156 THE PRINCIPLES OF SCIENCE. 



stances under it, or imagine that the name gives us an} 

 knowledge of the obscure origin of life. To name * 

 substance protoplasm no more explains the infinite variet} 

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

 does the vital force which may be supposed to reside ir 

 the protoplasm. Both expressions appear to me to b* 

 mere names for an unknown and inexplicable series o1 

 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 ofter 

 frame for the more ready investigation or comprehensior 

 of a subject. The mathematician, in treating abstrad 

 questions of probability, finds it convenient, to represen' 

 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. 

 p. 280). Many other such devices are also used b} 

 mathematicians. When Newton investigated the nature 

 of waves, he employed the pendulum as a conveniem 

 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 sud 

 creations of the mind may be called Representative Hypo- 

 theses, and they are only permissible and useful so far a* 

 they embody analogies. Their further consideration pro- 

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

 of language and representation, founded upon analogy. 



