The Science of Fingerprints by United States. Federal Bureau of Investigation (books to read in a lifetime txt) 📕

not enter into the determination of the primary.

The method of obtaining the primary can probably be shown best by illustrations. For example, assume that there is a whorl in the right index finger only. The value of a whorl in this finger is 16. When 1 over 1 is added the resulting primary is 17 over 1. If a whorl appears in the right thumb and right index finger, the value is 16 over 16 plus 1 over 1 giving a primary of 17 over 17. If whorls appear in both index fingers, the value is 16 over 2 plus 1 over 1 giving a primary of 17 over 3. When whorls appear in both thumbs and both index fingers, the primary is 21 over 19 and is obtained by the addition 16 plus 4 plus 1 over 16 plus 2 plus 1. If whorls appear in all 10 fingers, the primary is 32 over 32 (16 plus 8 plus 4 plus 2 plus 1 plus 1 over 16 plus 8 plus 4 plus 2 plus 1 plus 1). It will be noted that the primary classifications extend from 1 over 1 in the no-whorl group to 32 over 32 in the all-whorl group, providing 1,024 possible combinations. This does not mean that there are 1,024 even subdivisions of prints according to these primaries. Just as there is a preponderance of loops when the types of patterns are considered, there is also a preponderance of certain primaries, notably: the 1 over 1 primary, or no-whorl group; the 17 denominator; the 19 denominator; the 28 denominator, of which the 31 over 28 group is the largest; and the 32 denominator, including 2 large primary groups namely, 31 over 32 and 32 over 32. As a matter of fact, the 1 over 1 group, as a whole, contains over 25 percent of the total number of prints filed in the FBI. On the other hand, there are a number of primaries which rarely appear. It follows, therefore, that when a print is classified in one of these larger groups it is necessary to complete the classification to a greater extent than is necessary in the more unusual primaries, so that the group to be searched is small enough for convenience.

In connection with the counting of whorl values to obtain the primary, it might be noted that when the whorls outnumber the other patterns more speed can be achieved by counting those patterns and subtracting rather than by adding the whorls. This procedure should not be followed until enough experience is acquired so that it may be noted at a glance where whorls are not present.

The experienced classifier can tell in what fingers whorls are present by a glance at a primary classification. For example, a primary of 5 over 17 could mean that there are whorls in the thumbs only.

 

Fig. 348

[Fig. 348]

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The secondary classification: After the primary classification, the fingerprints are subdivided further by using a secondary classification. Before going into detail, it should be noted that after the primary is obtained the entire remaining portion of the classification formula is based upon the arrangement of the impressions appearing in the right hand as the numerator over the impressions appearing in the left hand as the denominator. The arrangement of the even over the uneven fingers is discarded after the primary is obtained. The secondary classification appears just to the right of the fractional numerals which represent the primary. It is shown in the formula by capital letters representing the basic types of patterns appearing in the index fingers of each hand, that of the right hand being the numerator and that of the left hand being the denominator (fig. 348). There are five basic types of patterns which can appear.

1. Arch   A 2. Tented Arch   T 3. Radial Loop   R 4. Ulnar Loop   U 5. Whorl   W

 

Fig. 349

[Fig. 349]

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Secondary classification (small-letter group): Prints with an arch or tented arch in any finger or a radial loop in any except the index fingers constitute the small-letter group of the secondary classification. Such "small letters," with the exception of those appearing in the index fingers, are brought up into the classification formula in their proper relative positions immediately adjacent to the index fingers (fig. 349). A dash is used to indicate the absence of each small letter between the index fingers and another small letter or between two small letters, as

1 aUa-t and 1 aU-t. 1 R-a 1 1 U-a

Thus, if a radial loop appears in the right thumb, the small letter "r" would be brought up in the numerator column of the classification formula and placed just to the left of the capital letter representing the index finger. Similarly, if an arch or tented arch or a radial loop would appear in the middle, ring, or little finger of the hand, the small letter representing such a pattern would be placed on the classification line to the right of the secondary in the numerator column if the letter is present in the right hand, and in the denominator column if in the left hand. When two or more small letters of the same type occur immediately adjacent to each other, they are indicated thus:

1 rU-2a and 1 aTa-a. 1 tU3a 1 tA2at

The small-letter groups are of vital importance to the classification system, as they are of relatively infrequent occurrence, constituting approximately 7 to 10 percent of all patterns. Generally speaking, since these patterns are of such rare occurrence, their very presence often enables the classifier to dispense with the usual subsecondary classification and the major division which in the majority of cases are used in the larger groups.

The subsecondary classification (grouping of loops and whorls): In classifying prints it is necessary to subdivide the secondary groups. This is accomplished by grouping according to the ridge counts of loops and the ridge tracings of whorls. The first of the groups filed in order, which it will be necessary to so subdivide, would ordinarily be the

1 R 1 R

group where no small letters appear. The Federal Bureau of Investigation, however, has found it necessary to extend this division to many of the small-letter groups which become cumbersome. The subsecondary is placed on the classification line just to the right of the secondary. Ridge counts are translated into small and large, represented by symbols I and O. The whorl tracings are brought up as I, M, or O denoting inner, meeting or outer ridge tracings of the whorl types. Only six fingers may be involved in the subsecondary—numbers 2, 3, 4, 7, 8, and 9.

A ridge count of 1 to 9, inclusive, in the index fingers is brought up into the subsecondary formula as I. A count of 10 or more is brought up as O. In the middle fingers a count of from 1 to 10, inclusive, is brought up as I, and 11 or more is O. In the ring fingers a count of from 1 to 13 is brought up as I, and 14 or more is O. A loop subsecondary could appear in the classification formula as

OIO. IIO

Analyzing this example of a subsecondary, one will know that in the index, middle, and ring fingers of the right hand there are counts of over 9, under 11, and over 13, while in the left hand there are in the index, middle, and ring fingers, counts of under 10, under 11, over 13, respectively. The subsecondary classification, therefore, relates to the groupings of the prints, and no difficulty should be experienced in ascertaining whether the I and O arrangement in the subsecondary relates to loops or whorls when analyzing a classification, because this information can be obtained from the primary classification. Figure 350 is an example illustrating the subsecondary in addition to other divisions of the classification formula.

 

Fig. 350

[Fig. 350]

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The chart, figure 351, will illustrate the manner in which the ridge counts are translated into the symbols I and O so they may be grouped and sequenced with the whorl tracings I, M and O.

 

Fig. 351

[Fig. 351]

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The major division: The major division is placed just to the left of the primary in the classification formula. Where whorls appear in the thumbs the major division reflects the whorl tracings just as the subsecondary does. For example, a major division of I over M in the primary 5 over 17 would reflect an inner-traced whorl over a meeting-traced whorl in the thumbs. Where loops appear in the thumbs, however, a table is used to translate the ridge counts into the small, medium, or large groups, designated by the letters S, M, L. An expanding table is used for the right thumb when large-count loops appear in the left thumb, as shown in the chart (fig. 351). This table is used because it affords a more equitable distribution of prints as a whole, for filing purposes within the groups indicated.

Table for major divisions of loops:

Left thumb denominator Right thumb numerator 1 to 11, inclusive, S (small) { 1  to 11,  inclusive, S (small).
{ 12 to 16, inclusive, M (medium).
{ 17 or more ridges, L (large). 12 to 16, inclusive, M (medium) { 1 to 11, inclusive, S (small).
{ 12 to 16, inclusive, M (medium).
{ 17 or more ridges, L (large). 17 or more ridges, L (large) { 1 to 17, inclusive, S (small).
{ 18 to 22, inclusive, M (medium).
{ 23 or more ridges, L (large).

The fingerprint card appearing in figure 352 shows a major division of L over L, which is obtained by counting the ridges (24 in the right thumb and 18 in the left thumb) which, according to the table, is translated into L in both thumbs.

The final: It is, of course, desirable to have a definite sequence or order of filing the prints within the subdivided groups. This order is attained through the use of the final, which is based upon the ridge count of the loop in the right little finger. It is indicated at the extreme right of the numerator in the classification. Note figure 352. If a loop does not appear in the right little finger, a loop in the left little finger may be used. It is then indicated at the extreme right of the denominator (fig. 353). If no loops appear in the little fingers, a whorl may be used to obtain a final, counting from left delta to core if in the right hand and from right delta to core if in the left hand. If there are two or more cores (usually applies to accidental whorls), the ridge count is made from left delta (right hand) or right delta (left hand) to the core which is the least number of ridges distant from that delta. An exception is made in the case of the double loop. The double loop is counted from the delta to the core of the upright loop. Where loops of a double loop are horizontal, the nearest core is used. Should both little fingers be a or t, no final is used. The use of a whorl in a little finger for a final is required only in connection with a large group or collection of prints, such as the 32 over 32 primary.

 

Fig. 352

[Fig. 352]

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The key: The key is obtained by counting the ridges of the first loop appearing on the fingerprint card (beginning with the right thumb), exclusive of the little fingers which are never considered for the key as they are reserved for the final. The key, no matter where found, is always placed to