SCIENTIFIC IMAGINATIVE POWER. 365 



cientific investigator is more difficult, or requires a 

 reater exercise of genius and intellect, than that of 

 magining an important and truthful hypothesis, and 

 udging of the degrees of its value and probability. It is 

 n this part of his occupation that the scientific investi- 

 gator assumes the function of a prophet. To predict 

 mportant new results, and judge of their value, requires 

 ot only extensive and accurate knowledge of science, as 

 ilready contained in books, but also a high degree of the 

 )ower of discerning essential resemblances between phe- 

 lomena apparently the most diverse, and of perceiving 

 he natural relations, affinities, and orders of dependence 

 >etween the various sciences, and between classes of 

 phenomena in different sciences. 



According to Brewster, ' the extravagant speculations 

 which often precede and lead to discovery differ in no 

 respect from the creations of a rich poetical fancy.' An 

 investigator who does not venture beyond the views 

 expressed in scientific books, cannot be very original, and 

 a man who is not speculative can hardly be fruitful in 

 scientific discoveries. The power of devising hypotheses 

 is dependent upon the fact that the human mind can 

 combine several ideas together to form a new one. Most 

 new ideas in science probably arise from the union of 

 old ones, and the process of evolving them is often pro- 

 longed and laborious. It is recorded that when Newton 

 had nearly completed the calculations which revealed to 

 him the universal action of gravity, he became so greatly 

 affected that he had to ask a friend to finish them for 

 him ; and most scientific investigators have experienced 

 the exhaustion produced by difficult thinking. 



Sir W. R, Hamilton has described in the following 

 words the origin of the first conception of his great dis- 

 covery of the method of Quaternions : ( To-morrow will 



