SCIENTISTS OF XVTH AND XVlTH CENTURIES. 107 



" If we believe them (the Schoolmen), that knowledge is 

 mechanical which is born from experiment, and science that 

 which is born from, and ends in, the mind ; semi-mechanical 

 that which is born from science and ends in manual operation. 

 But it appears to me that those sciences are vain and full of 

 error which are not born from experiment (experience), mother 

 of all certainty, and which do not end in a definite experiment 

 (che non terminano in nota experimentia) , that is, the principle, 

 the middle or the end of which does not pass through one of 

 the five senses. 



" If we are told that the eyesight prevents true and 

 attentive mental knowledge by which one penetrates into 

 the divine science, and that such an obstacle led a philosopher 

 to put his own eyes out, I reply to this that such an eye, as 

 lord of the senses, does its duty to put an obstacle to those 

 confused and lying reasonings (discorsi) about which men, with 

 loud shouts and agitation of hands, for ever go on disputing. 



"Avoid the precepts of those speculators who do not 

 confirm their reasonings by experiment." 



" Do not trust to those authors/' says he again, " who 

 have sought by their sole imagination to become the in- 

 terpreters between nature and man, but to those only who, 

 by the results of their experiments, have exercised their 

 minds to recognise how experiments deceive him who does 

 not know their nature, because those experiments which 

 often appear identical are very different." This about writers 

 who declared that being given a motor which shoots a weight 

 a given distance off, one may multiply the distance to infinity 

 by dividing the weight to infinity. 



The preceding injunction is another evidence of the value 

 which Leonardo da Vinci attached to verification. In fact, 

 in true scientific spirit, he used to write " false " (false) 

 under a proposition which he had enunciated, after experi- 

 ments had shown him its unsoundness.* 



All this had been done during the Revival when Francis 



Bacon entered the lists, and stood up as the herald and sole 



champion of science. " Our only hope," said Francis Bacon, 



"is in the regeneration of the sciences by regularly raising 



* For further evidence of Leonardo's science, see Appendix IV. 



