334 



NA TURE 



[Fed. 15, 1877 



this lighter water is raised above the level of its own basin it 

 will naturally flow off" in the direction in which it meets the least 

 resistance." 



To conclude, I argue that while the wind undoubtedly in- 

 fluences the direction taken by ocean currents, difference of 

 gravity, and not wind, is the principal promoter of them. The 

 perfect agreement between the two systems of ocean and atmo- 

 spheric currents alluded to in the Quarterly is, in my opinion, 

 to be accounted for from similar causes producing similar effects. 



How can the winds influence ocean currents running fcr thou- 

 sands of miles below the surface, or how can they influence the 

 direction of the lower strata of surface currents ranging say from 

 50 to 600 feet in depth, the latter being the depth of the Gulf 

 Stream off Hatteras ? Digby Murray 



January 25 



Mr. Digby Murray (vol. xv. p. 294), in common with a 

 great number of meteorologists, maintains that the surface-trades 

 have come, as upper-currents, from the Arctic and Antarctic 

 regions, and that the prevailing westerlies of the extra -tropical 

 regions have come, as upper- currents, from the equator, without 

 intermingling their volume in the district of the tropical calms. 



He argues that this must be the case, because the surface- 

 trades on the interior borders of the tropical calms differ from 

 the westerlies on the exterior borders in their degrees of electri- 

 city, and of saturation, and in other particulars. 



I regai-d this argument as incontestably sound, provided 

 always that no objection can be taken to the assumption on 

 which it rests. That assumption may thus, as I conceive, be 

 fairly stated : " Atmospheric currents differing greatly in cha- 

 racter must have travelled from widely distant regions of the 

 globe." 



This premise is plausible, and the objection which I have to 

 offer to it rests upon a fact which is, unfortunately, obscure, and 

 which has received very little attention. 



Some light is frequently thrown on the more general and per- 

 manent atmospheric circulation of our globe by the analogy of 

 the local and temporary systems of circulation which we examine 

 in our own latitudes. Now the most local currents often differ 

 very remarkably in character according to the direction in which 

 they move : e.g., the easterly winds felt on the south border of a 

 small anticyclone, if pursued for a very limited distance into the 

 district in which they begin to travel from the south, are often 

 found to have undergone complete change in their electrical con- 

 ditions, in the aspect of the clouds which they carry, in their 

 humidity, in their amount of ozone, and finally even in their 

 effects on the animal frame. Still more extraordinary are the 

 alterations often noticeable in the different segments of very local 

 cyclonic circulations. In the case of the smallest secondary 

 depressions I have, very frequently indeed, been struck by the 

 wonderful alteration in the several atmospheric conditions, and 

 especially by the reversal of the electrical conditions, which im- 

 mediately attends the springing up of a northerly breeze, when 

 the barometric minimum has passed to the east. This breeze, 

 in many of these examples, occupies a very short as well as very 

 narrow belt, and is only of a few hours' duration. What is more 

 important, it is usually of very limited depth. The synchronous 

 upper-current observations at which I have been for some years 

 at work, prove that in many instances of very local depressions 

 the cirrus travels from southerly or westerly points for many 

 hundred miles on all sides of the small depression, as well as 

 immediately over it, in some cases very slightly affected, in 

 others absolutely unaffected, by the limited circulation at the 

 earth's surface. 



Until therefore it can be shown (in contradiction to what is 

 indicated by this fact) that our most local currents, if differing in 

 character, have travelled to us at a great elevation from very 

 high and very low latitudes respectively, I cannot hitherto regard 

 Mr. Digby Murray's reasoning as furnishing an "absolute 

 proof " of the soundness of his position. 



From Mr. Murphy's criticisms on my former argument I do 

 not retire, as Mr. Digby Murray may possibly complain that 

 I have done from my discussion with himself, behind a veil of 

 cirrus, after the convenient fashion of the Homeric heroes. But 

 as I have already stated, my agreement with his view that " the 

 imperfection of the Arctic as compared with the Antarctic depres- 

 sion is due to the amount of land in the northern hemisphere " 

 (though differing from him as to the nature of the relation 

 between the cause and the effect), it is perhaps hardly necessary 

 for me to say that from his proposition in Nature (vol. xv. 



p. 312) I am bound to dissent. I do not think that on Mr. 

 Murphy's hypothetical globe, possessed of an atmosphere con- 

 taining no aqueous vapour, the cui rents would "act as in our 

 actual atmosphere," or in a marmer at all analogous to that 

 which he describes. On this point I am afraid we must agree to 

 difftr for the present. \V. Clement Ley 



February 7 



Auroric Lights 

 Have the auroric lights been studied in regard to their rela- 

 tions with changes in the weather ? From casual observations 

 made during the last twenty years it would appear that there are 

 at least two distinct kinds of light so classed. One is brilliant 

 and transparent, of a white, yellowish, bluish, or yellowish-red 

 colour : while the other is semi-opaque and of a bloody red 

 colour. The latter generally seems to be considered in Ireland 

 a foreruimer of bad weather, or, to quote a Connemara shepherd, 

 " Them bloody lights are bad." The first kind generally appear 

 as intermittent pencils of light, that suddenly appear and sud- 

 denly disappear. Usually they proceed or radiate from some 

 place near the north of the horizon ; but I have often seen them 

 break from a point in the heavens, this point not being stationary 

 but jumping about within certain limits. The b*illiant aurora of 

 September, 1870, was one of the latter class, except that the 

 centre of dispersion was not a point, but an irregular figure, 

 sometimes with three sides, but changing to four and five-sided. 

 It began as rays near the north horizon and proceeded up itito 

 the heavens in a south-south-east direction. Sometimes, however, 

 these lights occur as suddenly flashing clouds of light, like those 

 of July 16 last, which were of a white colour ; but at other times 

 I have seen them of blue and reddish yellow. If this class of 

 lights are watched into daylight they appear somewhat like faint 

 rays of a rising sun. One morning while travelling in West 

 Galway, in the twilight, they were very brilliant, and quite 

 frightened the driver of the car, who thought the sun was going 

 to rise to the north instead of at the east. 



The second, or bloody-red light, usually occurs in clouds float- 

 ing in one direction up into the heavens, but often depressed 

 over a portion of the sky. I have never seen them coming from 

 the eastward, and only on a few occasions from the southward, 

 they generally proceeding from the west, north-west, or north. 

 If both kinds of light occur at the same time, the second, while 

 passing over the first, dim them. If the second class are watched 

 into daylight they appear as dirty misty clouds that suddenly form 

 and disappear without your being able to say where they came 

 from or where they went to, or as a queer hazy mist over a por- 

 tion of the sky that suddenly appears and disappears, or as 

 misty rays proceeding from a point in the horizon. Generally 

 when these clouds occur thtre is a bank of black clouds to the 

 westward. 



This season has been very prolific in auroric light, as there have 

 been few nights since the ist of October last in which they did 

 not appear, sometimes, however, very faint. Generally they were 

 lights of the second class, but on a {^^ occasions there were a 

 few rays of the first associated with them; on wet nights they 

 made the rain-clouds or mist of a reddish purplish colour ; tints 

 of which could be seen in some of the excessively dark nights we 

 had in November. On many occasions they were late in the 

 night, being very common and brilliant during the " dark days" 

 of December a few hours before dawn (about five o'clock). I have 

 watched them carefully this season to see if we had a chance of 

 fine weather, but each time we had a fine clear day they ap- 

 peared also and the weather broke again. Last week I cnly 

 saw white lights of the first class, very faint on two nights, but 

 the weather has not cleared yet. It has, however, become sea- 

 sonable, as we have had showers of sleet and snow, while pre- 

 viously it was like spring weather, the trees all budding out, 

 innumerable birds singing morning and evening, and flies and 

 wasps flying about. G. Henry Kinahan 



Ovoca, January 27 



On the Sense of Hearing in Birds 

 The sense of hearing is doubtless of much assistance in dis- 

 covering the food of such birds as the s-cansores — to wit, wood- 

 peckers, creepers, wrynecks and the like, which feed on insects. 

 On one occasion, in a Canadian forest, whilst seated close to a 

 rotting pine trunk, I heard distinct scratchings in the interior, as 

 if mice were nibbling the wood, and oir splitting open the trunk, 

 numerous large white larva; oi Ilylesinidic "woodworms " were 

 found busily employed in making their tunnellings throughout 

 the soft substance of the decayed wood. 



