l62 



NATURE 



[Dec. 27, 1877 



it, a stratum thick enough for the radiation of the gas to over- 

 power the fierce glare of the photosphere behind it, and both 

 these views have been shown to be untenable, 

 December 21 R. Meldola 



Oxygen in Sea-water 

 At p. 267 of the second volume of the "Voyage of the 

 Challenger" Sir Wyville Thomson writes: — 



"Mr. Buchanan drew the conclusion in explanation of the 

 small amount of oxygen at depths of 300 fathoms and upwards, 

 ' that animal life must be particularly abundant and active at this 

 depth, or at least more abundant than at greater depths,' In 

 other words, that a permanent condition, probably of all con- 

 ditions the most unfavourable to animal life, is produced and 

 maintained by its excess," 



" This is entirely contrary to experience." 

 The words in inverted commas are part of a sentence in a 

 short report in Nature (vol, xvi. p, 255), of a paper which I 

 read before the Royal Society of Edinburgh, on the results of 

 the analysis of so many of the samples of air extracted during 

 the cruise, from sea-water of different sources, as I was able to 

 accomplish before my connection with the work of the expedition 

 ceased. I will not encroach on your valuable space by antici- 

 pating the discussion of the bearing of my observations and those 

 of others on the question of the greater or less abundance of 

 animal life at different depths in the sea ; but as the above 

 quotation, from its fragmentary character, is somewhat mislead- 

 ing, both as to the nature of the belief which I expressed and 

 my grounds for holding it, I must ask you to give place to the 

 concluding sentences of the above report : — 



"It is evident from these figures 1 that between 200 and 400 

 fathoms there is a great consumption of oxygen going on, and, 

 as it is difficult to conceive its being consumed otherwise than by 

 living creatures, the conclusion is forced on us that animal life 

 must be particularly abundant and active at this depth, or, at 

 ]er.st, more abundant than at greater depths ; for at less depths 

 there is more opportunity for renewal of the oxygen by reason 

 both of the greater proximity to the surface and of the existence 

 of vegetable life. This conclusion was borne out by the nume- 

 rous experiments made by Mr. Murray with the tow-net at 

 intermediate depths, which went to prove the existence of abun- 

 dance of animal life down to 400 fathoms, vegetable life never 

 extending to much below 100 fathoms. Below 400 fathoms life 

 is sparingly met with." 



It will be seen that the only independent experience which 

 exists, namely, Mr. Murray's observations with the tow-net at 

 different depths, is in favour of the conclusion at which I 

 arrived. J. Y. Buchanan 



10, Moray Place, Edinburgh, December 13 



abundant in our ponds and ditches, and which is so rich in 

 species in northern regions, is not, with the exception stated 

 below, known south of Mexico in the New World nor south of 

 the Himalayas in the Old ; but I have several species from Chili, 

 Araucania, and the Falkland Isles, 



I could already multiply parallel instances, but have said 

 enough to prove my case. 



Confessedly I have, at present, only crude theoretical notions 

 on the causes of this anomalous distribution. It might be said that 

 these insects are the remains of a former Antarctic glacial epoch. 

 But if this be so, then we must presuppose the existence of 

 former Arctic and Antarctic faunas similar in details ; all 

 other evidence tends, I think, to disprove this. It may truly be 

 said that, owing to the non-existence of large tracts of land 

 towards the south pole at all comparable with those that exist 

 towards the north, we are not in a position to acquire sufficient 

 data, yet we have the continent of Australia and the large 

 islands of New Zealand extending somewhat far south, and they 

 furnish us with no indication whatever of forms parallel with 

 those found in Chili. 



It has occurred to me as just possible, that at the conclusion 

 of the northern glacial epoch a few stragglers, instead of wend- 

 ing their way northward, mistook the points of the compass and 

 went southward. But there remains this great difficulty, viz., that, 

 with one possible excepuon, there are no indications of these 

 forms on the northern portions of the Andes of South America. 



I call attention to this subject as one deserving far more 

 consideration than it has hitherto received, and with the idea 

 that, by ventilating it in Nature, I may receive additional 

 information on a point that greatly interests me. 



39, Limes Grove, Lewisham R. McLachlan 



Arctic Auroras 



It will probably interest some of your readers to know that 

 in reply to a communication lately addressed by me to the 

 Admiralty I am informed that Captain Sir George Nares 

 reports that although the auroral glow was observed on several- 

 occasions between October 25, 1875, and February 26, 1876, 

 true auroras were seldom observed, and the displays were so 

 faint and lasted so short a time that the spectroscopic results were 

 not considered worthy of a special report. Although the cilron 

 line was seen occasionally, on only two occasions was it well 

 defined, and then for so short a time that no measure could be 

 obtained. A report is preparmg with a view to compare the 

 auroral displays with magnetic disturbance, meteorological 

 changes, and other phenomena which will include the few 

 spectroscopic observations obtained. J. Rand Capron 



Guildown, December 24 



On some Peculiar Points in the Insect-Fauna of Chili 



For some years past I have been particularly interested in 

 some points in the entomology of Chili and the extreme southern 

 portion of South America, which, although known to most 

 entomologists who have made special groups their study, have 

 never yet been, so far as I know, even more than casually alluded 

 to in works on geographical distribution, and are ignored in the 

 principal ones. I allude to the occurrence in that part of the 

 world of well-marked palaearctic or nearctic forms not found 

 otherwise in America south of Mexico, and utterly unknown in 

 the southern hemisphere in the Old World. 



I have collected a not inconsiderable amount of data con- 

 cerning this subject, and have the intention of addressing a 

 circular to zoologists and also to botanists, ^asking for further 

 information. 



I will here allude to such familiar genera as Carabus amongst 

 beetles and Argynnis and Colias amongst butterflies. Carabus 

 is very abundant in species in the palsearctic region, poor in the 

 nearctic, and reappears (for the whole world) only in Chili. 

 The distribution oi Argynnis and Colias is similar, only that they 

 Ere about equally abundant in the two northern regions, and of 

 Colias it appears probable that a single species occurs in Peru, 

 but this exception only proves the rule. 



In the Trichoptera, or Caddis-fiies, a group of insects in which 

 I am especially interested, there is even a still more striking 

 case. The typical family, Limnophilida:, comprising those insects 

 the larvse of which manufacture the cases of twigs and straws, so 



I A table of the mean amounts of oxygen in a hundred parts of oxygen 

 and nitrogen contained in waters from different depths 



Insects and Artificial Flowers 



In a late number of Nature a short account is given of 

 some experiments recently made by Prof. J. Plateau, of Ghent, 

 as to insects being deceived by artificial flowers. The nature of 

 these experiments is not given, but the result would appear to 

 have been of a somewhat negative character. In connection 

 with the subject the following incident will not, I think, be con- 

 sidered uninteresting. I was coming by one of the lake steamers 

 from Como to Menaggio, in September, 1875, and saw a hum- 

 ming-bird hawk moth, Macroglossa stellatarum, fly to some 

 bright-coloured flowers on a lady's hat on deck, and hang, 

 poised over them for a short time, and then fly away. During 

 the process it made one of those short familiar darts off, for a 

 moment, and then returned, after the manner of the moth when 

 disturbed, and it remained long enough to convince me that it 

 had tested the flowers and found them wanting. Another inci- 

 dent comes across my mind while writing this, which, tfiougi it 

 does not exactly bear upon the point, yet is of a somewhat 

 kindred nature. I was crossing from Harwich to Antwerp in 

 August of the same year, and as the weather was fine, and the 

 boat crowded, I remained on deck all night. About 4 o'clcck in 

 the morning I saw what appeared to be a bird or a bat flying 

 rapidly about the rigging. As I was watching it the funnel of 

 the steamer poured forth a thick column of black smoke, owing 

 to the fresh coaling it had just received. Off went the creature 

 as soon as it perceived the change, or, at all events, as soon as 

 the change took place, and flew for some time in and about the 

 smoke, now darting through it, close to the funnel mouch, and 

 then letting itself be borne along with it, for some distarce, as if 

 in sport, looking very strange and weirdlike in the process, 



