74 



NA TURE 



\yu.y 19, 1883 



vitiated by too many subdivisions. These subdivisions 

 are dealt with in the introduction, where a bewildering 

 scheme of classification is proposed "in order to ascertain 

 the opinion of anthropologists as to its merits." First the 

 science is grouped under three main heads, indicated by 

 terminations furnished by the three Greek words, ypd(j»], 

 \6yos, and vifios. Then each group is split up into 

 thirteen minor divisions, yielding altogether thirty-nine 

 distinct segmentations, and of course involving the whole 

 subject in dire confusion. The student is expected, for 

 instance, to distinguish between anthropography, anthro- 

 pology, and anthroponomy ; between pneumatography, 

 pneumatology, and pneumatonomy ; between hexiography, 

 hexiology, hexionomy, and so on. However in the biblio- 

 graphy the author considerately limits himself to eleven 

 headings, which will certainly be amply sufficient to try 

 the patience of those who may have occasion to consult 

 these alphabetical lists. Thus Nesbit's " Antiquity of 

 Man " is entered under Anthropogetiy, while Ameghino's 

 " Antiquedad del hombre in La Plata " must be sought 

 for in the section Archceology. These lists should 

 obviously be fused together in one general catalogue, and 

 all the nice subdivisions left to the fancy or ingenuity of 

 the reader. To show their utter absurdity it may suffice 

 to add that under the heading Hexiology there occurs the 

 solitary entry — Buckley, " Climatic Influences on Man- 

 kind." Why, it may be asked in conclusion, does B. B. 

 Redding's " Californian Indians and their Food," appear 

 in the section Technology f The interests of science are 

 not furthered by these minute subdivisions and barbarous 

 nomenclatures, which are especially uncalled for in the 

 case of a science whose broad divisions are already 

 marked out with sufficient clearness and accuracy to serve 

 all present practical purposes. 



Prof. Mason has been much more usefully employed in 

 the preparation of a series of " Miscellaneous Papers 

 Relating to Anthropology," which also consist of reprints 

 from the Smithsonian Report for 1881. Most of them 

 have reference to the sepulchral mounds, earthworks, 

 fortified lines, shell-heaps, and other remains of pre- 

 historic and historic man so thickly strewn over the 

 Mississippi basin, the eastern States and seaboard of 

 North America. The great number and magnitude of 

 these remains, their universal diffusion over an enormous 

 area, and the character of the objects found in them, all 

 tend to confirm the impression now generally entertained 

 regarding the vast antiquity of man in the New World. 

 On the other hand the views of those anthropologists who 

 still attribute the old works to some superior pre-Colum- 

 bian race of " mound-builders " distinct from the present 

 aborigines are not strengthened by a more careful exa- 

 mination of these relics. Speaking of the mounds 

 examined by him in Cass County, Illinois, Dr. J. F. 

 Snyder remarks that "the intrinsic evidence of many 

 prehistoric remains of this county sustains their claim to 

 extreme antiquity ; but no work or specimen of art of a 

 former race has yet been found here above the capacity 

 or achievement of the typical North American Indian. 

 And in studying the life, habits, and burial customs indi- 

 cated by these relics, I can see no necessity for ascribing 

 them to the agency of a distinct or superior race, when 

 they express so unmistakably the known status of Indian 

 intellect" (p. 53). This conclusion is amply confirmed 

 by the contents of the enormous shell-heap at Cedar 

 Keys, Florida, which has been carefully examined by 

 Mr. S. T. Walker. Here the pottery found in the suc- 

 cessive layers, down to a depth of over twelve feet, shows 

 a continuous advancement in the art from the rude heavy 

 earthenware often mixed with coarse sand or small 

 pebbles occurring in the lowest stratum, through the 

 better finished and slightly ornamented types of the 

 middle stage, to the delicate and beautifully ornamented 

 specimens found near the surface. These objects thus 

 show a progressive improvement upwards, not down- 



wards as would be required by the theory of an extinct 

 pre-Columbian civilised race, precursor of the present 

 aborigines. A. H. K. 



THE SIZE OF A TOMS > 



III. 



\ A 7 E must then find another explanation of dispersion. I 

 *' believe there is another explanation. I believe that, 

 while giving up Cauchy's unmodified theory of dispersion, 

 we shall find that the same general principle is applicable, 

 and that by imagining each molecule to be loaded in a 

 certain definite way by elastic connection with heavier 

 matter, — each molecule of the ether to have, in palpable 

 transparent matter, a small fringe, so to speak, of 

 particles, larger and larger in their successive 

 order, elastically connected with it, — we shall have 

 a rude mechanical explanation, realisable by the 

 notably easy addition of the proper appliances to the 

 dynamical models before you, to account for refractive dis- 

 persion in an infinitely fine-grained structure. It is not 17 

 hours since I saw the possibility of this explanation ; I 

 think I now see it perfectly, but you will excuse me not 

 going into the theory more fully under the circumstances. - 

 The difficulty of Cauchy's theory has weighed heavily 

 upon me, when thinking of bringing this subject before 

 you. I could not bring it before you and say there are 

 only four particles in the wave-length, and I could not 

 bring it before you without saying there is some other 

 explanation. I believe another explanation is distinctly 

 to be had in the manner I have slightly indicated. 



Now look at those beautiful distributions of colour on 

 the screen before you. They are diffraction spectrurus 

 from a piece of glass ruled with 2,000 lines to the inch. 

 And again look ; and you see one diffraction spectrum 

 by reflection from one of Rutherford's gratings, in 

 which there are 17,000 lines to the inch on polished 

 speculum-metal. The explanation by " interference", is 

 substantially the same as that which the undulatory 

 theory gives for Newton's rings of light reflected from 

 the two surfaces, which you have already seen. Where 

 light-waves from the apertures between the successive 

 bars of the grating, reach the screen in the same phase, 

 they produce light ; there, again, where they are in 

 opposite phases, they produce darkness 



The beautiful colours which are produced, depend on 

 the places of conspiring and opposing vibrations on the 

 screen, being different for light waves of different wave- 

 lengths ; and it is by the measurements of the dimensions 

 of a diffraction spectrum such as the first set you saw 

 (or of finer spectrums from coarser gratings), that Fraun- 

 hofer first determined the wave-lengths of the different 

 colours. 



1 have now, closely bearing on the question of the 

 size of atoms, thanks to Dr. Tyndall, a most beautiful 

 and interesting experiment to show you— the artificial 

 " blue sky," produced by a very wonderful effect of light 

 upon matter, which he discovered. We have here an 

 empty glass tube— it is "optically void." A beam of 

 electric light passes through it now; and you see nothing. 

 Now the light is stopped and we admit vapour of carbon 

 disulphide into the tube. There is now introduced some 

 of this vapour to about 3 inches pressure, and there is 

 also introduced, to the amount of 15 inches pressure, air 

 impregnated with a little nitric acid, making in all rather 

 less than the atmospheric pressure. What is to be illustrated 

 here is the presence of molecules of substances, produced 

 by the decomposition of carbon disulphide by the light. 



' A lecture delivered by Sir William Thomson at the Royal Institution, 

 on Friday. February 2. Revised bv thejAuthor. Concluded from p. 254. 



2 Farther examination has seemed to me to confirm this first impression ; 

 and in a paper on the Dynamical Theory of Dispersion, read before the Royal 

 Society of Edinburgh, on the 5th of March, 1 have given a mathematical 

 investigation of the subject. — W. T., March 16, 1883. 



