ON THE HISTORY OF TERRESTRIAL PHYSICS. 583 



is frequently made at present by a similar process ; others of the ancients 

 had remarked, according to Dr. Falconer,* that water usually froze the 

 more readily for having been boiled ; and it is possible that some other 

 detached observations of a similar nature may occur to those who have the 

 curiosity to make them objects of research. 



The thirteenth century may be considered as the date of the revival, if 

 not of the commencement, of physical discoveries. Our countryman, 

 Roger Bacon, was one of its principal ornaments : he appears to have 

 anticipated in his knowledge of chemistry, as well as of many other parts 

 of natural philosophy, the labours of later times. The polarity of the 

 magnetic needle is described in some lines which are attributed to Guyot, a 

 French poet, who lived about 1180 ; but some persons are of opinion that 

 this description was actually written by Hugo Bertius, in the middle of 

 the succeeding century ; and it is generally believed that the compass was 

 first employed in navigation by Gioja of Amain, about the year 1260 ; he is 

 said to have marked the north with a fleur de lis, in compliment to a 

 branch of the royal family of France, then reigning at Naples. The 

 declination of the needle from the true meridian is mentioned by Peter 

 Adsiger, the author of a manuscript which bears the date 1269. The poet 

 Dante, who flourished at the close of this century, distinguished himself 

 not only by his literary, but also by his philosophical pursuits ; and we 

 find among his numerous works an essay on the nature of the elements. 



The learned and voluminous labours, by which Gesner and Aldrovandus 

 enriched the various departments of natural history, may be considered as 

 comprehending the greatest part of what had been done by the ancients in 

 the investigation of the economy of the animal world ; but their works 

 have too much the appearance of collections of what others had asserted, 

 rather than of original observations of their own. 



The first of the moderns whose discoveries respecting the properties of 

 natural bodies excite our attention, by their novelty and importance, is 

 Dr. Gilbert, of Colchester : his work on magnetism, published in 1590, con- 

 tains a copious collection of valuable facts, and ingenious reasonings. He 

 also extended his researches to many other branches of science, and in 

 particular to the subject of electricity. It had been found, in the preced- 

 ing century, that sulfur, as well as amber, was capable of electric excitation, 

 and Gilbert made many further experiments on the nature of electric 

 phenomena. The change or variation of the declination of the needle is 

 commonly said to have been discovered by Gellibrand, a professor at 

 Gresham college, in the year 1625 ; but it must have been inferred from 

 Gunter's observations, made in 1622, if not from those of Mair, or of some 

 other person, as early as 1612 ; for at this time the declination was con- 

 siderably less than Burrows had found it in 1580.f 



In the beginning of the seventeenth century, Lord Bacon acquired, by 

 his laudable efforts to explode the incorrect modes of reasoning, which had 

 occupied the schools, the just character of a reformer of philosophy ; but 



* On the Knowledge of the Ancients, Manch. Mem. i. 261 ; iii. 278. 

 f Burroughs's Dissertation in Norman's New Attractive, 3rd edit. Gellibrand, 

 on the Variation of the Mag. Needle, 1635. See Robison, Mec. Ph. iv. 354. 



