6;6 



NATURE 



[August 21, 19 1, 



apart from the ridges, or ridge substance, any more 

 than the holes of which Pat's classic stockings con- 

 sisted can be considered without reference to the 

 slender remains of the fabric in which they occur. 



Dr. Edmond Locard, the writer of the article, " La 

 Poroscopie," alluding to certain landmarks in finger- 

 print patterns (pantos caracteristicos they have been 

 called), adduces in one of his illustrations some Hots 

 of a single dot, each containing the opening of a 

 single sweat-pore. The effect when printed is that 

 of a more or less regularly shaped O or ring. Of 

 course, if the smoked-glass method were used, what 

 I have called the negative effect would be produced, 

 and the pore would show up as a black dot on a 

 white ground. In such a case as that illustrated the 

 value of such a coincidence would be seen at once, 

 but the value belongs much more to the system of 

 ridges than to that of the pores. A dozen such pores 

 might easily be found to coincide in two patterns 

 having no real relation to each other by way of per- 

 sonality. I should not expect, however, after con- 

 siderable experience of finger-print patterns, to find 

 three volcanic or coral islets such as are depicted in 

 Fig. 3 coinciding in any but two prints from the same 

 person. But these volcanic islands are not mere pore 

 openings. It is the sharp definition of the ridge 

 element in them that gives character for identification. 



It is difficult to conceive of many cases in actual 

 practice where simple coincidence of pores could be 

 made convincing- to a jury. Such cases are presented 

 with a magnification of forty-five diameters. But 

 Dr. Locard says : — " Un jury, que trente ou quarante 

 points caracteristiques homologues auront laisse in- 

 different, sera frappe par la concordance de forme, 

 de position, et de nombre de quelques centaines de 

 pores trouves identiques sur les deux empreintes com- 

 parers. " If the illustrations are from the exhibits 

 in the criminal cases quoted, as one would be led to 

 infer, the jurv would seem to have been aided very 

 greatly with outlines filled in by official pens, by 

 which the rough places have been made smooth, and 

 coincidences which would not strike any but police 

 officials seeking a conviction, have been made vivid, if 

 not alwavs quite convincing. All this is, I trust, now 

 quite foreign to English criminal procedure. 



It is in cases where fewer than some twelve of what 

 an English detective would in the witness-box call 

 "characteristics" are to be found that the additional 

 scrutiny of the pores might be useful. I agree with 

 Dr. Locard that they remain locally fixed in position, 

 but I have mentioned in " Dactylography " (Twentieth 

 Century Science Series), which Dr. Locard does not 

 seem to have read, that, their physiological activity 

 being verv variable, their shapes are constantly alter- 

 ing. Thev mav be nearly closed one moment, and 

 quite patent the next, a useful fact which makes it 

 hopeless to forge finger-print signatures effectively 

 with rubber stamps. This variability is most vividly 

 xhown in the illustrations to the very article now 

 referred to, and where a finger-print pattern is doubled 

 the nores always agree in position but rarely in shape 

 or size. Henry Fauuds. 



36 Lichfield Street, Hanley, Stoke-on-Trent. 

 UtgUSt 13. 



Calanus a Further Record. 



On getting' back to Tobermory on Saturday, we 

 found the plankton to be in marked contrast to its 

 condition four weeks ago (see Nature, p. 504). The 

 vast swarm of Calanids has gone, and there are now 

 no signs of mackerel feeding in the bay. In fact, the 

 change has been noticeable for some days in the 

 seas outside, and we have not been getting latelv the 

 large plankton catches that were usual in the latter 



XO. 2 286, VOL. 91] 



half of July. On July 14 a haul of the large surface 

 tow-net, in the open sea off Ardnamurchan, gave such 

 a huge catch of Calanus (about 1000 c.c.) that we 

 promptly took a second similar haul, and had it 

 cooked as a sort of potted " shrimp " confection for 

 tea (sampled by ten persons, including the crew, who 

 were much interested to try this new edible "fish"); 

 while on August 11 a haul of the same net, taken at 

 the same spot, gave only a small catch of some 

 15 c.c, containing very few Calanids, along with the 

 usual scanty summer zoo-plankton. I have not yet 

 seen any statistics of the mackerel fishery, but should 

 not be surprised if this proves to be an exceptionally 

 good year in this neighbourhood, especially in July. 



I have only just received Nature for the last few 

 weeks, and am glad to read Mr. G. E. Bullen's further 

 remarks (p. 531) upon swarms of Calanids and the 

 fisheries. His excellent work — along with that of Dr. 

 Allen — on the connection between mackerel and 

 Calanus and sunshine in the English Channel, some 

 years ago, is valued as the type of observational and 

 statistical work that is required for the investigation 

 of many fishery problems. W. A. Herdm.w. 



S.Y. Riuia, off Island of Eigg, August 12. 



The Structure of X-Radiation. 



In a letter which appeared in Nature of June n> 

 we described some effects obtained with various metals 

 used as obstacles to X-radiation, which showed that 

 the bands and haloes produced on X-ray plates up to 

 distances of 450 cm. were neither dependent on 

 crystalline structure (other than metallic) nor should 

 probably be termed "diffraction" effects in the strict 

 sense. 



Further investigation, in which crystals have been 

 entirely discarded, lias led us to believe that some part 

 of these effects at least must be referred to the 

 structure of the primary beam. 



In one of our early trials arranged to studv the 

 disposition of the spots from a thin lamina of mica, 

 normal to the beam and covering a quarter of an 

 inch aperture, we were surprised to find that spots 

 were not present, but instead the photo plate, exposed 

 at a distance of 50 cm., was entirely covered by dark 

 parallel bands about half a centimetre in breadth and 

 normal to a sharply defined bright cross. In later 

 experiments without mica, and using cast-iron and 

 other screens, both with and without apertures, a 

 system of crossed similar bands has appeared, and 

 a great number of trials have confirmed the result 

 that particular metals (brass, lead, cast- and wrought- 

 iron, &c, of various thicknesses up to 1 cm.) cannot 

 be held responsible for these phenomena, which have 

 even appeared when no other obstacle than a thick 

 sheet of plate-glass has been interposed. A platinised- 

 nickel antikathode has generally been used and 0-5 

 to 1 milliampere was kept constant through the bulb. 



At it appears from Mr. Keene's letter in Nature of 

 August 14 he has used only thin sheets of metal 

 with apertures, we can understand that he has ob- 

 tained somewhat dissimilar effects from ours obtained 

 without any aperture in the screen. Also with super- 

 cooled glass plates there can scarcely be any question 

 of crystalline structure. We have substituted special 

 rapid plates of various makers and changed all the 

 non-essential conditions many times. When photo 

 plates are placed one behind the other at distances of 

 15 cm. (up to 100 cm.) from the source, these bands 

 have invariably shown most clearly on the plates 

 farthest from it. This certainly w-ould seem to sug- 

 gest masking, by secondarv radiation, of an effect 

 which properly belongs to the primarv or " hardest " 

 portion of the rays. W. F. D. Chambers. 



T. G. Rankin. 

 00 Gordon Road, Ealing. 



