OCEANIC DISCOVERIES. 283 



almost equally cold upper stratum of air from the equator 

 toward the poles, designate an important epoch in the history 

 of our physical knowledge. 



If, on the one hand, accidental ohservations, having a 

 wholly unscientific origin, favored this knowledge in the sud- 

 denly enlarged spheres of natural investigation, the age we 

 are describing was, on the other hand, from an unfortunate 

 combination of circumstances, singularly deficient in the ad- 

 vantages arising from a purely scientific impulse. Leonardo 

 da Vinci, the greatest physicist of the fifteenth century, who 

 combined an enviable insight into nature with distinguished 

 mathematical knowledge, was the cotemporary of Columbus, 

 and died three years after him. Meteorology, as well as hy- 

 draulics and optics, had occupied the attention of this cele- 

 brated artist. The influence which he exercised during his 

 life was made manifest by his great works in painting, and 

 by the eldquence of his discourse, and not by his writings. 

 Had the physical views of Leonardo da Vinci not remained 

 buried in his manuscripts, the field of observation opened by 

 the new world would in a great degree have been worked out 

 in many departments of science before the great epoch of Gal- 

 ileo, Pascal, and Huygens. Like Francis Bacon, and a whole 

 century before him, he regarded induction as the only sure 

 method of treating natural science (" dobbiamo cominciare 

 dalV esperienza, eper mezzo di questa scoprirne la regione").* 



As we find, notwithstanding the want of instruments of 

 measurement, that the questions of climatic relations in the 

 tropical mountainous regions the distribution of heat, the 

 extremes of atmospheric dryness, and the frequency of electric 

 explosions were frequently discussed in the accounts of the 

 first land journeys, so also it appears that mariners very early 

 acquired correct views of the direction and rapidity of the cur- 

 rents which traverse the Atlantic Ocean, like rivers of very 

 variable breadth. The actual equatorial current, the move- 

 ment of the waters between the tropics, was first described by 

 Columbus. He expresses himself most positively and gener- 



* Leonardo da Vinci correctly observes of this proceeding, " questo 

 e il methodo daosservarsi nella ricerca de' fenomeni della natura." 

 See Venturi, Essai surles Ouvrages Physico-mathematiques de Leonardo 

 da Vinci, 1797, p. 31 ; Amoretti, Memorie Storiche sit, la Vita di Lionar- 

 do da Vinci, Milano, 1804, p. 143 (in his edition of Trattato della Pittu- 

 ra, t. xxxiii. of the Classici Italian!) ; Whewell, Philos. of the Inductive 

 Sciences, 1840, vol. ii., p. 368-370; Brewster, Life of Newton, p. 332. 

 Most of Leonardo da Vinci's physical works bear the date of the year 

 1498. 



