XOVUM ORGANUM 231 



gent examination 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 

 circumstances 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 conse 

 quence 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 pro 

 pitious 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 illus 

 trious instances. 



XLV. 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 ultrct. 

 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 

 distance, as it were, nearer, as in the example of telescopes. 



Many powers act and take effect only by actual touch, as 



