172 THE FINE ARTS. 
For the purpose of lightening the labor, the so-called ruling-machines have 
been invented, which are used for copper and steel engraving, and also in 
lithography. These machines are so contrived that parallel lines may be 
ruled with them with the utmost exactness at any desired distance apart, 
so as to yield two thousand or more lines to the inch; they are furnished 
with a diamond-pointed needle, which slightly cuts into the plate. These 
machines are employed for laying what are called the flat tints, and like- 
wise for ruling parallel lines in drawings of architecture and machinery. 
Besides these there is the relief-machine, by means of which a relief is so 
minutely transferred by curved lines to a copper-plate as to give an 
astonishingly perfect imitation of the relief. M. Collas invented this machine 
in 1834, with which beautiful copies of gems and medals have been fur- 
nished. | 
D. Hyalography. 
The discovery that fluoric acid corrodes glass has led to a very pleasing 
description of ornament; it is produced by coating a glass plate with an 
etching-ground in such manner as to leave clear certain parts forming a 
desion. Ifsuch a plate be exposed to the fumes of fluoric acid, produced 
by pouring sulphuric acid over pulverized fluor, the exposed parts of the 
surface of the plate will be bitten in ; and when the plate has been cleansed 
from the etching-ground, the drawing will present a dull appearance on the 
transparent ground of the glass plate. This art has very recently been 
brought to great perfection, and the neatest drawings have been executed 
by it. This fact presented to Prof. Botticher, of Frankfort-on-the-Maine, 
who afterwards invented the gun-cotton, the idea of etching on glass with 
fluoric acid in the same manner that copper is etched. He coated a thick 
glass plate ground perfectly even with a peculiar etching-ground, and 
etched through it in the usual manner a design, which he then bit in with 
liquid fluoric acid. The process is kept a secret by the inventor, and nothing 
respecting it has been made public, except that several impressions of such 
plates have been exhibited. In order to print from the glass plate, it is 
cemented to a wooden block, and the impressions are taken by a litho- 
graphic press. 
The impressions produced by this process are of exceeding fineness, and 
the strokes exhibit great delicacy; yet the deep shades are wanting in 
force, and the whole lacks a certain warmth possessed by engravings on 
copper and wood. It almost seems as if the hardness of the material had 
an influence on the warmth of the engraving, which is very perceptible 
when we compare a wood-cut, a copper-plate, and a steel and glass engray- 
ing together. ; 
EL. Lathography. 
A very peculiar art is that invented by Sennefelder of printing on stone, 
ealled lithography. Instead of copper or steel plates, the artist makes use 
of finely ground slabs of the calcareous slate of Solenhofen, and the entire 
process is rather chemical than mechanical. 
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