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NATURE 



{Jan. 21, 1875 



certainly not simultaneous between Kew and Lisbon. 

 The abrupt disturbances constituting magnetic storms 

 are, however, probably simultaneous all over the world. 

 It is thus possible to imagine the former or rounded dis- 

 turbances to be caused by convection currents, but it is 

 quite impossible to regard the latter as so caused. How, 

 then, can these be accounted for consistently with this hypo- 

 thesis ? We reply, that when there is a considerable dis- 

 turbance in the convection currents of the earth, these 

 currents, as we have explained, conveying electricity, we 

 may then expect such currents to influence and alter the 

 magnetism of the earth. The earth gets out of relation 

 as a magnet to these currents, and rights itself abruptly ; 

 and this abrupt change of the earth occurring simul- 

 taneously all over it, may form the second kind of mag- 

 netic storm. 



Corresponding to these two varieties of magnetic dis- 

 turbances, we have, in all probability, two kinds of 

 auroras. 



The upper convection currents of the earth, if they 

 convey electric currents, may probably be self-luminous, 

 and this may account for auroras of a local nature, and 

 perhaps also for the nearly perennial displays of auroras 

 near the magnetic pole. 



On the other hand, whenever we have an abrupt mag- 

 netic storm we have the production of secondary currents 

 due to the small but abrupt changes taking place in the 

 magnetism of the earth, and these secondary currents will 

 manifest themselves both in the upper strata of the 

 earth's crust, which are conductors, and in the upper 

 strata of the earth's atmosphere, which are also con- 

 ductors. In the former case they will produce violent 

 earth-currents ; in the latter they will produce a magnifi- 

 cent auroral display, cosmical rather than local in its 

 characteristics. 



We have already alluded to the Greenwich seir-record- 

 ing instruments for registering earth-currents, and the 

 author of this notice has inspected several of the curves 

 given by the Greenwich instruments during violent mag- 

 netic storms. The characteristic of these traces is an 

 abrupt and violent change from positive to negative and 

 from negative to positive. Now, this is a behaviour quite in 

 accordance with the hypothesis that these are secondary 

 currents due to magnetic changes, but quite inconsistent 

 with the hypothesis that they are themselves the causes 

 of such changes. 



Altogether, we would venture to conclude, firstly, that 

 if the changes of terrestrial magnetism are not due to 

 some such cause as that which we have stated, then they 

 must be due to some cause of which we are entirely 

 ignorant ; and, secondly, that the laws of the magnetic 

 changes are, in all the points we h.ave examined, consistent 

 with the idea that they are due to the carriage of con- 

 ductors across the earth's lines of force. 



B. Stewart 



SIMON'S " SPIDERS OF FRANCE " 

 Lcs Arachtiides de Frana:. Par Eugene Simon, Vice- 

 President de la Society Entomologique de France. 

 Tome premier. (Paris, 1874.) 



EXCEPTING two or three, either partial or abortive, 

 attempts at the early part of the present century, 

 by Baron Walckenaer, no effort has, until now, been 



made to supply a history of the spiders indigenous to 

 France. This is the more remarkable, inasmuch as; 

 though Arachnology has but few votaries in any country, 

 yet England, Sweden, Prussia, and even Italy, have fur- 

 nished more or less complete works on their respective 

 spider-faunas. Looking again at the geographical posi- 

 tion of France, perhaps few other equal areas would give 

 such a promise of rich results to the araneologist ; with 

 all the advantages of an insular position, France com- 

 bines those of the general Continent of Europe ; and her 

 climate ranges from the sub-arctic, in hermountain regions, 

 to the semi-tropical on the Mediterranean shores. We 

 may confidently, therefore, expect a vast addition to our 

 knowledge of European spiders from the labours of the 

 industrious author who has stepped into the breach, and 

 whose first volume onithc Spiders of France stands at the 

 head of this notice. 



As its title imphes, the work is intended to embrace 

 more than the one order (Araneidea) of Arachnids ; cer- 

 tainly (it is understood) the orders Scorpionidea and 

 Phalangidea ; but whether it will extend also to the other 

 orders, is yet undecided. The present volume, pp. 1-269, 

 PI. i. ii. iii., embraces five families of the order Araneidea 

 (or Araneffi). It is a matter of regret that it had not 

 been practicable to retain a systematic sequence in regard 

 to the details of the order ; the reason given for this is 

 that the author has taken first those families of which he 

 was in possession of the amplest materials ; another 

 drawback also seems to be, that the Introduction, " com- 

 prising general remarks on the class Arachnida and its 

 bibliography," will not appear until later ; when it will, how- 

 ever, be specially paged for addition to the first volume. 

 The volume before us begins with a useful glossary of 

 special terms used in the descriptions ; to this follow (pp. 

 5-15) some general remarks on the characters of the 

 order AranE/E, and some criticisms on the more ex- 

 tended works of different authors upon it ; concluding 

 with the outlines of the classification adopted in the 

 present work. In regard to classification but little altera- 

 tion is proposed from that contained in a paper, "Ara- 

 ncides nouveaux ou peu connus du IMidi de I'Europe, 2° 

 memoire," by the author,* published (according to the 

 title-page of its author's presentation copies) in 1873, in 

 " Memoires de la Society Royale des Sciences de 

 Liege." 



For the principles of M. Simon's primary divisions of 

 the Araneidea we are referred to the second memoir 

 above mentioned ; there, after giving his reasons for 

 dissenting from the primary divisions adopted by 

 Dr. Thorell in his work " On European Spiders," 

 the author divides the Araneidea into four sub-orders : 

 — I. Theraphosa;; 2. Gnaphos*; 3. Arane^ ; 4. 

 OcuLAT^. The sequence of these is reversed in 

 the volume before us ; the name of the third is 

 changed to Araiica vcriT, and of the fourth to 

 Araiicu- ociilatcc. The addition to the name of the third 

 order was necessitated by the adoption of the term Araneae 



* This paper does not, however, appear yet to have been " published " in 

 the only true acceptation of the term ; that is, offered to the ptiblic for sale ; 

 and, it is understood, will not be so published until 1875. This is in some 

 respects a matter of importance, inasmuch as the, claim of many species and 

 some genera to the names under which they arc, or will be, characterised in 

 the present work, rests for their priority upon the date of publication of the 

 above paper in the M6m. Liege. Similar remarks apply to the i"^ Memoire 

 on " Ajaneides du Midi de I'Europe/' the presentation copies of which were 

 issued in 1870, while the volume containing it was not published until 1873. 



