534 



NA TURE 



[April 6, 1905 



insertion of a few additional pathological and physio- 

 logical terms, and that it would be unwise to trans- 

 late these in the fashion adopted at present in such 

 words as " luftweg. " 



]\cs.\es inlcniatioiiah'x de la XoiuciuialKrc zoo- 

 fogiquc. Pp. 63. (Paris : F. R. de Rudcval, 

 1905.) 



It has frequently been remarked that it is not of 

 much use making laws and regulations unless you 

 have the power to enforce their observation ; and this 

 trite saving applies, in our opinion, very forcibly to 

 this code of regulations for zoological literature, drawn 

 up bv an international committee the deliberations of 

 which have extended over some years. The code, 

 which is published in three languages, is adniirably 

 drawn up, and for the most part free from ambiguity ; 

 but the question is, will naturalists agree to abide by 

 it? In our opinion, a large number will refuse to 

 accept it, since a rigid and slavish adherence to the law 

 of priority is enjoined, and to many this is anathema. 

 Thi" rule' that when a genus-name is changed this 

 entails the change of the family title will be generally 

 regarded as satisfactory. -As regards emendation in 

 names, this is held to be justifiable only when an 

 error in transcription, a lapsus calaw.i. or a misprint 

 is apparent; but in the interpretation of this diffi- 

 culties may arise, as in the well-known case of 

 Neurogymnurus, which is believed to be an error 

 for Necrogvmnurus. Differences of opinion, again, 

 are likely to arise with regard to the rejection of 

 names on account of unsuitableness or similarity to 

 others already in use. The retention of such narnes 

 as Polvodon and .\pus when applied to animals which 

 do not properly come under such designation will, 

 no doubt, be generally accepted ; but what is to be 

 said when, for instance, an essentially .African species 

 is named asiaticus? Such names as Polyodus, 

 Polvodon, Polvodonta, Polyodontus, &c., are held not 

 to come under the category of synonyms, although 

 the converse rule is followed in many systematic works 

 and catalogues, such as Dr. Trouessart's " Catalogus 

 Mammalium." 



.\s a " pious " expression of opinion on the part of 

 the International Committee the " Regies " are, no 

 doubt, valuable ; but they would have been much more 

 so had a plebiscite of zoologists and palaeontologists 

 agreed to accept and abide by the ruling of the com- 

 mittee. R- L. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed 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 Nature, 

 ,Vo notice is taken of anonymous communications.] 



A New Thallium Mineral. 



The element thallium, discovered by Sir W. Crookes 

 in 1861, has up to the present been known as an essential 

 constituent of only two minerals, viz. crookesite. a selenide 

 of copper and thallium, and lorandite, a sulpharsenite of 

 the latter element. To these minerals a third must now 

 be added in hutchinsonite, a new sulpharsenite from the 

 Binnenthal, which also contains thallium as an important 

 constituent. The crystallographic characters of hutchin- 

 sonite were described about a year ago by Mr. R. H. 

 Solly, who, of late years, has been particularly successful 

 in discovering new mineral species in the Binnenthal. At 

 I he time of its discovery very little in the way of chemical 



vcstigation was possible owing to the extreme scarcity 

 NO. 1849, VOL. 71] 



of the mineral, but during the past year additional crystals 

 have been acquired for the British Museum, and from 

 these about eighty milligrams of fairly pure material have 

 been obtained for chemical analysis. Thallium is present 

 (up to nearly 20 per cent.), together with lead, silver, and 

 copper, in combination with arsenic and sulphur. A full 

 description of the mineral will appear shortly in the 

 .Mincralogical Magazine. G. T. Prior. 



The Legendary Suicide of the Scorpion. 



I HAVE recently come across the following passage in the 

 Rev. John Campbell's " Travels in .South .-Africa " (London, 

 1S15), p. 38 : — " Having caught a scorpion near our tent, 

 we tried whether naturalists were accurate in relating, that 

 if that animal be surrounded with fire, and sees he cannot 

 escape, he will sting himself to death. However, it died 

 as quietly as any other animal, only darting its sting from 

 it, as if to oppose any ordinary assailant." The experi- 

 ment was made near Zwellendam, Cape Colony, on 

 February 20. 1813. Edward B. Pollton. 



Oxford, March 31. 



Propagation of Earthquake Waves. 



.\ FEW days ago I read -Major C. E. Dutton's book on 

 " Earthquakes in the Light of the New Seismology." 

 While acknowledging the high merits of this book, I take 

 the liberty of pointing out some statements which seem 

 misleading. 



I refer to chapter xiii., where the author, quoting the 

 results of the experimental investigations of Mr. Nagaoka, 

 gives the speeds V, and \\ of the normal and transverse 

 waves. Now a glance at the table on pp. 230 and 231 

 shows that for many rocks the two moduluses E, and Ej 

 perpendicular and parallel to the bedding planes are far 

 from being equal; on the contrary, the quotient E,/E, 

 varies so much as from 143 249 for rhyolite tuff to 

 32i/i7-5 for rhyolite. Hence the physical properties of 

 the rocks in question are different in different directions, 

 and the speeds of propagation of waves are also different 

 in different directions, so that the speeds V, and V, of 

 the table being the same for all directions have no real 

 meaning for many rocks. 



.'Vgain, in chapter xiii. and in other chapters of the 

 book, the author refers to normal and transverse waves 

 in rocks. It would be better, perhaps, to speak of dila- 

 tational and torsional waves : but leaving the question of 

 terminology out of consideration, I observe that it is only 

 for perfectly elastic homogeneous and isotropic bodies that 

 the separation of the dilatational (normal) from the 

 torsional (transverse) wave takes place with certainty. 

 We have no right to extend this property to a?olotropic 

 bodies. When the body is a^olotropic the deformation of an 

 element on the passage of a wave need not be of a purely 

 dilatational (normal) or of a purely torsional (transverse) 

 ch:iracter ; it is rather of .1 mixc_'d nature. 



I will not say that aeololrupic bodies able to propagate 

 purely dilatational and purely torsional waves cannot exist, 

 but I observe that such bodies are to be considered rather 

 as possible exceptions, inasmuch as certain special con- 

 ditions must be fulfilled in order that the generation of 

 purely dilatational and purely torsional waves should be 

 rendered possible. So, for example, the elastic potential of 

 a perfectly elastic homogeneous uniaxial body implies five 

 independent constants. When we introduce the condition 

 that purely dilatational waves may be propagated apart 

 from torsional ones, we find that two definite relations 

 between the constants must be satisfied so that the number 

 of independent constants is reduced to three. But we 

 have no reason to maintain a priori that the conditions in 

 question must be always satisfied. 



Of course it is to be understood that a perfectly elastic 

 homogeneous uniaxial body cannot be considered as an 

 exact " model " of stratified rocks; it is only very similar 

 to them ; but it is more than highly improbable that the 

 effect of internal friction would neutralise the effect of 

 aeolotropism. M. P. Rudzki. 



K. K. Sternwarte, Krakau (.\ustria), March 24. 



