ATOMIC THEORY. 403 



though he attended twice every Sunday at the Friends' 

 Meeting-house, he never took other than a silent part in their 

 devotional exercises. When such was his reserve upon this 

 point, even to those most intimate with him in life, we have 

 no right to hazard suppositions of our own which can never 

 be verified, and which might perchance be widely removed 

 from the truth. 



After this short sketch of Dalton's life and personal cha- 

 racter, we have still to speak of the discovery which gives 

 the greatest lustre to his name ; of its connection with prior 

 systems or theories ; and of the influence it has had on the 

 subsequent progress and direction of physical enquiry. On 

 several of these points, however, we have dwelt so far in 

 preceding articles, that we shall now limit ourselves chiefly 

 to what may be called the history of the Atomic doctrine, as 

 it comes down from antiquity to our own time. This, too, 

 must be a mere sketch ; but it has interest, not solely as a 

 part of science, but as a picture of the human intellect in its 

 progress towards truth. 



Such history, however, is not without its difficulties. In 

 discussing the atomic theory, we often touch on that de- 

 bateable ground between mathematics and metaphysics, 

 which D'Alembert has well named ' I'abime des incertitudes ; ' 

 there being scarcely a step in the argument which does not 

 approach in some point or other to this boundary of human 

 intelligence. While modern science is defining by strict 

 numerical formulae the proportions in which the molecular 

 combinations of bodies take place and often with such 

 certainty that the chemist can foretell the results of an 

 analysis before the labours of the laboratory have begun - 

 the demonstration of facts thus obtained is at every step 

 urging the mind towards those unseen properties and pro- 

 found laws of the material world, where thought is forced to 



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