xvi. Proceedings. [December 1st, 1896. 



tendency to invent well-rounded and symmetrical systems, 

 and to ignore or minimise troublesome facts which will not 

 fall in with them. The idols of the Cave are those peculiar 

 to each individual mind, prompting it to accept narrow or 

 distorted views in preference to taking a survey from a wide 

 and open standpoint. The idols of the Market-place are 

 those which arise from a perverted use of language, elevating 

 such words as Fate, Fortune, Nature, &c, into realities, and 

 ascribing functions to them which a little consideration 

 would show they cannot bear. Lastly, the idols of the 

 Theatre are the visionary and sophistical systems of philo- 

 sophy, founded on a few hasty generalisations of facts, or 

 upon unwarranted speculations or superstition. 



Following the lines thus suggested, it is possible to 

 classify scientific errors under four heads, viz., General and 

 Historic, Productive, Obstructive, and Occasional errors. 

 No hard and fast lines can be laid down, but the four classes 

 are sufficient, and in most cases it is not difficult to decide 

 upon the heading under which any particular error should 

 go. In the first class are included Astrology, Alchemy, the 

 ancient cosmogonies, especially the Ptolemaic, and several 

 minor "idola" or phantoms which, to use a simile of 

 Bunyan's, have lured many a good intellect " to the top of 

 the hill called Error, which was very steep on the farthest 

 side"; as, for instance, squaring the circle, and finding a 

 source of energy which would work continually without 

 replenishing, commonly known as the perpetual motion. 



Among Productive errors we may reckon the doctrine of 

 Phlogiston and Prout's hypothesis in Chemistry, the impon- 

 derable fluids of Magnetism, Electricity, and Heat in 

 Physics, the theory of Epigenesis in Biology, and of 

 Catastrophism in Geology. All these have borne good fruit 

 by stimulating inquiry and controversy, and it is noticeable 

 how in several cases what seemed to be a well-founded 

 doctrine has for a time fallen into disrepute, to be after- 

 wards revived with modifications. Thus Phlogiston or the 

 principle of combustion died a very hard death, and no 



