110 MINUTENESS OF PARTICLES. SECT. XIV. 



composed of atoms, on whose magnitude, density, and form, 

 their nature and qualities depend ; and, as these qualities are 

 unchangeable, the ultimate particles of matter must be incapable 

 of wear the same now as when created. 



The size of the ultimate particles of matter must be small in 

 the extreme. Organised beings, possessing life and all its func- 

 tions, have been discovered so small, that a million of them 

 would occupy less space than a grain of sand. The malleability 

 of gold, the perfume of musk, the odour of flowers, and many 

 other instances might be given of the excessive minuteness of the 

 atoms of matter. Supposing the density of the air at the surface 

 of the earth to be represented by unity, Sir John Herschel has 

 shown that, under any hypothesis as to its atoms, it would re- 

 quire a fraction having at least 1370 figures in its denominator 

 to express its tenuity in the interplanetary space ; yet the 

 definite proportions of chemical compounds afford a proof that 

 divisibility of matter has a limit. The cohesive force, which 

 has been the subject of the preceding considerations, only unites 

 particles of the same kind of matter; whereas affinity, which 

 is the cause of chemical compounds, is the mutual attrac- 

 tion between particles of different kinds of matter, generally 

 producing a compound which has no sensible property in common 

 with its component parts except that of their combined gravit} r , 

 as, for example, water, which is a compound of oxygen and 

 hydrogen gases. It is merely a result of the electrical state of 

 the particles, chemical affinity and electricity being only forms of 

 the same power. In most cases it produces electricity, as in 

 the oxidation of metals and combustion, and in every case with- 

 out exception heat is evolved by bodies while combining chemi- 

 cally ; and as he at isan expansive force, chemical action is changed 

 into mechanical expansion, but it is not known in this case why 

 heat is produced, nor the manner in which the particles act. 



It is a permanent and universal law in vast numbers of unor- 

 ganised bodies that their composition is definite and invariable, 

 the same compound always consisting of the same elements 

 united together in the same proportions. Two substances may 

 indeed be mixed ; but they will not combine to form a third 

 substance different from both, unless their component particles 

 imite in definite proportions, that is to say, one part by weight 

 of one of the substances will unite with one part by weight of the 



