MICROSCOPIC DRAWING AND ENGRAVING. 
demand of Science upon Art lias been adequately and admirably 
responded to. 
6. Mechanism has been invented, by which minute tracings are 
made by a diamond point on the surface of glass ; such tracings 
being adapted to serve three distinct purposes:—1st. As standard 
measures of microscopic objects by superposition on them, just as 
ordinary lengths and breadths are determined by the application 
of the standard measure of yards, feet, and inches; 2ndly, To 
serve as tests of the degree of excellence attained in the con¬ 
struction of microscopes, and as means of comparing the relative 
excellence of different microscopes, by observing the degrees of 
distinctness with which they enable the observer to see such 
minute tracings; and, 3rdly, to serve for the production of micro¬ 
scopic engravings on its proper scale of any desired design. 
This last process cannot be said to have been applied hitherto 
to any useful purpose other than the exhibition of an artistic 
tour deforce , being, so far as relates to its means of execution, by 
far more difficult and ingenious than either of the former. 
7. Microscopic objects are measured by divided scales of known 
dimensions ; their lengths and breadths being ascertained by the 
number of divisions of the scales on which they are placed, in¬ 
cluded between their limits or within their contour. Such scales, 
like larger measures, vary with the magnitude of the objects to 
which they are to be applied, but, even when largest in their divi¬ 
sions, are still very minute. They are generally traced upon small 
oblong slips of glass, the divisions being marked by fine parallel 
lines, every fifth division being a little longer than the intermediate 
ones, and every tenth still longer, as is shown on a greatly nag- 
nified scale in fig. 2. 
Fig 2. 
8. The slip of glass upon which the scale is engraved is usually 
set in a brass framing, in which it is capable of sliding longitudi¬ 
nally, being pressed forwards in one direction by a fine screw, and 
in the other direction by the action of springs. 
The diamond point by which the divisions are traced, is urged 
upon the glass, with a regulated pressure, so as to make traces so 
52. 
