MICROSCOPIC DRAWING AND ENGRAVING. 



demand of Science upon Art has 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 mag- 

 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 



