jg 2 NINETEENTH CENT'JRY. FT. in. 



But here we must remember that we are travelling 

 beyond our knowledge. In spite of the great discoveries 

 made in this century as to the nature of the sun, we are still 

 in doubt as to the source from which this heat is derived ; 

 still less have we any idea what is the source of that energy 

 by which the heavenly bodies were first set in motion. We 

 speak glibly of the universe, but our most powerful instru- 

 ments, by revealing at every step in advance that more 

 remains beyond, only open before us an ever-widening 

 prospect, to which we cannot even conceive a limit 



Molecular Theory of Gases. We stand on more solid 

 ground when we investigate the energy exerted in our own 

 planet, yet even here mathematicians and physicists have 

 advanced so rapidly that their conclusions are almost beyond 

 our grasp. Familiar as are the . names of Graham and 

 Andrews, Faraday and Tyndall, Helmholtz, Clerk-Maxwell, 

 and Sir W. Thomson, yet the structure of matter, the 

 theories of heat, electro-magnetism, and thermo-electricity, 

 and similar subjects in which their grandest work has been 

 accomplished, are only to be thoroughly understood by 

 scientific men. 



Perhaps the best way of giving some notion ot their in- 

 vestigations is to state roughly firstly, that they have followed 

 energy, or the power of doing work, into its most hidden 

 forms, detecting its action among the particles of a gas, 

 measuring it in the electric current, and showing how it may 

 be lost to us by dissipation (see p. 361), even though it is in 

 itself indestructible ; and secondly, that they have succeeded 

 in measuring not only the movements, but even the size ot 

 the smallest existing portions of matter, and have come 

 very near to telling us even the nature of the atoms of which 

 matter is composed. 



The celebrated Swiss mathematician Daniel Bernoulli, in 



