Proceedings of the Polytechnic Association. 1043 



Petrified wood, called also silicified wood, containing the texture of 

 the original wood, which when sawn across and polished is remark- 

 ably beautiful. 



Quartz crystals are often found inclosed with other minerals, such 

 as rutile, asbestos, actinolite and topaz, oxyd of iron, tourmaline, 

 chlorite- and anthracite coal ; those containing the rutile look as if 

 needles or fine hairs passed through them in every direction, and when 

 cut for jewelry, pass by the name of love's arrows, ox fleches W amour. 



The opal^ one of the most fashionable jewels, is silica, with some 

 water ; it exhibits internal reflections of rainbow colors, and forms a 

 gem of rare beauty ; it is usually cut with a convex surface. Among 

 the varieties of opal are fire-opal or girasol, it has yellow, bright 

 hyacinth, or fire-red reflections. The common or semi-opal, has a 

 milky opalescence, but does not reflect a play of colors. 



Hydrophane, cacholong, hyalite, raenilite, wood opal, jasper, 

 silicious sinter, pearl sinter and fabasheer, all belong to the same 

 class of silicious minerals, and are of greater interest to the miner- 

 alogist than to the general reader. 



Among all the discoveries relating to the arts, none exceed in 

 importance and usefulness to mankind, the art of glass making. Glass 

 is a chemical combination of sand and alkali or alkaline earth, heated 

 to fusion, and presenting after fusion a transparent and hard body. 

 The benefits conferred by it upon all classes of human society have 

 been immense ; the spectacle, the microscope, the telescope, and spec- 

 troscope, have showered incalculable blessings upon the world, and 

 there are probably still greater discoveries in store for us. The his- 

 tory of the manufacture of glass may be traced from the present time 

 through that of the Romans and Phcenicians, to the Eg}^)tians, some 

 of whose productions remain to this age. The art flourished in Tyre, 

 in Alexandria, and lastly in Rome; and after being depressed for 

 some ages, again revived under the Venetians, who transmitted the 

 improved art to the rest of the nations of Europe. Pliny relates that 

 glass was first discovered by accident in Syria, at the mouth of the 

 river Belus, by certain merchants driven thither by the fortune of the 

 ■sea and obliged to remain there and dress their victuals by making a 

 fire in the ground. There being great abundance of the herb kali in 

 that vicinity, the ashes of the plant, mixed and incorporated with the 

 sand, formed glass. 



Boerham says, that the art of glass making is of ancient origin, 

 being first cultivated in Egypt, while glass was rendered malleable in 



