October ic, 1901J 



NA TURE 



S77 



sidered report of Prof. Dufour, of Lausanne, the Swiss member 

 of the jury. 



"L'Angleterre vit, dans le domaine des instruments scientifiques, 

 dans un isolement assez grand par rapport aux autres pays. Elle 

 a ses habitudes et ses traditinns, des instruments bien fait-s, mais 

 ces constructeurs, ne paraissant guere se soucier de ce qui se fait 

 hors de chez eux, ont peu d'influence sur I'elranger. " 



C. V. Boys. 



Notes on Minerals from the Lengenbach Binnenthal. 



In a recent visit to Binn I obtained some interesting minerals 

 — viz Ilia new mineral {2) Dufrenoysite, (3) Hyalophane. 



(1) .A new member of the sulpharsenites of lead, crystallising 

 in the oblique system 



3 = 82^42 j'. a:b:c = I '36817 : I : ■947163. 

 Very similar to dufrenoysite in appearance, but distinguished by 

 the rounding of the dome and pyramid planes and well-marked 

 oblique symmetry. 



I found an imperfect crystal three years ago, but it was not till 

 last August that I obtained sufficient material to fully determine 

 this new mineral. 



(2) I also found some very finely developed crystals of dufre- 

 noysite having fifteen new faces, also a twinned crystal, twin 

 plane (o. 1.14), thus resembling rathite, whose twia plane is 

 (0.15. il. 



(31 Hyalophane, the baryta felspar which is isomorphous 

 with orthoclase, is now shown by some of my specimens to twin 

 according to the B.iveno and Manebach laws of twinning in 

 orthoclase. 



A full account of the above will appear in the next number of 

 the Mineialogical Joui-nal. R. \\. SoLl.Y. 



Cambridge. 



Gog and Magog. 



VoURinterestingparagraph in Nature of September 26 on the 

 local Flemish giants carried annually in procession omiited the 

 parallel most suggestive to English readers : Gog and Magog, 

 cousins German of Gayant and Phinar, used also to figure 

 annually in the Lord Mayor's Show, as is noted in Chambers's 

 Encyclopaedia. According to tradition "the Guildhall giants 

 are images of the last two survivors of a race of giants who in- 

 habited Albion, descendants of wicked demons and the thirty- 

 three infamous daughters of the Emperor Diocletian, who, after 

 murdering all their husbands, sailed to Albion. These giants 

 Brute and his Trojans finally overcame, leading the last two 

 survivors prisoners to London, where they were kept as porters 

 at the palace-gate. This is Caxton's account ; another represents 

 one of the giants as Gogmagog, and the other as a British giant 

 who killed him, n^imed Corineus. These giants have stood in 

 London since the days of Henry V., and have witnessed all its 

 history since. The old giants were burned in the great fire, 

 and the new ones, which are 14 feet high, were constructed in 

 1708. The ancient efiigies, which were made of wicker-work 

 and pasteboard, were carried through the streets in the Lord 

 Mayor's Shows, and copies of the present giants were in the 

 show of 1S37. Formerly other towns in England and abroad 

 had their giants, as the Antigonus of Antwerp, 40 feet in height, 

 and Gayant, the giant of Douay, 22 feet in height." D.P. 



Edinburgh, October 3. 



/ 



Fireball of September 14. 



A VERY memorable meteor fell into the Atlantic on September 

 14, 1492, and is recorded in the diary of Columbus. It would 

 be interesting to know whether his notes are sufficiently precise 

 (o enable one to say whether the radiant of that meteor is the 

 same as that of more recent ones. C. E, S i'RO.meyer. 



Lancefield, West Didsbury. 



A New Name for an Ungulate. 



In a paper published in the Geological Magazine for September 

 1 901 I described a large ungulate from the Eocene of the 

 Fayiim, Egypt, under the name Bradytheriian grave. I now 

 find that the name Bradytherium had been employed a few 

 months previously by G. Grandidier for a large extinct edentate 

 from Madagascar [Bull. Mas. d'Hist. Nat., Paris, 1901, p. 54), 

 and I therefore wish to propose the name Barytherium for my 

 genus. Chas. \V. Andrews. 



British Museum (Natural History), October 7. 



NO. 1667, VOL. 64] 



ON THE MAGNETIC ROTATION OF LIGHT 

 AND THE SECOND LAW OF THERMO- 

 DYNAMICS. 

 T N a paper published sixteen years ago I drew atten- 

 ^ tion to a peculiarity of the magnetic rotation of the 

 plane of polarisation arising from the circumstance that 

 the rotation is in the same absolute direction whichever 

 way the light may be travelling. " A consequence remark- 

 able from the theoretical point of view is the possibility of 

 an arrangement by which the otherwise general optical law 

 of reciprocity shall be violated. Consider, for example, 

 a column of diamagnetic medium exposed to such a force 

 that the rotation is 45', and situated between two Nicols 

 whose principal planes are inclined to one another at 45°. 

 Under these circumstances light passing one way is com- 

 pletely stopped by the second Nicol, but light passing the 

 other way is completely transmitted. A source of light 

 at one point A would thus be visible at a second point B, 

 when a source at B would be invisible at .\ ; a state of 

 things at first sight^ inconsistent with the second law of 

 thermodynamics." (Phil. Trans. 176, p. 343, 1885 ; 

 Scientific Papers, vol. ii. p. 360). It is here implied that 

 the inconsistency is apparent only, but I did not discuss 

 it further. 



In his excellent report (" Les Lois theoriques du 

 Rayonnement, Rapports presentcs au Congrfes Inter- 

 national de Physique,-" Paris, 1900, vol. ii. p. 29), W. Wien, 

 considering the same experimental combination of Nicols 

 and magnetised dielectric, arrives at a contrary conclusion. 

 It may be well to quote his statement of the case. " La 

 rotation magnetique du plan de polarisation constitue un 

 cas e.xceptionnel digne de remarque, et Ton pourrait ici 

 imaginer un dispositif qui mettrait en echec principe 

 de Carnot s'il n'existait pas une compensation in- 

 connue. 



" Faisons, en eft'et, les suppositions suivantes ; Deux 

 corps de temperature egale sont entouri^s d'une enveloppe 

 adiabatique. - Les rayons qu'ils s'envoient reciproquement 

 traversent deux prismes de nicol. Entre ces prismes se 

 trouve une substance non absorbante sur laquelle agissent 

 des forces magnetiques qui font tourner le plan de polar- 

 isation d'un angle determine. La radiation emanant du 

 corps I penetre dans le nicol i. Nous supposerons que 

 le rayon subissant la reflexion totale n'est pas absorbe, 

 mais renvoye dans sa propre direction par des miroirs 

 convenablement disposes. .Admettons que le plan de 

 polarisation soit tourne de 45" par les forces magne- 

 tiques. La section principale du deuxieme nicol 

 etant orientee dans la direction parallele au plan de 

 polarisation du rayon emergent, toute la lumiere transmise 

 par la substance absorbante {sic.) traversera le nicol. 

 Par consequent, la moiti^ des rayons emis par le corps i 

 frappera le corps 2. 



" Les rayons einis par le corps 2 se divisent en deux 

 parties egales, dans le nicol 2. Une moitie est, comme 

 precedemment, renvoyee par r(^flexion. L'autre moitie, 

 aprt;s que son plan de polarisation a subi une rotation de 

 45" dans le meme sens que le rayons emis par le corps 

 I, vient frapper le premier nicol. La section principale 

 de ce nicol etant perpendiculaire au plan de polarisation, 

 aucune radiation ne le traverse, et nous pouvons renvoyer 

 toute la lumiere au corps 2. 



" Le corps 2 recoit ainsi trois fois plus d'energie que le 

 corps I. [That is, 2 receives the whole of its own radia- 

 tion and the half of that of i, while i receives only the 

 half of its own radiation.] L'un de ces corps s'echaufTera 

 par consequent de plus en plus aux depens de l'autre." 



Wien then suggests certain ways of escape from this 

 conclusion, but it appears to me that the difficulty 

 itself depends upon an oversight. It is not possible to 

 send back to 2 the whole of its radiation in the manner 



1 The italics are in the original. That magnetic rotation may 

 interfere with the law of reciprocity had already been suggested by 

 Helmholtz. 



