30 COMB USTION A CASE OF IMPETUS. PART I. 



as that is, the investigations of recent years have demon- 

 strated the fact, that the mechanical energy resident in 

 a pound of coal and liberated by its combustion is 

 capable of raising to the same height ten times that 

 weight. 3 The quantity of coal existing in the whole 

 globe is believed to be inexhaustible, hence the energy 

 in abeyance is incalculable. The chemical energy C9n- 

 tinually and actually exerted in the great laboratory of 

 nature is greater than that which maintains the planets 

 in their orbits. 



The act of the combination of the atoms of carbon 

 and oxygen in combustion is ' now regarded exactly as 

 we regard the clashing of a falling weight against the 

 earth, and the heat produced in both cases is referable 

 to the same cause ; ' 4 so chemical combination in com- 

 bustion is only a particular case of falling bodies, 

 j Drummond's light, the most brilliant of artificial illu- 

 "nminations, is produced by a simultaneous shower of the 

 atoms of oxygen and hydrogen gas upon lime ; and 

 platinum, the least fusible of metals, is vaporized by a 

 similar shower from the oxy-hydrogen blowpipe, and 

 thus impetus generates both light and heat, for although 

 the atoms are too small to admit of an estimation of 

 their individual vis viva, there can be no doubt that 

 like causes produce like effects. 



In what manner or under what form magnetism and 

 electricity exist when quiescent in matter we know not, 

 but the compass needles show that numerous lines of 

 magnetic force, subject to periodic and secular varia- 

 tions, perpetually traverse the earth and the ocean ; 

 and that waves of magnetic force occasionally sweep 

 rapidly over great tracts of the globe. These pheno- 

 mena would seem to stand in some periodic connection 



3 The address of the president, Sir William Armstrong, C.B., to the 

 British Association at Newcastle-on-Tyne, 26th August, 1863. 



4 J. Tyndall, Esq., on Force. 



