facts perform the office of a cross, erected at the meeting of two roads, to $ 

 direct the traveller which way he is to go. On this account, Bacon j 

 gave them the name of instantia crucis. Suppose it were inquired into ; 

 why metals become heavier when calcined, various explanations might \ 

 be conceived. But the cxpcrimentum 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 to 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. 



In cases where an exyerimentum crucis cannot be resorted to, there is 

 often a great want of conclusive evidence. This is the case in agricul- 

 ture, in medicine, in political economy, &c. To make one experiment 

 similar to another in all respects but one, is what the cxpcrimentum crucis 

 and the principle of induction in general requires. But this, in the sci- 

 ences just named, can seldom be accomplished. Hence the great diffi- 

 culty of separating the causes, and allotting to each its due proportion of 

 the effect. Men deceive themselves in consequence of this continually, 

 and think they are reasoning from fact and experience, when in reality 

 they are drawing their conclusions from a mixture of truth aid false- 

 hood. Facts so incorrectly apprehended only serve to render srror 

 more incorrigible. 



Of the twenty-seven classes into which instantia are arranged by 

 Bacon, fifteen address themselves immediately to the understanding ; 

 five serve to correct or inform the senses ; and seven to direct the hand 

 in raising the superstructure of art on the foundation of science. The 

 examples which we have selected are from the first of these divisions. 

 The other two are of inferior importance, and may be omitted in this 

 imperfect summary. 



Such are the rules laid down by B&con for prosecuting the sciences by 

 induction. The effects which were ultimately produced by the " Novum ' 

 i| Organiun" must have been very great. It may be questioned, indeed, > 



