FfiANCIS BACON. 21 



merely an introduction to, and example of, his new mctliod of 

 Indtu'tion, the introduction forming- the first hook, and the cxamjde, 

 the nature of heat, forming the greater part of the second. In tlio 

 first book the principles of correct induction are laid down, and the 

 errors to be guarded against, the false idols, are pointed out. In 

 concluding it he says that " if men had a just history of nature and 

 experience, and could bind themselves by two rules, first, to lay 

 aside received opinions, and secondly to restrain themselves from 

 seeking at once to ascend to the highest generalisations, they would 

 be able to interpret nature rightly." In the second book more 

 precise rules are given with special reference to the immediate 

 subject of inquiry. These rules have been much condemned, the 

 chief ground of condemnation being that he ignores, in formulating 

 them, the fact that invention and discovery as a rule require 

 genius, thinking that, if only his rules were followed, the secrets 

 of nature would be open to all investigators ; and yet we find that, 

 although he cannot be considered to have shown any special genius 

 for physical research, and, unfortunately for physical science, was 

 not a mathematician, in the one case in which he did apply his 

 own rules, he gave a definition of heat which it would be difiicult 

 to express with greater terseness and precision at the present day. 

 ''Heat," he says, "is a motion, expansive, restrained, and acting 

 in its strife upon the smaller particles of bodies ; " and this motion 

 "is not sluggish, but hurried and with violence." Heat then, and 

 for two centuries afterwards, was thought to be material rather than 

 a form of energy, and was called 'caloric,' a notion which Bacon 

 rejected on account of its being generated by friction, and it is note- 

 worthy that it is by experiments on friction in recent years that the 

 correctness of his interpretation of the nature of heat has been proved, 

 and the determination of the mechanical equivalent of heat has 

 been made. Equally happy, and equally in advance of the know- 

 ledge of the time, is his example of the discovery of truth from a 

 Solitary Instance, one class, out of twenty-seven, of his Prerogative 

 Instances, another being the well-known Crucial Instance. " If," 

 he says, "we are enquiring into the nature of Colour, prisms, 

 crystals, which show colours not only in themselves but externally 

 on a wall, dews, etc., are Solitary Instances. For they have 

 nothing in common with the colours fixed in flowers, coloured 

 stones, metals, woods, etc., except the colour. From which we 

 gather that colour is nothing more than a modification of the image 

 of light received upon the object, resulting in the former case fi'om 

 the different degrees of incidence, in the latter from the various 

 textures and configurations of the body." The far-reaching import 



