MICROSCOPIC DRAWING AND ENGRAVING. 



exact aliquot part of a standard unit of length, has, nevertheless, 

 produced bands engraved by a diamond point on slips of glass, 

 consisting of a greater or less number of parallel lines, separated 

 by intervals of surprising minuteness. 



Some remarkable specimens of the production of this eminent 

 artist were presented at the Great Exhibition in Hyde Park, in 

 1851. They consisted of ten bands, each composed of a certain 

 number of parallel lines ; those in each band being closer together 

 than those in the preceding one. In the following table, we have 

 given in the second column the number of lines which would fill 

 the breadth of an inch in each succeeding band in one of these 

 specimens. 



I. . . 11265 



II. 



III. 



IV. 



V. 



VI. 

 VII. 

 VIII. 



IX. 



X. 



13142 

 15332 

 17873 

 20853 

 24309 

 28433 

 33153 

 38613 

 49910 



Thus it appears that, in this specimen, the closeness of the ruled 

 bands varied from 11000 to 50000 to the inch. 



These bands are ruled on glass in parallel directions, being sepa- 

 rated band from band, by comparatively wide intervals, so that, 

 if sufficiently magnified, they present such an appearance as is 

 shown in fig. 24. The highest band being that in which the lines 

 are most separated, and the lowest that in which they are closest. 

 It is very difficult to convey a correct idea of the real appearance 

 of this system of engraved bands before it is magnified ; let us 

 suppose, however, that fig. 23 represents the real magnitude of the 

 slip of glass upon which the engrav- 

 ing is made, and that the white 

 circle in the centre is the part of the 

 glass across which the series of ten 

 bands, shown in a magnified form 

 in fig. 24, are drawn. The entire 

 space occupied by all the ten bands 



will then be less in width than the black line which is drawn 

 across the white circle in fig. 23. It must not be imagined that the 

 white circle in fig. 23 represents that shown in fig. 24, the latter cor- 

 responds with a minute circular space in the centre of fig. 23, not 

 much greater in diameter than the breadth of the black line. 



28. Various other test-plates have been engraved, and put in 

 circulation by Mr. Robert; I subjoin the analysis of one consisting 

 68 



