104 FINGER PRINTS
CHAP.
by the square. No. 1 was then removed, and a second sheet, No. 2, was laid on, and the margin of the patch was outlined on it as before, together with the ridges leading up to it. Next, a corner only of No. 2 was raised, the square patch was whisked away from underneath, the corner was replaced, the sheet was flattened down, and the actual courses of the ridges within the already marked outline were traced in. Thus there were two tracings of the margin of the square, of which No. 1 contained the ridges as I had interpolated them, No. 2 as they really were, and it was easy to compare the two. The results are given in the first column of the following table
INTERPOLATION OF RIDGES IN A SIX-RIDGE-INTERVAL SQUARE.
|
Result. |
Double
Enlargements. |
Six-fold scale
with prism. |
Twenty-fold
scale with
chequer-work. |
Total. |
|
Right . |
12 |
8 |
7 |
2 7 |
|
Wrong . |
20 |
12 |
16 |
48 |
|
Total . |
32 |
20 |
23 |
75 |
II. In the second method the tracing-papers were discarded, and the prism of a camera lucida used. It threw an image three times the size of the photoenlargement, upon a card, and there it was traced. The same general principle was adopted as in the first method, but the results being on a larger scale, and drawn on stout paper, were more satisfactory and convenient. They are given in the second column of
