94 HISTORY OF SCIENCE. 



fleeted in the plane mirror, so that you may read without difficulty." 

 When, a few years before Porta's death, the telescope had become 

 widely known as Galileo's Tube, Porta claimed the invention as his own, 

 and much discussion took place as to the validity of this claim, which 

 is, however, now admitted to rest on an insufficient basis. 



Contemporaneous with Porta there lived at Colchester an English 

 physician whose name is memorable as the founder of the sciences ot 

 Magnetism and Electricity. Dr. WILLIAM GILBERT (1540 1603) 

 published in the year 1600, under the title " De Arte Magnetica" an 

 admirable treatise in which the facts of magnetism are investigated and 

 its general laws are for the first time enunciated. This work is re- 

 markable also because it is a fine example of inductive reasoning, al- 

 though the great treatise of Francis Bacon, in which the methods of 

 inductive science were first laid down in a systematic form, did not ap- 

 pear until many years after Gilbert's time. Galileo was acquainted with 

 Gilbert's treatise, and he says of it, "I extremely admire and envy this 

 author. I think him worthy of the greatest praise for the many new 

 and true observations that he has made, to the disgrace of so many vain 

 and fabling authors, who write not from their own knowledge only, but 

 repeat everything they hear from the foolish vulgar, without attempting 

 to satisfy themselves of the same by experience perhaps that they may 

 not diminish the size of their books." 



Gilbert, after completely discussing the phenomenon of the load- 

 stone, proceeds to examine the apparently analogous fact of amber 

 attracting light bodies after it has been rubbed. From the time of 

 Thales to that of Gilbert this remained almost the only electrical phe- 

 nomenon known to philosophers, the exceptions being some very few, 



FIG. 39 . 



FIG. 40. 

 FIG. 38. 



and perhaps doubtful, additions to the list of bodies possessing the like 

 property. The explanation of Thales, that amber has a breath which 

 draws light bodies, or the theory of Pliny, that by friction the amber 

 acquires warmth and life, appear in ancient and mediaeval times to 

 have satisfied men's curiosity on this subject. Amber and jet both 

 costly substances, from their comparative rarity and the demand for 

 them as material for ornaments were before Gilbert's time the only 



