156 THE PRINCIPLES OF SCIENCE. 



stances under it, or imagine that the name gives us any 

 knowledge of the obscure origin of life. To name a 

 substance protoplasm no more explains the infinite variety 

 of forms of life which spring out of the substance, than 

 does the vital force which may be supposed to reside in 

 the protoplasm. Both expressions appear to me to be 

 mere names for an unknown and inexplicable series of 

 causes which out of apparently similar conditions pro 

 duce the most diverse results. 



Hardly to be distinguished from descriptive hypotheses 

 are certain imaginary objects or conditions which we often 

 frame for the more ready investigation or comprehension 

 of a subject. The mathematician, in treating abstract 

 questions of probability, finds it convenient, to represent 

 the conditions to his own or other minds by a concrete 

 analogy in the shape of a material ballot-box. The funda 

 mental principle of the inverse method of probabilities 

 upon which depends the whole of our reasoning in in 

 ductive investigations is proved by Poisson, who imagines 

 a number of ballot-boxes, of which the contents are after 

 wards supposed to be mixed in one great box (vol. i. 

 p. 280). Many other such devices are also used by 

 mathematicians. When Newton investigated the nature 

 of waves, he employed the pendulum as a convenient 

 mode of representing the nature of the undulation. 

 Centres of gravity, oscillation, &c., poles of the magnet, 

 lines of force, are other imaginary existences solely em 

 ployed to assist our thoughts (vol. i. p. 422). All such 

 creations of the mind may be called Representative Hypo 

 theses, and they are only permissible and useful so far as 

 they embody analogies. Their further consideration pro 

 perly belongs either to the subject of Analogy, or to that 

 of language and representation, founded upon analogy. 



