368 PERSONAL PREPARATION FOR RESEARCH. 



sity and excitement of thought at the moment obliterates 

 from the memory what we were thinking of immediately 

 before, and thus the mental origins of many discoveries, 

 particularly the important ones (which require the 

 deepest and most exciting thought), are not secured to 

 mankind. 



It is usually by associating the ideas relating to one 

 science or experiment with those of the phenomenon 

 or experiment under consideration, that new hypotheses 

 are formed. Newton superimposed the idea of universal 

 action, of intensity varying as the inverse square of the 

 distance, upon the previously known idea of bodies being 

 attracted by the earth, and thus imagined the hypothesis 

 of universal gravitation. The origin of his hypothesis 

 is related thus : In 1666, ' as he sat alone in his garden, 

 he fell into a speculation on the power of gravity, that, 

 as this power is not found sensibly diminished at the 

 remotest distance from the centre of the earth to which 

 we can rise, neither at the tops of the loftiest buildings, 

 nor even on the summits of the highest mountains, it 

 appeared to him reasonable to conclude that this power 

 must extend much farther than was usually thought: 

 Why not as high as the Moon? said he to himself; and, 

 if so, her motion must be influenced by it ; perhaps she is 

 retained in her orbit thereby.' l In a similar manner, to 

 a scientific investigator the idea of a new force would at 

 once suggest some of its quantitative relations, such as, 

 Does its strength vary inversely as the square of the 

 distance ? &c. ; to a chemist, the idea of a new elementary 

 substance suggests the ideas of its various possible com- 

 pounds, and the different proportions in which the new body 

 may combine with substances already known. ' The means 



1 Whewell, History of the Inductive Sciences, 3rd edit., vol. ii. pp. 

 121 and 451. 



