6 2 HEROES OF INVENTION AND DISCO VER Y. 



expectations, this guiding idea upon which the experimenter 

 proceeds must be regarded merely as a conjecture. But such 

 a conjecture or hypothesis he must have in his mind, or he is 

 in no condition to set about the inquisition of nature. What 

 progress would the conductor of a trial in a court of justice be 

 likely to make, in questioning a witness, without some previous 

 notion of the truth which the evidence was likely to establish ? 

 He might waste the whole day in putting questions and 

 receiving answers, and at last have ascertained nothing. Just 

 as unprofitably would the interrogator of nature spend his time 

 if he had no directing anticipation in every case, according to 

 which to order his experiments. Accident might, it is possible, 

 throw a discovery in his way ; but his own occupation would be 

 evidently as idle and as little that of a philosopher as the 

 rattling of a dice-box. W7ienever, ifideed, a discovery is tfiade 

 witJwut being anticipated, ive say that it has been made by chance. 

 On the other hand, the history of all discoveries that have been 

 arrived at by what can with any propriety be called philosophical 

 investigation and induction, attests that necessity which has 

 been asserted of the experimenter proceeding in the institution 

 and management of his experiments upon a previous idea of 

 the truth to be evolved. This previous idea is what is properly 

 called a hypothesis, which means something placed under as a 

 foundation or platform on which to institute and carry on the 

 process of investigation. A theory is a completed view of a 

 harmonious system of truths, evolved and proved by calculation 

 or induction. As the latter is the necessary completion of every 

 philosophical inquiry, so the former is its equally indispensable 

 beginning. It is the aim in the mind of the philosopher, 

 without which he cannot philosophise. It makes, in short, the 

 main difference between the experiments of the philosopher in 



