98 PROGRESS OF SCIENCE. 



of the Schoolmen, and show that Roger Bacon had regal 

 successors. 



In Practical and Theoretical Science, in metallurgy, 

 chemistry, geology, astronomy, physics, the XVth and XVIth 

 centuries were equally fruitful of results. AGRICOLA had 

 created modern METALLURGY ; Antonio de Dominis had ex- 

 plained the correct theory of the rainbow, which Harriot made 

 clearer still ; MERCATOR had created modern GEOGRAPHY ; 

 Santorio, with true scientific insight, had shown the use, not 

 only of the thermometer, but also of the hygrometer, and 

 even of the scales in physiological research ; Ubaldt had 

 developed mechanical laws ; STEVINUS had published his 

 book on the principles of equilibrium, determined the funda- 

 mental property of the inclined plane, and solved the general 

 problem of forces acting obliquely elucidating all along some 

 of the LAWS OF PRESSURE, motion, THE LEVER, and the 

 equilibrium of liquids ; PORTA had invented the CAMERA. 

 OBSCURA, the magic lantern, and demonstrated light to be the 

 cause of vision ; Tycho Brahe had constructed several in- 

 struments of great precision, catalogued nearly 800 fixed 

 stars, and drawn up the RUDOLPHINE TABLES after twenty- 

 five years' incessant observations an immortal work ; he- 

 had determined the COURSE OF COMETS, and shown the third 

 inequality of the moon ; CASTELLI had founded hydraulics;. 

 SNELL had discovered the LAW OF REFRACTION, one of the 

 most important in optics ; GILBERT, one of the great masters 

 of the inductive method, had determined the principles of 

 MAGNETISM and ELECTRICITY after years of experiments one 

 of the best proofs that the experimental method was used in 

 earnest ; he had determined the poles of the magnet, described 

 the DIFFERENCE BETWEEN THE MAGNETIC and the ASTRO- 

 NOMICAL meridian, demonstrated the POLARISATION OF IRON 

 BARS by being placed in the direction of the magnetic meridian 

 teaching that the EARTH IS A MAGNET, which accounted, 

 according to him, for the inclination and declination of the 

 compass. Harvey had explained the CIRCULATION OF THE 

 BLOOD a discovery of supreme importance in physiology, 

 due to deductive and inductive reasoning in an equal degree. 



Leonardo da Vinci, " whose knowledge/' as Hallam 



