444 



NATURE 



[September 9, 1897 



characters, the former relating to the bony skeleton — 

 particularly the skull — while the latter include such 

 secondary characters as the colour of the skin, form of the 

 hair, &c. He holds that the former are persistent, and that 

 even in the case of a mixture of races they are not modi- 

 fied, but rather that the type of one or other of the 

 parent stocks is maintained. The external characters are 

 subject to modification from the influence of environment 

 and other causes, so that the only trustworthy criterion 

 of race is supplied by the internal. 



Having in the body of the work examined in detail the 

 various groups of Hamites in Africa, the author discusses 

 in the final chapter the position occupied by them in the 

 scheme of classification. Their internal characters show, 

 he holds, a decided unity of type, which corresponds also 

 with that found among the peoples of South Europe, 

 already studied by him in a previous work. He there- 

 fore places the African Hamites with the South 

 Europeans (and possibly the Semites) in one group, 

 which he considers entitled to rank as a species, the word 

 being understood in the sense of an animal group with 

 fundamental characters not common to other groups. 

 To it he applies the term " Eurafrican," but in a different 

 sense to that in which it is employed by Brinton, Flower 

 and Keane. Prof. Sergi's whole system thus rests on the 

 supposed permanence of one set of characters, whidi 

 is unlikely to be accepted as proved without further 

 evidence, but the book is suggestive and valuable for 

 the mass of facts which it brings together. It is 

 abundantly illustrated with portraits of the different 

 Hamitic types. 



The A. B.C. of the X-Rays. By William H. Meadowcroft. 



Pp. 189. (London : Simpkin, Marshall, Hamilton, 



Kent, and Co., Ltd.) 

 " The main object of this book," says the author, " is to 

 present to the reader a practical explanation of apparatus 

 and methods employed in producing and utilising the 

 X-rays." To introduce the subject, there is a chapter in 

 which various properties of light and electricity are 

 described for the benefit of the general reader, to whom 

 lenses and photography and the electric current are 

 mysterious things. Following this is a brief mention of 

 the apparatus used for exciting vacuum tubes, and then 

 come chapters on induction, induction coils, contact 

 breakers and condensers, and high frequency apparatus. 

 There is a chapter on influence machines, and in it we 

 have the usual descriptions of positive and negative elec- 

 tricity, with diagrams of their distribution upon an electro- 

 phorus in various stages ; the attractions and repulsions 

 of positive and negative are also traced in detail in the 

 account of the Holtz machine. Eventually (Chapter ix.) 

 we arrive at " The Crookes' tube," and are informed how 

 Prof. Elihu Thomson, "as early as January 1896," found 

 after an " exhaustive series of experiments," that the 

 form of tube known as the focus tube was the best for 

 Rontgen ray work. We also learn that Mr. Shallen- 

 berger and Mr. Scribner used this standard form of tube 

 early in 1896, but nothing is said of the prior use of the 

 focus tube by Mr. Herbert Jackson in this country. Mr. 

 Edison is given "the credit of making the practical 

 device known as the Fluoroscope," to the description of 

 which a chapter is devoted. Probably Mr. Edison would 

 not himself claim much credit for the very obvious exten- 

 sion of Prof. Rontgen's original observations involved in 

 the construction of the fluoroscope. Moreover, the instru- 

 ment is practically the same as the cryptoscope described 

 by Prof. Salvioni at the beginning of February 1896. 



The remaining short chapters of the book deal with 

 the sources of excitation of vacuum tubes, manipulation 

 of apparatus, practical suggestions, and photographic 

 plates and developers. 



Though published in London, the book is evidently an 

 American production. 



NO. 1454, VOL. 56] 



LETTERS TO THE EDITOR. 



{The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Naiurb. 

 No notice is taken of anonymous communications.'^ 



The Corona Spectrum. 



In your article on the approaching solar eclipse (page 393, 

 paragraph 2), reference is made to the apparent absence of the 

 corona line, 1474 K, from the chromosphere and prominences. 

 I would like to point out that occasionally this line is clearly 

 I seen reversed in metallic prominences ; and that the form of the 

 prominence, generally a very small one, can be made out with the 

 widened slit as in the other chromosphere lines. Such an instance 

 is recorded by Fenyi, who has published a drawing of the pro- 

 minence as seen in the lines 6677, C, and 1474 K ; the height as 

 measured in the last-named line being 33" ("Astronomy and 

 Astro-physics," xi. 432, 1892). 



Prominences of 1474 light very rarely reach this altitude 

 above the limb, but the writer has several times noted small 

 metallic prominences reversing the corona line ; and during 

 1895 (a year of great relative frequency) the line was recorded 

 "bright" in the chromosphere twelve times in 134 days of 

 observation ; always in the spot latitudes, and at the very 

 base of the chromosphere, never in the coronal region above. 

 Although not therefore truly coronal in this sense, these re- 

 versals may possibly have formed the bases of the bright coronal 

 streamers which emanate from the spot zones during a maximun> 

 spot period. 



With regard to the H and K radiations, the evidence now 

 seems conclusive that these lines were not present in the corona 

 of 1893, 2.nd it may be assumed that the lines photographed by 

 Deslandres during this eclipse, with slit spectroscopes, were due 

 to atmospheric diffusion of the brilliant chromosphere radiations, 

 as suggested by the writer at the time the results were published 

 (Nature, xlviii. 268, 1893). The relative displacements measured 

 by Deslandres on opposite sides of the solar equator would 

 seem, therefore, merely to prove a rotation of the chromosphere, 

 not of the corona. J. Evershed. 



August 29. 



The late Earthquake in India. 



The following extract from a letter just received from my son, 

 who is at present in Assam, investigating the effects of the 

 recent earthquake, may be of interest. In communicating it to 

 Nature, he wishes it to be understood that his remarks on the 

 cause of the event are but tentative and subject to revision on 

 further information which is being collected by his colleagues ork 

 the Survey. J. D. La Touche. 



Stokesay, Craven Arms, August 18. 



" Shillong, fuly 23. 



" You will, no doubt, have been greatly interested in hearing 

 of this earthquake, though from the accounts that have been 

 telegraphed home you will not have got much information about 

 it. All this talk of railways disappearing, and whole villages 

 being swallowed up, is very far beyond the facts ; though, indeed, 

 things are bad enough. The whole of the damage was done by 

 the first great shock, which lasted in these parts about two 

 minutes. After that there were a number of other shocks, esti- 

 mated at between 300 and 400, in the first twenty-four hours, 

 but none of them nearly so violent as the first. The ground 

 certainly was fissured in many places, and a large quantity of 

 sand and mud was thrown out ; but this is a secondary effect of 

 the earthquake, and happens only in loose soil or in the alluvium 

 of the valleys. Such fissures occur near river-banks and such- 

 like places, and are due to the forward movement of the soil 

 where no mass exists in front of the wave to carry on its motion, 

 somewhat analogous to the forward movement of waves of water 

 when they reach the shore. The fissures are quite superficial, 

 and the sand and water is merely jerked out of them, of course 

 during the actual progress of the shock only. The statement 

 that sand and mud are constantly spurted out, is quite misleading. 

 These fissures were studied by Dr. Oldham in the Cachar earth- 

 quake of 1869, when he found out the cause of them. The loss 

 of life has been very small : only one child at Dhubri and a few 

 at Goalpara, where one of these fissures opened under one side of 

 the bazaar, and filled the street and houses with sand. The river 

 there only rose eight feet, and did not reach the ba2aar itself. A 



