PHYSICAL SCIENCE. 



XV 



of things. Some proceed too rapidly, others too 

 slowly. Almost every person has acquired a 

 partiality for some branch of science, to which 

 he is prone to fashion and force every other. 



The idols of the forum are those which arise 

 out of the intercourse of society, and especially 

 from language, by means of which men com- 

 municate with each other. It is well known that 

 words, in some measure, govern thought, and that 

 we cannot think accurately unless we are able to 

 express ourselves accurately. The same word 

 does not convey the same idea to different per- 

 sons. Hence many disputes are merely verbal, 

 . though the disputants may not be aware of the 

 circumstance. 



The idols of the theatre are the deceptions which 

 have taken their rise from the systems of different 

 schools of philosophy. These errors affected 

 the philosophy of the ancients more than that of 

 the moderns. But they are not yet without their 

 effect, and often act powerfully upon individuals 

 without their being aware of their effect. 



After an historical view of science from its 

 dawn among the Greeks to his own time, and 

 pointing out the little progress which it had 

 made, in consequence of the improper way in 

 which it had been cultivated, Bacon proceeds, in 

 his second book, to point out the true way of 

 advancing science by induction. 



The first object ought to be to prepare a 

 history of the phenomena to be explained, in all 

 their modifications and varieties. This history 

 is to comprehend not only all such facts as 

 spontaneously offer themselves, but all the ex- 

 periments instituted for the sake of discovery, or 

 for any of the purposes of the useful arts. It 

 ought to be composed with great care ; the facts 

 should be accurately related, ad distinctly 

 arranged their authenticity carefully ascertain- 

 ed, and those that are doubtful should be marked 

 as uncertain, with the grounds for the judgment 

 formed. This record of facts Bacon calls natural 

 history. 



The next object is a comparison of the differ- 

 ent facts, to find out the cause of the phenomenon. 



The method of induction here laid down is 

 applicable to all investigations where experience 

 is the guide, whether in the moral or natural 

 world. 



It is obvious that all facts, even supposing 

 them truly and accurately recorded, are not of 

 equal value in the discovery of truth. Some of 

 them show the thing sought for in its highest 

 degree, others in its lowest ; some show it simple 

 and uncombined, while others are confused with 

 a variety of circumstances. Some facts are 

 easily interpreted, others are very obscure, and 

 are understood only in consequence of the light 

 thrown on them by the former. This led Bacon 



to consider the comparative value of facts as 

 means of discovery. He enumerates twenty- 

 seven different species ; but we shall satisfy 

 ourselves here with noticing a few of the most 

 important of them. 



1. InstantitB solitaries are examples of the 

 same quality existing in two bodies, which have 

 nothing else in common ; or of a quality differ- 

 ing in two bodies, which are in all other respects 

 the same. 



2. The instantice migrantes exhibit some natore 

 or property of bodies passing from one condition 

 to another, either from less to greater, or from 

 greater to less. Thus, glass while entire is 

 colourless, but becomes white when reduced to 

 powder. 



3. The instantiae ostensivce show some par- 

 ticular nature in its highest state of power or 

 energy. In this way the thermometer shows 

 the expansive power of heat, and the barometer 

 the weight of air. 



4. The instantios analogical consist of facts 

 between which an analogy or resemblance is 

 visible in some particulars, notwithstanding great 

 diversity in all the rest. Such are the telescope 

 and microscope in works of art, compared with 

 the eye in the works of nature. 



5. The instantice crucis is the division of this 

 experimental logic which is the most frequently 

 resorted to in the practice of inductive investiga- 

 tion. When in such an investigation, the under- 

 standing is, as it were, placed in equilibrio be- 

 tween two or more causes, each of which accounts 

 equally well for the appearances, as far as they 

 are known, nothing remains but to look out for 

 a fact which can be explained by the one of 

 these causes, and not by the other. If such a 

 fact can be found, the uncertainty is removed, 

 and the true cause becomes apparent. Such 

 facts perform the office of a cross, erected at the 

 meeting of two roads, to direct the traveler 

 which way he is to go. On this account, Bacon 

 gave them the name of instantias crucis. Suppose 

 it were inquired into why metals become heavier 

 when calcined, various explanations might .be 

 conceived. But vhe experimentum crucis of 

 Lavoisier removed the ambiguity. He enclosed 

 a quantity of tin in a large glass vessel, which 

 was hermetically sealed. Heat being then 

 applied, the tin melted and was partly calcined. 

 The process being finished, the weight of the 

 glass and its contents were found unchanged. 

 But the glass being opened, a quantity of air 

 rushed in, amounting in weight to ten grains ; 

 and the tin was found to have increased in 

 weight ten grains. It was obvious from this, 

 that by the calcination of the tin a portion of the 

 air had been absorbed, which had occasioned the. 

 increase of the weight. 



