EDITOR'S TABLE. 



489 



But, in extensive divisions of thought, 

 truth is only a relative tiling ; of ines- 

 timable value for its time, and most of 

 all valuable as a means of getting away 

 from it and attaining more perfect 

 truth. Logic is the art or science of 

 arriving at truth by ratiocination ; but 

 science is the field where logic is put 

 to practical application and subjected 

 to the most rigorous tests. The human 

 mind if left to logic alone may go wild 

 in any direction ; science holds it stead- 

 ily to the observed order of Nature as 

 the standard by which it is to be tried. 

 The whole circle of the sciences bears 

 witness to the correctness of scientific 

 thinking; and the history of every sci- 

 ence abounds in proofs of the relativity 

 of truth. Certain parts of elementary 

 facts may remain constant, but even 

 the interpretations of these, true only 

 for their time, are changed, age after 

 age. The science of chemistry aftbrds 

 an admirable exemplification of this 

 view. 



There was vague and indefinite truth 

 even in the chimeras of the alchemists, 

 mixed indeed with an enormous amount 

 of gross error and preposterous specu- 

 lation as seen from subsequent points 

 of view ; but there was sufficient of 

 verity and correspondence to reality in 

 those mystical times to guide men to 

 important discoveries. The alchemists 

 found out a great number of new and 

 valuable things. Tliey worked under 

 delusions, but these were far from be- 

 ing destitute of plausibility; and were 

 in fact in no small measure consistent 

 and rational. Experimental knowledge 

 at any rate grew in extent, and some- 

 what in coherency, until the absurdi- 

 ties of the epoch fell away and a definite 

 and rational chemical system ensued. 



This was the epoch of Phlogiston^ 

 which was held to be a kind of subtile 

 matter or energetic essence, present in 

 all combustible bodies and absent in all 

 incombustible bodies, and which caused 

 combustion-changes in its escape. It 

 was a theory of the nature and cause 



of fire; and, as heat is implicated in 

 nearly all chemical changes, it was a 

 crude theory of chemical action. It 

 served the most important uses. It 

 was a principle of connection and asso- 

 ciation, and explication, which stimu- 

 lated investigation, guided inquiry, and 

 enlarged the domain of actual knowl- 

 edge. A chemical belief that the dis- 

 coverer of oxygen. Dr. Priestley, held 

 to the day of his death, could certainly 

 not have been an absurdity. Prof. 

 Cooke has the following excellent re- 

 marks on this early theory : "That it 

 was not absurd a single consideration 

 will show. Translate the word phlo- 

 giston, energy, and in Stahl's work on 

 chemistry and physics, of 1731, put en- 

 ergy where he wrote phlogiston, and 

 you will find there the germs of our 

 great modern doctrine of conservation 

 of energy one of the noblest products 

 of human thought. It was not a mere 

 fanciful speculation which ruled the sci- 

 entific thought of Europe for a century 

 and a half. It was a really grand gen- 

 eralization ; but the generalization was 

 given to the world clothed in such a 

 material garb that it has required two 

 centuries to unwrap the truth." Nev- 

 ertheless there was invaluable truth in 

 it, but truth obscured, imperfect, and 

 in relation to the time. 



The phlogistic doctrine broke down 

 as the facts accumulated and outgrew it ; 

 and chemical science passed into a new 

 phase. That which had long helped 

 at length became an obstruction, and, 

 M'ith the abandonment of the entity, 

 chemical eflfects began to be referred to 

 inherent attractions among difierent 

 kinds of matter. But the facts must 

 still be interpreted by principles or the- 

 ories, and, at the epoch of Lavoisier, af- 

 finity, or the energy of chemical change, 

 was viewed simjdy as a coupling force. 

 Combination and decomposition were 

 supposed to take place directly among 

 bodies in pairs; elements uniting with 

 elements to form binary compounds, 

 and these uniting again by twos to form 



