8 4 



NA TURE 



[November 27, 1902 



the body becomes incandescent." Both Prof. Armstrong 

 and Dr. Welsbach attribute the importance of the 

 special composition of the mantle to this particular 

 mixture forming a solid solution of a dilution favourable 

 to the occurrence of the oscillatory changes. 



We have endeavoured to put forward a summary, of 

 necessity brief, of some of the principal theories which 

 have been advanced to account for the luminosity of the 

 mantle. Although it is true that some of these theories, 

 if regarded as individually sufficient to account for the 

 phenomena, lead to conclusions mutually inconsistent, 

 yet there is no reason why they should not all contain 

 some part of the truth, unless the experiments of Messrs. 

 White, Russell and Traver be considered as sufficiently 

 conclusive against the idea of the mantle being hotter 

 than the flame. Such a result does not preclude the 

 possibility of catalytic action, for the additional energy 

 thereby developed may be all dissipated in luminous 

 radiations. It seems that the most satisfactory explan- 

 ation that the present experimental data justify is that 

 the high luminosity is due to a combination of the good 

 radiating power, the high temperature and the selective 

 emissivity of the mantle. The first accounts for the high 

 candle-power at the temperature attained ; the second, 

 which is due partly to the selective emissivity diminish- 

 ing the useless radiation losses and partly, no doubt, to 

 the catalytic action of the ceria molecules, is responsible 

 for the high luminous efficiency of the light, so far as 

 this is a function of the temperature ; whilst the third, 

 most probably due to the recurrent chemical changes, 

 accounts for the high luminous efficiency so far as it is a 

 function of the material. Thus all these causes, operating 

 together and assisting one another, combine to produce 

 one of the most efficient artificial illuminants that the 

 ingenuity of man has devised. 



Maurice Solomon. 



THE EXPLANATION OF A REMARKABLE 

 CASE OF GEOGRAPHICAL DISTRIBUTION 

 A MO AG FISHES. 



TVyr OST text-books and papers discussing geographical 

 ■'•*■*- distribution have made much of the range of a 

 genus of small fishes, somewhat resembling trout, the 

 Galaxias, commonly described as true fresh-water 

 forms, which have long been known from the extreme 

 south of South America, New Zealand, Tasmania and 

 Southern Australia. The discovery, within the last few 

 years, of a species of (he same genus in fresh water near 

 Cape Town, whence it had previously been described as 

 a loach by F. de Castelnau, has added to the interest, 

 and has been adduced as a further argument in support 

 of the former existence of an Antarctic continent. In 

 alluding to this discovery when discussing the dis- 

 tribution of African fresh-water fishes in the introduction 

 to my woik " Les Poissons du Bassin du Congo," in 1901, 

 I observed that, contrary to the prevailing notion, all 

 species of Galaxias are not confined to fresh water and 

 that the fact of some living both in the sea and in rivers 

 suffices to explain the curious distribution of the genus ; 

 pointing out that in all probability these fishes were 

 formerly more widely distributed in the seas south of the 

 tropic of Capricorn and that certain species, adapting 

 themselves entirely to fresh-water life, have become 

 localised at the distant points where they are now known 

 to exist. Although as recently as October last the dis- 

 tinguished American ichthyologist D. S. Jordan wrote 

 {Science, xiv. p. 20) '"We know nothing of the power of 

 Galaxias to survive submergence in salt water, if carried 

 in a marine current," it is an established fact, ascertained 

 some years ago by F. E. Clarke in New Zealand and by R. 

 Vallentin in the Falkland U\ands,\.ba.t Ga/axiasai/enuatus 

 lives also in the sea. In New Zealand, it periodically de- 



NO. 1726, VOL. 67] 



scends to the sea, where it spawns, from January to March, 

 and returns from March to May. In accordance with these 

 marine habits, this species has a much wider range than 

 any of the others, being known from Chili, Patagonia, 

 Tierra del Fuego, the Falkland Islands, New Zealand, 

 Tasmania and Southern Australia. 



I now wish to draw attention to a communication made 

 by Captain F. \V. Hutton in the last number of the 

 Transactions of the New Zealand Institute (xxxiv. p. 198), 

 "On a Marine Galaxias from the Auckland Islands." 

 This fish, named Galaxias bollansi, was taken out of the 

 mouth of a specimen of Merganser anstralis during the 

 collecting excursion to the southern islands of New 

 Zealand made in January, 1901, by His Excellency the 

 Earl of Ranfurly. 



It is hoped that by giving greater publicity to these 

 discoveries, the family Galaxiida; will no longer be in- 

 cluded among those strictly confined to fresh waters and 

 that students of the geographical distribution of animals 

 will be furnished with a clue to a problem that has so 

 often been discussed on insufficient data. As observed 

 by Jordan {I.e.), "all anomalies in distribution cease to 

 be such when the facts necessary to understand them are 

 at our hand." 



Of the fresh-water species of Galaxias, eight are known 

 from New Zealand and the neighbouring islands, seven 

 from New South Wales, three or four from South 

 Australia, one from West Australia, two from Tasmania, 

 seven from South America, from Chili southwards, and 

 one from the Cape of Good Hope. 



G. A. BOULENGER. 



LOCAL MAGNETIC FOCUS IN HEBRIDES. 



IN the course of a recent survey in the Hebrides, 

 Captain A. Mostyn Field, in H.M.S. Research, 

 found and examined an area in the entrance of East 



^fcA 



P 



10 Cable* or 

 ~1 Sea. Mile 



Fig. i.— Examination in 1902 by H.M.S. Research of an area of magnetic 

 disturbance in East Loch Roag, Lewis. 



Lines of equal disturbance westerly from the norma declination shown in 

 continuous line. . , 



Lines of equal disturbance easterly from the normal declination shown 10 

 broken line. 



Normal declination 22 s W. 



The figures express degrees and decimal parts. 



Depth of water over area from 15 to 17 fathoms. 



Loch Roag, Lewis, where there is considerable local 

 magnetic disturbance. A plan showing the deviation 

 from the normal declination of the compass needle at 



