INTRODUCTION. . 31 



> and wonders, while die regular operations of nature scarcely attracted 

 5 attention. The method of investigating nature by observation and ex- 

 ' periment was scarcely thought of, except by two individuals, who, by 

 I means of them, made some progress in mechanics and hydrostatics, and 

 in astronomy : these were Archimedes and Hipparchus. The mechani- 

 cal discoveries of Archimedes were slightly extended by Ctesibius and 

 Hero, by Anthemius, and by Pappus ; while the astronomical observa- 

 tions begun by Hipparchus were continued by Ptolemy. 



But at the revival of letters, in the sixteenth century, a spirit of obser- 

 vation and inquiry awoke, which nothing could damp, and men began to 

 pry into the secrets of nature, by the way of experiment. Galileo, in 

 Italy, and Gilbert, in England, especially the former, constitute remark- 

 able examples of the successful investigation by experiment. But it was 

 Francis Bacon, Lord Verulam, who first investigated the laws according 

 to which such experimental investigations should be conducted, who 

 pointed out the necessity of following these laws in all attempts to ex- 

 tend the physical sciences, and who foretold the brilliant success that 

 would one day repay those who should adopt the methods which he 

 pointed out. This he did in his " Novum Organum," published in the 

 early part of the seventeenth century. 



Before laying down the rules to be followed in his new, or inductive 

 process, Bacon enumerated the causes of error, which he divided into 

 four sets, and distinguished, according to the fashion of the times, by the 

 following fanciful but expressive names: 



Idols of the tnbe ; 

 Idols of the den ; 

 Idols of the forum ; 

 Idols of the theatre. 



The idvls of the tribe are the causes of error, founded on human na- 

 ture in general. Thus all men have a propensity to find in nature a 

 greater degree of order, simplicity, and regularity, than is actually indi- 

 cated by observation. This propensity, usually distinguished by the 

 title of spirit of system, is one of the greatest enemies to its progress that \ 

 science has to struggle with. 



The idols of the den are those that spring from the peculiar character 



