^iHlii: Astronomical and Physical Society, TORONTO. IL.IBK,.A.I?,'5r. r\o. / > -/ \^L ^ An Illustrated ^ Av MAGAZINE OF SCIENCE. SIMPLY AYORDED-EXACTLY DESCEIBED- Edited by A. COWPER RANYARD. " Let Knowledge grow from more to more. " —TENNYSON. YOLUME XYI. JANUARY TO DECEMBER 1893. NEW SERIES, VOL. VIII. LONDON: WITHERBY & CO., 326, HIGH HOLBORN, W.C. 189 3. [All Rights Reserved^ rRiKTri* BT wrTHBKBT * CO., 32**, nnn holbokn, w.c. KNOWLEDGE INDEX HI. Absorption— On the Origin of the Solar Dark Lines . . . 177 Algol Stars— The Light- Changes of Y Cygni Alkali— Eival Alkali Manufactures Anderson, Dr. T, D.— The Story of d Eridani Anthony, Edwyn — Di\isibility by 7 and 13 Apennines — The Lunar ; by A. C. Eanyabd 166 25 124 74 31 Argus— The vj Argus Kegion of the Milky Way 50, 69 Astronomy — The Astronomy of Shakspeare 35 Atmosphere — Exploration of the Upper Air by Balloons . . . 107 Equilibrium of a Solar Atmosphere ... 177, 190 On the Atmosphere of Mars 153,173 On the absence of a Lunar Atmosphere ... 193 Bacteria — And the Flavour of Tobacco . . . Ball Lightning- Supposed Photograph of ... 30 193 Barnard, Prof. E. E.— Photograph of Nebula to the north of the Trifid Nebula ... 11 On the Period of the fifth Satellite of Jupiter 71 Beck, H.— Shakspeare and the Seven Stars Blashill, Thos.— Letter on a Phosphorescent Meteor ... Boraston, J. Maclair— On the Grouping of Stars 89 113 ... 133 Boys, Prof. — His Eadio-Micrometer Brester, Dr. A. — His Theory of the Sun 71 14, 28, 49 Bright-Line — The Sun as a Bright-Line Star ; by Miss A. M. Clerke IIG Bruce, Wm. S.— Antarctic Seals 221 Buckley, Miss A. B.— Notice of her book, " The Moral Teachings of Science " ... ... ... ... .. 155 Bulman, G. W.— On some recent Investigations of the Geology of the Punjab Salt Eange 137 The Migration of Birds 155 Butler, E. A.— Caterpillars Caterpillars' Dwellings Galls and their Occupants Curious Cocoons Caterpillars— Articles on ; by E. A. Butler Caterpillars' Dwellings — Articles on ; by E. A. Butler 4,33,41 ... 61, 85, 104 125, 143, 164, 186 214,225 4,33,41 ... 61,85,101 Clerke, Miss A. M.— Dr. Brester's Theory of the Sun ... ... 28 Notice of her book, " Familiar Studies in Homer" ... ... ... ... ... 51 The Distribution of the Stars 66 Stellar Spectra and Stellar Velocities ... 84 The Sim as a Bright-Line Star 146 The Light-Changes of Y Cygni 166 Absorption in the Sun ... ... ... 177 On the Solar and Stellar Photospheres ... 207 Cluster— What is a Star Cluster ? by A. C. Eanyard 90, 109 IV. KNOWLEDGE. CoUinson. H. M.- Tlie Seven Sta: l-^ Comets— Notice of Mr. L^-xns book, " Remaikible Cornels" 51 Copernicus - The tlreat Lunar Crater ; by A. C. Raxyard H'.m Coral Reef— I'hotograpb of Cornish, Vaughan I'luorcscence and Phosphorescence . Chemistry and Cuisine Nitrogen as Food for Animals und Plants Craters— The Origin <>! iIk' Lunar Cygni The I nycs of Y Cygni ; by Miss A. ;■. ..: Dark Markings- On the Lunar Plains Dark Structures — In the Milky Way Davison, J. Ewen— Queensland Fishes Deslandres, H.— The Solar I'acuht Dewar, Prof. — His Kxperimonts on Liquid Air Evaporation — On the connection between the Intensity of Gravity at a Planet's Surface and Evapo- ration . ... ... ... • 171 Evershed, J. — Explosions in the Sun 207, 2.S3 Explosions- Ill the Sun 189,207,233 Faculae— Photographs of Solar Faculro ; by O. E. H.KLE 107 The Solar Facula? ; by M. Deslankrks and Geo. E. Hale 280, 283 24 l:ir, Fluorescence- 237 119 1C6 212 24 10-12 l:i Diptera — Notice of Mr. F. V. The'k book, " An Account of British Flics " Id Article on ; by Vaucjhan Coknish Fry, Sir Edward— The Disaster at St. Gervais ... ... 1 Galls - And their Occupants ; bv E. A. BrrLKR 125, 113. IGl, 186 Galton, Francis — Ethnographical Survey of Great Hritaiii !( Method of Telegraphing Outline 1 )rawings by Letters or Numbers . ... 53 Gases — Tlie Constitution of; by J. J. Stewart 53, 75, 195 Gilbert, 0. K.— His Paper on the Origin of the Lunar Craters 149 Giraffe — Article on the ; by R. Lvdekker . . . . 202 Glaisher, J. — f,2 His Highest Balloon Ascent ... 107 Glew, F. H.— Method of rapidly detecting Variable Stars 2;!(i Dixon, Chas. — Noiicc of his book, " The Nests and Eggs of British Birds •• ... 112 Earthquakes- Photographs of ; by Prof. Joii.N Milm :;| Eclipse Ob9er^^ltion of Total Eclipac of April 15th, 1V.»3 61 Tlio Life-History of a SoUr Eclipse ; by K. \V. MAt-.<ER iHl Eridani — The Stojy of i Endani ; by I>r. T. I). 124,171 Am>KR!I<>-. in I'hotograplis ... 193 Gore, J. E. - I'he Numl)er and Distance of the Visible Stars . . ... ... ... ... 7 Graham, G. W.— Mexican Homed Toads ... ... ... 13 Gregory, R. A.— iMmensions of the Solar System compared witli Distances from St. Paul's Cathedral 228 Hale, Prof. Geo, E.— Contract for the Yerkes Telescope ... !) Photograph of the Spectrum of a Solar Prominence ... ... ... ... ... eci3ion as to Possession of ■>! Meteors- On certain Low-lying Atmospheric Meteors ; by Chas. TnMussoN, F.R.S -AG Variation of the Light of Meteors in passing through the Air ■■ 229 Meteors, Phosphorescent— Lttter ou, from Tiiot*. Ulasiiill . 113 Michelson, Prof.— M '.ts made with his Interference :mler 22H Migration— The Migration of IJirds ; by G. W. Bli.man... 155 Milky Way— The r, Argus Region of the The Structure of the flalaxy ... Mitchiner, J. H.— The T. ' ' ■ nil Tabl< ts The (I - in the World Mitton. G. E. Insect Plagues of Uruguay Moles An.1 th 90, 109 The Great Plains on the Moon 129 The Great Lunar Crater Tyclio ... 149 The Great Lunar Crater Copernicus .. ... 109 Absorption in the Sun ... ... 177 What is the Sun's Photosphere ? . 1H9 Halo round Photographic Images of Bright Stars 191 On the Presumption that the Material of the I'uiverse has been uniformly distributed ... 207 The Tints of the Lunar Plains 209 Shooting Stars and their Trails ... 229 KNOWLEDGE. vu. Read, F. W.— The Coffin of the Builder of the Third Pyramid 223 Riviere, Mons. — Skeletons found in Caves in the Eiviera ... 10 Theobald, P. Y.— Notice of his book, " An Account of British Flies" 130 Roberts, Dr. J.— Photograph of the Hercules Cluster . . Russell, H. C— Photograph of the Lunar Apennines . Sadler, Herbert — Face of the Sky every Month. Scheiner, Dr. J. — His Chart of the Hercules Cluster . . . Schooling, William — The Earth in Space . Seals- Antarctic ; by Wm. S. Bkuce Seven Stars — A Name for Charles' Wain 91 32 !)1 19fi 221 48 Shakspeare— The Astronomy of; by Lieut. -Col. Makkwick 85 Shooting Stars — And their Trails ; by A. C. Ranyakd . Simmonds, P. L. — On Animal Plagues ... 229 9 Smithells, Prof. A.— His Theory of Explosions in the Solar Atmosphere ... ... ... ... ... 189 On Explosions in the Sun ... 208 Stars — The Distribution of the ; by Miss A. M. Clerke 66 Stellar Velocities and Stellar Spectra ; by Miss A. M. Clerke 84 Stewart, J. J. — The Constitution of Gases ... ... .53,7.5,195 St. Gervais — The Disaster at ; by Sir Edward Fry ... 1 Sweeting, C. W.— On the absence of a Lunar Atmosphere ... 193 Tel-el-Amarna — The Tablets found at ; by J. H. Mitchiner 25 Temperature — Of the Solar Photosphere 190 Of Mars 153,173 Of the Moon 193 Heat developed by the passage of Meteors through the Earth's Atmosphere 220 Tomllnson, Charles — On the St. Gervais Disaster 2 The Ir/iiis Fiitum 46,73 On certain Low-lying Meteors ... 46,96 Townsend, C. P.— A Volatile Series of Metallic Compounds ... 3 Eival Alkali Manufactures ... ... ... 25 Tree-Creeper— Habits of the ; by H. F. Witherby 128 Tusks— And their Uses; by R. Lydekker ... . 121 Tycho— The Great Lunar Crater 149 Volcanoes — Origin of the Great Lunar 149,169 Yoles— The Governmental Inquiry with respect to Field- Voles 184 Watson, W. H.— Account of a Brilliant Meteor ... Wells, H. G.— The Making of Mountain Chains 30 204 Whalebone— And Whalebone Whales ; by R. Lydekker ... 184 Whales — Toothed Whales and their Ancestry ; by R. Lydekker ... ... ... ... 161 Williams, W. Mattieu— Obituary notice of ., ... ... ... 12 Wills, The Hon. Mr. Justice— The Glacier d'Orny ... .. ... .. 1 Wilson, W. E.— On the Comparison of Stellar Photographs .. 209 Witherby, Harry P. — Woodpeckers ... The Nuthatch The Tree-Creeper Woodpeckers— By Harry F. Witherby Yardley, Yincent — The 1) Argus Nebula 88 Young, Prof. C. A.— Observation of the fifth Satellite of Jupiter ... 51 64 87 128 64 \ 111. KNOWLEDGE. INDEX OF THE PRINCIPAL ILLUSTRATIONS. TAOt Anteater— Hairs - I'lrturrofUicComnwuSpim .. 1'" »>t i :i.. rpniar of TiKor M..1I1 ApennlBW- ^^"^ „ , . , . i , iM , .~„l,. „f .1.. TuMr .^2 'lO I'"*" '"^ R.rt. i.i,.,toi;r,.i.l.ic I'liit.- HH *'*"* " , , Hedgehog S.r John Her^-l..;!-. r ....f.l..- ^^^ IV.urt- of tho Common .. 1"2 Hercules— 111 Vhotoemphs and Drawings of Iho (•l,.-».Tin -H Ml-.'. 1(1(1 Ichneumon- Cocoon* of Ichneumon Flip* ... 22s ..,., Larva — Of tho Kin]n-ror Motli '> Leaf- Ni-sts ot Li-nt-niilmg CntorjuUar- ''i' Lemurs— Artichoke Gall Artionyx II. ml F.-.t • Babimsa- - Skull .'I 10:1 Ball Lightning— Su[>i-i»«d I'hotogmi'li of Caterpillar*— ^!f'.K'"«'"^;'''u,ti; ?! t Tl.c SlcmU-r lx.ri. in Sleeping and ( »f thf lUei.u- Sloth ... •« U„lin,. l'o«liires i'< '^'I'r'T:''"'"'"''^'''''''"' 4:^ Tl.eT»"Lofs7:^g-car' .7 Centaur! - i Lightning- n.eSt.rCl <■ " V- Su,,,-.-.-.l Photographs of... 1!>:<. l':U _, , Lunar Mountains Clavlns— , , , , . _., , ^, . I ,„ I'hotocraph of tlic l.unnr A|n-ii- Tlir l.unnr Cmter II!' . '^ ' .,.> ninp? ... • ■■ •'- Coeoo"- i Maps- of the 0»k Egger Miitli ... ^1'' 1. ,1, 11 Of the Drinkrr ami llumet Moths 217 liepin» - , Mastodon- Copernicus ,. , , , ., , ,. ,,,n 1-.. Skel.toii of tl IL'l Coral Beef— l'h'ilt>j{T»ph of a Dark Stmctnres— In .Milln Way to thr north of the Triful Nebula Dolphin - Th.- Bn.ll.l Egger Moth- Kitij Ctiil of, on Ilairtti"" 'run' »tt f>f Emperor Moth - rl,r Ck-.k.t, of III. Ermine Moth I'li-turr of Gall oinur*- Picture of Meteor Traces - I'liotogropli nhinviug Mrlfor Truck, 23" Oak Apple Si'.-lioii ot nil Mhi-Mo Gi.ll Observatory Of Dr. Mux Wolf ... Pentacrinid- l.iiiiij: Form of Photosphere— rhologmphs of the Sun's Plcurotomaria — Sliill of. nftcr Dr. W.Mnhvanl Porcupine— Tirtiirc of the Common Porpoise— rill' Inilian .. Puss Moth — I'lileriiillar of the ... Rainfall— CliiirtK of British Sea Cow— Skeliton of till' Novtlieni Sea Lion - riie Patagoniaii Serenitatis — riiolo;;r-a|>liof ihfMnre ... Seven Stars- War" iikshire Inn Tree-Creepers ( III an Oak '{'{■•■•■ li:i Dili l!)ii 1(1.1 ir,:t 33 23r. 22 211 H9 12H Milky Way n I'liotouraph of, to the north of the Trifiil Xebuln " 161 62 A3 215 Moiet— The Cape Oohlen Mole, the Long Clawed Mole-Vole, and the Marsupial Mole ' ^2 Moon— rhotogrnplm of the, bv the Brothers ll.i.ry ' 12<>. 150, 170. 210 Moonlight - IMiotogmph taken liv -':''•• '■' Narwhal- I'l.l.ir.' (if 111.' '-■-' I4f. I ""' JIK ' Of .-rii:ill Kgtjir .Molh I ai.r|iiliiir ii.t NuthaUhes - 2112 .\nd Xe»t ]ilBi>terc Ulntathere — Skull of » Yaporum- I'liotograph of the Mai"e Yapourer Moth - (■,,,•....11 ot till- Whale Skull of the On-enlaiut Williams, W, Mattieu r,,rlniil of ,., Woodpeckers— (Ircen, and NeM 123 211 2211 IHI 13 111 January 2, 1893.] KNOWLEDGE. AN ILLUSTRATED MAGAZINE OF SCIENCE SIMPLY WORDED— EXACTLY DESCRIBED LONDON: JAM AHY .V, 189;^. CONTENTS. The Disaster at St. Gervais. (A Sii|iiiU'iiK-nf.) By tlu' Tii-lit II, .11. Siv KiiwARii F»y. 1.1..1> . F.K.S. &.• A Volatile Series of Metallic Compounds. l!y C. F. TowNsKMi, F.C'.S. Caterpillars— Til. By E. X. Butler The Number and Distance of the Visible Stars. I!\ .1 Iv (.i.MiK, F.E.A.S Science Notes ■■ What is a Nebula? Hy -\. C. Ranyakp ... The late W. Mattieu Williams Notices of Books Letters :- G. W. Grabham, il.D. (LoikI.)i.T. Ewkn Davidson ; W. T. Ltnx ; Dr. A. Beester, Jz Lemurs By E. 1 tdekkee, B.A.Cantab. The Face of the Sky for January. By Herbert Sadler, F.R.A.S Chess Column. By C. D. Locock, B.A.Oxon. 9 ]0 12 12 13 14 18 19 THE DISASTER AT ST. GERVAIS. A Supplement. By the Right Hou. Sir Edwabd Fry, LL.D., F.K.S., Ac. THE article wliicb appeared on this subject iu the November number of Knowledge has brought me some letters which appear to me well worthy of the attention of my readers, and with the per- mission of their writers, and with some slight alterations and additions kindly made by their hands, they appear below. I am desirous also of availing myself of this opportunity to make a few additions and corrections to my article. First, I may mention that three papers on the subject have appeared in the Comiitcs Ficmhis : one by M. Forel, in the number of the 18th -July, 1H02 (p. 103), another by MM. Vallot and Delebecque on the '2.'jth .July, 1.S02 (p. 2(M), and the third by M. Demontzey on the 8tli August, 1892 (p. 305). The last paper mentions the fact that some workmen saw the moving mass from a distance in the clear moonlight, and they gave live minutes as the time it occupied in passing from the gorge of St. Gervais to Le Fayet, a distance of 1800 metres, or at the rate of six metres a second. The writer also mentions the fact that the passage of the torrent has stripped the beds of the streams of Bionnassay and the Bon Nant of all the granite blocks which for long have been found there, and that the torrent when entering the Bon Nant at Bionnassay first drove right across the stream, and deposited materials of all sorts on the left bank at a considerable height. Referring to what I said on p. 203, second colunm, as to the moving power of water, I think that it should be observed that the moving mass was by no means pure water, it was water, ice and mud, and I apprehend that the ino\nng force of such a mass (which as a whole must be somewhat viscous) differs from that of pure water or any other true liquid. Fig. 7 is so drawn as to represent the height of tlie water in the two communicating cavities as different. This is, of course, impossible, and I must ask my readers to make the necessary mental correction. The following are the letters above referred to : — h'rom tlw Hon. Mr. .Justice Wills. The acciiniulatioii of such ii raas.s of water at such a height is a very remarkable fact. I have once or twice seen cavities in the neve on a scale comparable with that on which the two holes in question were, but only once or twice. One was a very remark^iblc case indeed: on September l.")tli. 18.58, 1 was descending the glacier d'Oniy with a friend and two guides: we were still on the neve, and I noticed a thing which looked like ii dark patch on the ice at a short distance from us. I said I should like to go and see what it was. As I drew nearer I saw it was a hole and I took the precaution of continuing in the rope, which we had not yet taken off. On reaching the spot, I went to the edge of the hole on my hands and knees and lay down to look into it. As soon as my eyes got accustomed to the comparative darkness into which I was gazing I saw to my horror that we were all of us on the crown of an arch of ice which from side to side was, if my recollection serves me, some 30 yards across, and which, at the top and at the very spot on which I was lying, was not more than a foot or 18 inches thicii. The chasm extended in length further than I could see in either direction, but this was the only spot in which the top had given way. It was of great depth, I should think 100 to 150 feet, and there were many places in which pendants <.f ice, evidentlv formed by drip, were hanging from the roof ; others in which lilocks that had had ice pendants hanging from them had fallen into soft snow, or else merely got gently dislodged, for the ice pendants were still unbroken and yet pointing in many directions. It was a scene of really awful magnificence, and made a great impression upon all of us. We had walked across the arch without a suspicion of a hollow beneath, and yet the hollow was sufficient to engulf an army : we saw no water there. I saw a thing of the same sort once on our own Buet, where the glacier is on so small a sc:ilc that we never dream of being roped. I saw a similar dark spot, went to look at it, found it was the top of an arclied Oiivitv on a very infeinor scale to that on the glacier d'Orny, but still calcidated to teach one respect and caution. I had a ball of string witli me, and I tied my stick to the end of it and let it down what proved to be S4 feet before it touched bottom. Here, again, tliere was no water. Melting at 9000 feet in height is a totally different thing to melting at 6000 or 7000 feet, and I have never seen a large crevasse in the neve charged with water, nor do I remember to have read of one. The highest of such that I ever remember to have had my attention called to, was on the upper plateau of the glacier des Bossons, perhajis 8000 feet or even more above the sea. We lost a little dog who fell down the crevasse by jumping short, and we heard him swimming quite out of sight. We let down a porter — fortunately we were a strong party and could pull him up again — and he found the dog on a ledge of ice at the edge of a deep pool. The de;id weight of a big man to haul up again by main force was something I shall never forget. The crevasse tvristed, and at one moment his broad shoulders got jammed and I thought we should not get him out again. But whatever height this was, it was far below the limits (at that place) of the neve, and the ice had none of the character- istics of the neve. There is, however, very likely more drainage on the glacier des Tetes Rousses than on most glaciers of that height. I cannot say from personal recollection, as the only time I crossed a part of the glacier des Tetes Rousses, on an ascent of Mont Blanc by the Aiguille de G-oute, my attention was not drawn to the point, but I think it very likely that a part of the drainage from the Aiguille de Goute may fall on to its side and get into its interstices. The Aiguille de Goute is too steep for a permanent glacier to form on those ridges and furrows which are so great a characteristic of its structure. Vast quantities of snow fall and lodge upon these ridges and furrows, and melt very KNOWLEDGE [January 2, 1893. rapidly in fine and hot weather, espeeiallv in the long days of June and jiilv. It certainly needs some such contribution to account for so va?t a store of water from mere drainage at that height. The surface snow of the nerc is porous, and though a cake of ice often forms at night, it is sure to disappear witli a tew hours of sunshine, and to leave free access to soft snow beneath, and the surface meltings, which are never very great on the neve, filter into this, and do not run off as they do off hard ice — such as you meet with in your way up the Her de Glace, for instance. The circumstance of this vast accumulation of water in such a place is so very exceptional that a notion has been suggested (I forget where I have seen it — my son says it is in Freshfield's paper) that ( there are underground springs tliere. It would be very curious if this really were so. The distribution of underground water has always seemed to me a very interesting subject, and one which remains to be efficiently treated. That water travels very far under ground there can be no doubt I have seen in the Bay of Bengal, about forty miles north of Sumatra, a little island called Pulo Rondo. It is not two miles round, and rises about 2.')0 feet out of the sea. A broatl stream of water flows from its highest ])art down into the sea. In shape the island is like a barber's basin turned upside down, and tliere is no gathering ground, or none but the very smallest, above the top of the waterfall. That water must travel at least forty miles underground if the fall is brought about by liydi'Ost;itic pressure. But there are other collections of water whicdi it is very dillicult to account for by any such simple means. I know a small and very deep lake, about 1000 feet higher than the Lac Cornu (which is behind the Brevent from C'hamonix), and nearly 90OO feet high, above which there is MO gathering ground the least adequate to explain its existence, and I have always thought the Lac Cornu itself much larger than the area of which it receives the drainage can account for. In 1872 I noticed, during the X.W. monsoon and after a long period of dry weather, a small stream of water within a very short distance of the top of Pedro tallagalla, the highest mountain in Ceylon. I have reason to think that there is no great intrinsic improbability in the notion of a spring even at 9000 feet, and my son says that in Freshfield's article he mentions that De Saussure noticed a stream of pure water issuing from the base of the glacier des Tetes Rousses. It is a very rare thing indeed for the meltings of a glacier, which have passed any distance under the glacier, to be clear when they issue. You know what the Arve is at Chamonix in summer ; I am told that in winter, when its volume is enormously diminished, it is clear, which may and probably does mean that it has a nucleus of spring water, which is what flows in winter. But whatever the source of the sub-glacial accumulation, I think two things are clear : (I) That those large tanks, so to speak, are due to the motion of the glacier and not to the mere action of water. Water woidd, no doubt, do some little melting at the sides and on the floor of its receptacle, but in so confined a space tlie melting would be trivial ; aiifl as the water was accumulating and not changing, the action of melting ice round it would be to lower its temperature greatly. Such sheets of water as the Miirjelen See hollow out great vaults underneath the ice. I once saw there a block of many hun- dreds of tons, on which it was the merest chance that four of us were not standing at the time, break off and fall into the lake, undermined. But then there is a lake nearly a mile long, above the freezing tem- perature, and with the surface warmed a good deal by the summer sun and the surface water between 32" and .39° sinking so as to keep the whole mass from getting down to the freezing point. In the cavities, in the present instance, the sun can have done nothing to warm the water after it got into them. (2) It is clear, I think, that the natural and u.sual drainage must have got blocked. As a rough general rule, where you have any very marked feature in glacial structure at any one time, you have it always. The seracs of the Col du Geant are constant. Particular passages over berg- schrunds or through great mazes of crevasses, with a good deal of local variation, have yet a great amount of general constancy, and I suspect that whatever circiunstanccs in the bed of the glacier, or what not, make a chasm, such as that in my glacier d'Orny, one year make it in a great many other years ; and yet this accumulation i.s a new thing, or with the perpetual shifting of the ice wliich takes place in motion some such hurst would almost certainly have taken place before. Tliat there was a channel between the two cavities, I should have very little doubt, especially considering that the lower cavity is at a place where the incline of the glacier becomes much steeper than before. Generally speaking, no doubt, the cracks below the lower cavity give abundant outlet for the water, but some move- ment of the glacier mu.-.t have blocked them up — a thing which one knows perfectly well does take place in numerous spots from time to time — and then the accumulation became formidable. The roof of either cavity was, in the course of glacier motion, bound to come down some day, and that it should break suddenly was to be expected. The ice avalanches that one lias to look out for on the Petit Plateau, for instance, always happen without warning. That is to say, you see that the masses are getting dangerously near the edge of the cliff, but whether they will fall within'five minutes or five days no human being can do anything more than guess. Wlien the roof once did fall, being as it was very large the pressure on the containing system would be very great. In the instance 1 mention of the Marjelcn See I was immensely struck with the commotion produced in the water, and yet there was an open lake a mile long with a long flat margin round a considerable part of it. It was half an hour Ijefore the recoil waves sent back from the end of the lake ceased to boom with ominous sounds against the ice cliffs, aim the earlier recoils brought down fresh falls of ice. I am not the least surprised at the dam at the end being burst, and at the rush of water from above sweeping the lower hole pretty clear of water. An illustration of the fact that drainage through the lower strata of a glacier sometimes gets blocked for long periods together oi'curs to me. When I first knew the Mer de Glaee well, in 18.57, there was, at the foot of the Taeul, in the angle between the glacier du Geant and the glacier del'lCchaud, a large lake certainly more than a quarter of a mile long. I have visited the same spot in fourteen dift'ercnt years since. I ha\e never seen it so large again, and many years it lias nol existed at all. The difference is chiefly due to drainage. I think your paper on the St. Gervais disaster, as far as I can judge from what has so far been ascertained, is quite right as to the modus operandi. If all be well, I hope to go and see the course of the torrent next autumn, and it is fairly certain that one year will make very little dift'erence in the physical appearances. It is the second time I have known the broader valley below St. Gervais covered with dJI/ris. In 1852 there was a wonderful fail of warm rain over the whole range of mountains for nearly three days. I got to Chamonix on the tliird of these days, having come down the Great St. Bernard and through Martigny, and liaving met with floods which gave us some very long detours to make. Parts of the valley of Chamonix, but very much more the embouchure of the stream which comes from the Col du Bonhomme and receives all the lateral drainage from the Mont Blanc chain, were covered at least three or four feet deep with dehrix and glacier mud. Now, I fancy, the depth of deposit is nearly ten times what it was then. I am sure what I saw then was terrible enough. In one place we saw the actual birth of a torrent of mud, saw it burst out of the mountain side and spread over the cultivated patches above the hamlet of Le Tour. From Charles Tomlinson Esq., F.R.S., &c. It may be thought presumptuous in me to form any opinion ou the subject, seeing that I have not visited the spot, nor studied the phenomena in situ as you have done. But I venture to remark that I miss from the account any reference to the hydrostatic force of water, which is suflicient of itself to do any amount of mechanical work without subsidiary aid of any kind. A cubic foot of water weighs u|)wards of 62 pounds, and in con- sequence of the perfect distribution of fluid pressure in all directions the pressure on a square foot of water at the depth of ten feet is upwards of 623 poinids. But the cavity containing the pent-up water which caused the disaster is estimated at a vertical depth of 130 or 1 60 feet, which gives a pressure on the lowest foot of water of 8060 and 9920 pounds, which pressure is repeateil on every cubic foot along the lowest line but diminishes upwards to the surface cubic foot pressure of 62 pounds. Hence, we have a force acting day and night all the year round, which in time must break through any icy barrier that la likely to be opposed to it. The fall of ice from the roof could not act as a piston or lend any eflicient aid to the result. There are also objections to the word " suction." My conclusion (subject to the objections noted at starting) is that hydrostatic pressure alone was the only moving originating cause of the aalamity. There are, however, a few other considerations which I take the liberty of adding to this proof which the Editor has been so good as to forward to me. The warm weather that preceded the catastrophe would tend to fill u]illic sub-glacial reservoirs, and also to thin the outer wall of ice. If an opening had been made at the base of the deeper or 160 feet cavity (the velocity of the outflow being as the square root of the depth) the rush of water would have been thirteen times greater than at the top. But I imagine there was no point or line of least resistance at or near the base of the cavity but was spread over its whole surface, so that as the water accunudated, a uioment arrived when the resistance was not equal to the prcssui'e, and the whole ex])Osed fat'C of the icy barrier was burst open at once, aud the contents of the reservoir, thus set free, proceeded rapidly on the work of destruction. January 2, 1893.] KNOWLEDGE A VOLATILE SERIES OF METALLIC COMPOUNDS. By C. F. TowNSEND, F.C.S. THE progress of chemical science is continually bringing to light new wonders and startling paradoxes. Nothing more remarkable and unexpected has occurred in the recent history of chemistry than the discovery of the compounds of nickel and iron with the gas generally known as carbon monoxide or carbonic oxide. The new compounds are called respectively nickel and iron carbonyls, and have evidently a great future before them. Judging from chemical precedent, one would quite as soon have expected oil and vinegar to form a homogeneous mixture as a com- bination of the bodies referred to. In fact, so anomalous did it appear when Mr. Ludwig ]\Iond first brought the accidentally discovered nickel compound to the notice of the Chemical Society in the middle of 1890, that many almost refused to believe in the possibility of its existence. However, there is no doubt about it. Nickel carbonyl, a con- siderable quantity of which was exhibited at a cimnTSinidm' of the Royal Society held in -June last, and also at the meeting of the British Association, is obtained by merely passing carbon monoxide — a product of the incomplete combustion of coke or charcoal, and which may often be seen burning with a lambent blue tlame at the top of a clear tire — over the finely divided metal, and condensing the resulting vapour in a tube surrounded with ice and salt. Its properties have been very fully investigated botli by its discoverers, Messrs. Mond, Langer, and Quincke, and also by M. Berthelot, who published his results in the Comptrs riendu.s. It is a liquid of very high refractive power and brilliant appearance, and considerably heavier than water, under which it may be kept without change, provided the vessel is completely filled and the water contains no air. It solidifies at 13° F., and boils at 109^ F., and the vapour, if lighted, burns with a strongly luminous tlame, which appears smoky in consequence of the separation of metallic nickel. The liquid is very volatile, and if the vapour is suddenly heated a sharp detonation is caused. A mixture of nickel carbonyl with air takes fire if brought into contact with a very hot body, and occasionally explodes. A mixture of the dry vapour and oxygen may be detonated by simple agitation over mercury, and strong oil of vitriol produces the same effect in a few minutes. The vapour, when heated to 358'^ F., splits up again into its original constituents, the metal and the gas, and the nickel deposits itself as a brilliant coating on the sides of the vessel. Advantage is taken of this circumstance to apply the carbonyl to nickel-plating, and a patent has been taken out by its discoverers for working it on a commercial scale. At the last meeting of the British Association, Mr. Ludwig Mond described the various uses to which the discovery might be put, and the possibilities which it opened up. The nickel-plating can be accomplished by simply exposing the goods, after being heated to the temperature just mentioned, to nickel carbonyl vapour, and solid articles can be similarly formed by passing the vapour through heated moulds. For this jjurpose, it is found advantageous to dilute the vapour considerably with air. Nickel can also be deposited on any substance by treating it with the liquid itself, or better, by nickel carbonyl dissolved in suitable solvents. These processes possess a great advantage over electro-plating, as not only metal, but any substance, however intricate in design or fragile in structure, can be coated with a brilliant film of nickel by its means without the tedium and risk of first covering it with a surface of blacklead. Some very beautiful specimens of real flowers, plated with different metals, principally gold and silver, so as to bring out the various parts of their structure, were exposed for sale at the Frankfort Electrical Exhibition. A syringa blossom, for instance, would have its stamen and anthers plated with gold, its corolla with silver, and the stalk and calyx with copper. Needless to say, they found a ready market. The field before this new process is practically unlimited, for not only could it be applied to ornaments and articles of household use, but, if required, to delicate muslins, and dress or other fabrics. The liquid nickel carbonyl is highly poisonous, and, if injected siibcutaneously, acts very powerfully on the animal system, producing an immediate and remarkably prolonged fall of temperature. It might, perhaps, be introduced into medical practice as an antipyretic in the treatment of fevers, were it not for the difficulty of administering it in sufficiently small doses, and its intensely poisonous action. The carbon monoxide alone is the active agent in causing this effect, the symptoms being those of respiratory poison- ing ; and the blood of animals killed by it exhibits the same appearances as that of persons suffocated by inhaling the fumes of burning charcoal. This kind of poisoning is par- ticularly dangerous, and in cases of recovery the effects do not wear off for several hours after. The red corpuscles of the blood owe their colour to a complex chemical sub stance known as hagmoglobin, which acts as the carrier of oxygen. In passing through the lungs oxygen is taken up, and it is converted into oxy-luemoglobin, which, when placed so as to intercept the rays of light in the spectro- scope, gives quite different absorption bauds to the h;emo- globin itself; from the lungs the oxygen is carried to different parts of the body to be exchanged for carbonic acid, which is brought back to be eliminated and again replaced by oxygen, thus completing the cycle. Carbonic oxide combines with the htemoglobin to form carboxy- haemoglobin, an exceedingly stable substance which can only be displaced by oxygen with the greatest difficulty. The consequence is that the blood is unable to perform its functions, and the animal rapidly dies from suffocation. The absorption spectrum of this last body is remarkably characteristic and quite unmistakable, forming an infallible test in case of suspected poisoning by charcoal fumes. The vapour of nickel carbonyl is as deadly as the liquid, and is dangerous in air even to the extent of only 0-.5 per cent. The extraction of the metal from its ores is another valuable use to which the discovery of this compound will almost certainly be put. The principal sources of nickel are the copper-coloured arsenical mineral which the German miners — after working it unsuccessfully for years in the hope of obtaining copper — called kupfer-nukii (iu\, false copper), and in which the metal was first discovered by Cronstadt in 17-51, and s/n-isn, an impure residue formed at the bottom of the melting-pots in the manufacture of the bright blue pigment known as smult, which is largely used by paper-stainers. Metallic nickel is obtained f'-om these by heating them with charcoal in a furnace, but the product only contains about BO per cent, of the pure metal. It appears now that it will be sufficient to pass carbon monoxide over the crushed mineral, and by simply heating the resulting nickel carbonyl to 358^ F. chemically pure nickel will be deposited. All attempts to obtain a similar compound with other metals for a long time proved unsuccessful. As it seemed improbable that nickel should be the only metal forming such a compound, the investigators persevered with the 4 KNOWLEDGE r.jANUARY 2, 1893. work, and finally succeeded in volatilizing distinct quan- tities of iron in a current of carbon monoxide. The issuing gas burneri with a yellowish flame, and if passed through a heated tube deposited a metallic mirror in the glass, which answered to all the tests for iron with unusual brilHancy. The quantity produced was, however, very small, and the process exceedingly laborious, for it took no less than six weeks to volatilize about thirty grains of iron. Even under the most favourable conditions the gas never contained more than 02 per cent, of the compound, but by varymg the details of the process a much larger yield was obtained. The iron carbonyl thus produced is a pale yellow viscous Hquid, nearly half as heavy again as water. It distils without decomposition at 220" F., and solidifies below 6'^ F. into yellowish needle-shaped crystals. It decomposes slowly on exposure to air and, like the nickel compound, is completely broken up by heating its vapour to 356" F. On the other hand, it is much less active than its analogue and is not attacked by dilute oil of ^-itriol. Its composition was at first thought to be similar to that of nickel carbonyl, but on accurate analysis it was found to contain five proportions of carbon monoxide [Fe (CO).] instead of the four which consticute the latter [Ni (CO),]. Whilst engaged in some experiments on the utilization of water-gas (which is manufactured by passing steam over red-hot coke, and contains about 40 per cent, of carbonic oxide) for illuminating purposes by means of the Farnehjelm system, in which a comb of magnesia is raised to incan- descence by a number of fine gas jets. Sir H. E. Roscoe and Mr. Scudder noticed that a red deposit of oxide of iron was formed on the rods after the water-gas had impinged on them for a few hours. This was a very serious drawback, as the illuminating power became considerably reduced. As the experiments were being conducted in a steel works the first supposition naturally was that the stain was caused by fine particles of iron present in the atmosphere, but closer inspection showed that the deposit was of a " coralloid " structure and must, therefore, have been produced by the gas itself. In order to ascertain whether the iron existed in the gaseous state or was carried forward chemically, the gas was filtered through several tight plugs of cotton wool. No difference, whatever, was observed and it was concluded that the gas contained a very minute quantity of a volatUe compound of iron. Shortly after it was sub- jected to various chemical tests, which left very little doubt as to its identity with iron carbonyl. Coal gas has also been found to contain iron, derived, no doubt, from the slow action of the 7 or H '"/. of carbon monoxide it contains on the iron of the mains and gas pipes. This accounts for the hitherto unexplained black stain so frequently observed on steatite and other burners. Compressed coal gas has begun to take the place of hydrogen in the production of lime-light, and the stain formed on the lime cylinders is very noticeable, being, it is almost needless to say, somewhat of a drawback to its use. The discovery of this series of compounds is quite a i-evelation to the metallurgical chemist, and already explains many mysteries. In the cementation process for the manufacture of steel, bars of iron are embedded in powdered charcoal, and kept at about the melting point of copper (2192'-' K.i for eight or ten days. Steel, as is well known, is an alloy of iron, with a combination of carbon and iron, called carbide of iron, and the principle of all ateel-making is the same : carbon must be added to soft iron in definite proportions. If the iron contains no carbon it is comparatively soft and malleable. Wrought iron contains less than 0-3 '',v, of carbon ; steel from 0-3 to 1-5 7 : above this the metal takes the character of cast- iron. The charcoal which surrounds the bars of iron in the process just referred to, occludes a large quantity of air in its pores, which, when heated, forms carbonic oxide. This gas permeates the iron and gives up its carbon to the metal, returning again to take up a fresh supply from the charcoal, and thus acts as a carrier of carbon to and fro in the interstices of the iron, which it gradually converts into almost homogeneous steel, known technically as hlister- fiteel, owing to its peculiar vesicular appearance caused by the penetration of the gas. These compounds must play a very important part too in the blast furnace, and in both the Siemens and the Bessemer process, especially the latter. Bessemer steel is made from cast-iron ; the carbon and impurities are burnt out of it by driving a current of air through the molten metal. When this has been accom- plished, a highly carburetted cast-iron, called npiciiclcisen, is thrown into the converter in properly regulated quantity, and the carburation of the iron is rapidly eft'ected. Renewed attention has recently been directed to some volatile compounds of platinum with chlorine and carbon monoxide, which are broken up by water with deposition of pure platinum, thus forming a possible way of extracting the metal from its ores. If any discovery of this kind were to facilitate the extraction of gold, which at its present rate can barely keep up with the demands of the increasing consumption, an immense boon would be con- ferred on the civilized world. CATERPILLARS.-III. By E. A. Butler. {Continued from pane 229, Vol.w.) IN some caterpillars the usual complement of ten prolegs is greatly reduced, only the last two pairs being present ; thus all the six central segments of the body are left without means of support. This, of course, necessitates a special method of progression, the wave-like motion already described being clearly impossible. Caterpillars of this kind take a firm hold alternately with the two ends of the body, the central part being by turns arched up and extended, as the animal advances, not with the creeping motion of small paces, but with the stately gait of long strides. Thus, when the insect is in a fully extended position and wishes to advance, it clings tightly with its six true legs, and then, releasing its claspers and lifting the hinder part of the body, hooks them on again close up to the legs, thereby causing the intervening portion of the body to assume the form of a perpendicular loop ; then, holding tightly by the claspers, it lifts the legs and advances the fi'ont part to the fullest extent, straightening out the loop and bringing itself again into its former horizontal position. From tlieir peculiar mode of walking, by curves and loops, caterpillars of this kind are called geometers or loopers. They are always long, narrow, thin-bodied creatures, usually green or brown in colour, and often with the head divided on the crown into two prominences like faint indications of horns. They are noted for the extraordinary positions they assume, and the remarkable way in which they mimic little twigs or stems. When at rest, the body is usually kept straight and stiff at an acute angle to the twig, inclined to about the same extent as the twigs themselves are to the main stem, the mechanical difdoulties of such a position being met to some extent by an exceedingly fine thread of silk stretching from the spinneret to the twig, or less frequently by the anterior legs clasping another twig in the neighbourhood. The silken thread provides means of January 2, 1893.] KNOWLEDGE suspension in the air if a sudden displacement of the claspers should take place, and sometimes prevents a fall to the earth, and saves the consequent labour of getting over uneven ground to reach the tree trunk and then climbing, perhaps, many feet of rough bark before the former position can be regained, and at the same time it forms a considerable security against the fatal results which might follow from striking against intervening branches while falling with gradually increasing velocity. The general resemblance to a small twig, caused by the cylindrical shape and the brownish colour, is often heightened by the presence on the backof excrescences of various kinds, similar to what may be seen on the twigs of the food-plant. A very abundant insect, the caterpillar of the brimstone moth (Bw'iia cratmiata), a pretty sulphur-coloured moth with a few reddish patches and streaks, and a common inhabitant of gardens in summer-time, may be taken as an excellent exemplification of this. It is tinted with almost exactly the same mixture of purplish and reddish brown as the twigs of its commonest food-plant, hawthorn ; its thick- ness is about that of the young twigs amongst which it lives, and halfway down its back it bears a wart-like excrescence which very closely resembles the knotty little protuberances seen in similar positions on short stumpy twigs of hawthorn. This same insect exhibits also another very beautiful arrangement whereby the resemblance to a twig is rendered still more perfect. When the two pairs of claspers are in position grasping a twig, it is evident that, if that part of the body which lies between them were of the usual shape, evenly cylindrical in outline, there would be a space between its under surface and the twig, which would be thrown into shadow, and the presence of this clearly-defined dark line of shadow just where the pretended twig ought to pass uninterruptedly into the parent stem would be a flaw which would detract from the perfection of the mimicry. Hence we find that the skin between these two pairs of claspers runs out into numerous little irregularities, forming flaps which reach to the twig itself, and therefore break up the shadow and soften the contact with the stem. If this irregularity of outline were found all along the body, it would hardly be safe to lay much stress upon its presence bet>veen the hind legs ; but this is not the case. The fringe occurs only where the body comes into contact with the twig, and its presence just where it is needed, aud its absence elsewhere, lend probability to the above explanation of its function. A thoughtful consideration of cases such as this will serve to show what an endless field of iuvesiigation is opened up, when even the knobs and humps aud ex- crescences of caterpillars are found to be not the mere meaningless freaks of some sportive and erratic force, as they at first appear, but exquisite adaptations whereby the organism has been brought more completely into harmony with its environment ; adaptations, therefore, which have some bearing either upon its preservation amidst its present conditions of life, or upon its past history and the course of events which have constituted its life as a species. In this latter connection we may refer to the caudal horns of the caterpillars of the hawk moths (Sp/iiniiidir). These insects have on the back of the last segment but one a curved horn, which contributes in no shght degree to the air of stateliness that characterizes them when they assume the sphinx attitude. The hom usually points more or less upward, and shows only a single curve, but in some cases, as in the death's head moth (Aclurontia Atropos), it is depressed, and doubly curved into an S-shape. When a hawk moth caterpillar is first hatched, the horn is much longer, proportionately to the body, than when fully grown ; it is also straight, almost erect, and forked at the tip (Fig. 7), and its surfasd is bsjet with prickles. As the insect grows, the prickly tubercles on the horn become, in some species, less conspicuous, aud finally entirely disappear, the horn becoming smooth and polished ; in others they are retained throughout life. Fi&. 7. — Caudal lioru of CoiivoItuIus Moth Caterpillar, at different stages. A, B, f, magnified 58, 3, and 2 diameters; D, natural size. The magnification is not suffieient to slion- the tubercles. (From Poulton.) The forked appearance of the tip disappears after the second moult, and the horn curves more and more downwards. Not only is the horn of the newly-hatched larva thorny, but the whole surface of the body is covered with minute tubercles, each of which emits a small hair^ In some species, such as the poplar and eyed hawk moths, these tubercles are retained throughout life, giving rise to that roughness of skin which is described as shagreening. In other cases, such as the privet hawk moth, they are lost after the early stages, and the skin becomes quite smooth. In this f.i.mily of moths, then — a family whicli consists of insects whose general resemblance testifies to their real relationship — we see caterpillars that commence life with well-marked characters, which they afterwards lose to a greater or less extent. Such characters do not seem to bear any special relation to their present surroundings, and may therefore be fairly regarded as common ancestral relics, implying that the insects are descended from progenitors with forked and tuberculated horns. Some of the species, however, have advanced farther from this ancestral condition than others. There is another family of large and handsome moths, very different in shape, style, and habits from the hawk moths, but nevertheless exhibiting some curious resem- blances to them in the caterpillar condition. This is the family Saturniilir, or emperor and silk-producing moths, distinguished by the coloured or transparent, circular or crescent-shaped eye-spots in the centre of the wings. The family is very poorly represented in Great Britain, only two species, the Kentish glory and the emperor moth, being native with us. The former of these is in some respects very unlike its associates, and the caterpillar is quite distinct; but the emperor moth {Saturnia carpini) may be regarded as a good illustrative type of the group. Thfi caterpillars of this family are generally large and fleshy creatures, adorned with rows of rounded tubercles from which spinous hairs project. Our British species is a bright green insect with a row of pink tubercles on each segment. In some species there are not only the usual tubercles, but various spines or hornlike projections as well in diflerent parts of the body. These show a tendency to be developed about the thoracic and caudal regions. In some cases the spines are single-pointed, but in others forked and tuberculated. Moreover, when the spines are large, the tubercles on the rest of the body are small, as though the spines were enormously-developed tubercles, which, by reason of their superior protective p iwers, could afford to dispense with their smaller and weaker brethren. But the most remarkable facts of all are to be found in connection with the caterpillar of the Tau emperor (Aglia tau), a species about 2^ inches in expanse of wings, and so KNOWLEDGE [January 2, 1898. uamed from the white T-shaped mark contained in the blue " eyes" on its wings. This fine insect is found in several parts of the world, including some Em-opean coTintries, though not in Britain. The newly-hatched caterpillar is green with five red-forked and tuberculated horns (Fig. 8), two pointing straight forward above the head, Fig. S. — Yiiung larva of Tan Emperor Motli, magnified 7 clianietiTs. (After Poulton.) two projecting from the sides of the thorax, and one pointing upward and backwards from the dorsal surface of the last segment but one, just the position of the caudal horn of the Sjihiiiifidir. The hair-bearing tubercles on the rest of the body are also present, but small. This remarkable appearance is retained by the caterpillar during its first three stages, but at the next moult the whole of the apparatus of spines and tubercles suddenly and entirely disappears, the only trace of the former condition being a general shagreening of the body similar to that of some of the hawk moths. There are now also other resemblances to the SjiliiniihUe, such as the assumption of the sphinx attitude, and the presence of oblique coloured stripes on the sides. Facts such as these, pointing as they do to a kinship between the two great families of hawk moths and emperor moths, evidently impart a new inte- rest to the caudal horn of the former, and suggest that it may be the solitary and modified remnant of a complete ancestral armature, a monument of bygone times, and a key to the past history of the race. A curious point is suggested in connection with these horns, viz., as to the accommodation within the oval egg- shell for caterpillars of shapes so awkward for packing up into a small compass. The problem is not in all cases solved in the same way. Before hatching, the horn of the Sphiii'iid'i is flexible, and is bent round along the sides of the eggshell ; but a different method of stowage is adopted in the case of A;ilia fan. Here there are five horns instead of one to be packed away, and tliey would evidently get rather in the way if dealt wth in the same manner. Accordingly, it is found that they are not of full size in the egg, but appear as small curled tubercles, which expand to the full form and size aftn- hatching, by the passage into them of blood from the body, in much the same way as the wings of a Lepidopterous insect are expanded after it has left the chrysalis. From horns, tubercles, spines and tails the transition is not difficult to hairs — in fact it is not easy to say where spines cease and hairs begin ; the structures arc similar in plan, and differ chiefly in diameter and in the degree of flexibility or stiffness tjiat results therefrom. Hairs and spines may be either simple or branched. Good examples •of branched spines may be seen in the caterpillars of many butterflies, such as the tortoise-shells, peacock, red admiral, painted lady, and fritillaries. Densely hairy larva; are specially characteristic of the group of moths called Bombyces (tigers, ermines, eggers, &c.). The common "woolly bear," or caterpillar of the garden tiger moth I Anti,, r„i„\, mav be taken as the most familiar example. Fm 9.— Hiiirs of Tiger magnified. of Caterpillar Moth, niiieh The hairs here emanate from small white tubercles placed on a velvety black body ; in fi-ont and at the sides they are rust-coloured, but on the rest of the body black tipped with white. To the naked eye they seem to be simple, but the microscope easily shows them to be finely feathered (Fig. 9), with minute branches placed at considerable intervals alternately along the main stem. Their length is so great that their effect is to more than treble the insect's apparent diameter : they are, moreover, pre-eminently elastic and recoil powerfully when bent. When disturbed, the catei-pillar rolls itself into a ring, and the hairs, then radiating in all directions, make it a most difficult object to handle, their elasticity causing it to elude the grasp again and again, so that it is impossible to seize it firmly. Obviously, therefore, they are a valuable means of protection. The habit of rolling into a ring is closely connected with the hairiness of the larva, the one fact indeed being the complement of the other ; as with the hedgehog, the only vulnerable parts are by this means protected, and it is easy to see that a smooth caterpillar would gain little by the device. Hence we find that the habit of rolling into a ring is very prevalent amongst densely hairy caterpillars, though not universal ; moreover, it is a habit not entirely confined to such larvfe, though much commoner amongst them than in other groups. It is often said that hairy caterpillars are avoided by birds ; but this again is not universally true. That extremely shaggy creature, the larva of the fox moth (Luxinfampa nilii), than which it is scarcely possible to imagine anything hairier, might, one would suppose, be a sufficiently disagreeable mouthful ; yet the Rev. Harpur Crewe speaks of a bee- eater, which one autumn visited the Scilly Islands, as having lived principally upon these larvte ; it seized them with its beak, and then, beating them on the ground till they were dead, swallowed them whole. The distribution of the hairs varies very much in different species. When they are fine and collected m closely-compacted tufts along the back, like a row of shaving brushes cut oft' Hat at the top, they form what are called "tussocks" (Fig. 10). The most beautiful example of this is the caterpillar of the pale tussock moth {Ihisychii-n jiuilihiDiihi), an insect of a very pale and delicate green colour, with velvety black crescentic bands at the junctions of the central segments. These black patches are not seen under ordinary circumstances, being concealed by the overlapping of the segments, but they are suddenly revealed when the insect bends its its terrifying attitude, and more distinctly adopts its final refuge and rolls into the back are four large dense tussocks yellow colour, in startling contrast to them, which by the effect look more cuusiiicuous and Fig. jo.— Central segments of body of Caterpillar witli tussoeks. head under in still when it a rmg. On of a bright the l)lack bamls between of irradiation make them larger than they really are ;■ at the hinder end, in the position of a caudal horn, is a sort of tail consisting of a brush of rose-coloured hairs. This lovely caterpillar, one of the most exquisite of J5ritish species in the delicacy and purity of its tints, is common in most places, and may be found in the summer feeding on a variety of trees ; to the country folk it is known as the *' hop-dog." Tlie hairs of Januaky 2, 1893.] KNOWLEDGE the tussocks very easily come out, though the tussocks themselves look solid anil unyicldiug, and seem to be the most appropriate parts for an enemy to seize upon ; but if they be roughly seized, their silkiness causes them to slide from the grasp, the caterpillar thus escaping: and leaving with its would-be captor a little bundle of tickling hairs as the only trophy. Mr. Poulton has pointed out that the tuesocks may in this way be of some protective value. He ofl'ered a "hop-dog" to a hungry green lizard. The animal was apparently experienced enough to know the deceptiveness of the tussocks, but, nevertheless, the promptings of hunger were imperative and it resolved to make a venture, but it carefully avoided the tempting tufts and kept trying for some minutes to find a more suitable point for attack ; it finally seized the caterpillar on the back some distance behind the tussocks, whence the moral seems to be that a less hungry assailant would probably have left the hairy morsel alone. A somewhat similar caterpillar, that of the vapourer moth (Onjijia nntiiiua), on being offered to another and, as it proved, less cautious lizard, was at once seized by the tussocks, but its assailant had the mortification of losing its prey, and getting only a mouthful of hairs for its pains; these were by no means to its taste, and it thus learnt a lesson of prudence by the experiment, and made no attempt to mend its fortune by any other venture in the same direction. (To be cuittiinieil.) THE NUMBER AND DISTANCE OF THE VISIBLE STARS. By .J. E. GoKE, F.R.A.S. THAT the visible stars are not uniformly scattered through space, and are not of uniform size and intrinsic brightness, is clearly shown by modern researches. Measures of stellar parallax show that some small stars (that is, faint stars) are actually nearer to our system than many of the brighter stars, while the period of revolution of some binary stars shows that their mass is relatively small compared with the brilliancy of their luminous surfaces. We may, however, perhaps assume that the stars out to some limited distance in space are scattered with some rough approach to uniformity. We can at least calculate the average distance between the neighbouring stars, which would give a certain number of stars in a sphere of given radius. This is easily done by supposing the stars placed at the angular points of a tetrahedron. A tetrahedron is a solid figure bounded by four equal surfaces, each surface being an equilateral triangle. It is clear that in such a solid each of the angular points is equidistant from the other three angular points of the figure. If e be the length of the side of each equilateral triangle (or edge of the tetrahedron) it may be eas:ly shown, that the volume of the tetrahedron is ^V ''' ^ '• ^^ ^^e make e=l the volume is jV ^'-. Now it is clear that the number of equidistant points contained in a sphere of given radius will be equal to the number of these tetrahedrons which the sphere contains. If '■ be the radius of a sphere, its volume will be f IT J-*, and if n be the number of equidistant points or stars contained in the sphere, we have J n r''=ii x Jj ^^-, whence r = v'^^^, and n -= r x 35-548. From these formuliB we can compute the radius of a sphere containing a given number of equidistant stars, or the number of stars contained in a sphere of given radius. This formula, however, only applies to a sphere of a radius large in comparison with the distance between the stars distributed through it. For if we make e=i=l. or the distance between tlie stars equal to the radius of the sphere, the formula would give 35 equidistant stars in the sphere of unit radius. This number is evidently too groat, as the number of stars which can be placed on the surface of a sphere of given radius, equidistant from each other and from the centre of the sphere, is only 12. The difference is clearly due to the fact that in this case the volume of the tetrahedron is so large in proportion to the volume of the sphere that the latter cannot be acci ritely divided into tetrahedrons. In the case, however, of a sphere whose volume is large in proportion to the volume of the tetrahedron formed by four adjacent stars, the formula will be approximately correct. Let us call the distance between two adjacent stars the unit ilistcinrr. Now considering a Ccntauri, for which the largest parallax has been found (about 0-70"), it is obvious at once that this star cannot be at the " unit distance" from the sun. For if a Centauri was at the " unit elistance " we might expect to find some ten or eleven other stars with a similar large parallax. Such is, however, probably not the case, and we may therefore conclude that this star is comparatively near our system, and forms an exception to the general rule of stellar distance. To make this point clearer, let us see what number oi stars should be visible to the naked eye — say to the sixth magnitude inclusive — on the assumption that the distance between the sun and a Centauri forms the " unit distance" between two stars of the visible sidereal system, or at least that portion of the system which is visible without a telescope. To make this calculation it will of course be necessary to assume some average distance for stars of the sixth magnitude, based on actual measurement. Now Peters found an average parallax of 0-102" for stars of the first magnitude, Gylelen found 0-083", and Elkin 0-089". These results are fairly accordant, and we may assume the mean of these values, or 0-09" as the mean parallax of an average star of the first magnitude. With a "light ratio" of 2-512, the light of a fir.=t magnitude star is 100 times the light of a sixth, and hence the distance of an average sixth magnitude star would be ten times that of a first. Its parallax would therefore be 0-009." Hence the radius of a sphere containing all stars to the sixth magnitude mclusive would be ^.l^^ or 84--1 limes the distance of a Centauri. Hence we have ?^=(8i•4,3x 35-548=21,372,000, a number enormously greater than the known number of stars to the sixth magnitude. This leads us to doubt whether the mean parallax of sixth maguituele stars is so small as 0-009". I find that the sun placed at the distance indicated by this paiallax would shine only as a star of the eleventh magnitude ; that is, a sixth magnitude star would be five magnitudes, or 100 times brighter than the sun placed in the same position. If of the same intrinsic brilliancy of surface, this would imply that an average sixth magnitude star has ten times the diameter of the sun, and therefore 1000 times its volume ! Some sixth magnitude stars may possibly exceed our sun in size, but that the afeiw/e volume of these small stars is 1000 times that of the sun seems wholly improbable. Certainly the calculated masses of those binary stars for which a parallax has been deter- mined do not give any grounds for supposing that such enormous bodies exist among stars of the sixth magnitude. Assuming, however, that the parallax of a first magnitude star is 0-09", and that of a sixth magnitude is one-tenth of this, or 0-009", let us see what number of stars should be visible to the sixth magnitude. As already stated, the number of equidistant stars which can be placed on the KNOWLEDGE. [January 2, 1893. surface of a sphere of unit rndius is 12. Hence, on the surface of a sphere of double this radius, four times the number, or -18 equidistant stars may be placed ; on a sphere of three times the radius, nme times the number. and so on. Now the sum of ten terms of this series 1-, 2", 3-, etc., is 385, and as the twelve stars which may be placed on the first sphere nearly represent the number of stars of the first magnitude and brighter visible in both hemispheres, we have the total number of stars to the sixth magnitude inclusive, 88.5 x 12 = 4620. Now the number of stars to the sixth magnitude in both hemispheres as observed by Heis and Gould, is 4181, and the number contained in tlie " Harvard Photometry" and the rianometrin Ar(ientina is 37.*)5, so that the number of stars computed on the above principle does not differ widely from the number actually observed. Let us see, however, what the unit parallax would be for the observed number of stars to the sixth magnitude, assuming a parallax of 0009'' for stars of this magnitude. Taking the number as 3735, we have by the tetrahedron formula ) = \^|i|l=4-7187 times the average distance between the stars, and since )•=''"—, we have the " unit parallax " =c xO-OOn' ^-4-71H7x0009 ^0-042408; thatis, the mean parallax of the nearest stars to the earth would be 0-042". Excluding stars with a large parallax, this may not perhaps be far from the truth. I find that in 31 binary stars brighter than the sixth magnitude (and for which a parallax has not yet been determined), the average " hypothetical pfaallax" — or the parallax on the assumption that the mass of the system is equal to the mass of the sun— is OOCH". If we assume the mass of each of these systems to be, on an average, twice the sun's mass, we must divide this by the cube root of 2. This gives for the average parallax0054", which does not differ widely from the unit parallax found above for stars of the sixth magnitude. But we are still confronted with the difficulty that with a parallax of only 0-00!(", stars of the sixth magnitude would be on the average considerably larger than the sun. The same remark applies to stars of the sixteenth magnitude, for which the parallax would be (with the light ratio of 2'512) only 0-00009". Placed at this vast distance the sun would, I find, be reduced to a star of magnitude 21-3, and would, therefore, be utterly invisible in the largest telescopes yet constructed. It would be over 100 times fainter than a star of the sixteenth magnitude ! To reduce the sun to a star of the sixth magnitude, it should be placed at a distance corresponding to a parallax of 0-1". Unless, therefore, stars of the sixth magnitude are, on the average, considerably larger than our sun, we seem justified in thinking that their average parallax is not less than one-tenth of a second. But, as has been stated, this is about the average parallax of stars of the first magnitude, and it is difficult to believe that these bright stars are as far from the earth as the comparatively faint stars which lie near the limit of naked eye vision. There seems, however, no escape from the conclusion that sixth magnitude stars are probably nearer to us than their brightness might lead us to suppose, and to explain the difficulty with reference to the bright stars, we may perhaps assume that their brilliancy is due rather to their great size than proximity to our system. From the small parallax found for Arcturus, Vega, C'apella, Canopus and other bright stars, we have good reason to think that these stars are vastly larger than our sun. Spectroscopic obsoivations of 'C Ursie Majoris indicate that this second magnitude star has a mass about forty times the mass of the sun, and possibly other bright stars may have similarly large masses. Wirins and a Centauri, however, form notable exceptions to this rule. Assuming an average parallax of 0-1" for stars of the sixth magnitude, the parallax of a star at the " unit distance " from the sun would — on the tetrahedron formula — be 0-47". This is about the parallax found for 61 Cygni, and does not much exceed that of Sirius. There are several other stars with a parallax of somewhat similar amount, and possibly there may be others hitherto undetected. With a parallax of 0-1" for a sixth magnitude star, the parallax of an eleventh magnitude would be 0-01", and that of a sixteenth magnitude 0-001". Now, with the unit distance corresponding to a parallax of 0-47", let us see what would be the number of equidistant stars con- tained in a sphere of radins equal to the distance of a sixteenth magnitude star. We have r=JJ-^, or 470 times the distance between the adjacent stars. Hence n = (470)' x35-548=3, 690,700,000, a number about 36 times greater than the number of the visible stars, generally assumed at 100 millions. According to Dr. Gould's formula (sum of stars to //i"' magnitude inclusive = 1-00.51 X (3-9120) '"), the number of stars to the sixteenth magnitude would be 3,024,057,632, or about 30 times the number actually visible. Probably, however, we are not justified in assuming a uniform distribution of stars to the sixteenth magnitude, most of these faint stars belonging to the Milky Way. Professor C'eloria found that, near the pole of the Galaxy, a small telescope which showed stars to only the eleventh magnitude revealed as many stars as Herschel's gauging telescope of 18-8 inches apertux-e. Here, therefore, we seem to have the extension of our sidereal system limited to the distance of eleventh magnitude stars. Let us now assume a uniform distribution of stars to the eleventh magnitude. With a parallax of 0-01", and a " unit parallax" of 0-47", we have (■=(47)3x35-548 = 3,690,700. The number by Gould's formula is 3,283,876. Both ■ results are largely in excess of the number actually visible, and show, I think, that there is probably a " thinning out " of the stars before we reach the eleventh magnitude distance, at least in extra galactic regions. If we suppose that of the 100 millions of visible stars, 50 millions are scattered uniformly through a sphere, with a radius equal to the distance assumed for stars of the eleventh magnitude — the remaining 50 millions being included in the Milky Way — we have an average " unit parallax '"" for these 50 millions of aboutO-ll', which seems to indicate a " thinning out" of the stars towards the boundaries of the sidereal system. If this be so, we may conclude that the stars with a larger parallax than 0-11" are exceptions to the general rule of stellar distribution, and form perhaps comparatively near neighbours of our sun. These near stars seen from the outskirts of the visible universe might perhaps form a small open cluster. Thus the parallax of a Centauri being 0-76'', the distance of a sixteenth magnitude star would be 760 times the distance of a Centauri, and it follows that the sun and a Centauri seen from a sixteenth magnitude star — equally distant from both — would appear as two faint stars about i^ minutes of arc apart. The above results are of course based on the assumption that the faint telescopic stars lie at a distance indicated by their brightness. Such, however, may not be the case. Many of these small stars may be in reality absolutely small. The apparently close connection between bright and faint stars, as shown by photographs of the Milky Way near a Cygni and a Crucis, suggests that bright naked eye stars and faint telescopic objects may, ia some cases at least, lie in the same region of space. If this be so, the * Tliat is, the panillnx of a sUii- as seen from its iioiii-est neighbour. Januaby 2, 1893.] KNOWLEDGE 9 difference in the size of these distant suns must be enor- mous, and would lead us to the conclusion that possibly the Jlilky Way may not lie so far from our system as has been generally supposed. If, as has been suggested, there is any extinction of light in the ether, the faintest stars cannot be placed at a distance corresponding to their apparent brightness. Sfttnrc Kotfs. In a letter recently received from Prof. G. E. Hale, he says that the contract for the Yerkes 40-inch refractor has been given to Messrs. Alvan Clark, and that "Sir. Clark is now at work upon the discs doing the rough grinding. Messrs. Warner and Swasey have been given the contract for the moimting, and they expect to have it set up in Chicago before the summer is over. — .-♦-, — Mr. Burnham has definitely decided not to devote him- self again to astronomy professionally, but he will be given every facility for using the great instrument. Prof. G. E. Hale has recently obtained, at the Kenwood Observatory, Chicago, a photograph of the spectrum of a solar prominence, showing 74 bright lines in the ultra- violet between X 3970 and A 8630. A 4-inch grating was used on a 12-inch refracting telescope, with glass objectives for the collimator and telescope of the spectroscope. In the x^hotograph obtained all the lines are shown which have been previously photographed by M. Deslandres, of the Paris Observatory, with apparatus in which no glass is used ; and in addition to these, 32 lines appear which have not been previously photographed. Science Gossip contains a highly interesting paper by Mr. P. L. Simmonds, F.L.S., on animal plagues. After giving some statistics with regard to the enormous numbers of human beings and cattle amiually lost by death from snake-bites, or from lions, tigers, wolves, and crocodiles, he gives an account of the rabbit plague in Australia. Speaking of India, he says that in 1889, 25,204 persons were killed by wild animals and snakes — chiefly the latter. In Australia it is reckoned that kangaroos consume on an average as much grass as sheep ; hence it is very im- portant that their numbers should be reduced. But rabbits (introduced by Europeans) are the chief plague. The extent of the evil may be imagined from the fact that 15,000,000 rabbit skins have been exported from New South Wales in one year ; and that in the thirteen years ending with 1889, 39,000,000 rabbit skins were exported from Victoria. The property destroyed by rabbits is esti- mated by millions of pounds. In spite of the determined efforts that have been made by colonial governments and private individuals, there are some districts where it has become a question whether the farmers can keep up the struggle with them. The fencing off of small districts with wire netting seems to be the best means that has been tried of keeping them out of a particular district. — .-♦-, — Since Darwin's investigations on so-called " carnivorous plants,"' a great deal has been written on the habits and powers of these remarkable organisms, but the question how flies, &c., were dissolved and digested seems to have remained unsolved. It is now maintained that digestion in the case of carnivorous plants is due to the activity of certain micro-organisms, which are always present in the sap of the mature plant, and that their secretions are favourable to the development of such minute organisms. Dr. Francis Galton and other eminent anthropologists have issued a circular letter on behalf of the committee appointed by the British Association, for an ethnographical survey of Great ]5ritain. It is proposed to take certain typical villages and their surrounding districts and to record the physical types of the inhabitants, their current traditions, the peculiarities of dialect, the monuments and other remains of ancient cultivation, and historical evidence as to continuation of the race. A correspondent (Sereno E. Bishop) writes to Xiitnrc from Honolulu (November 8th) to say that during the last three weeks there has been a remarkable renewal of the " afterglow.'' It seems as if the dust tioating in the upper atmosphere, which produces the afterglows, had been added to. Is this owing to the August eruption in Alaska, which is said to have distributed volcanic ash at a distance of 250 miles "? The writer says that no such afterglow has been seen since 1886, or three years after the Krakatao eruption. — •-♦-, — The famous German Professor Rudolf Virchow receives this year the Royal Society's Copley medal for his researches in pathology and prehistoric archasology, Sir Joseph Hooker receives the Darwin medal, as being one of the earliest supporters of the author of "The Origin of Species," and Mr. .1. N. Langley receives a Royal medal for his researches on the secreting glands and on the nervous system. Norwich Castle, an ancient building of historical interest, has been acquired by the committee of the Norfolk and Norwich Museum with a view to the transfer of their valuable collections as soon as the castle has been fitted up for the purpose. When the scheme is completed, the trustees are to make over the building and collections to the Corporation, who have agreed to accept the trust, and to hold the castle and its contents for the benefit of the citizens of Norwich. It is to be hoped that the good example thus set may be followed in other places. The Castle Museum Committee are fortunate in having Lord Walsingham for their chairman. He is an ardent naturalist, whose important contributions to the British Museum of Natural History are well known. From The Geoloi/icul Mai/azine we learn that Bristol* is following on the same lines. At a recent meeting of the shareholders of the Bristol Museum and Library a resolution was adopted for the transference of the institu- tion to the Corporation of Bristol. By a generous offer of =£3000 from Sir Charles Watken, together with a small endowment fund, the liabilities will be cleared off. The December number of T/w Field Cluh contains the following story, from a correspondent, of a rat that has acquired the habit of catching trout : " Within a mile of where I now write, on the Braid Burn, which runs through Blackford Hill public park, Edinburgh, I have seen a rat — not the ordinary grey species, but the black, with short head, not unlike that of a guinea-pig — dive after and catch a trout, bring it to the bank, and devour it. An old quarry- man, who worked by the stream, first told me of the rat's habit, and together we have watched him creep along the branch of an alder overhanging a small pool, sit immovable, as if part of the tree, until a trout swam within his ken, when, like a flash, he dived after his prey, and almost invariably succeeded in his sub-aquatic chase." 10 KNOWLEDGE [January 2, 1893. Not only is electricity being now largely used in the production of aluminium from clay, but in other directions also electricity is being made extremely serviceable. For exampb, the manufacture of caustic soda, which was hitherto a slow process, is being carried on fi'om brine by the aid of electricity, chlorine and other chemical products being obtained at the same time. As compared with present methods, the new process is at least fifty per cent, cheaper, and much simpler. The chlorine, which is very valuable, is saved for the production of bleaching powder. It seems probable that the chemical industries of the country will be greatly modified and benefited by the elec- trical methods now being introduced. At the recent anniversary meeting of the Eoyal Society, the president (Lord Kelvin) referred in his address to an extra number of the " Proceedings " (No. 310) which is devoted to a first report of the Water Itesearch Committee on the present state of our kmw ledge concerning the bacteriology of water, by Professors Percy Frankland and Marshall Ward. This committee was appointed by the society, in alliance with the London County Council. The report is full of most valuable information regarding the vitality of micro-organisms in drinking water, to which in a large measure the spread of Asiatic cholera, typhoid fever, and other zymotic diseases is now known to be due. Mr. W. H. Preece, the well-known electrician, has succeeded in sending a telephonic message from the shore of the Bristol Channel, near Cardiff, to the island of Flat- holm, three miles off, without the intervention of a con- necting wire. This truly wonderful result seems to open out a great vista of future possibilities. A HIGHLY interesting discovery of human remains has lately been reported from the Riviera. The caves in which the bones were found were discovered in 1872 by a W. Riviere, and since that date explorations have been vigorously carried on. The skeletons that have been discovered belonged to a long-headed (dolichocephalic) race, and the individuals they represent were e%idt ntly strong and muscular. Three more skeletons were discovered early last year, one of which represented a tall man, whose height was about 6 feet C inches ; with these bones were found necklaces made of fish bones, canine teeth of stags, shells, &c. Some of the stone implements found with the bones were finely worked, but none of them polished, and some of the bone implements were very rudely made. Many mamma- lion bones were also found, but none of extinct species, or even ot reindeer. But the absence of polished stone imple- ments seems to indicate an early period in the stone age — say the beginning of neolithic times. There is still one cave unexplored, and the Prince of Monaco, whose property it is, has given orders that the work of excavating it is to begin next spring. One curious fact about the human bones here discovered is, that those belonging to adults are all f jund to have been painted red with peroxide of manganese ; and the Marquis de Nadaillay, who reports the discovery in Science (September 23rd), says that a similar custom was observed by some Indian tribes. — I • I — The remains of ancient lake-dwellings, well known in Scotland and Ireland under the name of " crannogs," are very scarce in England. But Dr. R. Mnnro, in the Times of October '24th, calls attention to a newly-discovered example in Somersetshire. The discovery was made by Mr. Arthur Bulleid, of Glastonbury, whose observations are of special interest. The site of this ancient lake-village is about a mile north of Glastonbury, on the road to the village of Godney. A number of low mounds were noticed here, each rising from one to two feet above the surrounding soil, and extending 20 to 30 feet across. Excivations having been made, some of the original piles were dis- covered. The total number of mounds is between sixty and seventy, and they extend over an area of some five acres. Each mound, it seems, contains a fireplace. The hearths were generally formed of large stone slabs, placed over a bed of clay, or of small stones embelded in it in the form of a pavement. An old seventeenth-century map of the district shows that it contained a lake called " The Meare Poole," into which three streams found their way. This pool was not far dist.mt from the site of the present discovery. It is probable that the lake once covered a larger area. Bronze rings, fibulie, a broach, and a few decayed iron objects have been found here ; pottery is abundant ; also articles of bone and horn, and some flakes and cores of flint. Articles of "late Celtic" date pre- dominate, and at present nothing Roman has turned up. It is to be hoped that this interesting site will in time be thoi-oughly excavated. — •-♦-• — There has lately been some discussion in one of our evening papers on a question of considerable importance to " the masses," viz., whether tinned meats, shell-fish, fruits, &c., are sometimes poisonous, and what are the causes that produce the jroison. One cause is supposed to be the lead used in some inferior kinds of solder. The lead is believed in this case to be dissolved by meat acids, or the acids of fruit, as the case may be. Another supposed cause is the presence of bacteria in- meat, shell-fish, &c., owing to insufficient boiling before the tin is soldered up. Another and more obvious cause is the occasional cracking or breaking of a tin, so that air gets in, and that of course would start decomposition. It is comforting, however, to find that one writer denies the possibility of lead poisoning, and maintains that every precaution is taken by the leading American firms to secure complete sterilization by means of the hot bath. In cases where air has afterwards got in through a crack, the smell ought to bo a sufficient indica- tion of the fact. The deaths from eating tinned foods appear to be a very small percentage when the millions who use tinned eatables are taken into account. WHAT IS A NEBULA? By A. C. Eanyard. IN the article under the above heading published in the October number, it was shown that nebula? are as a general rule extremely transparent, and that the density of the larger nebulfc must be very small, the density of the Orion nebula being probably less than one ten thousand millionth of the density of our air at the sea level. The Orion nebula shines with a faint green light, giving a gaseous spectrum, and if it were a quiescent mass of gas we should expect the cooler outer layers to absorb the radiations given out by the glowing gas within, and its greenish light would consequently not reach us. Again, the great transparency of the Orion and many other nebula; would lead us to conclude that even its interior parts can radiate freely into space, and that cou- seijuently they would probably cool rapidly ; but if the nebulous matter is cold, how can we account for its faint luminosity '? If we suppose a mass of hot gas consisting of a great variety of chemical elements to be projected into space, most of its chemical constituents would, as the gas cooled, be precipitated into a glowing mist, the particles of which January 2, 1893.] KNOWLEDGE 11 would, as the cooling proceeded, cease to glow, but they would still be surrounded by the more volatile gaseous constituents of the original nebulous mass. We should expect to find the uncondensed gases arrdngiag themselves round the li(]uid or solid particles, forming a sort of atmosphere about them, very loosely packed, owing to the small attracting power of the particles. The particles would be moving with the general velocity of the vapour from which they were condensed, each carrying around it an atmosphere of uncondensed gas of considerable diameter, compared with the diameter of the solid or liquid particle, and wherever two streams of the original nebulous matter impinged upon one another, we should have far more frequent collisions of the atmospheres surrounding the particles than collisions of the particles themselves. The collisions of the particles themselves, if moving with planetary velosity, as supposed by Mr. Lockycr in his mjteoric hypothesis, would give rise to a continuous spectrum, but the much more frequent collisions of their atmospheres, would, it seems probable, give rise to a gaseous spectrum, even though the matter of the nebula were extremely cold. Before endeavouring to make a further step in the Sorrn Fig. 1.— Blofk etclied by a laliotogvaphic proL'ess from the central region of Prof. Barnard's photograph, enlarged about three diameters. enquiry " What is a Nebula?" I will ask the reader to devote a little time to a careful examination of the remark- able photographs reproduced in our plate. Near the centre of Prof. Barnard's large photograph is a bright nebulous patch, thickly strewn with stars, and within the bright region, or projected upon it, is a darker patch with straggling arms or projections, which appear to have spnmg from the dark area and spread out in their upper parts somewhat after the manner of solar prominences, though on a vastly larger scale. Again, within the dark area there are two black or nearly black starless regions, which appear like holes in the stellar cluster and its associated nebulous matter, except that one star is seen projected upon the larger of the two black regions. The question whether the dark structure is nearer to us than the bright nebulous cloud and its associated stars — that is, whether it is only by chance seen projected upon the bright background, or whether the dark structure is surrounded by the nebulous haze and stars, and is only partly seen through the bright nebulous matter — is one of very great iutarest and importance in deter- mining the theory which we may be led to adopt in order to explain the phenomena observed. The facta referred to in the paper on " Dark Structures in the Milky Way," published in the December number of Knowledge for 1891, would lead us to conclude that the dark and bright structures of the part of the Milky Way there described are all at about the same distance from us, and are intimately associated together. The dark arch and dark tree-like structures, referred to in the December number, 1891 (Fig. 5, page 232), spring from a large dark area in Sagittarius, about ten degrees to the south of the region shown at the centre of Prof. Barnard's photograph, which we are now discussing, and the dark structures there appear to have been projected into surrounding bright nebulous matter. Similarly, in the case now before us, the dark structures seem to be intimately associated with lines or streams of stars in the stellar cluster, and the stellar cluster appears to be associated with a general nebulosity which seems to be brightest where the stellar points cluster most thicldy. One of the most remarkable of these branching lines or streams of stars is situated between the dark structures marked a and b in Fig. 2. It is best seen in the enlarged copy of Prof. Barnard's photograph, and is marked with South. Fu , 2. — Block etched by a i5hotograj)hic process from the central region of Prof. Barnard's photogi-aph. Tlie same scale as the original. the letter A in Fig. 1, but it can be distinctly traced in Prof. Max Wolf's photograph. It seems to aflbrd evidence of a stream of matter which has rushed outward from the dark region, for it forks or branches in a direction awav from that region, as also do the dark structures marked () and /' in Fig. 2, and the almost linear dark branching structure marked C in Fig. 1. So also does the dark structure marked r in Fig. 2, for it is connected with the central dark region by a narrow dark stem, which, after haviu" attained a certain height, spreads into a broader head, from which diverge narrow branching streams which fork outwards. Stretching westward from the base of '■ is a remarkable hne of stars, with an adjacent narrow black channel. In view of these facts, we are led to the con- clusion that there is an intimate connection between the dark structures and the stellar cluster, and that the dark region is probably surrounded by bright nebulosity. It seems to me that the easiest explanation of the two black holes is to assume that they correspond to the places where two dark structures similar to a, i or c (Fig. 2) stretch out from the central mass in a direction towards the observer, and that they reach to the surface of the 12 KNOWLEDGE [Januaby 2, 1893. surrouading cluster aud nebulosity, while the structures a, h and ( are seen tbrouG;b a certain depth of nebulosity, so that they appear veiled and less black than the summits of the dark structures which extend in a direction towards US. If we adopt this explanation of the facts observed, we are forced to conclude that the ejected matter, when it is fii'st shot outwards from the central region, is dark or opaque, and that it afterwards becomes luminous and gives rise to the stellar points which we have spoken of as stars, though they may really correspond to considerable areas of tiocculent nebulous matter, giving much less light, area tor area, than the photosphere of our sun. According to Prof. E. C. Pickering's estimate of the sun's light in stellar magnitudes, our sun, if it were removed to a distance where it would appear to shine like a star of the fourteenth magnitude, would (if there were no abioptiou of light in its passage through space) have an apparent diameter of only the iifty-thousandth part of a second," but the smallest stars shown have in these photographs an apparent diameter of at least fifteen seconds of arc, so that it is ! possible that the bright regions we are referring to, and I which we have hitherto spoken of as stars, may have \ diameters many thousand times greater than that of our sun, and may be many million times less bright, area for ' area, than the solar photosphere. The branching character of the dark prominence forms, and the spreading nature of their summits, indicates that they are projected into a resisting medium, and that in expanding they are doing work against resistance ; con- sequently if the dark prominences are composed of gaseous matter, they must cool as they expand. It seems also highly probable that matter shot up from the interior of a cluster or nebula, which is cooling into space, would be hotter than the matter which has been in the exterior parts of the nebula or cluster for a considerable time. We are therefore, no doubt, warranted in concluding that [he ejected matter, as it first issues in a hot condition, is j dark and opaque, aud that as it cools it becomes luminous and comparatively transparent, or transparent in the inter- spacBS between highly luminous regions. It seems to me that the phenomena we observe are very much what we might expect to see if a mass of mixed vapour at a high temperature were projected into a region occupied by cooler vapour, or any resisting cooler medium, such as a cloud of dust : the elements having the highest evaporating ' and melting points would first condense into a luminous mist, the particles of which would act like floating bodies on a stream, and be swept aside into the eddies and vortices surrounding the mam current of the outrushing gas. To judge of large things by comparatively small, we see the same tendency to collect into fiocculent masses in the willow-leaf and rice-grain structure of the solar photosphere, and in our own "mackerel" clouds in a gale of wind. According to my theory, the dark structures of the Milky Way and nebulous clusters are the stellar analogues of the solar spots. When a large sunspot is near to the centre of the sun's disc, and we are able to look down into it, wo do not see the heated central body of the sun, nor do we see the I bright shell of photosphere which, it is only reasonable to j assume, is shining both upwards and downwards on the opposite side of the sun. We are, no doubt, looking into a deep mass of heated vapour, and the wave-lengths, which are radiated by the hotter and deeper strata, are entirely swallowed up and absorbed by cooler vapour at a higher level, or, to speak with greater caution, such a large * Sec The Old and Sew Anli'onoini), ]>agL' 777. proportion of the radiated energy is swallowed up that the intensely heated gaseous mass looks comparatively black beside the relatively cooler incandescent mist into which tbe outer gaseous matter condenses where it can radiate freely into space ; aud this is the case even though a portion of the hght of the incandescent mist is absorbed by vapours above it, as is evident from the channels cut out of its continuous spectrum. In the same manner, we should expect the intensely heated gas issuing from the hotter parts of a nebula or cluster to appear black and opaque compared with the relatively cooler matter com- posing the outer parts of the nebulous mass or cluster. In the case of the sun, where there is a rapid fall in the temperature as we pass upward through a few thousand miles, we should expect the incandescent clouds of condensing vapour to form a comparatively thin spherical layer corresponding to the photosphere ; but in the case of vast streams of heated gas which are carried to enormous distances from the heated region from which they are ejected, before they become sufficiently cooled for any part of the constituent vapours to condense into a white-hot mist, the conditions of cooling would be altogether different. The condensing gas is probably much rarer than in the sun at the level of the photosphere, and it seems not improbable that in the nebula the regions of most rapid cooling and condensation would be intimately associated with the vortices formed in the surrounding medium, where the most rapid contact of heated and cooled material would take place, and where the most rapid com- pression and expansion of gases causing changes of tem- perature would also be localized. Such at least seems to me to be the most probable solution of the great riddle presented to us in the complicated phenomena observed. It seems certain that the stars of irregular soar-clusters cannot be movmg under the action of gravity so as to form a permanent system with motions about the common centre of gravity of the cluster. It is possible that the individual stars of such a cluster might exist for a hmited time until a collision took place and they were shot forth again on a new orbit ; but it is also possible that the stars of such clusters are not bodies similar to our sun, but that they correspond to regions of rapid condensation where a white-hot mist is formed in a gaseous medium pervading the whole region of the cluster. The curvihnear streams of. stars with forking branches which have been noted in so many clusters (see Miss Gierke's " System of the Stars," p. 243), seem to indicate that they are intimately associated with streams of gaseous matter projected into a resisting medium, and recent photographs also seem to point to the conclusion that all star clusters are nebulous. THE LATE MR. MATTIEU WILLIAMS. M ANY of our readers will hear with sincere regret of the death of Mr. W. Mattieu Williams, who was formerly, during the editorship of Mr. Proctor, a very constant contributor to the pages of Knowledge. Mr. Williams was born in 1820, and was at the time of his death in his seventy-third year. He left school at the early age of eleven, and was appren- ticed to a Mr. Street, an optical instrument maker in London. During this hard-working period of his boyish life he attended a mechanics' institute in the evenings, and taught himself French aud German. On coming of age he inherited a small sum of money, which enabled him to go to Edinburgh to study chemistry, and he subsequently further continued his education by making a tour through the principal countries of Europe on foot. In 1851, on January 2, 1893.] KNOWLEDGE 13 the foundation of the Birmingham and Midland Institute, Mr. Williams was appointed master of the industrial department, a position in which he greatly developed his powers of lecturing. Besides his work at the institute he time of his death he was at work at a book upon the brain, which it is understood will shortly be published by Messrs. Chatto and Windus. He leaves a widow and three sons. Tlie late Mr. W. Mattieu Wilmams, from a photograpli taken sliortly before liis death. practised as a consultmg chemist and commenced wi'iting science articles. During one of his summer holidays he visited Norway, and walked through a considerable portion of the country, then comparatively little known to English tourists. He published the results of his experiences in 18.59, under the title of " Through Norway with a Knapsack," a book which was illustrated by the late Mr. John Steeple from sketches made by Mr. Williams during his walk. It passed through more than one edition. At a later period he again described Norwegian travelling in a book entitled "Through Norway with Ladies." In 1870 Mr. Williams published a volume of philosophical speculations on the cause of the sun's heat, and other cos- mical problems. The volume was issued imder the title " The Fuel of the Sun," and was widely read. Mr. Williams assumes the existence of a universal atmosphere, and that the density of the atmospheres surrounding the various planets depends upon the amount of the universal atmosphere which the planets can, by reason of their mass, condense about their surfaces. Though none of Mr. Williams" speculations have been generally adopted by astronomers, the book is very suggestive, and many able writers have acknowledged their indebtedness to it. Mr. Williams was a lucid and most interesting lecturer on the chemistry of common life. In the early volumes of Knowledge he wrote an excellent series of articles under the title " The Chemistry of Cookery," which were widely quoted at the time, and were afterwards collected and published as a small volume. He also wrote " Science in Short Chapters," a " Simple Treatise on Heat," the " History of the Manufacture of Iron and Steel," and an excellent little book entitled " The Philosophy of Clothing." He was a frequent contributor to the i ienthntdun Mmiddne on scientific subjects, and was the author of a system of shorthand entitled " Shorthand for Everybody." At the IL 1 1 1 c r 9 . — *-^-* — [The Editor does not hold himself responsible for the opininna or statements of correspondents.] To the Editor of Knowledge. Sir, — Having noticed in your last number some remarks upon the so-called "horned toads" of Mexico, you will perhaps allow me to mention my experience of their habits. While staying at San Diego, in Southern California, I drove some miles inland, on the borders of Mexico, with my son. On a sandy waste we saw numbers of these toads, running with great rapidity, and burying them- selves in the sand by means of a lateral wriggling movement. We captured three, and placed them in the empty basin of a fountain until we left for San Francisco, en mute for England. They soon became very tame ; but the largest (presumably a male) was so troublesome in spirting out what looked like blood that we left him behind. The other two we brought to England, where they hved for several months. The blood appeared to come from small orifices directly above and behind the eyes, and the discharge was so forcible and profuse as to cover my son's naked fore-arm quite up to the elbow. Great prostration followed, and lasted for a day or two. The "horned toad" has the chameleon-like faculty of rapidly changing his colour to that of the soil upon which he may be placed. The two smaller animals never exhibited the "spirting." Yours fiithfnlly, Wilmer Road, Bradford, C. W. Grabham, M.D. (Lond.) December 6th, 1892. — ►-♦-< — To the Editor q/ Knowledge. Mackay, Queensland, October 1.5th, 1892. Dear Sir,— In the September, 1892, number of Know- ledge, in an article by R. Lydekkeron " The Oldest Fishes and their Fms," the Ceratodus Forsteri of Queensland is repeatedly called " Barramundfl." The aboriginal word Barramund/ simply means large fish, and is indiscriminately applied throughout Australia to whatever fish happens to be the largest in that particular locality ; but the name should be legitimately restricted to the Osteoiilossum Leichardti, Leichardt ha^^ng been the first to describe this fish by that name. I append tracings of (hteo