OCEANIC DISCO VERIKS. 283 



almost equally cold upper stratum of air from the equatoi 

 toward the poles, designate an important epoch in the history 

 of our physical knowledge. 



If, on the one hand, accidental observations, 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 knov.'ledge, was the cotemporary of Columbus, 

 and died three years after him. Meteorolog}^ 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 eloquence of his discourse, and not by his writings. 

 Had the physical view^s 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 coniinciare 

 dalV esjoerienza, eper mezzo di questa scoj^rir^ie la regione").* 



As we find, notwithstanding the want of instruments of 

 iiieasurement, 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 pi'oceediiig, " questo 

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

 See^Yenturi, Essai surles Ouvrages Phy sico-mathematiques de Leonardo 

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

 do da Virici, Milano. 1804, p. 143 (in his edition of Trattalo della Pittn- 

 ra, t. xxxiii. of the Classic! Italiani) ; 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. 



