FRANCIS BACON. 



139 



when in search of any cause the mind comes to an equilibrium, or is 

 suspended between two or more causes, these facts decide the ques- 

 tion by rejecting all the causes but one." No term employed by Bacon 

 has passed into such general use as that by which he designates these 

 instances : we speak in ordinary language of crucial tests and crucial 

 experiments. One of the crucial experiments which Bacon suggested 

 in illustration of his instantia cruets is very remarkable, the point to 

 be determined being whether the tendency of bodies downwards to 



FIG. 53. 



FIG. 52. THE GUINEA AND FEATHER EXPERIMENT. 



the earth is the result of some mechanism in the bodies themselves, 

 or whether it is the consequence of an attractive power in the earth 

 " by the corporeal mass thereof, or by a collection of bodies of the 

 same nature." He proposes to solve the question by ascertaining 

 whether bodies fall to the earth with greater velocity when nearer to 

 it, and vice versa; and his experiment consists in comparing the time 

 required for the slow descent of the weight in a fly-clock when the in- 

 strument was placed on a high building and in a deep mine, the 

 standard of comparison being another similar clock, actuated not by 



