August 8, igoij 



NA TURE 



)53 



a- = 

 M„ = 



M, = S 



the form of the curve. When this plate is photographed, 

 a series of dark hnes, the intensity of which depends on 

 the size and shape of the corresponding transparent areas, 

 is produced. By superposing this photograph on the 

 former one which gave the general distribution of light 

 and shadow, a representation of the linear spectrum of 

 the holograph is obtained. Clearly, considerable skill 

 and judgment are required in such a process, and the 

 linear spectra are only introduced to show the general 

 effect and to enable the reader to compare the infra-red 

 with the visible spectrum ; the measurements of the 

 position of the lines are all made on the selected holo- 

 graphs themselves. 



Chapter vii. contains an interesting account of the 

 variations of absorption in the infra-red spectrum, which 

 is shown to be the seat of great terrestrial atn<ospheric 

 absorption, the relative intensities of energy changing 

 greatly at different periods of the year in some |3ortions 

 of the spectrum, while in others they remain fairly con- 

 stant in amount. 



But little space is left to refer to Part ii., subsidiary 

 researches, which to a student of theoretical optics may 

 prove even more interesting than the main research. The 

 first of these deals with the dispersion of rock salt and 

 fluorite. It is sufficient, perhaps, to say that the disper- 

 sion curve for rock salt is drawn from wave-length 

 o'5 fL to 6'5 n, and the results compared with a formula 

 — Kettelefs formula, 



^A.--A.,- \{--\'^' 



where 



5-174714 

 o 0183744 

 0-OI5S4I 

 49-520 

 = 3i45"695- 



This formula agrees admirably over the whole range. 

 Another appendix gives a full account of the construc- 

 tion of the galvanometer used for the research. In this 

 instrument, various sizes of wire were used in the different 

 sections of the coil ; its resistance was 28 ohms, and the 

 e.\ternal radii of the three sections of which each coil is 

 composed are respectively '383, -741 and 1-632 cm. 



Two magnet systems were tried, the one being 

 2-4 mgs. in weight, the other 6-5 mgs. With the former, 

 which proved too light for the work, a deflection of one 

 millimetre at a distance of one metre was given by a 

 current of 5 x io~'- ampere ; with the latter the current 

 required was 23 x 10 '- ampere. 



Enough, perhaps, has been written to indicate the 

 interest and importance of the work. Prof. Langley is 

 to be congratulated in having brought it to so successful 

 a conclusion. R. T. G. 



SOUTH A M ERICA . ' 

 T N the volume under notice, Mr. A. H. Keane gives a 

 ■*■ much needed compendium of the geography of 

 South America. Since its independence from Spain and 

 Portugal, that half-continent has been making great 

 commercial strides, until its trade now equals in value 

 that of British India. The importance of its varied 

 products, its peculiar ethnological history, its wonderful 

 physical features, its modern political advancement, make 

 it a region of constantly increasing interest to the mer- 

 chant, the man of science, the student and the states- 

 man ; while the fact that only about five-sevenths of it 

 have thus far been e.\plored and partially mapped makes 

 it a favourite field for the geographer. Mr. Keane 

 appears to have understood e.xactly what the world in 



1 "Stanford's Compendium of Geography and Travel (new issue) 



Central and South America." Vol. i. By .\.-H. Keane. Edited by Sir 



Clements Markham, K.C.B., F.R.S. Pp. xxii -I- 6ii. (London: 

 E. Stanford.) Price 15^. 



NO. 1658, VOL, 64] 



general required from his able pen, and instead of con- 

 fining himself to geography pure and simple, as the title 

 of his work indicates, he has taken his subject in its 

 most comprehensive sense. He gives us, in three pre- 

 liminary chapters, the physical features of the country, 

 its orography, great plains, plateaux, fluvial systems, 

 seaboard, fjords, outlying islands, climate, flora and 

 fauna and a valuable dissertation upon the ethical and 

 later ethnical and historical relations of its much scattered 

 tribes. He holds it to be " beyond reasonable doubt that 

 man had spread in early Pleistocene times from his 

 eastern cradle to the Xew World, probably by two routes 

 — from Europe by the still persisting land connection 

 with Greenland and Labrador, and, from Asia, by the 

 narrow Bering Strait." He bases this assertion upon the 

 fossil remains of man which are found in North and 

 South America, "representing the two primordial types, 

 which may be called the long-headed Afro-European and 

 the round-headed Asiatic. These, strange to say, are 

 found in far greater abundance in the southern than in 

 the northern division." ... " The inference seems in- 

 evitable that South America was already in Pleistocene 

 times peopled to its utmost limits by two primitive races 

 that still persist in the same region " — a statement which 

 admits of doubt. "The long-heads are believed to have 

 been the first arrivals . . . and later the round-heads," 

 the latter "generally keeping to the Pacific side." The 

 former are supposed to have afterwards migrated from 

 their early settlements in southern Brazil and Argentina 

 over a greater part of eastern South America. 



There is no more delightful and vexatious field for 

 anthropological and ethnological research than South 

 America. The physical alterations which it has under- 

 gone, even in very recent geological periods, the separa- 

 tion of its eastern from its western portion by immense 

 inland seas, the vast denudation of the orographic system 

 of the Brazilian and the recent uplifting of the Andean 

 section, the formation of its wonderful rivers, all probably 

 largely effected since the occupation of the continent by 

 inan, have woven many factors into the problem of racial 

 development there. The few traces which forgotten 

 peoples have left under extraordinary physical changes 

 and climatic influences, and the fragmentary knowledge 

 existing regarding South American tribes, make it appear 

 venturesome to indicate the routes by which their pro- 

 genitors first penetrated the southern half of the Xew 

 World. The problem seems to require more study than 

 it has yet received before its solution can be safely 

 approached. But the somewhat extensive remarks of 

 Mr. Keane upon South Ainerican ethnology are very 

 valuable— doubly so from the fact that he not only 

 sumrnarises his views in his " General Survey," but 

 elaborates them as he afterwards passes each country in 

 review, thus making his work of great importance to the 

 student of tribal origin and development on the western 

 continent. Mr. Keane justly comments on the purity of 

 race in the United States in comparison with Latin 

 America, " where all the ethnical elements have, from the 

 first, tended to be merged in a fresh division of mankind, 

 which may eventually acquire a uniform character, but 

 must long continue to betray its diverse origins in the 

 heterogeneous nature of its physical and mental qualities." 

 And yet it is not entirely improbable that in several 

 of the Spanish American States, notably Mexico and 

 Bolivia, the mentally and physically strong native race 

 are reasserting themselves, and absorbing, thinning- 

 down and gradually dissipating the blood of their 

 conquerors. 



The description of each State includes its boundaries, 

 so far as they are claimed or defined, its physical features, 

 hydrography, climate, flora, fauna, inhabitants, wild tribes, 

 topography, chief towns, period of discovery, conquest, 

 settlement, colonial rule, religion, education, natural re- 

 sources, mineral and agricultural productions and a 



