172 NOVUM ORGAN UM. 



one, a plate of iron between the magnet and other iron the 

 effect of the magnet. But the proper place for mentioning 

 these will be also amongst the supports of induction. 



44. We have now spoken of the instances which assist 

 the senses, and which are principally of service as regards 

 information ; for information begins from the senses. But 

 our whole labour terminates in practice, and as the former 

 is the beginning, so is the latter the end of our subject. 

 The following instances, therefore, will be those which are 

 chiefly useful in practice. They are comprehended in two 

 classes, and are seven in number. We call them all by the 

 general name of practical instances. Now there are two 

 defects in practice, and as many divisions of important in 

 stances. Practice is either deceptive or too laborious. It 

 is generally deceptive (especially after a diligent examina 

 tion of natures), on account of the power and actions of 

 bodies being ill defined and determined. Now the powers 

 and actions of bodies are defined and determined either by 

 space or by time, or by the quantity at a given period, or 

 by the predominance of energy ; and if these four circum 

 stances be not well and diligently considered, the sciences 

 may indeed be beautiful in theory, but are of no effect in 

 practice. We call the four instances referred to this class 

 Mathematical instances and instances of measure. 



Practice is laborious either from the multitude of instru 

 ments, or the bulk of matter and substances requisite for any 

 given work. Those instances, therefore, are valuable, which 

 either direct practice to that which is of most consequence 

 to mankind, or lessen the number of instruments, or of matter 

 to be worked upon. We assign to the three instances 

 relating to this class the common name of Propitious or 

 Benevolent instances. We will now separately discuss these 

 seven instances, and conclude with them that part of our 

 work which relates to the prerogative or illustrious in 

 stances. 



45. In the twenty-first rank of prerogative instances we 

 will place the instances of the Rod or Rule, which we are also 

 wont to call the instances of completion or non ultra. For 

 the powers and motions of bodies do not act and take effect 

 through indefinite and accidental, but through limited and 

 certain spaces; and it is of great importance to practice 

 that these should be understood and noted in every nature 

 which is investigated ; not only to prevent deception, but 

 to render practice more extensive and efficient. For it is 

 sometimes possible to extend these powers, and bring the 



