OCEANIC DISCOVERIES. 661 



the sinking of an almost equally cold upper stratum of air 

 from the equator towards 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, favoured this knowledge in the suddenly 

 enlarged spheres of natural investigation, the age we are de- 

 scribing was, on the other hand, from an unfortunate combina- 

 tion of circumstances, singularly deficient in the advantages 

 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 mathema- 

 tical knowledge, was the cotemporary of Columbus, and died 

 three years after him. Meteorology, as well as hydraulics 

 and optics, had occupied the attention of this celebrated 

 artist. The influence which he exercised during his life, was 

 made manifest by his great works in painting, and by the elo- 

 quence 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 Galileo, 

 Pascal, and Huygens. Like Francis Bacon, and a whole cen- 

 tury before him, he regarded induction as the only sure method 

 of treating natural science ("dobbiamo cominciare dalV 

 esperienza, e per 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 



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

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

 Venturi, Essai sur les Ouvrages physico-maihematiques de Leonardo 

 da Vinci, 1797, p. 31; Amoretti, Memorie storiche su la Vita di Lio- 

 nardo da Vinci, Milano, 1804, p. 143 (in his edition of Trattato della 

 PiUura, L xxxiii of the Classici Italiani); Whewell, Pkilos. of the 

 Inductive Sciences, 1840, vol. ii. pp. 368-370 ; Brewster, Life of Neva- 

 ton, p. 332. Most of Leonardo da Vinci's physical works bear thn date 

 of the year 1498. 



