Science in Early England. 25 



the others follow their course, so that it is very necessary 

 to those who navigate the sea." Again, Guyot de 

 Provence, in a love song of the early part of the 13th 

 century, has these lines: — 



They know its position for their route, 



When the weather is completely without light, 



All those who employ this contrivance. 



Whoever thrusts a needle of iron 



So that it remains almost entirely outside 



In a bit of cork, and rubs it on the brown loadstone 



If it be put in a vessel full of water 



So that nobody push it out. 



As soon as the water becomes quiet, 



To whatsoever side the point turns 



There is certainly the polar star. 



Lastly, Dante's preceptor, Brunetto Latini, writing 

 about 1260, just after a visit to Roger Bacon, says: "He 

 shewed me the magnet, an ugly black stone to which iron 

 spontaneously attaches itself. They touch it with a needle, 

 and thrust this into a straw, then put it in water ; it swims, 

 and the point turns towards the polar star. If the night 

 be dark, and one can see neither star nor moon, the 

 mariners can keep their right course." Bacon is the only 

 writer, as far as I know, who mentions magnetic repul- 

 sion — "as the lamb flees the wolf," he puts it. 



Neckam's remarks on animals are of little interest, as 

 they reflect all the popular errors. He is the only author, 

 except Bacon and Grosseteste, who deals with optics. He 

 describes the well-known basin and coin experiment (this, 

 however, was known to Cleomedes in the 1st century a.d.), 

 and speaks of glass mirrors. He tells us that in a concave 

 mirror the image is inverted, and in a plane or convex 

 one erect, but remarks despairingly, " Who can assign a 

 sufficient reason for these things?" An interesting observa- 

 tion, which he might have learned from Eratosthenes, of 

 the 3rd century B.C., is that verticals to the earth's surface 

 must be inclined to one another ; he goes rather too far, 

 however, and says that the walls of buildings must 



