October i, 1891] 



NATURE 



519 



or when escaping from a human enemy or from a dangerous 

 animal, the thickness of the sole, its insensibility to pain, and 

 its resistance to wear and tear must have often determined life 

 or death. A man who became sore-footed after a long day's 

 tramp, or one whose thin sole was easily cut or torn by stones 

 or stumps, could never compete with his thicker soled com- 

 panions, other things being equal ; and it seems to me that it 

 would be difficult to choose a single physical character whose 

 variations would be more clearly subject to the law of selection. 

 With the greater portion of Prof. Lloyd Morgan's very inter- 

 esting address I am in perfect accord, and it is because his 

 remarks and suggestions are usually so acute and so well founded 

 that I have thought it advisable to point out where I think that 

 his objections have a less stable foundation. 



Alfred R. Wallace. 



A Rare Phenomenon. 



The rare phenomenon to which your two correspondents refer 

 in their letters in your last issue (p. 494) was visible here at pre- 

 cisely the same time, and, viewed from Nottingham Forest, it 

 presented a most interesting sight. It is curious that, as both 

 the time and duration of the phenomenon coincide with its 

 appearance here, its characteristics should be so dissimilar. It 

 had more the appearance of a well-defined display of the 

 aurora. Rays of light springing from the horizon penetrated 

 high into the heavens, lasting about 10 or 15 seconds, and then 

 disappeared, others taking their places. Its centre appeared to 

 me to be almost due north, and, from notes made at the time, 

 the beams or luminous rays reached an angle of about 50°, stars 

 being vi-ible through them. There was no arc visible of the 

 character described by your correspondents, but vertical changing 

 ravs, several of which were distinctly orange-tinted. 



Nottingham, September 26. Arthur Marshall. 



Your columns record, from Ireland and Scotland, observa- 

 tions of the aurora to which I called attention last week. It 

 was seen also in Warwickshire, the coruscations being so marked 

 as to remind my informant of the search-light at the Naval Ex- 

 hibition. Mr. E. B. Knobel informs me that, from 8 to 10 p.m. 

 on the nth, during which time the appearance was visible, 

 active magnetic disturbances were noticed at the Royal Observa- 

 tory, Greenwich, illustrating the close connection which has 

 been established between auroral and magnetic phenomena. 



W. TUCKWELL. 



It may be of interest to your readers to know that the 

 " rare phenomenon " mentioned (p. 494) was seen by me from 

 Ryde, I.W., on Friday, the ilth. A streak of light (at first 

 thought to be a ray proceeding from a search-light), was visible 

 near the Pleiades, at about 9.30, extending over an arc of about 

 45\ the width being probably about 1°. It gradually faded away, 

 and at 10 no trace of it was left. F. C. Levandrr. 



30 North Villas, Camden Square, N.W., September 28. 



Instruments in Just Intonation. 



As you have raised once more the question of justly in- 

 toned instruments, may I oft'er the following remarks ? It does 

 not seem likely that any arrangement for the organ would be 

 practically adopted unless it permits as much freedom of modu- 

 lation and of execution as that of equal temperament. To 

 permit perfectly free modulation, with practically perfect inter- 

 vals, nothing short of the cycle of fifty-three will suffice. Now to 

 construct a key-board with fifty- three notes to the octave which 

 can be played upon with the facility of a twelve-note key-board 

 seems impossible. But the problem may be approached differ- 

 ently : as it is only necessary to'use twelve notes at a time, the key- 

 bo ird might remain as it is, and cnly a mechanical device would 

 be required to make these twelve keys correspond to the right 

 twelve out of fifty-three pipes ; if the services of an assistant be 

 allowed (as i-; often necessary on large organs) the mechanical 

 difficulties could easily be overcome. For example, arrange a 

 number of studs — say 117, as suggested by Dr. Ellis — as a 

 "duodenarium," and connected electrically to the fifty-thiee 

 trackers ; i.e. each tracker would be connected to two or three 

 studs — B'[j[j, C^'pljiy, A 3^' studs to tracker 46 for instance, 



NO. II 44, VOL. 44] 



Opposite these studs would be another set of 117 connected to 

 the twelve keys, e.g. C, ^^, ^<^, D^i^tj, &c., all to the key C. 

 Between the two sets of studs would be a frame carrying twelve 

 contact pieces ; the frame would then be moved along guides by 

 the assistant, so that the twelve keys were electrically connected 

 to the right duodene of studs, and hence could be made to open 

 the right group of pipes. 



Thus the only alteration in printing required would be to 

 mark the duodene on the music. All the extra complication 

 would be thrown on the mechanical arrangements, and the 

 organist would be left in the same position as now. It seems to 

 me that any more complicated key-board would fail in a large 

 organ, through overburdening the organist. 



RoBT. A. Lehfeldt. 



Firth College, Sheffield, September 14. 



Unusual Frost Phenomenon. 



The following is extracted from a letter dated Dubbo Creek, 

 near Tumut, New South Wales, July 26, 1891 :— 



" I noticed the other day a strange effect caused by the late 

 very hard frosts. It was a peculiar upheaval of the crust of the 

 ground by a mass of innumerable threads of ice taking the form 

 of spun glass or fine asbestos fibre. There were five layers of 

 this ice-fibre, the uppermost bearing the raised earth-crust. 

 Every night's frost was shown by its distinctive layer of 

 fibres. 



"As perhaps you may never have seen this form of ground 

 frost, I append a rough sketch of its very singular appearance. 



I have only shown three layers ; there were five, but this may 

 give you some idea of its appearance — quite a columnar basaltic 

 appearance. 



"Every morning here after a sharp frost, the whole of the 

 ground, where not covered by grass or rubbish, is raised up 

 thus. On the sides of the cuttings and banks of our claim, these 

 ice-fibres may be seen projecting from the walls in bunches of 

 snowy filaments, like spun glass. The sun, however, soon 

 causes them to drop off, and they lie in heaps of some six inches 

 in dep'h." A. H. White. 



Richmond, Surrey. 



The Destruction of Mosquitoes. 



On two occasions, when proceeding northwards to Arctic 

 Norway, I was much interested in observing the fact that the 

 plague of mosquitoes, which is so intolerable there, especially 

 prevails in latitudes beyond the northern range of the swallow. 



This may possibly be a mere coincidence, but 1 think it is not 

 — an opinion strongly supported by another and very broad fact, 

 viz. that in a given district in our own country the gnats become 

 more abundant immediately after the departure of the swallows, 

 martins, &c. If this view is correct, the protection of these 

 birds should be added to the devices named in your review of 

 " Dragon- flies v. Mosquitoes." Such protection is very dif- 

 ferent from the indiscriminate sentimentalism about "small 

 birds " which breaks out periodically at this season in the news- 

 papers, and includes such feathered vermin as the thick-billed, 

 seed-grubbing, pea-shelling, graminivorous sparrow among the 

 objects of its tenderness. W. Mattieu Williams. 



The Grange, Neasden, N.W. 



