The Science of Fingerprints Part 6

Tented arches and some forms of the loop are often confused. It should be remembered by the reader that the _mere converging of two ridges does not form a recurve, without which there can be no loop_. On the other hand, there are many patterns which at first sight resemble tented arches but which on close inspection are found to be loops, as where one looping ridge will be found in an almost vertical position within the pattern area, entirely free from and pa.s.sing in front of the delta.

Figure 134 is a tented arch. The ridge marked "A--A" in the sketch enters on one side of the impression and flows to the other with an acute rise in the center. Ridge C strikes into A at point B and should not be considered as a bifurcating ridge. The ridges marked "D--D"

would form a tented arch if the rest of the pattern were absent.

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Figure 135 is a sketch of a pattern reflecting a ridge, A--B, entering on one side of the impression, recurving, and making its exit on the other side of the impression. The reader should study this sketch carefully. It should be borne in mind that there must be a ridge entering on one side of the impression and recurving in order to make its exit on the same side from which it entered, or having a tendency to make its exit on that side, before a pattern can be considered for possible cla.s.sification as a loop. This pattern is a tented arch of the upthrust type. The upthrust is C. There is also an angle at E. D cannot be termed as a delta, as the ridge to the left of D cannot be considered a type line because it does not diverge from the ridge to the right of D but turns and goes in the same direction.

In connection with the types of tented arches, the reader is referred to the third type. This form of tented arch, the one which approaches the loop, may have _any combination of two of the three basic loop characteristics, lacking the third_. These three loop characteristics are, to repeat:

- _A sufficient recurve._

- _A delta._

- _A ridge count across a looping ridge._

It must be remembered that a recurve must be free of any appendage ab.u.t.ting upon it at a right angle between the shoulders, and a true ridge count is obtained only by crossing a looping ridge freely, with a white s.p.a.ce intervening between the delta and the ridge to be counted.

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Figures 136 and 137 are tented arches having loop formations within the pattern area but with deltas upon the loops, by reason of which it is impossible to secure a ridge count. The type lines run parallel from the left in figures 136 and 137. These tented arches have two of the loop characteristics, recurve and delta, but lack the third, the ridge count.

In figure 138, the reader will note the similarity to the figures 136 and 137. The only difference is that in this figure the type lines are running parallel from the right. It will be noted from these three patterns that the s.p.a.ces between the type lines at their divergence show nothing which could be considered as delta formations except the looping ridges. Such patterns are cla.s.sified as tented arches because the ridge count necessary for a loop is lacking.

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Figure 139 is an example of a tented arch. In this pattern, if the looping ridge approached the vertical it could possibly be a one-count loop. Once studied, however, the pattern presents no real difficulty.

There are no ridges intervening between the delta, which is formed by a bifurcation, and the core. It will be noted that the core, in this case, is at the center of the recurve, unlike those loops which are broadside to the delta and in which the core is placed upon the shoulder. This pattern has a recurve and a separate delta, but it still lacks the ridge count necessary to make it a loop.

Figures 140 and 141 are examples of tented arches. These two figures are similar in many ways. Each of these prints has three abrupt ending ridges but lacks a recurve; however, in figure 141 a delta is present in addition to the three abrupt ending ridges. This condition does not exist in figure 140, where the lower ending ridge is the delta.

When interpreting a pattern consisting of two ending ridges and a delta but lacking a recurve, do not confuse the ridge count of the tented arch with that of the ridge count for the loop. The ridge count of the tented arch is merely a convention of fingerprinting, a fiction designed to facilitate a scientific cla.s.sification of tented arches, and has no connection with a loop. To obtain a true ridge count there must be a looping ridge which is crossed freely by an imaginary line drawn between the delta and the core. The ridge count referred to as such in connection with the tented arches possessing ending ridges and no recurve is obtained by imagining that the ending ridges are joined by a recurve only for the purpose of locating the core and obtaining a ridge count. If this point is secure in the mind of the cla.s.sifier, little difficulty will be encountered.

Figures 140 and 141, then, are tented arches because they have two of the characteristics of a loop, delta and ridge count, but lack the third, the recurve.

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Figure 142 is a loop formation connected with the delta but having no ridge count across a looping ridge. By drawing an imaginary line from the core, which is at the top of the rod in the center of the pattern, to the delta, it will be noted that there is no recurving ridge pa.s.sing between this rod and the delta; and, therefore, no ridge count can result. This pattern is cla.s.sified as a tented arch. There must be a white s.p.a.ce between the delta and the first ridge counted, or it may not be counted. Figure 143 is also a tented arch because no ridge count across a looping ridge can be obtained, the bifurcations being connected to each other and to the loop in a straight line between delta and core. The looping ridge is not crossed freely. No white s.p.a.ce intervenes between the delta and the loop. These patterns are tented arches because they possess two of the characteristics of a loop, a delta and a recurve, but lack the third, a ridge count across a looping ridge.

Figure 144 is a tented arch combining two of the types. There is an angle formed by ridge _a_ ab.u.t.ting upon ridge _b_. There are also the elements of the type approaching a loop, as it has a delta and ridge count but lacks a recurve.

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Figures 145 to 148 are tented arches because of the angles formed by the ab.u.t.ting ridges at the center of the patterns.

Figure 149 is a tented arch because of the upthrust present at the center of the pattern. The presence of the slightest upthrust at the center of the impression is enough to make a pattern a tented arch.

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An upthrust must be an ending ridge. If continuous as in figure 150, no angle being present, the pattern is cla.s.sified as a plain arch.

Figures 151 to 153 are plain arches. Figure 154 is a tented arch.

Figure 155 is a plain arch because it is readily seen that the apparent upthrust A is a continuation of the curving ridge B. Figure 156 is a tented arch because ridge A is an independent upthrust, and not a continuation of ridge B.

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Figures 157 and 158 are plain arches. Figure 158 cannot be said to be a looping ridge, because by definition a loop must pa.s.s out or tend to pa.s.s out upon the side from which it entered. This apparent loop pa.s.ses out upon the opposite side and cannot be said to tend to flow out upon the same side.

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In figures 159 and 160, there are ending ridges rising at about the same degree from the horizontal plane.

Figure 159, however, is a plain arch, while 160 is a tented arch. This differentiation is necessary because, if the first pattern were printed crookedly upon the fingerprint card so that the ending ridge was nearer the horizontal plane, there would be no way to ascertain the true horizontal plane of the pattern (if the fissure of the finger did not appear). In other words, there would be no means of knowing that there was sufficient rise to be called an upthrust, so that it is safe to cla.s.sify the print as a plain arch only. In figure 160, however, no matter how it is printed, the presence of a sufficient rise could always be ascertained because of the s.p.a.ce intervening between the ending ridge and the ridge immediately beneath it, so that it is safe to cla.s.sify such a pattern as a tented arch. The test is, _if the ridges on both sides of the ending ridge follow its direction or flow trend, the print may be cla.s.sified as a plain arch. If, however, the ridges on only one side follow its direction, the print is a tented arch_.