THE ART OF SCIENTIFIC INVESTIGATION 



Malthus gave a clear exposition of the checks to increase in the 

 human population and mentioned that these eliminated the least 

 fit. Then it occurred to Wallace that the position was much the 

 same in the animal world. 



" Vaguely thinking over the enormous and constant destruc- 

 tion this implied, it occurred to me to ask the question, * Why 

 do some die and some live? ' and the answer was clearly that on 

 the whole the best fitted live. . . . Then it suddenly flashed upon 

 me that this self-acting process would improve the race . . . 

 the fittest would survive. Then at once I seemed to see the whole 

 effect of this." ^^ 



Here is Metchnikoff's own account of the origin of the idea of 

 phagocytosis : 



" One day when the whole family had gone to the circus to 

 see some extraordinary performing apes, I remained alone with 

 my microscope, observing the life in the mobile cells of a trans- 

 parent starfish larva, when a new thought suddenly flashed across 

 my brain. It struck me that similar cells might serve in the 

 defence of the organism against intruders. Feeling that there was 

 in this something of surpassing interest, I felt so excited that I 

 began striding up and down the room and even went to the 

 seashore to collect my thoughts." ^^ 



Poincare relates how after a period of intense mathematical 

 work he went for a journey into the country and dismissed his 

 work from mind. 



" Just as I put my foot on the step of the brake, the idea 

 came to me . . . that the transformations I had used to define 

 Fuchsian functions were identical with those of non-Euclidian 

 geometry." ^^ 



On another occasion when baflfled by a problem he went to the 

 seaside and 



" thought of entirely different things. One day, as I was walking 

 on the cliff the idea came to me, again with the same character- 

 istics of conciseness, suddenness and immediate certainty, that 

 arithmetical transformations of indefinite ternary quadratic forms 

 are identical with those of non-Euclidian geometry." 



Hadamard cites an experience of the mathematician Gauss, 

 who wrote concerning a problem he had tried unsuccessfully to 

 prove for years, 



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