266 



compass in the ship had undergone (he same 

 change. 



An odd discovery has been lately made, that not 

 only iron, as has been generally thought, but brass 

 too, by being hammered and properly touched, will 

 contract a true magnetic virtue. And perhaps it 

 will be hereafter discovered, that other metals may 

 receive the same. 



Before closing this article, it may be proper to ob- 

 serve first, the peculiar qualities wherewith some 

 other stones are endued ; and secondly, the remark- 

 able uses they are of to us. As to the former, we 

 may observe, 1. The colour. The carbuncle and 

 ruby shine with red, the sapphire with blue, the 

 emerald with green, the topaz with a yellow or gold 

 colour, the amethyst is as it were tinctured with 

 wine, {he opal varies its colour like changeable taf- 

 feta, as it is variously exposed to the light. Observe, 



2. The hardness wherein some stones exceed all other 

 bodies, the diamond in particular, which is so ex- 

 tremely hard, that no art is able to counterfeit it. 



3. As to the uses, some are serviceable for building, 

 and for many sorts of vessels and utensils ; for pil- 

 Jars and statues ; for porticos, conduits, palaces, as 

 free-stone and marble ; some to burn into lime; some 

 (with the mixture of kelp; to make glass, as common 

 Hints ; some to cover houses, as slate; some for mark- 

 ing, as chalk, which serves also to manure land ; and - 

 for medicinal uses, some to make vessels which will 

 endure the fire. I might add the warming stone, 

 digged in Cornwall: which being once well heated 

 at^the fire, retains its heat for a considerable time. 



17. Of the third class are inflammable fossils, the 

 chief of which are sulphur and bitumen. Both arc 

 highly inflammable, but the substance of bitumen is 

 more fat and tenacious, whereas sulphur may easily 

 be broken and reduced to a fine powder. 



The bitumen of the Latins was by the Greeks 



