June 1, 1865.] THE TECHNOLOGIST. 



MINERAL SUBSTANCES FOR WRITING ON. 511 



distinct species, cleavage taking place in two directions instead of one. 

 Clay-slate is not quite so extensively found as the other two sorts, mica- 

 slate and gneiss. It is met with in Germany in the Yeschken-Gebirge 

 in Bohemia, on the southern flanks of the Biesen-Gebirge, in several 

 parts of the Erzgeburg, and in the Forest of Thuringia, where the slate- 

 quarries of Lehesten are the most important. It is also met with in 

 rich abundance in England, in several departments of France, as also 

 in the State of Pennsylvania in North America. 



The uses of slate are very manifold ; it being not only applied 

 to roofing, but also, in larger and stronger slabs, to the pavement 

 of apartments, mantel-pieces, and other purposes. In the peasants' 

 houses in the Thuringian forests tables are often seen formed of this 

 material. Next to the roofing slate, however, the writing slate is chiefly 

 of importance, for which, however, only such slate is fitted as will split 

 evenly and finely, being free from all foreign substances, not too hard, 

 and of a nice dark colour. This slate is cut according to the sizes of 

 the tablets, and assorted at the quarries. The further manufacture 

 consists in smoothing the uneven surface, which is effected by means of 

 a planing machine ; then the slate is set in a wooden frame, and thus 

 we have the writing-slate, an article of commerce. 



The writing-slate is an invaluable writing material for public 

 schools. "We have most of us, probably, made our first feeble attempts 

 at writing upon it, and, slate-pencil in hand, covered its dark surface 

 with strange hieroglyphics, until gradually the strokes grew steadier, 

 and, assuming the wavy form of the line of beauty, approached nearer 

 to perfection. 



There is by no means any lack of paper nowadays, yet for thousands 

 of the poorer classes it is too expensive a material, whereas a cheap 

 slate, lasting as it does for many years, saves a quantity of paper. It 

 has certainly been asserted that children learn writing better upon 

 paper, acquiring thereby a lighter hand, and at the same time accus- 

 toming themselves to guide the pen, whereas the slate with its rough 

 surface and the slate-pencil, wanting as it is in elasticity, tend to form a 

 heavy hand. This is, however, on]y true of the slate and pencil as they 

 have been hitherto. A perfectly smooth slate and a soft pencil permit 

 of the finest distinction between up- and down-strokes ; while you are 

 just as able to draw well as to write well upon them, besides which 

 there is this advantage, that a child, unpractised in handling the pen, is 

 at once enabled to use the slate-pencil, while writing on paper, for 

 which ink and a well-made pen, or at least a steel one, are requisite, is 

 much more inconvenient. After a little practice on the slate, the child 

 easily exchanges it for pen, ink, and paper. 



The chief advantage of the slate, however, is, that the writing is 



very easily effaced, and thus the scholar is enabled to continue his 



exercises at pleasure, which is a very great advantage in many branches 



of learning in public schools, such as arithmetic, mathematics, writing, 



vol. v. 3 H 



