342 PERSONAL PREPARATION FOR RESEARCH. 



science by means of pure reason is largely different from 

 that of rinding them by testing hypotheses by means of 

 experiment and observation. By the latter we discover 

 sensible facts, and data for inference, but by the former we 

 are able to find causes, coincidences, and abstruse relations. 

 The conception of hypotheses requires an imaginative mind, 

 but that of drawing conclusions requires a judicial one ; and 

 this involves logical skill, and a readiness in the manipu- 

 lation of ideas which can only be acquired by practice. In 

 arranging the ideas contained in the scientific knowledge 

 we possess, so as to extract as many new truths as possible 

 from them, we often find the evidence incomplete which 

 is necessary in order to draw logically a particular con- 

 clusion ; and in that case we have to devise and execute 

 new experiments in order to obtain the deficient knowledge. 



The scientific knowledge gained directly from nature 

 by means of our senses is not that of general laws or prin- 

 ciples, because our senses cannot perceive them ; but of 

 isolated sensible facts, in the form of ideas of -substances, 

 properties, conditions, actions, and various phenomena ; 

 and it is only by drawing inferences from those facts by 

 means of our reasoning powers that we evolve from them 

 a knowledge of principles, laws, forces, and abstruse truths. 



As all the scientific facts we possess are gained, 

 either directly or indirectly, by means of experience, 

 both that of others and of ourselves and our reasoning 

 power is only influenced through the medium of such facts 

 and the conclusions we draw from them anything which 

 cannot affect our senses, or is not evolved from sensory 

 impressions by reasoning processes, cannot affect our reason. 

 A thing, therefore, which is without properties is to us 

 incapable of being known, reasoned upon, or even con- 

 ceived. We only know of the existence of force through 

 the medium of matter, and of matter by means of our senses. 



