FRANCIS BACON. 137 



has triumphantly prevailed over all other hypotheses, and proved itself 

 one of the most fertile conceptions of physical science. Unlike Bacon's 

 conclusion, however, the dynamical theory of heat rests on a vast mass 

 of exact experimental research, and is supported by many converging 

 lines of inquiry, as we shall afterwards have occasion to show. 



Bacon devotes a part of his great work to illustrations of the various 

 kinds of facts which are of most importance in an inductive inquiry, 

 and such truths he denominates Prerogative Instances, dividing them 

 into classes ranged under the three heads of ist. Instances address- 

 ing themselves to the understanding. 2nd. Those which assist the 

 senses. 3rd. Those which conduce to practice. The total number of 

 classes enumerated by Bacon amount to no fewer than twenty-seven; 

 but the distinctions sometimes appear to be arbitrary and fanciful, and 

 sometimes the relations of a given truth to a given inquiry are such 

 that the instance may with equal propriety be referred to several of 

 Bacon's classes. We shall quote the characters of some of the more 

 important of the Prerogative Instances, without following the laborious 

 details of our author. 



The first class are the solitary instances, and this includes, perhaps, 

 the class of facts most important of all in an inductive inquiry namely, 

 examples in which the quality or nature under investigation occurs in 

 bodies otherwise as unlike each other as possible. This limits the field 

 of inquiry into the cause of the quality, for the cause must be some 

 one of the few circumstances in which the bodies are alike. For in- 

 stance, bright colours may be seen in prismatic pieces of glass, in 

 crystals, in ice, in dew-drops, etc. These instances, having nothing 

 in common with coloured bodies such as flowers, minerals, etc., are 

 called solitary instances by Bacon, who draws a remarkable conclusion, 

 wherein he appears to be anticipating the results of Newton's famous 

 experiments, for he infers that colours in crystals are nothing but modi- 

 fications of the rays of light depending upon the degrees of incidences 

 with which these fall upon the crystal, and that the fixed colours of 

 other bodies are due to certain textures or configurations of their sur- 

 faces. The class of solitary instances comprises also the instances of 

 the kind converse to those just named, viz., those in which bodies re- 

 semble each other in every way but in respect to the quality under con- 

 sideration, which one possesses and the other does not possess. It is 

 plain that in such cases the form or cause cannot exist in those things 

 wherein the bodies agree. Bacon illustrates this kind of solitary in- 

 stance by black veins and white veins in marble, and by the variety of 

 colours observed in flowers of the same species ; and his infenerce as 

 regards the cause of colours is again that they do not depend on the 

 internal and essential properties of bodies. We may here remark that, 

 while it is comparatively rare to find in nature instances agreeing in all 

 but one particular, it is the special end and aim of the investigator who 

 proceeds by experiments to produce precisely this condition. This is 



