716 The Outline of Science 



material ; thus our ideas regarding the constitution of matter and 

 the framework of the Universe have been completely changed. 

 "The superlatively grand question" is, what is the inner mech- 

 anism of the atom? 



It is the business of the Chemist to attempt to fathom the 

 mysteries of the properties of the various chemical elements, to 

 evolve order and system out of them. It is to the Chemist that 

 we owe our knowledge that the atoms of different substances can 

 be arranged in a definite order, and also that they show an in- 

 creasing complexity of structure. Heavier atoms appear to 

 behave as though they were evolved from the lighter. 



Forms of Matter 



It is well known that under suitable conditions, the 

 same type of matter can exist in three distinct forms solid, 

 liquid, and gas. In passing from one state to another, it is a 

 matter of common knowledge that there are remarkable 

 changes in appearance and physical qualities of an element. 

 These changes are believed to be connected with the average 

 distance which separates one atom or molecule from the other, 

 and in the rapidity of motion. In the gas or vapour form, the 

 molecules are on an average so far apart that the r mutual 

 attractions are relatively unimportant. The lowering of the 

 temperature, the distance and rapidity of motion of the mole- 

 cules, diminish, until under certain conditions the attraction 

 of the molecules for one another predominates, resulting in a 

 much closer packing and the appearance of the liquid form. 

 The molecules, however, still retain a certain freedom of 

 motion, but this is diminished with lowering of the tempera- 

 ture, until at a certain stage the molecules form a tighter 

 grouping, corresponding to the solid state, where the freedom 

 of motion of the individual molecules is much restricted. In 

 order to account for the resistance of solids to compression 

 or extension, it has been supposed that the force between 

 molecules is attractive at large distances, but repulsive at 

 small distances. While we are able to offer a general ex- 

 planation of the passage of an element from one state to 



