December 27, 1894] 



NA TURE 



199 



the relativity of motion it is manifestly the same thing to say ( i) 

 that referred to axes fixed in the earth all the stars describe 

 circles every day about the polar axis, or (2) that referred to 

 axes fixed among the stars the earth rotates about its polar axis 

 ■once a day. If any ground can be alleged for holding that one 

 of these statements is the simpler, that is a ground for a certain 

 •choice of axes, not for saying that one motion is "real" or 

 "absolute," and the other "relative" or "apparent." 



All the so-called "proofs of the earth's rotation" are de- 

 ductions from particular experiences which show that other 

 motions besides the diurnal relative motions of the e.arth and 

 ,tars are more simply expressed by referring to axes fixed among 

 the stars than by referring to axes fixed in the earth. They all 

 ■depend on the specification of " the acceleration due to gravity" 

 near the earth's surface. The neighbourhood of the earth is a 

 field of force, and the magnitude and direction of the force at 

 any point depend on the axes of reference. The specification 

 of the field of force is simplest when referred to thecenire of the 

 earth as origin, and to axes fixed in direction with reference to 

 the stars. The field is then expressed by the law of gravitation. 



It is worth while to elucidate this matter in greater detail by 

 an examination of the most famous of these "proofs," that by 

 means of Foucault's pendulum. What is observed is that if the 

 pendulum is really free to swing about a point, and if the bob 

 alwayspassesabove the same pomtofa horizontal table (fixed with 

 reference to the earth) when at the lowest point of its swing, then 

 the plane of vibration turns slowly round, so that the line of 

 vibration is above now one, now another line drawn on the table, 

 the oscillation in the line being practically simple harmonic. 

 If this motion were referred to axes fixed with reference to the 

 table, there would be a component acceler.ition from the bob of 

 the pendulum towards the point of support (to be accounted for 

 by the constraint), a component acceleration in the plane of 

 vibration at right angles to the former (which we should 

 recognise as a component of gravity), and a component ac- 

 celeration perpendicular to the plane of vibration, and pro- 

 portional at any instant lo the velucity in the simple harmonic 

 motion. If we had nothing else to guide us, no observation of 

 the stars, no theory of gravitation, but knew only from less 

 refined observations that free bodies fall downwards with constant 

 acceleration, we should have to do two things : we should have 

 to try to simplify the specification of the acceleration of the bob 

 of the pendulum by referring to a new set of axes, and we 

 should have to conclude that our previous observations of falling 

 bodies had not disclosed all the facts about the field of force in 

 the neighbourhood of the earth. We should simplify the 

 specification of the observed accelerations by referring to axes 

 which (relative to the earth) rotate with the pl.-ine of vibration 

 of the pendulum, and we should conclude that such axes are re- 

 quired in order that the laws governing the motion of falling 

 bodies may be correctly formulated. What the experiment with 

 Foucault's pendulum really proves is not that the rotation of the 

 earth relative to the stars is an "absolute motion," but that the 

 system of axes, with reference to which the acceleration of a free 

 body near the earth's surface is of constant amount and directed 

 towards the earth's centre, is not fixed in the earth, but (relative 

 to axes fixed in the earth) these axes rotate with the stars. 



It will be found on examination that every other so-called 

 " proof of the earth's rotation " is of the same character. By 

 each it is shown that the earth rotates in the same time and in 

 the same way relative to the axes required for the statement of 

 the law of gravitation as relative to the stars. It is not 

 legitimate to suppose that two relatives make one absolute. 



It is true that the conclusion at which we have arrived takes 

 longer to state, and appears at first .'■ight less simple than the 

 statement by way of " absolute motion," but it contains no un- 

 defined terms, and no reference to anything assumed to exist, 

 but about which nothing can be known. 



Objection has been taken to the attempt to express mechanical 

 theory in terms of relative motion, on the ground that it will be 

 perplexing lo beginners, and diflicult at any stage. In answer 

 to this it may be urged that in teaching beginners there is no 

 need to say anything about either relativity or absoluteness. 

 The motions that interest them are motions relative to the earth ; 

 the motions of boats, trains, cricket-balls, billiard-balls, and 

 machinery ; things that can be sufficiently described by reference 

 to lines fixed in the earth. It is only at a later stage when 

 general mechanical theories have to be studied, and a founda- 

 tion laid for physical astronomy and mathematical physics, that 



is proper to insist on the relativity of motion ; and at this 



NO. I3I3, VOL. 51] 



stage it appears to me more important that our statements of 

 principles should be free from metaphysical obscuiity than that 

 they should be verbally short. A. E. H. Love. 



The Antiquity of the "Finger-Print " Method. 



.Sir William Herschel, in his letter to Nature (Nov. 

 22, p. 77), expresses his unbelief in the statement in the Nint- 

 ieenth Centitry (No. 211, p. 365), which ascribes to the Chinese 

 the original invenlion of the " finger-print" method of personal 

 identification. While I do not know upon what Mr. Spearman 

 has founded this statement, I have collected from a few sources 

 some facts which seem to justify the claim made on behalf of 

 the Chinese. 



Although at present I have no record to refer to, it is a fact 

 that every Japanese, old enough lo have outlived the ancien 

 regime that passed away in 1869, well remembers the then cur- 

 rent usage of "stamping with the thumb" (Bo-in) on legal 

 papers, popularly called "nail-stamp" (Tsnme-in), on account 

 of the common use of a thumb with the edge of its nail in ink ; 

 whereas on papers of solemn contract, accompanied by written 

 oath, the "blood-stamp" (A't-//aH), or the stamp of the ring- 

 finger in blood drawn therefrom, was demanded.' 



Chiirjo Katsuiakawa, the Japanese antiquary (1754-1S08), 

 writes on the subject as follows : " According to the ' Domestic 

 Law ') (Korei), 10 divorce the wife the husband must give her a 

 document stating which of the .Seven Reasons-' was assigned 

 for the action. . . . All [letters] must be in the husband's 

 handwriting, but in case he does not understand how to write, 

 he should sign with a finger-print. An ancient commentary on 

 this passage is : 'In case a husband cannot write, let him hire 

 another man to write the document . . . and after the husband's 

 name sign with his oivn index-finger." Perhaps this is the first 

 mention [in Japanese literature] of the ' finger-print ' method " 

 (i) This "Domestic Law "forms a part of the "Laws of 

 Taiho" enacted in 702 a.d. ; with some exceptions, the main 

 points of these " Laws" were borrowed and transplanted from 

 the Chinese " Laws of Yung-IIwui" {eirca 650-55 a.d.) (2) ; 

 so it appears that the Chinese of the 7th century a.d. had 

 already acquired the " finger-print"' method. 



After the above-quoted passage, Katsurakawa continues 

 thus : " That the Chinese apply on divorce-papers the 

 stamps of the ends of the thumb and four fingers, which they 

 call ' Shau-miiying '{i.e. hand-pattern stamp) is mentioned 

 in ' Shwui-hii-chuen,' &c." (3). This " Shwui-hii-chueo" is 

 one of the most popular novels enjoyed by the modern 

 Chinese — so popular that I have met with many Chinese 

 labourers possessing it in the West Indies ; its heroes 

 flourished about 1160, and its author lived in the twelfth 

 or thirteenth century a.d. (4). As is usual with many 

 other examples, this novel gives us more accurate descriptions 

 of minor institutional features that co-existed with either the 

 heroes or the author, or both (5). .\fter making careful search 

 in this novel, I can now affirm that the Chinese in the twelfth or 

 thirteenth century used the finger-prints, not only in divorce, but 

 also in criminal cases. Thus the chapter narrating I. in Chung's 

 divorce of his wife, has this passage: "Then Lin Chung, after 

 his amanuensis had copied what he dictated, marked his sign- 

 character, and stamped his 'hand-pattern '" (6). /Vnd in an- 

 other place, giving details of Wu Sung's capture of the two 

 women, the murderers of his brother, we read : "He called 

 forth the two women ; compelled them both to ink and stamp 

 their fingers ; then called forth the neighbours ; made them 

 write down the names and stamp [with fingers] " (7). 



It has been lately suggested by my friend, Mr. Teitaro 

 Nakamura, that possibly the "finger-stamp" was merely a 

 simplified form of the "hand-stamp," which latter method had 

 once been so current in [apan that it gave to the documents the 

 common names " Tegata" ((.c. hand-pattern) and " O.-hite " 

 {i.e. impressed hand)' (8). This view applies equally well to 



1 '1 lie '■ tliumb-stump " w.is equally reg.'»rded witti the forni;il engraved 

 sea\(/iisii-:ii), but the "bioud-st.imp " had nuthing to do for ideutiticatiori. 

 For the formula of the latter mode of stamp, 7-iWe Ola, *' Ichivva Ichigen," 

 new edition. Tokyo, iSSz. vol. xiii. p. 39. 



- The Seven Reasons for divorcing the wife are ; (1) filial disol>edicnce ; 

 (2) banenness; (3) hcenttousDess ; (4)jealousy; (5) leprosy ;^(6) loquacity ; 

 (7) larceny. 



•> It must not be presumed .is a fact that after the " fioger^stanip " was 

 introduced, it soon supplanted the " hand-stamp" : for even ill the seven- 

 teenth century the falter was sometimes used, as is instanced in the writ- 

 ing of Katn-Kiyomasa (1562-1611) preserved in a monastery near Tokyo. 

 C/. Kitamura, " Kiyii Shuran," new edition, 1SS2, vol. iv. p. 16. 



