positive. It is thought that the centre of the 

 atom is composed of a nucleus of protons (positives) around which 

 an equal number of electrons (negatives) form a succession of 

 shells. According to some theories, the electrons describe regular 

 orbits at fixed distances from the nucleus. The different properties 



