'(je groLu jrom more w more. - TlNNYSOM. \jL \ An Illustrated ^^ ^V MAGAZINE OF SCIENCE. SIMPLY WOEDED-EXACTLY DESCEIBED- Edited by A. COWPER RANYARD. Let Knowledge grow from more to more. -TENNYSON. VOLUME XIY. JANUARY TO DECEMBER 1891 NEW SERIES, VOL. VI. LONDON: Wnill'Kr.V & CO.. 326, HIGH IIOLUORN. W.C 189]. [-1// liiijiit.-' livfvrred.] LONDON ; I'llINTKll IIV WITHERBY & CO.. 'MiS. IIIliH 110I,1'."HN. W.C. KNOWLEDGE INDEX. bis "Popular Abbe, Cleveland — Distribution of Nebulas witb respect to the Milky Way Absorption — Evidence of Absorption of Light in Space ... Airy, Sir G. B.— Notice of new etlition of Astronomy" America— Origin of the Name America Ames, J. S.— Notice of bis paper " On the Rhythmical Group of Hydrogen Lines " Aragonite — Frequently replaced by Calcite in Fossil Shells Arcturus — On the proper Motion and actual Magnitude of Atmosphere — Height of the Solar Atmosphere Height of the Earth's Atmosphere Backhouse, T. W.— On the Magnitude of Canopus Ball, Piatt— Notice of his book, " Are the Effects of Use and Disuse Inherited '? " Balloons- Photographs taken from Balmer, J. J. — His Formula connecting the Positions the Hydrogen Lines Barnard, E. E. — His I'liotograph of the Sagittarius Region On the Comparison of Photographs of the Milky Way Barrett, T. S.— Letter on Magic Squares Letter on Recurring Decimals Article on the ^lagic Square of Four Letters on the Magic Square of Four of 156 155 171 224 170 68 21 28 214 212 12 212 170 The Factorials of High Numbers 50, 232 93 16 17 45 15(5 210 71, Beynon, Richard — International Yachting ... ... ... 183 Explosions on Petroleum Vessels .. ... 233 Boeddicker, Dr.— His Drawing of the Milky Way ... ... 93 Boys, Prof. C. Y.— Soap Bubbles and the Forces which Mould them 110 Buckland, Miss A. W. — Our invisible Foes ; or Bacteria in Agriculture 75 Buckton, G. B.— Monograph of the British Cicadaj Ill Burnham, S. W.— Note on the Orbit of the Double Star 2)2 ... 48 His Selection of the Site of the Lick Observatory ... ... ... ... ... 31 The Companion to a Ursre Majoris (jS 1077) 129 Butler, E. A.— The Book-louse ... ... . 3 The Silver-fish Insect ... ... . 25 The House Cricket 82 Gnats, Midges and Mosquitos 121, 141, 161 Earwigs 181,201 On Human Pediculi 221 Calendar — The Day of the Week for any Date 47, 70, 94, 133 California — Observatories in ... ... 31 Chambers, G. F.— Notice of his " Pictorial .\strouomy " ... 171 Chartres, R. — Letter on Recurring Decimals ... .. 30 Letter on the Attraction of a Thin Shell ... 134 Christie, R. W. D. Rule for finding the Day of the Week for any Date ... .". 30 Letter on Perpetual Calendars ... 94 Christopher, H.— On the Cause of Volcanic .\ctiou ... .. 131 KNOWLEDGE Gierke, Miss Agnes M. Notice of ber book, "Tlie System of the Stai-s" Article on ^■al■iable Stars of tlie Algol Type Tbe Observation of Ked Stars Letter on tbe Observation of Red Stars Clodd, E.— Review of Dr. Nansen's " First Crossing of (ireenland "... Clusters- Relative Size of Stars in Clusters . . Clusters of Stars about a Crucis Coal Sack — RefTton of the Milky Way Cobbe, Miss F. P.— Letter on Effects of Snake Poison Cooke, T.— Notice of book on " The Adjustment and Testing of Telescopes " ... ... . .■ Cornish, Yaughan— Artificial Cold V Calcite and Aragonite in Shells ' The Artificial Production of Rubies and other Precious Stones The Experimental Method in Geology The Chemistry of the Dairy ... The Mineralogy of Meteorites The Diamond Mines of South Africa 32 58 150 101 9-2 112 22!) 211 81 125 147 163 18C Corona- Temperature of Bodies situated within the Corona 14, 28 Cowan, T. W.— Notice of his book on " The Honey Bee " ... 89 Crookshank — His Bacteriological Investigations ... ... 70 Crowe, Eyre— Tlie Observation of the Transit of Venus by •Jeremiah Horrocks 107, 129 Dark Areas— In Milky Way Ill, 230 Darwin, Prof. George — Collisions of Meteors ... ... ... ... 29 Davidson, J. Gwen — liooks on Astronomical Photography ... 1 1 .J Denning, W. F.— Stationary Radiant Points of Meteors .. 110 Notice of his book, " Telescopic Work for Starlight Evenings " ... ... ... 132 Dicker, Theodore W. — Dissemination of Seeds ... ('i-"i Draper, Dr. Henry First Photograph of a Nebula by .. (Note) 1G9 Egyptian- Villages built on Ruins of Earlier Villages ... 69 Electric Discharges — Application of Photograpliy to the Study of 32 Elkin, Dr.— His Estimate of the Parallax of Arcturns ... 22 His Investigations with respect to the Pleiades Cluster . . . . 92 Ellis, Havelock — Notice of his book on " The Criminal " ... 62 Equatorial — Early Use of Equatorial ^Mountings ... ... 130 Espin, The Rev. T. E. On the Red Stars near the Cygnus Nebula ... 211 Pranks, W. S.— Letter on the Observation of Red Stars . . . 173 Fraunhofer — His Improvements of the Achromatic Tele- scope and Observation of Stellar Spectra (Note) 168 Fry, Lord Justice — British Mosses 221 Gattie. W. Montagu- Whist Columns 37, 58, 79, 90, 139, 158 Geikie, Sir Archibald — Notice of his " Outlines of Field Geology ' ... Gordon, A. W.— Sums of Digits of Square and Cube Numbers Gore, J. E.— Clustering Stars and Star Streams A Double Planet On tbe Mass and Brightness of Binary Stars Letter on the Magnitude of Canopus On some Peculiarities of the Variable Stars . Gossip, G. H. D.— Chess Column for .January ... Griffiths, A. B.— Notice of his " Manual of Assaying '' Guillemard, F. H. H.— Notice of his book on •• Ferdinand Magellan '' Gunsberg, L — Chess Column ., Haggard, Rider— On his Astronomy in '• King Solomon's iMines '' 171 228 175 209 191 193 20 172 33 4U KNOWLEDGE r.iGE PAGE Hale, Geo. E.— Kinetic — Hydrogen Lines in Solar and Stellar Spectra 169 Theory of Gases 28,29,51 , 213 Hansard, Arnold S. — Kirby, R. H., Jun.— Perpetual Calendars ... 70 Letter on the Astronomy of Mr. Rider Haggard's " King Solomons Mines " 29 Hart, C. F.— Letter on the Earthy Smell after Eaiu 230 Lick Observatory — Life at, in Winter 31 Henry, Monsieur Paul- Letter on the Supposed Duplicity of Wega . . . 16 Locock, C. D.— His Photographs of Stellar Spectra ... 169 Chess Columns from May onwards. Herschel, Sir W.— Lovell, K. B.— Eecognizes that Stars are more Thickly Notice of book, " Nature's Wonder- Workers " 111 Grouped in the Eegion of the ]\Iilky Way than elsewhere 41 Lund, C— His Observations of Double Stars ... 115 Letter on Perpetual Calendars 133 Holden, Prof.— Lydekker, R. — The Winter Snows at the Lick Observatory 32 Primeval Salamanders ... 3 j Rudimentary Structures 23 Horrocks, Jeremiah— Giant Birds 43 His Observation of the Transit of Venus of 2ith November, 1639, O.S. ... 107, , 130 Numuhtes and Mountains Swimming Animals ... .. .. 152 Flying Anunals ... 112, 127 (i4 , 168 , 165 Huggins, W.— Crocodiles and Alligators ... Sea Urchins 206 235 H is Observations of Stellar Spectra 169 Lynn, W. T.- Hughes, F. S.— Notice of his book, " Celestial Motions " 90 \\liist Column for January 18 Letter on Mitchel's papers in the rhilDsophuul Tt'tfusficlioiis... 115 Hutchinson, The Rev. H. N.— What is a Volcano ".' ... 87 Martin, Annie- What is the cause of Volcanic Action ? 101 Notice of his book, " The Autobiography of Notice of her book, " Home Life on an Ostrich 12 the Earth " 111 Farm " Lunar and Terrestrial Volcauos 115 Martin, Edward A.— Ingall, Herbert— The London Basin 216 Hydroid Zoophytes 176 Maunder, E. W.— Janssen, Dr. J.— On the actual magnitude of the Star Arcturus 21 His Photographs of the Solar Photosphere ... 11 Letter on the Intelligence of a Cat ... 49 Johnson, B. B.— Article on the Classification of Stellar Spectra 71 Second Article on the Classification of Stellar Notes from Cambridge "Anatomy" in the Spectra 101 olden days oU Note on the Brightness of Double Stars 183 Keltie, J. Scott— Max Wolf- ^ Notice of his book on " Applied Ceography " 13 llis Photographs of the Milky Way 172. 168, 230 •^ Kemp, J. T.— McPherson. Dr. J. G.— The Origin of the Chalk 103 The Meteorology of Ben Nevis 214 Kendall, P. F.— Distribution of Boulders over the North of McRay, Charles- England 150 Notice of his book, " Fathers of Biology" ■■ 33 Kimball, Arthur L. Mendola, Raphael- Notice of his book on "The Physical Properties Notice of his book, •• Coal, and what we get of Gases " ■■ ■■■ 51 from it ' 172 KNOWLEDGE 14 Meteorites — Clashing of, could not pioduee Heat nl fSiii Meteor Radiants — Accuracy of Identification of ... Michell, The Rev. John— His Application of the Theory of Probabilities to the Distribution of Stars in Space 41, 91 His papers in the rhilusophkul Tramactionx 115 Milky Way— On the Form of the ; by J. E. Svtto.x The Milliy Way in the Southern Hemisphere ; by A. C. Eanyakd The Coal Sack Region of the; by A. C. Raxy.\ed On the Plan of the Sidereal System ; by J. R. Sutton On the Distance and Structure of the Milky Way in Cygnus; by A. C. Ranyakd On the Dark Structures in the Milky Way ; by A. C. Eanyabd .. ... ..". Monck, W. H. S.— Letter_ on Stationary and Long-Enduring Radiants of Meteors ... ... 95,117 41 50 111 123 3 88 280 Letter on the Brilliancy of Double Stars Mosses — Paper on British Mosses ; by Lokd Justice Fry Nansen, Dr.— Review of " First Crossing of Greenland'' ... Nebecula Major — Spiral Structure of . . . Nebulae — Distribution of SmaU Planetary Distribution of Spiral Nebulas 135 221 51 155 50 Newton, Sir Isaac — Rejects Theory that Sun could be a Cool Body surrounded by a Heat-Giving Envelope (Note) 105 Owen, J. A. — Notice of bis book, " Annals of a Fishing Village" Peal, S. E.— Letter on the Rays from Lunar Volcanoes . . Pharaoh — Rameses 11., the Pharaoh of the Oppression Photographic Irradiation— Note on... Photography — Books on Celestial Photography 33 191 69 111 115 Photosphere- Structure of the Solar Photosphere Brightness of the Photosphere of Stars (Note) 9(5 Pickering, Prof. E. C- His paper on the Dimensions of the Fixed Stars (Note) Spectra of Stars in the Pleiades Cluster Nebulous Streak passing through 16 Faint Stars ... Catalogue of Stellar Spectra 13 22 92 93 231 Polarization — Of the Light of the Corona . . . Prince, C. L. — A Perpetual Calendar... Proctor, Mrs. S. D.— Paper on Californian Observatories Proctor, R. A. — Memorial Observatory Distribution of Nebula' Proper Motion — Of Arcturus ProYis, F. J. — Letter on Cross-FertiUzation... (Note) 14 47 31 155 21 71 Ranyard, A. Cowper— The Sun's Photosphere ... ... ... 13 The Milky Way in the Southern Hemisphere 50, 75 The Pleiades Cluster and its Probable Con- nection with the Milky Way Astronomy as taught in Academy Pictures ... The Coal Sack Region of the MUky Way . . . On the Space-Penetrating Power of Large Telescopes ... On the Rhythmical Group of Hydrogen Lines visible in many Stellar Spectra On the Distance and Structure of the MUky Way in Cygnus The Upper Atmosphere Dark Structures in the Milky Way ... Note on the Temperature of the Planet Mars Note on Magic Squares Note on the Brightness of the Photosphere of Stars 22 Note on the Height of the Solar Atmosphere Note on Possible Duration of a Solar Eclipse Note on Variation of Light during the transit of a Star of the Algol type ... Note on the Classification of Stellar Spectra Note on Supposed Long-Endiu-ing Meteor Radiants Note on Mr. Eyre Crowe's picture of Jeremiah Horrocks Note on the Attraction of a Thin Shell Note on the Rays or Streaks from Lunar Volcanoes ... .. .. 147,191 Note on the Absence of a Lunar Atmosphere 193 91 107 111 154 168 188 212 230 16 17 73 28 30 72 96 130 134 KNOWLEDGE' Ranyard, A. Cowper — contimird. Note on the Distributiou of Short Period Vari- able Stars 104 Note on Sums of Digits of Square and Cube Numbers Star- Zone- Zone of Large Stars associated with the Milky Way 91 Rectus, Elie— Notice of his book on " Primitive Folk " Recurring Decimals Letter on ; from T. S. Barektt Letter on; from R. ('hartises Roberts, Isaac— Ills Photographs of the Pleiades Cluster Roper, E.— Notice nf his lionk, " By Track and Trail ' 220 Stewart, J. J.— Articles on Some Practical Applications of P^lectricity 33,174,225 232 Rubies- Artificial Production of 17 30 03 111 81 41 1 -23 60 223 ir.l Russell, H. C— His Photographs of the Milky Way and Nebula in the Southern Hemisphere ... "il Letter on the Comparison of Photographs of the Milky Way 172 Sadler, Herbert — Face of the Sky for each month. Salamanders — Paper by Mr. Lydekkek ou ... Sawer, J. Ch.— The Perfumes of Antiquity Shaw, J. — Snow on Mars ... ... Stellar Evolution irian Stars — Comparative P)rightness of, as compared with Solar Stars ... 8 Smith, J. Pentland — Insectivorous Plants Contrivances for the Cross-Fertilization of Plants 34 A Seed, and what it contains ... .. . . (il Sutton, John Richard — ( )n the Form of the Milky Way ( )n the Plan of the Sidereal System . . . Taylor, A. G.— Temperature of the Corona . . Taylor, Canon Isaac — Excavations at Luxor... A (iossip on Ghost-Names Telescopes— Space-Penetrating Power of ... Temperature — Of Bodies within the Solar Corona .. 14, 28 Of Surface of the Planet Mars ... ... 16 Note on the Temperature of the Interior of the Earth ... ... ... ... ... 105 Tree-Like Form — Of Structure in Mr. Barnard's Photograph of the Milky Way in Sagittarius ... ol, 232 , TrouYelot, Monsieur — Apphcation of Photography to the Study of Electric Discharges ... . 32 l^-'^ Turner, H. H.— Notice of his new edition of Airy's "Popular Astronomy " ... . ... 171 Yogel, Dr. H.— His Measures of the Positions of the Hydrogen Linos ... ... .. ... 160 73 Whale— Rudimentary Hind Limb of . . ... ... 24 White, Arthur Silva— Notice of his book ou " The l^evelopment of Africa" 13 10 20 The Travels and Life-History of a I'ungus . . ' 107 Williams, Joseph W The Potato Fungus ... ... ... .. 13;j The Fertilization ol' two Common British Orchids 140 The Mushroom ... ... ... ... ... 203 Spectra— Of Stars, the Classification of Spencer, Herbert - On the r>istiibulion of Nebula' Spiral Nebulae Not symnietricalK' Arran^fd with re.spect to the Milky Way' ... SO The Life-History of l-'ilaiin S,iiiiii(iiii>. Honiinis ... ... ... ... ... 143 Willow-Leaf — Structure of Photosphere 13 71 Wilson, The Rev. Alex. S. I'lirds and Berries .. .. ... ")2, 133, 21.) 15(5 Wright, Lewis — Notice of his book on "Optical Projection" 133 Young, Prof. C. A. - On the Cpper Limit of the Atmosphere ... 214 KNOWLEDGE INDEX OF ILLUSTRATIONS, Algol-Stars— Diagriiins ilhistniting Variaticins of Liglit of ,. :irt Alligators- Skulls of 207 Ammonite Shell of ir,4 Argus — Photosrai'li of till' 1/ Argus Region of tlu- Milkv Way Hi' Atmosphere— J)iagraiu illustrating Tloight of ,, 213 Balloon — riiofograplis taken from 212 Bones of tlie Kore-limb of the Bat 12!) Bee- Sting, Poison-glanil, Heart, and Salivary glands of Honey-bee . 91 Book-louse — Head, Mandible, Wings, and Body of '. 6 Burnham — Orbits of Double Stars 48 Calendar- Perpetual Calendars IS, 70, 75 Cluster — ttf Stars round o Vulpeeuhe So Coal Sack — Photograph of the Coal Sack Eegion of the Milky Way 112 Cricket— ilandible and Mouth Organs of 83 Wing and Auditory Organ in Tibia of . . ' 84 Crocodile — Skidls of 20(i. 203 Cygnus— Photographs of Regions rounil a, e, and ^ Cygni 188, ISii, 231, 232 Dark Structures — In Milkv Wav Filaria — Filaria sanguinis liomiuis ,.. Flying Fish- Flying inseet and Pterodactvle Ganoid — An Extinct franoid Fish Gnat-^ TAOK 144 114 inn Photographs of the Larva and Pupa of 122 Figures of spirarular Horn. &c. 142, Hi i Grampus — The Common Gramjius .. 152 Greenland — Pii'tures from Dr. Hansen's ■• First Crossing of (ire.-nland" 2 Honeycomb — Brood Comb and Royal Cells 89 Ichthyosaurus — Skeleton of 167 Lick Observatory Photograph of, taken after Snoiv- Metacarpels — Of Extin.'t I'ngulate Animal Milky Way- Diagram illustrating Mi-. Proctor Spiral Theory of Photographs of the The Human Far 230, 231, 232 . 25 Moa - lioiies of Leg of Giant Moa ... 44 Mosquitos — Figures illustrating Life-History of Gnats, ilidges and Mostpiitos 122. 142 Mosses Pictures of Hvpnum Polvtrichum, &e. ' . 221,222 Mushroom — Diagram showing Mveclinm Gills, &c. ' ' 204 Nebecula — Photographs of the \ebecula. Major and Minor 50 Earwigs — Forceps and other parts of 181. 182. 201. 203 Echinoderm — Pictures of Fossil and Alodern Sea- I'rchins 23(i. 237 Electric Discharges - Photograiihic traces left b\ 32 Fein- Transverse Section of Leaf, and rructification of Leaf and Spor- nnginiii (il Numulite — Wcv; and Section of fi4 Orchid — Diagraiinuatic view of Orchis .Maeulata 149,151 Photograph of Cattley a Mossije , . . 150 Orion — Photograph of .Nebula and Stars in .50 Ovule — Diagrams and Sections of ... ... 03 Pediculi — Female Head Louse 227 Proboscis of Body •use,, 228 Pelican — Webbed Foot of ]fi7 Perch— The Coiniuon Perch 1(!5 Photosphere — Photographs of (he Sun's Photo- sphere by Dr. Janssen .,, 10 Pitcher Plants — .Modified Leaves and Tendrils of ... 8, 9 Epidermis and Digestive Surface of Glands and Pitcher .. 10,11 Pleiades — I'hotograph of the Pleiades Nebula, by Mr. Isaac Roberts 92 Potato Blight- Pictures illustrating gniulli of Fungus . . 13() Rameses II. — Photograph of Stone Figure of ... 69 Rudimentary- Rudimentary Hiuil Limb of Whale 24 Sagittarius — Photograph of Rich Region in 50. 232 Diagram sho\ying Stars ])hoto- graphed in ... 94 Salamander - Teeth and .law of Primeval S. 3 Skull of Giant Primeval S. 4 Sea Urchin — Picture's of Fo.ssil Kclnnoids 236, 237 Seal— Dr. Hansen's Party shooting liladder-nosed S.mI-' I The Common Seal , , l.s5 Silver Fish — Lalirum, Mandible, Scale, and whole Body of Silver Fish insect 36 Spherical Shell- Diagram illustrating attraction of 134 Stellar Spectra- Photographs and Drawings of ... 169 Sun Spots Diagram illustrating Development of Spots ill various Heliograpluc Latitudes 14 Temple- Photograph of Intaglio, represent- ing front of an Egyptian Temjile 09 Variable Stars — Diagrams showing distribution of Short Period Variable Stars .. 194 Wheat Rust- Rust or MihlcH Hydroid Zoophyl,' 108 176 March 2, 1891,] KNOWLEDGE 41 ^>* AN ILLUSTRATED '^«/ MAGAZINE OF SCIENCE SIMPLY WORDED— EXACTLY DESCRIBED LONDON: MARCH 2, 1891. CONTENTS. On the Form of the Milky Way. By John Richard Sutton, B.A. Cantab 41 Giant Birds. By R. Lvdekkkr. B.A.Cantab .. 43 The Magic Square of Four. By T. Squire Barrett, F.S.S. 4.5 A Perpetual Calendar ... 47 Note on the Orbit of the Double Star 2 2. By S. VV. BURVIIAM ... ... ... ... ... ... ... ... 48 Letter:— E. W. Maundeu 49 The Milky Way In the Southern Hemisphere By A. C. Ranyard ... ... ... ... ... ... ... 50 Notices of Books 51 Birds and Berries. By the Rev. Alex. S. Wil.son, M.A., B.Sc. 52 Variable Stars of the Algol Type. By Miss A. M. Ci.erke 53 Notes from Cambridge. By R. B. Johnson 56 Artificial Cold. By Vacghan Cornish, B.Sc, F.G.S. ... 56 Whist Column. By Montagu Gattie, B.A.Oxon 58 Chess Column. By C. D. Locook, B.A.Oxon. 59 ON THE FORM OF THE MILKY WAY. By .John Richard Sutton, B.A.Cantab. THE late Mr. Proctor shone as a critic. One gets the same impression from a literary review by him as from one of Matthew Arnold's literary reviews, viz. that in most cases common sense has little more to say. His essays on the star-work of the two Herschels are among the most masterly in the language, and are destined, no doubt, to be read for generations. But his original speculations are not always so happy. His genius was iconoclastic rather than creative ; and although few who have appreciated the significance of the work of Michell and the school he set up will question the fact that Proctor has successfully summed up, once for all, the case against Sir William Herscliel's " cloven-llat-disc theory " of the Milky Way, yet it is doubtful if the same success can be claimed for the " spiral theory," which he advanced as comprehending all the results of observation on the stars and nebulas. It would be out of place here to enter into a discussion of the stellar researches of the Herschels. It will be sufKcient to say that the elder Ilerschel assumed the stars to be, on the (iirrdi/c, scattered more or less uniformly throughout the visible universe, and hence, by counting the number of stars visible in any one direction, he was, as he thought, able to arrive at a pretty fair approximation to the depth of the star-system in that direction. [It is not hard to see that when the telescope is ti.\ed on any point in the sky, the boundaries of vision trace out a cone in the celestial sphere of which the eye is the vertex.] The yoimger Herschel seems to have accepted his father's results with little more than a twinge of doubt, although it is not so certain that he placed a very great faith in the trustworthiness of the star-gauging methods from which they were derived ; for he could also see, brilliant mathematician as he was, that Michell's application of the doctrines of probability had practically set at rest the fact that in in'iieml star-grouping was physical and real, and not merely optical, and hence that the stars were by- no means imiformly distributed. Still, the doctrine of probabilities had not sufficient hold upon his mind to cause him to give up the delightfully systematic results of star- gauging, to say nothing of the paternal authority by which the old theory was backed. Proctor, however, took higher ground. In his hands Michell's researches were, so to speak, born again. The star-groups were physical facts (which, indeed, Sir William Herschel had never doubted, though he left it out of account) ; the constellations were realities of association (of which Sir William Herschel had never even dreamed) ; immense streams of stars, physically connected inter sc, were to be traced across the sky ; and, last of all, the Milky Way itself was a great stream of stars" — and not a solid disc — to which all the other streams and groups were subordinate. These different conclusions were advanced from time to time for many years, and, taken together, they comprise an analysis of stellar phenomena whose immense value cannot be denied. It would be an agreeable task for me to give here, as far as possible, an account of Proctor's very successful work among the stars. But such a course is just now out of the question ; moreover, most readers whom this paper may concern will have read his original papers. I shall content myself by remarking that he veiy early con- cluded that all available evidence pointed in one direction, namely, that the characteristic feature of our universe, the Milky Way, was one long stream of stars of a spiral form, whose plane passed very nearly through the sun's place. He says : "It is very clear what views we are to form respecting the Milky Way. If the galaxy is, lirst, a clustering aggregation separated from us by an interval comparatively clear of small stars ; sirondh/, so shaped that the cross-section of the stream is everywhere not far from a roughly circular figure ; and, thirdlij, associated * Sir William Heischel's language, even in his early papers of 1784 and 1785, and much more in his later papers on the Construc- tion of Heavens, published in the Phil. Trans, of 1802 and 1811, clearly prove that ho fully appreciated the fact that there are actual clusters and streams of stars, as well as vacant spaces, in the heavens. It is evident, also, that he recognized the connection between the di.stribution of stars and the distribution of nebul.t. As early as 1802 Sir W. llerschel's language clearly shows that he con- sidered the Milky Way to be a roughly circular ring-shaped region, in which the stars are more thickly grouped than in the space im- mediately around the sun. He says, in a pap^r published in the P'lil. Trims, in 1802: "The stars we consider as insulated are also surrounded by a magnificent collection of innumerable stars, called the Milky Way, which must occasion a very powerful balance of opposite attractions to hold the intermediate stars in a stite of rest. For though our sun. and all the stars we see, may truly be said to be in the plane of the Milky Way, yet I am convinced, by a long inspec- tion and continued examination of it, that the Milky Way itself con- sists of stars very differently scattered from those which are immediately about us." Sir John Herschel also clearly recognized the close clustering of stars in the region of the Milky Way. Mr. Proctor was well aware that both the Herschels had recognized the existence of star-streams as well as groups of nebul:e. But I agree with Mr. Sutton that neither Sir William nor Sir John Herschel pro- ceeded to the conclusion which should have logically followed. namely, that their method of star-gauging could not be relied upon for determining the form of the stellar universe. — A. C. Ranyaru. 42 KNOWLEDGE [Mabch 2, 1891. very closely with the bright stars seen in the same field of view, then must its structure be somewhat as shown in the figure. ... It will be seen at once how, to an observer placed at S, the various features of the Milky Way can be accounted for by this figure. Towards 1 would Ho the gap in Argo ; towards 3, 4, 5, two branches, one faint, and in part evanescent through vastness of distance, the other forming the brightest part of the spiral ; towards G the projection in Cepheus ; towards 7 the faint part of the IMilky Way in Gemini and Monoceros. The Coal-sacks would be simply accounted for by conceiving that branches seen towards the same general direction, but at different distances, do not lie in the same general plane, and so may appear to interlace upon the heavens. We are not only justified in supposing this, but forced to do so by the way in which the stream of milky light is observed to meander on its course athwart the heavens. The branching extensions serve very well to account for the appear- ance of the Milky Way between Cepheus and Ophiuchus, where the interlacing branches and the strange convolutions and clustering aggregations described by Hir -John Herschel are chiefly gathered."— Otfin- Worlds, p. 2.50. Proctor's affection for this spiral is remarkable. It was advanced first of all with some caution as a conformation which seemed to account for all the known peculiarities of structure in the galaxy — in short, it supplied a useful working theory. For example, he makes the following admission : " I would not have it understood, however, that I at all insist on the general shape of the spiral shown in the figure. On the contrary, that curve is only one out of several which might fairly account for the observed appearance of the Milky Way ; and I fig. have often felt inclined to doiibt whether a single spiral of this sort is in reality the best way of account- ing for the observed appearance of the galactic zone. What I do insist upon as obviously forced upon us by the evidence is that (1) the apparent streams formed by the Milky Way upon the heavens indicate the existence of real streams in space ; and (2) that the lucid stars seen on the stream are really associated with the telescopic stars which form, so to speak, the body of the stream. Whether that stream form a smgle spiral or several, or whether, instead of spii-als, there may not be a number of streams of small stars, placed at dili'erent distances from us, and lying in all directions round the medial plane of the galaxy, but more or less tilted to that plane (the sun not lying within any one of the streams), are questions which can only be resolved by the systematic scrutiny of this wonderful zone." But just as Sir Wilham Herschel's working-theories of star-distribution came eventually to be regarded as esta- blished facts, so in course of time, without any more apparent grounds. Proctor came to regard his theory with increasing confidence. Scattered throughout his writings will be found very trustful remarks on the conformation of " that strange spiral." Without doubt, if the star-groups, such as the Pleiades, are real, and not merely caused by stars far apart, though near the same visual-line, being seen projected into a small area of the celestial sphere (and Michell's, not to mention later results, seem to make it certain enough) ; if the star-streams are real, and not mere optical coinci- dences ; if the manifold signs of association and dissocia- tion among the stars are what common-sense would teach ; then it is as certain as the doctrine of chances can make it that the Milky Way is a stream, or collection of streams, of stars. So much, but no more. Proctor has proved. What he has not proved, nor even made pos- sible, is that the Milky Way partakes in any way of a spiral form. Fig. 1. — The Milky Way as seen in the Heavens. -The Spir.\l Stream which Mr. Proctor assumed represented the actual form of the MiUiy Way. Let US see what the brightness of the Milky Way can tell us. Proctor assumed the brightness of its various parts would be a good rough test of their relative dis- tances— a curious mistake for one so conversant with the laws of brightness. [It may be noted that Sir .lohn Herschel erred in the same direction.] Now it may be proved that brightness alone is no test of distance. For let a be the apparent area of any small portion of the Milky Way at some distance taken as unity, and contain- ing n stars, X the average amount of light received from each star, /S the average brightness of the area. If this area be removed to distance d, the light received from each star will be reduced to -j^ ' ^lut the apparent area containing the n stars will be reduced to ,.,, and hence the stars are apparently compressed into a smaller area in the same proportion as their light is reduced. /3, there- fore, remains unaltered. The apparent breadth of the galaxy would be a much safer test of its distance than the brightness, although its actual breadth may vary between very wide Umits. As a matter of fact, the broadest parts of the Milky Way are, on the whole, the faintest ; whereas in its narrowest part, at the " isthmus " leading into the Southern Cross, it is almost at its maximum brilliancy. During the course of his long review of the elder Herschel's cloven-flat-disc theory, Proctor pointed out again and again the remarkable tendency of the brighter stars to congregate along the course of the Milky N\'ay and its branches. This feature is so noticeable in the Maech 2, 1891.] KNOWLEDGE. 43 southern hemisphere that on a bright moonhght night, when the fainter hicid stars are invisible, the position of the Millcy Way can be traced by the condensation of the brighter stars alone along its course. Now, there is no antecedent reason why the naked-eye stars should collect upon one part of the Milky Way and not upon another ; and hence there is no reason why the fainter parts of the galaxy — assuming them for the moment to be the most distant — should not have collected fourth and fifth mag- nit ade stars in the same way as the brighter and (there- fore assinned) nearer parts have collected the brighter magnitudes. But we should not expect to find many of the brightest stars on the fainter and more distant parts. Yet it is a fact that there are stars on the (assumed) more distant streams, and obviously associated with them, as bright as those on the (assumed) nearer ones. Moreover, between the two streams, where the Milky Way is double, and in the Coal-sacks, scarcely a single lucid star is to be seen. This is a singular circumstance. If the spiral theory, or any modification of it as suggested by Proctor, were true, we shoidd expect more, or at least as many, bright stars between the two branches where the Milky Way is double, and in the Coal-sacks, as upon the borders of the Milky Way in any other place. On the other hand, if we regard the two branches as lying at very nearly the same distance from the Sun, we can see at once that the cause which separated them, or keeps them apart — what- ever the agency may be scarcely matters in this inquiry — would also ih-i-dn, as it were, the lucid stars from the space between. Add to this the circumstance that the meander- ings of one branch correspond to those of the other, and that in one place one branch is made up of alternating bright and faint patches corresponding to faint and bright patches respectively on the other, then we have strong presumptive evidence that the two branches are closer together than any spiral conformation would admit. All this leads us to conclude that the Milky Way is much as it seems to be at first, namely, a very complex stream of stars roughly hoop-like, and not spiral-like, in form. A piece of old rope thrown into a circular shape represents the Milky Way very well. The frayed ends not quite meeting represent the fan-shaped expansions of the stream on each side of the rift in Argo (a spiral theory does not explain why these expansions should occur just here). A strand untwisted of nearly half the length of the rope, and divided in the middle, would represent the divided branch running from Cyguus through Ophiuchus and Scorpio. Smaller departures would represent the lateral extensions in Cepheus and Perseus. These may be of any size ; and it scarcely needs Proctor's assumption that a vast void separates the galactic stars fi'om the faint streams discovered by Sir .John Herschcl to account for them. This faintness is very likely caused either by sparcity of distribution or by the smallness of the stars (as we have seen brightness is no test of distance so long as light is not lost in its passage through space) ; indeed, it is pretty clear that the Milky Way is made up of stars of all orders of size and brightness. Local unravellings in the rope would correspond to the Coal-sacks in Crux and Cygnus, and to the lacunre in Scorpio and else- where. In conclusion, let me add that the aspect of the Milky Way in Argo gives a very strong impression that the stream has been forcibly torn asunder at this place, an impression which is to some extent corroborated by the positions of the bright stars round about, and by the numifold signs of decomposition exhibited l)y the galaxy in Scorpio and the adjacent constellations. GIANT BIRDS. By R. Lydekker, B.A.Cantab. THE only birds existing at the present day which in any sense merit the epithet "gigantic" are the Ostriches of Africa and Arabia, the Eheas of South America, the Cassowaries of Papua and North Australia, and the Australian Emus ; and even the largest of these — the male Ostrich — seldom ex- ceeds seven feet in height. The researches of palicontolo- gists have, however, revealed to us that these four groups are but the solitary survivors of a considerably more extensive assemblage of Criant Birds which was once spread over a large portion of the globe, and some of whose members as much surpassed the Ostrich in size as the latter exceeds the Eheas in this respect. Indeed, with our present knowledge of the meaning of the geographical distribution of animals, the very circum- stance that the existing Ciiant Birds are all more or less closely allied, and are fovmd scattered over the globe in areas widely separated and totally disconnected from one another, would of itself have been amply sufficient to indicate that they are the remnants of a group which was at one time of much larger extent, and inhabited regions where such creatures are now unknown. It is unfortu- nately the case that there are still many gaps in the chain which should link all the existing Giant Birds together, but we may confidently hope that the progress of geo- logical research will little by little reduce the number and length of these gaps. All the Giant Birds, it may be observed, both living and extinct, are linked together by their incapacity of fiight, and the consequent absence of that strong bony ridge or keel which we may observe on the breast-bone of a duck or a fowl, and the presence of which is essential to form a firm support for the powerful muscles requked to move the wings. Whether, however, this incapacity for flight is a feature which was always possessed by the Giant Birds, or whether it has been gradually acquired by disuse, is a question which has seriously exercised the minds of those best fitted to decide it, and, since it is still unanswered, may be put aside on this occasion. Moreover, in saying that the Giant Birds are all incapable of fiight, it must by no means be inferred that all birds in that con- dition have any affinity to this group. On the contrary, precisely the opposite is the case, since in the extinct Dodo of the Mauritius we have an instance of a huge pigeon which had evidently lost the power of flight ; and the superficial deposits of New Zealand have yielded the remains of a large rail and a goose which were in the same predicament. These and other flightless birds difler, however, essentially in several parts of their organiza- tion from the true Giant Birds, and thus have no sort of connection with the subject of this article. There are, however, certam birds, namely the little Kiwis of New Zealand, which, although by no means entitled to rank as Giant Birds in the proper sense of that term, yet as being closely related to the typical members of that group, must find a place therein. 15efore, however, we can consider the fossil members of this group it is necessary that we should have some idea of the general structure of the leg of a bird, since it is this part of the skeleton which is most commonly met with in a fossil eoudition, and which aftbrds the most important clue as to the size and affinities of the bird to which it belonged. Some observations on this point have already been made in the article on Giaiit Keptiles ; but since those observations were mainly directed to showing the resemblance between 44 KNOWLEDGE [Makch 2, 1891. Fig. 1. — The Bokes OF THE Right Leg OF the Giakt Moa. About jij nat. size. {After Owen.) the leg of a bird and that of a reptile, they are not well suited to oui- present pui-pose. A bird's leg, then, as shown in Fig. 1, is composed of four segments ; the upper short one corresponding to the human thigh-bone, and the lowest representing the toes, which are com- posed of several small bones. Between these two segments are the two long and slender bones shown in the figiu-e. The upper and longer of these two corresponds with the human leg-bone, plus the knuckle-bone welded on to its lower end. The lower and shorter bone, of which another example is shown in Fig. 2, is a very remarkable bone indeed, and may be conveniently ca:lled the cannon-bone. It is reaUy composed of three separate long bones, of which the ends remain free at the lower extremity and carry the toes, and also of the lower part of the ankle welded on to the upper end. The middle long bone corresponds exactly with the cannon-bone of a horse, the nature of which has been explained in the article on " Eudimeutal Organs"; and the whole compound bone would correspond with the meta- tarsus of the extinct three-toed horse known as the Hipparion, if its three metatarsals were wielded together, and these again with the bones of the lower half of the ankle. It will, accordingly, be evident that a bird is an odd-toed animal like a horse (that is to say, the toe representing the middle one of the typical five is symmetrical in itself and larger than either of the others), having a cannon-bone, but no sepa- rate ankle-bones ; the upper ankle- bone having become welded on to the leg-bone, and the lower ones similarly united to the cannon-bone. In these respects, therefore, a bird is a very specialised kind of creature, as departing widely from the original type. With these necessary ana- tomical explanations, we shall be in a position to enter on the subject of the extinct Giant Birds. The first of these extinct birds brought to the notice of the scientific world were the Moas of New Zea- land, in which islands the largest existing representatives of the group the diminutive Kiwis. The original determina- tion of the former existence of these giant birds affords, uideed, an mteresting instance of the certainty of ana- tomical deductions, when made with proper care and suflicient knowledge. Thus, many vears ago a man brought to Sir R. Owen the broken shaft of the thigh- bone of some large animal, which he stated had been obtained from New Zealand, where the natives beUeved that similar bones were those of a large eade. The specimen was a somewhat unpromismg one,%ut after careful comparison the Professor confidently pronounced that It belonged to an extinct bird considerably larger than any ostrich, for which he proposed the name of Dimniis. Other specimens soon after brought to this country triumphantly estabhshed the correctness of this bold identification, and showed that giant birds far sur- Fiii. 2. — Frost and Back Views of the Left Caxxon-bone of A Partridge. are passing in size any pre\'iously known must have existed at a comparatively recent date, and in extraordinary numbers in New Zealand. In the swamps — especially the well- known one of Glenmark, near Canterbury — these bones, and in some cases nearly entire skeletons, are very abun- dant ; wliile in caves there have been obtained not only parts of skeletons with the skin still adhering to them, but even well-preserved feathers, and broken egg-shells. Although the JIaoris well know that these remains belonged to gigantic birds, and give them a name of which the word Moa is generally considered to be a corruption, yet there is some difference of opinion as to whether tlieir ancestors ever saw these birds in the flesh ; some autho- rities considering that they were killed off by the race which is believed to have inhabited New Zealand before the advent of the Maoris. Still, in any case, Moas must have existed up to a very late epoch ; and it is even said that the " runs " made by them were visible on the sides of the hLUs up to a few years ago, and may, indeed, stUl be so. The leg-bone of a Moa may be at once known from that of all living Giant Birds by the circumstance that on the front surface of its lower end, immediately above the knuckle-bone, there is a narrow bar of bone forming a bridge over a small groove (this being indistinctly shown in Fig. 1). In the Giant Moa, of which the leg is repre- sented in Fig. 1, the leg-bone attains the enormous length of one yard, and in an allied species from the South Island its length is upwards of 39 inches. The cannon- bone (as may be seen in the figure) is comparatively long and slender, and is more than half the length of the leg- bone. A skeleton of a smaller individual in the Natural History Museum has an approximate height of 10| feet, and we may thus conclude that the larger birds did not stand less than 12 feet. There were other species of true Moas, of about the dimensions of a large male ostrich, although of stouter build ; and resembling the larger birds in having only three toes to the feet, and not the slightest trace of a wing. Alongside of these giants there w^ere, however, other species of much smaller size, in which there were four toes to each foot, and the cannon-bone was relatively much shorter. Thus the Dwarf Moa, of which the Natural History JIuseum possesses a complete skeleton, was not more than three feet high, while Owen's Moa was of still smaller dimensions. There were also other species of this group nearly as large as an ostrich. Perhaps, however, the most remarkable of all these bu-ds is the Elephant-footed ]\Ioa, which, although by no means equal in height to the Giant Moa, was of much more massive build. In this extraordinary bird the leg- bone is much shorter and thicker than in the Giant Moa, while the cannon-bone is so short and thick that it almost loses the character of a " long bone." In one unusually large example of the last-named bone, while the length is only 9J inches, the width at the lower end is upwards of 6|. By the side of such a bone the cannon-bone of an ox looks small and slender, and the effects of a kick from such a leg can be better imagined than described. The total number of kinds of Moa inhabiting New Zealand was probably at least fifteen, and, from the enormous accumulations of their bones found in some districts, we may assume that these creatures were ex- tremely common, and probably went about in droves. Nothing like this bird-faima is known in any other part of the world ; and its exuberance may be probably ex- plained by the absence of mammals from New Zealand, so that when the ancestors of the Moas once reached these islands they found a fr'ee field for unhmited development. March 2, 1891.] K N O WL EDGE 45 The nearest allies of the Moas are the small Kiwis ; but whereas the latter have long pointed bills for probing in soft mud after worms, the bills of the Moa were short and broad like those of the Ostrich. Moreover, although the Kiwis have no wings visible externally, they retain rudi- mentary wing-bones, which have totally disappeared in the Moas. The plumage of the Moas appears to have been of the hair-like nature of that of the Kiwis. Since the latter differ from the Ostriches in that the females are larger than the males, we may assume that the same condition obtained among the Moas. The Kiwis are further remarkable for the enormous proportionate size of their eggs ; and if anything like the same relative proportions held good with those of the Moas, the egg of the Giant Moa must have been of stupendous dimen- sions. It is, however, probable that the eggs of the larger Moas were relatively smaller than those of the Kiwis. Passing to Australia, we find in the superficial deposits remains of a bird as large as some of the medium-sized species of Moa, but at once distinguished by the absence of a bridge of bone at the lower end of the leg-bone. This bird, which has been named Dnimnrnis, is, however, as yet but very imperfectly known, so that we are to a great extent in the dark as to its affinities, though it was probably a distant giant relation of the Cassowaries. Before we again meet with fossil giant birds we have to cross the whole extent of the Indian Ocean to Madagascar. Here there occurs the enormous bird known as the /Epyornu, the existence of which was first revealed by its eggs, which are foimd sunk in the swamps, but of which bones — mostly imperfect — were subsequently discovered. One of these enormous eggs measures three feet in its longer circumference, and 2i feet in girth ; its cubic contents being estimated at rather more than two gallons. The leg- bone of this bird has no bony bridge at its lower end, and the cannon-bone (of which only a portion is known) is as wide as that of the Elephant-footed Moa, but is much longer and thinner. The natives search after the eggs of this bird by probing for them in the soft mud of the swamps with long iron rods. The Moas, the Dromornis, and the iEpyomis indicate, then, three totally distinct groups of Giant Birds ; and since their various habitats occupy islands on both sides of the Indian Ocean, it is a fair presumption that their common ancestors originally inhabited some part of the great contmental mass of the Old World. Hupport is ailbrded to this hypothesis by the occurrence of the Ostriches on the west, and the Cassowaries and Emus on the eastern side of the same great ocean. IMoreovcr, there is historic evidence to the effect that Ostriches, which are now confined to Africa and Arabia, formerly existed in Baluchistan and Central Asia ; and since their fossil remains occur in the Pliocene deposits of Northern India, there is little doubt that at least this group of Giant Birds originated in the northern part of the Old World. Again, the Indian deposits already mentioned have also yielded remains of a bird dift'ering from the Ostrich in having three in place of two toes, and thereby agreeing with the Cassowaries and Imuus, to which it was doubtless allied, and thus indicating that these birds likewise had their original home on the great Euro- Asiatic continent, from whence they have gradually migrated southwards till they reached regions free from the large carnivorous mammals of the continents. Looking back through the Tertiary rocks of I'hirope to see if we can find there traces of ancestral Giant Birds, it is not till we come to the Lowest Eocene, or period immediately below the Loudon clay, that our search is rewarded. Here, however, both in England, France, and Belgium, we meet with limb-bones and other remains of Giant Birds, which, from their huge size, must almost certainly have belonged to the group under consideration. In this bird, which is known as (Jaxtornis, the lower end of the leg-bone has a bony bridge, as in the Moas ; and since this is a feature common to the great majority of flying birds, it suggests a community of origin between them and the Giant Birds ; the loss of this bridge in the living members of the latter thus being an acquired character. Although we are still very much in the dark as to the real affinities of the Gnstornia, yet it appears to be more nearly related to the Moas and the Dromornis than to any other birds, and it might, therefore, have well been one of the ancestors of the group. This is at present the extent of our knowledge of the former distribution of Giant Birds ; but it may be confi- dently expected that whenever the Tertiary formations of Northern Africa and Southern and Central Asia are fuUy explored, we shall be rewarded by the discovery of other kinds, which will tend to more or less completely connect together those at present known to us, and which will also show how these have gradually migrated, since the Eocene Period, fi-om the great continental northern mass to those southerly areas wherein some have existed up to a comparatively late period, and where others still remain as the sole living witnesses in the Old World of a group which has all but passed away. THE MAGIC SQUARE OF FOUR. By T. Squire Baerett, F.S.S. TO treat fully of the square of 4 alone would take a good-sized volume. The ancient Egyptians and Pythagoreans, in their ignorance of mathematics, thought it so wonderful that a series of numbers could be arranged to add up alike, upward, across, or diagonally, that they regarded such combmations with superstitious veneration. We, however, know that it would be much more wonderful if magic squares could not be made. For example, considering the difficulty with which a person, without some knowledge of the subject, could make a magic square with an arithmetical series of sixteen numbers, it would naturally be thought that it could be done in very few ways. But it was shown by Frenicle that it could be accomplished in at least 880 ways. Nor is this surprising when we consider that there are nearly three billion (2,615,348,736,000) ways of arranging 16 things in the form of a square. It is more than possible that Freuicle"s list does not exhaust the number of such squares. I have never seen his collection, and was therefore rather surprised to find that I could make exactly the same number, but no more. Nevertheless, I should not like to say that others could not be constructed. These 880 squares, consisting as they do of numbers in arithmetical progression, may obviously be classified according to the relative position of each pair of comple- mentary numbers. When the numbers ai-e the natural series from 1 to 16, each complementary pair wUl sum 17; 1 -f 16, 2 + 15, 3 -t- 14, and so on. This classification shows the existence of 12 different types, some of which are very curious. The most perfect of them is the mixik square. [For definition of a uasik magic square, see foot-notf, in KNowi.KixiE, p. 277.] Of this type (which I call A) it can be mathematically proved that only 48 variations are possible. I give an example on the next page. 46 KNOWLEDGE [Makch 2, 1891. N><^^ 10 15 4 a o /^VfX p 8 1 11 n A y Xx X /\0(v/\ 13 12 7 2 o/CxC-^ 3 6 9 16 The diagram on the left shows the Relative position of complementary numbers, a line in each case running fi-om one to the other. The remaining 11 types, with examples, are as fol- lows : — *-v ^\? 1 15 12 6 ^ 'x>C^ 8 10 Hi 3 B y\)\/\ ) o^ x^X^ 1-1 4 7 9 I <=^ ^> 1 4 3 12 8 4 0 4 7 10 (1) 1.3 4 3 2 1 0 4 8 12 (1) IS a square of type C; and (2) and (3) are two skeleton squares which on being added together produce Now, on examining the structure of the squares (2) and (3), we see that their own complementary pairs are arranged in accordance with the type of (1), that is C. In (2) the sum of each pair is 5 ; in (3) the sum is 12. On further examination of the squares, wo may observe that the numbers may be transposed in various ways so as to produce difl'erent results, still belonging to the same type. Thus, in square (2) each 2 may be written 3, and ricf rersii, and each 4 may be written 1, and (■(<■(' rei\t,L Tliis will give in combination with square (3) three addi- tional squares of the same typo, or four in all. Furthermore, the numbers in scpiare (3) may be trans- posed in similar manner, 4 for 8 and 0 for 12, and ricr rt'isii, giving another 4 varieties, which, combined with the 4 varieties of the other skeleton square, give us 4x4, or 10 squares of the type. Again, the arrangement of the two skeleton squares may bo reversed ; we may write down tlic 1, 2, 3, 4 in the way the 0, 4, 8, 12 are written down above, and rice rcisd. 'L'liis doubles the number of squares producible, giving us 10 x 2, or 82. Once more, a partial transposition may be made in the numbers of square (2). For example, the 2 and 3 may bo transposed in the top and bottom rows, whilst those in the middle rows are undisturbed. This partial transposition may be performed on what- ever numbers occupy the middle cells of the top and bottom rows. This again doubles the number, bringing it up to 32x2, or 64. Nor is this by any means all. There are two other ways of decomposing these squares. Instead of putting 1, 2, 3, 4 into one, and 0, 4, 8, 12 into the other skeleton square, we may put 1, 2, 5, 6 into one, and 0, 2, 8, 10 into the other ; or 1, 3, 5, 7 into one and 0, 1, 8, 9 into the other. Thus 1 2 5 C, 0 2 8 10 1 4 13 16 5 6 1 i ID 8 2 0 15 14 3 2 2 1 0 ,') 10 8 2 0 12 9 8 5 6 5 2 1 0 2 8 10 6 7 10 11 (4) (5) (0) ■ 1 3 5 7 0 18 9 1 4 13 1(5 5 7 1 3 9 8 10 14 15 2 3 3 1 7 ,T 9 8 10 12 9 8 5 7 5 3 1 0 1 8 9 7 0 11 10 (7) («) (9) The second set of series in (4) and (5), and the third set in (7) and (8), have just the same arrangement re- spectively as the numbers in (2) and (3). The resulting squares (0) and (9), it may be noticed, are different from (1) and different from each other. Using aU these three sets of series therefore trebles the number of squares pi'e- viously arrived at — gi\dng us 64 x 3, or 192. These 192 squares, however, do not exhaust the type C. I am in- debted to Mr. James Cram, the author of an ingenious little book on magic squares, for five other squares of this type, each of which may be transposed in all the ways above described excepting two, thus producing 16 varieties of each instead of 04. This gives us 5 x 16, or 80 additional squares — making up the 272. 1 give below the analysis of one of these 80, as it is very peculiar : 1 0 12 10 114 4 0 4 8 12 15 11 (! 2 3 3 2 2 12 8 4 0 14 8 9 3 2 4 13 12 4 8 0 4 10 7 13 4 2 3 1 0 8 4 12 (10) (11) (12) The skeleton squares (11) and (12), it will be observed, both sum wrongly in their diagonals. Nevertheless, on combination, the resulting square is found to be correct ; the errors having an opposite character, and neutralising one another. The decomposition of squares is easily effected by aid of little tables like the following : — 1 2 ;! 4 0 4 8 12 1 2 .-i 4 5 C 7 8 9 1(1 11 12 13 14 15 1(! 1 2 5 (! 0 1 2 5 (i 9 3 4 7 8 8 9 10 13 14 0 11 12 15 1(5 1 3 5 7 0 1 3 0 7 1 2 4 6 8 8 9 11 13 15 9 10 12 14 16 Find the number you wish to decompose in the table belonging to the series, and in a line with it will be found at the top the number for one of the skeleton squares, and at the left-hand side that for the other. A PERPETUAL CALENDAR. Mr. C. L. Prinok, of Crowborough, has sent us a very simple perpetual calendar devised by him a few years ago, which avoids the necessity of committing to memory the rather complicated rules given in Mr. R. W. D. Christie's letter in our last number. The accompanying block may bo cut out and mounted oil two pieces of cardboard. The inner circle of Domi- 48 KNOWLEDGE [March 2, 1891. nical letters and days of the month should be mounted on a circular piece of cardboard, affixed by a paper- fastener or button and thread through its centre to a larger piece of cardboard, on which the outer circle con- JULY %8 o. .4^ \rK^<'' I taiuiiig the days of the weeli and months should be gummed concentrically with the inner disc. Mr. Prince's rules for finding the day of the week A List of Sunday Letters Corresponding to any date in this from A. D, iSooto iSqq. ccntury, are as follows : — " Kotate the Circular Index until you place the Sunday Letter for the Ye.ui under the Month you require, when it will show the day of the week for any day in that month, and will thus serve as a Calendar for any number of years. The Letters in the first column of the adjoining Table are the Sunday Letters for each year in the same line." " Li the case of Leap Year (to Feb- ruary 29th only), make use of the first of the two Sunday Letters for that year ; thus, for the year 1888, A woidd be the letter to February 29th, and G for the remainder of the year. " "Each Letter in sixth column de- notes that all years between it and that in column one are Leap Years. This table renders the Calendar use- ful for ascertaining the day of the week of any date during the present century." The days of the week for next century may be at once determined by finding the day of the week for the corre- sponding day of this century, and gomg back two days ; thus, the 1st of January 1801 was on a Thursday, and the 1st of .January 1901 will be on a Tuesday, The days of the week for last century, from the 1-lth of September 1752, when the eleven days were dropped, till the end of the century, may be determined by finding the day of the week for the corresponding day of this century and going forward two days ; thus, the 1st of January 1853 was on a Saturday, and the 1st of January 1753 was on a Monday. To determuie the days of the week for the twenty-first n 1 I 1 29 1 57 1 8S 1 C 1 3 1 30 1 58 1 86 1 B 1 3 1 31 i 59 1 8» 1 A 1 4 1 32 1 f.o 1 88 1 U i' 1 5l33|0T|89l E 1 b 1 34 1 62 i 90 1 D 1 7 1 35 1 63 1 9" 1 C 1 8 1 36 1 64 1 92 1 B A 1 9 1 37 1 65 1 93 1 G 1 10 1 38 1 66 1 94 1 r 1 II 1 39 1 67 1 95 1 E 1 12 1 40 1 68 1 96 j D C 1 13 1 41 1 69 1 97 1 B 1 14 1 42 1 70 1 98 1 A 1 15 1 43 1 71 1 99 1 G 1 16 1 44 1 72 1 1 F E 1 H 1 45 1 73 1 1 0 1 18 1 46 1 74 1 1 C 1 19 1 47 1 75 i 1 B 1 2o 1 48 1 76 1 1 A G 1 21 1 49 1 77 1 1 F 1 22 i JO 1 78 1 1 E 1 23I51 I75I 1 D 1 24 1 52 1 80 1 i C B 1 25 1 53 1 81 1 1 A 1 26 1 54 1 82 1 1 G 1 27 ( 55 1 83 1 1 F 1 28 1 56 1 84 1 IE century we must go backwards three days in the week from the corresponding day of this century, for the year 2000 will be a leap year, while the years 1900, 2100, &c. are not leap years. For the twenty-second century the rule will be — go backwards five days in the week, which is the same thing as going forward two days. In the twenty-third century, people will keep the tetra- centenaries, or fourth-century celebrations of events which have happened in this century, on the same day of the week as that on which they actually happened or are suj)posed to have happened. In future all tetracentenaries will occur on the same day of the week as the event they commemorate, for a period of 400 years must always include one year which will divide by 400 without leaving a remainder. NOTE ON THE ORBIT OF THE DOUBLE STAR 5 2. By S. W. Buknham. IT would have been hardly possible to get even an approximate orbit of this star with the measures made during the fifty years following its discovery. At the time of the first observations by Struve it was comparatively easy to measure ; but the stars slowly approached each other, and after 1858 the measures are few and very imcertain. Many of the estimated, or partly measured position-angles are obviously very largely in error, judging from the earlier measures which may be assumed to be reasonably exact, since the distance between the components was sufficient to make it easily measure- able with a moderate aperture. No attempt, so far as I am aware, has been made to compute an orbit from these measures. The entire angular motion from 1830 to 1858 was only 12^. The principal change was in the distance, which at the last-named date was only one-half that at the time of the first measures by Struve. So far as these observations are concerned, they coidd be as well repre- M.uicH 2, 189].] KNOWLEDGE. 49 sented by rectilinear motion as any other. The proba- bilities, however, in the case of a pair of this kind are greatly in favour of the relative change being due to orbital motion, and it was safe to assume that these stars were far more likely to be physically connected than that one was drifting past the other from proper motion. In using the 30-inch telescope for double star work, as far as time would allow, I have looked up and re-measured some of the old pairs which have either been single for many years, or so difficult that they were practically non- measurable with ordinary telescopes. The result has been that in a number of instances a single set of measures of each star made it possible to get a reasonably accurate idea of the periods. In this case, the change in angle since the last measure of Otto Struve amounts to over 160°, so that the apparent path of the companion in the future is confined within narrow limits. I had overlooked, when placing this star on the working list, an excellent set of measures by Tarrant in IHHH, made vn.th a 12-inch reflector. These measures are remarkably accordant with my own made with a much more powerful instrument. I have taken all the measures of this pair wliich can be used in any investigation of its motion, and laid them ofl' accurately to scale (5 inches=l"), with the distance to the second decimal place, and the angles to the nearest tenth of a degree. As nearly as possible through these positions an ellipse has been drawn which will make the areas proportional to the times, and allow of the minimum correction of the observed angles and distances. The figure shown on the accompanying diagram is in sub- stantial compliance with these conditions, and the errors of observation are practically insensible in measures of this kind. The following are the measures made use of : — 1830 -85 1840 -50 1848 -22 1808 -.50 1880 -58 1888 -0!) 1890 -82 341-5 338-4 334 •■'.) 329-3 0"-81 0"-74 0"-52 0"-44 5 5n 02 3n 05 (5 n 02 10 n Certainly single /3 182--8 0"-3± T 3n 177''1 0"-29 13 3n During the interval of about thirty years, in which there are no measures, it was frequently noted as single, and doubtless was apparently so with the instruments used ; but much of the time the distance must have been at least 0"-2, and of course this would have been noticed with a larger aperture. I have given above my own negative results in 1880, as the observation was made with the l8-;'j-inch of the Dearborn Observatory, and the distance must have been very small to have escaped detection. According to this orbit, at that time the distance should have been a little less than 0"-15, and so slight an elon- gation probably would not have been noticed with that aperture. With the Lick telescope it would have been measureablc at all times. It is not claimed that anything more than approximate results can be derived from these investigations, but the graphical method is probably as good as any other with the present data. It is evident that the period is a long one ; and according to this ellipse it would be about 450 years. Wo have also the following : — Maximum distance - - - 0"-98 Minnnum distance - - - 0"-13 (1870) Major axis . . - - l"-55 Minor axis ... - 0"-58 Position angle of major axis - lC4°-5 The change for some time will be mamly in distance. In about five years more it should be 0"-4 ; and it will then be easily measurable with almost any instrument. Frequent measures of a pair of this class are not neces- sary. A few careful sets of measures every five or ten years will be all that is required for any purpose. Hcttcrs. [The Editor does not hold himself responsible for the opinions or statements of correspondents.] HOW DID HE FIND THE WAY ? To the Editor of Kxowledge. Dear Sir, — If it will not trespass too greatly on your space, I shoidd be glad if you coidd afford room for the following incident : — In August 1889 a gentleman and his family removed from Stockport to St. Leonards-on-Sea, taking with them a fine Tom cat they had had several years. Tom seemed restless at this change of quarters, and, after about a fort- night, disappeared. Some weeks later, Tom's master received a letter from one of his sons who was resident in Stockport to the effect that Tom had been seen by the neighbours prowling round his old home. Shortly after, he disappeared again, and about three weeks later again arrived at St. Leonards in a very dejdorable condition — reduced to a mere skeleton. His master, on returning home late one night, found the cat on the door-step, and was welcomed by him with every possible demoustration of delight. Tom has been very feeble ever since, and is most unwilling to leave the house. The puzzle is. how could the cat find his way from St. Leonards t) Stockport, a distance of 200 miles, seeing that he was brought by train, and was shut in a sack for most of the way. And to make the puzzle yet more difficult, the railway journey was necessarily broken in London, and the cat was conveyed from the northern to the southern station in a cab. The return journey to St. Leonards one can understand, but how did he find his way to Stockport "? — E. W. Mavnder. [The weak link in this remarkable story seems to be that Tom was only seen and recognised by the neighbours, prowling round his old home. A recognition by tlie son would have been more satisfactory, especially if he had marked Tom. — A. C. Ranyard.] I have made inquiries, and find that — 1. The intimation that the cat had appeared in Stock- port was an independent one, i.e. before the people at Stockport knew that the cat had been missed at St. Leonard's. 2. The cat was away just over seven weeks in all, and was seen at Stockport during the middle week of the seven. 3. The cat was seen, recognised, fed, and taken care of by the next-door neighbours of its owners. The son resi- dent in Stockport was unfortunately unable to come to identify the cat until after it had set out on its travels again. 4. The cat, which was formerly very fine and healthy, has sulfered over since from severe bronchitis. 5. ^'either the owners of the cat nor the neighbours have the slightest doubt as to its identity. Indeed they are disposed to be rather indignant if it is hinted that there may be the possibility of a mistake. If it was not the same cat that turned up at Stockport,, then there certainly were some remarkable coincidences. E. \V. M.UTNDER. 50 KNOWLEDGE. [March 2, 1891. THE MILKY WAY IN THE SOUTHERN HEMISPHERE. ]')Y A. C. Ranyaku. Tl 1 1', plates illustrating this paper have been made from photographs taken by Mr. Russell, Director of the Sydney Observatory, New South Wales. They will bear close examination with a magni- fying glass, and the sharp images of the small stars show how very accurate and steady must have been the motion of Mr. Russell's driving clock, which kept the camera directed to the stars during the exposures by a motion about the polar axis of the instrument in a con- trary direction to the earth's motion about its axis. The driving clock was controlled by an electrical apparatus, contrived by Mr. Russell, which connects it with a govern- ing clock and two heavy pendulums. These photographs form a very satisfactory certificate of Mr. Russell's method of electrical control, and show that the differences of re- fraction due to the changes of the altitude of stars during long exposures may be more accurately compensated for than had hitherto been supposed. The scale of these star-pictures will be best appreciated from photograph No. II., which shows the greater part of the lower or southern portion of the constellation of Orion. The three stars at the bottom of the picture form the belt of the constellation giant. The three stars in a nearly vertical line above them, with the Great Nebula about the central star, form the sword ; and the two stars on either hand towards the top of the picture form the feet of the giant. Unfortunately the printers have turned this pic- ture, as well as No. III., with the south point at the top instead of at the bottom of the pictures, as in Nos. I. and IV. Picture No. II. enables us to show that the central line of symmetry of the Orion Nebula, towards which the great curving structures springing fi-om the neighbourhood of the trapezium are synclinal, is, as nearly as one can judge, at right angles to the medial plane of the Milky Way. A reference to any good star map or globe showing the Milky Way, will show that the line passing through the stars of Orion's Belt is nearly parallel to the plane of the Milky Way, the axis of sym- metry of the Great Nebula is nearly square to the line of the belt, and consequently at right angles to the general plane of the Milky Way. Another fact worth mentioning, as showing an apparent symmetry with regard to the plane of the Milky Way, is that the two remarkable nebu- lous lines joining stars in the Pleiades Nebula* are approxi- mately parallel to the general plane of the Milky Way, though neither of the lines are quite straight or parallel the one to the other. The edges of the great curving structures of the Orion Nebula are all harder on the inside towards the axis of symmetry which passes through the trapezium, and softer or more nebulous on their outer or convex edges. The scale of picture No. II. is too small to show this, though it is partly shown on the larger picture published in the May number of Kno^\xedge for 1889, and referred to in the accompanying article on the Nebula. It is still more evident on the original negatives, and would alone prove, even if we knew nothing of the symmetry of curvature of the tree-like structures which spring from the trapezium region, and of the canopy which overhangs the whole nebula, that there are mighty forces acting towards and away from the axis of symmetry — that is, parallel to the plane of the Milky Way. * See Knowledge for January 18S9, pp. 69-70. It will be remembered that both the Pleiades Nebula and the Orion Nebula lie a little to the south of the Milky Way, at about the same distance from its medial plane. There seems to be no obvious connec- tion between the plane in which the Great Nebula in Andromeda lies and the plane of the Milky Way, and the same remark applies with regard to the Ring Nebula in Lyra. The elliptic patches of light into which these nebulne project have not their major and minor axes parallel and perpendicular to the medial line of the Milky Way, as would lie the case if the planes of these nebulre were either parallel or perpendicular to the plane of the Milky Way ; but though these two nebulae are both on the borders of the Milky Way, the spiral nebubf do not seem to be associated with the Milky Way in the same intimate manner that the other large and irregular nebulie are ; thus the spiral nebulie in Ursa Major and Canes Venatici are at some distance from the Milky Way, and their planes are evidently not parallel to one another. Even the small elliptic nebube H.V. 18, discovered by Miss Caroline Herschel close to the great Andromeda Nebula, evidently lies in a different plane from the Great Nebula. Picture No. I. represents the part of the Milky Way in Sagittarius photographed by Mr. Barnard, which we reproduced in the .July and August numbers of Knowledge. The differences between Mr. Russell's photograph taken at Sydney on the 2nd October 1890, and Mr. Barnard's photograph taken at the Lick Observatory on the 1 st .\ugust 1889, are very curious and worthy of close attention. Both photographs were taken with six-inch portrait lenses of about 31 inches focus, so that they are on about the same scale, and the pencil of light falling on the sensitive plate was in each case of about the same intensity. Mr. Barnard's photograph was exposed for .Sh. 7ni., and Mr. Russell's for 4h. 2m. Nevertheless, Mr. Barnard's photograph shows much more of the nebulous structure of this region of the Milky Way than Mr. Russell's. This might be due to dift'erences in the method of development, or to a difi'erence in the sensitiveness of the plates used (Mr. Russell seems to have used Ilford extra lapid plates ; and Mr. Barnard, I believe, used some plates prepared by the American Seed-plate Company). But it is remarkable that the relative brightness of the nebulous areas on difl'erent parts of the plates do not correspond with one another on the Russell and Barnard plates. The reader should refer to the large picture from Mr. Barnard's nega- tive published in the July number of Knowledge in order to follow what I am about to say. He will then see that there are great differences in the brightness of different parts of the nebulous structure, while the relative bright- ness of the stars is much the same on both the plates — with one notable exception, which it may be weU to draw attention to before referring to the difi'erences in the brightness of the nebulous light. In Mr. Barnard's picture there are two clusters of stars near to the edge of the field at the bottom of the plate. Only one of these clusters, \-iz. that to the right hand or western side of the field, is shown in Mr. RusseUs plates. The almost equally brilliant cluster near to the bottom of Mr. Barnard's plate is missing in the Sydney photographs, for Mr. Russell has sent over silver prints from two nega- tives, one taken on the 17th September 1890, and the other, reproduced in our picture No. I., taken on the 2nd October 1890. I at first thought it possible that both photographs might by mistake have been copied from the same negative, and that the dift'erences between the Lick and Sydney photographs might possibly be due to in- equahties in the sensitiveness of different parts of the film of Mr. Russell's plates. But it is evident that no "!«"ll"J March 2, 1891.] KNOWLEDGE. 51 such mistake can have been made, for Mr. Russell's photograph of the 2nd of October contains a trace made by the planet Mars during the exposure, while the photo- graph we have here reproduced does not. There seems, therefore, to be no doubt that we have two independent photographs, and we seem to liave evidence of very rapid change in the brightness of the southernmost of these two star-clusters. While the nebulosity in the upper part of Mr. Russell's picture corresponds generally with that in the upper part of Mr. Barnard's picture, making allowance for differences ■of sensitiveness of the plates used, that in the middle and lower parts does not. The brightest" nebulous region in Mr. Barnard's picture is on the right-hand side of the tree- like form which stretches across the middle of the plate at the base of its lowest right-hand branch. Hut this bright region is entirely wanting in Mr. Russell's photographs, as also is the very bright nebulous region to the left-hand side of the base of the great tree-like structure. It is, of course, possible that such differences might be due to the nebulosity of the upper part of the tree-like structure being caused by a stippling produced by larger stars than those which give rise to the nebulous appearance on the lower part of the plate, and that while the small stars have left their trace on Mr. Barnard's plate, only a larger grade of stars have impressed themselves sufficiently to leave a developable trace on Mr. Russell's plate. It is also pos- sible that the lower part of the nebulous mass may shine with a dift'erent kind of light from that with which the upper part shines, and that while Mr. Barnard's plates were sensitive to both kinds of light, Mr. Russell's were only sensitive to the one. But it is also possible that we may here have e\'idence of the existence of a vast variable nebula which undergoes changes in the relative brightness of its parts with surprising rapidity. I sliould like to call attention to the fact that the branching tree-like form shown in Mr. Barnard's picture (the upper part of which appears in Mr. Russell's pictures) seems to afl'ord us e\-idenceof the projection of matter into a resisting medium just as certainly as the tree-like forms in the great Orion Nebula and the tree-like forms f in the Corona bear witness to explosions on a colossal scale, which have taken place below their bright bases, causing a stream of matter to be projected upwards, which stream has subsequently been divided and its branches deflected from their original course by a resisting medium. If there were no resistmg medium and the only force acting on the projected matter was gravity towards the region from which the explosion took place, the streams would have the form of trajectories, and they could only bo projected into conic sections. The actual existence of the great tree-form on Mr. Bar- nard's picture seems to be confirmed by the arrangement of the stars in lines along its branches, which is best shown in the small photographs published in the August number of Knowleduk for 1890, and in the Munthli/ Xoticcs of the Royal Astronomical Society for March IK'JO. To see the stars in these small pictures they should be examined with a magnifying glass. The brighter streams of stars will be recognized in Mr. Russell's photographs after they have onco been seen in Mr. Barnard's. We seem, therefore, to have evidence that there is a resisting medium which occupies a vast region of the * The ne.irly circular white patch at the top of tho picture ie, as was explained in the July number, duo to an over-exposed image of the planet Jupiter, with the Trilid Nobula below it. Jupiter has moved away and the Tritid Nebula remains on Mr. Hussell's pictures. t See Knowledge for May 1889, p. HO. Milky Way ; and perhaps the whole nebulous circle which surrounds the sky is not one vast nebula. The resisting medium need not be gas ; dust mo\'ing in space, or larger particles, would equally offer resistance. The variability in brightness over so vast a region, if substantiated by future photographs, will need us to assume the existence of forces travelling far more swiftly than Ught or elec- tricity, and giving rise to the synchronous dimming or glowing of the light-giving matter. Picture No. III. represents the Nebecula Major (the larger Magellanic cloud), taken by Mr. Russell on the 17th of October 1890 with an exposure of 7h. 3m. In a private letter enclosing me the silver print of this picture Mr. Russell says : " This negative has brought out the grandest spiral structure in the heavens. Herschel estimated this object to cover 48°. It is now shown to be one great spiral structure supported, as it were, by two smaller ones in which Mars onhj are visible. One is situated on the North follawlnii, and the other on the South priredimj side of the great spiral." These spirals are just visible on our plates, but they are not so well shown as on the silver print or on the transparency which Mr. Russell has kindly sent me. Picture No. IV. represents the Nebecula Minor, taken on October 11-15, 1890, with an exposure of 8 hours. It is also spiral in structure, though not so clearly so as the Great Nebecula. Within it and around it are some curious streams of small stars, all of about the same magnitude. One of such streams, shown in our plate on the upper left-hand side of the chief cloudy mass, is like a double W. M r. Russell has also sent over a most interesting contact print from a negative of the Coal-sack region. Instead of being a completely closed space, it is seen to be open on the south side, and very numerous small stars are seen to be scattered over three-fourths of its area. It is only at its northern jiart that there is the absolute absence of stars so frequently referred to by Mr. Proctor. jSToticrs of Boofes. The Flii/aical Properties of Gaxex. By Arthur L. Kim- uALL, of Johns Hopkins University. (William Heinemann, London. 1890.) Professor Kimball's book will be wel- comed as giving, in simple, untechnical language, and in a manner easily to be comprehended by the non-mathe- matical section of the community, the reasoning by which physicifts have been led from the properties of gases as they were discovered by experiment to the present gene- rally accepted kinetic theory of their constitution. After having given in brief outline a historj' of the discovery of some of the more important gases and their behaviour under pressure and expansion by heat, Prof. Kimball deals with the easily condensable vapours, and the gases which do not obey Boyle's law. He then treats of air- pumps and diffusion and occlusion. .\vagadro's law that equal volumes of all gases, under tlie same con- ditions of temperature and pressure, contain the same number of molecules, is illustrated and explained in a manner that must make it clear to the most obtuse. Crookes's experiments with high vacua and radiant matter are also well explained and illustrated. It is, perliaps, a pity that Prof. Kimball does not go a little further and show, as he might have done in an ele- mentary manner, how the average velocity of the molecules of a gas may be determined from its density when the pressure which it exerts at a known temperature is measured, and how the number of molecules may be 52 KNOWLEDGE [March 2, 1891. estimated from experiments on the diffusion and ^^scosity of gases. One of the most striking illustrations in the book is given in the chapter describing Sprengel pumps and high vacua. He says, " These high exhaustions are called by coui-tesy vacua, as they are the nearest approaches that physicists have been able to make to an absolute vacuum by the most refined methods known to science ; and yet we should hardly call that space a vacuum in every cubic inch of which there are 350 million million molecules of the gas ; and, according to the latest con- clusions of the molecular theory, that is about the number in a cubic inch of air when it is reduced to one-millionth of the atmospheric pressure. To form some conception of the vastness of this number, we may consider that if, through the side of a little glass bulb of one cubic inch capacity that had been exhausted to this extreme degree, a hole were to be made through which a million molecules could enter in every second, it would take ten years for the pressure inside the bulb to be doubled ; that is, for as many more molecules to pass through as those already contained in the bulb." Unfortunately, the book does not contain an index. Tlifi Crimiudl. By Havelock Ellis. (Walter Scott, 1890.) During the last fifteen years the study of criminal anthropology has been carried on with great activity, and the rich harvest of facts which has already been collected is likely to lead to valuable conclusions, which may pro- bably in the future enable us to deal more wisely with the criminal residuum that will always exist m a civilised society, in spite of school boards aud free libraries and the other panaceas of certain theorists and philanthropists which are constantly proclaimed, like the patent medi- cines of the advertising quack, as a cure for all ills, social and political. The sentimentalist, who generally sympa- thises so much more with the notorious criminal than with his poor neighbour or relation, wiU be surprised to read what Mr. Havelock Elhs says about the physical sensi- bility of the criminal classes. He instances the wide pre- valence of tattooing among them, fi'equently of the most sensitive parts, which are rarely tattooed amongst bar- barous races, as showing the deficient sensibility of criminals to pain. Lauvergne mentions a convict who smiled with pleasure when, moxas having been applied to him, he saw his skin bm-niug and heard it crack. Though loud in their complaints of trivial ailments, thej- are often unconscious of severe Ulness. At Chatham, in 1888, a prisoner dropped down dead on returning from labom- ; both lungs were foimd to be affected, and death was probably due to syncope. He had made no complaints to anyone. Prisoners will inflict severe injuries on them- selves in order to gain some trifling object. At Chatham in 1871-72, 811 voluntary wounds or contusions are recorded ; 27 prisoners voluntarily fractured a hmb ; and 17 of them had to submit to amputation ; 62 tried to mutilate themselves, and 101 produced woimds by means of corrosive substances. BIRDS AND BERRIES. By the Kev. Alex. S. Wilsox, M.A., B.Sc. NATURAL History furnishes many curious illus- trations of the mutual relationships subsisting between the animal and vegetable kingdoms. Of these we have remarkable examples in the weU-known adajstations of flowers to the visits of insects. It is of the highest importance to a plant to have its seeds properly crossed, and this involves the transference of pollen from one flower to another of the same species. Insects frequenting flowers get dusted with this substance ; they carry it with them to other flowers, where some of it adheres to the stigma prepared for its reception. The honey is not provided merely to gratify the bees, but as an inducement to them to visit the flowers and effect their fertilisation. A flower, in fact, is httle more than an apparatus for securing cross-fertili- sation. The scent and colour serve to guide the insects, while the shape of the flower is generally such that the bee cannot reach the honey without effecting the object for which it has been attracted. Insects are not, however, the only animals to which plants are thus related. A considerable number of flowers appear to be adapted to birds rather than to insects. Humming-birds in America, sun-birds in Afiica and India, the Malayan lories, and the Australian honey- eaters, visit flowers and efiect cross-fertilisation very much as butterflies and bees do in Europe. The bird- fertilised class includes species of Fuchsia, Passiflora, Salvia, Abutilon, Impatiens, Lobelia, Marcgravia, Ery- thrina, and Cassia. Ornithophilous, or bird -fertilised, flowers are generally of large size, tubular in form, and secrete abundant nectar. Their colours are extremely brilliant, scarlet being perhaps the most frequent. Flowers of this description are rarely produced by her- baceous plants ; they occur, as a rule, only on shrubs and trees. Birds are employed to carry seeds much more frequently than for the transport of pollen ; these bird-fertilised flowers have, however, a special interest as throwing light on the relations between birds and coloured fruits. Fruits and seeds constitute a large proportion of the food of many animals ; but if any animal were systematic- ally to consume the seeds of a particular plant, the latter would run no small risk of extermination. To the animal itself this would be a serious misfortune if thereby it were deprived of its usual food. In the interest of the plant, as well as of the animal supported by it, some limitation to the consumption of seeds is necessary. Hence many plants conceal their seeds ; in other cases these are obscurely colom-ed or encased in hard shells in order that at least some of them may escape being de- voured. Other plants have been able to avail themselves of the services of animals, and can thus reimburse them- selves for the loss they occasion. In some parts of Africa visited by the late Dr. Livingstone the grasses of the pastures frequented by herds of antelopes had their seeds adapted for dispersion by these animals. This arrange- ment is a mutual benefit, for in disseminating the seeds of the grass the antelopes imconsciously provide for their own futm-e. The same thing may be said of birds which feed on berries and other succulent fruits. These are useful to plants in scattering their seeds, and in return they receive the soft, sweet pulp of the fruit, with the prospective advantage of a future crop from their own sowing. In plants which employ birds for then- dis- persion the adaptation is seen in the succulence, sweet taste, and bright colour of the fruit ; and in the hardness, bitter taste, and emetic or purgative properties of the seed. There are two perfectly distinct objects to be secured ; the attraction of the birds, and the protection of the seeds. Hence the succulent portion is not as a rule the seed itself, but some part of the pericarp or wall of the fruit. Berries have the pericarp entirely succu- lent, the hard seeds being embedded in pulp. Drupes, or stone-fruits like the cherry, have only the outer layers of the pericarp soft ; the inner wall of the fruit, called the endocarp, is indm-ated, and forms the stone enclosing March 2, 1891.] KNOWLEDGE 63 the seed or kernel. Where the seed is so protected, it may itself be comparatively soft. The pomegranate and gooseberry are exceptional in this respect, that the testa, or outer layer of the seed, is developed in a succulent manner, the central core of the seed being, however, hard. The strawberry has the top of the flower-stalk very much enlarged ; the edible portion is, in fact, formed from the thalamus (or spreading portion of the stalk from which the flower springs), the fruits being the little yellow seed- like bodies studded over its surface. The raspberry and bramble, on the other hand, have a dry, conical thalamus, on which are arranged a number of drupes corresponding in structure to the plum and cherry. In the mulberry the succulent portion is furnished by the calyx, and in the apple and fig the hollow receptacle, or flower-stalk, supplies the food material. From the small size of the seeds of berries we may infer that they are adapted to be swallowed along with the pulp. In the larger drupes the size of the stones and their rough or jaggy exteriors, as seen in the peach-stone, seem to indicate that the intention here is to induce the bu'd to fly to a distance with the fruit, and after devouring the soft portion, to drop the hard endocarp containing the seed. Where a fruit is not intended to be eaten it invariably acquires a hard and dry character. Fruits adapted to birds are for the most part sweetly tasted. They contam, in addition to sugar, organic acids and essential oils, which confer an agreeable or even delicious flavour to the fruit, and constitute an attraction to birds as powerful as the nectar of flowers is to insects. If these quaUties appeared too soon there would be a danger of the seeds being removed before they were ripe. Accordingly the fruit remains sour until the seeds are matured. Succulent fruits are brightly coloured, to be easily recognised from a distance. Conspicuousness may be increased, as in the clusters of the grape, rowan, and elder- berry, by the massing together of the single fruits in groups, just as happens in composite and other flowers where the florets are crowded on a contracted inflorescence. The colour of the fruit in general presents a strong con- trast to the foliage. If the fruit remain on the tree after its leaves have fallen, its colour will challenge attention all the more as the season advances. The scarlet fruits of the wild rose thus remain on the bare branches and pre- sent a most conspicuous appearance. When the ground is covered with snow, coloured berries form prominent objects in the country landscape. Artists frequently avail them- selves of this contrast, and introduce into snow scenes a sprig of holly with its scarlet berries. When Zeuxis painted the picture that deceived the birds, he may have taken advantage of this contrast ; but perhaps it was left for Father Christmas to reveal to us how perfectly the colours of fruits serve the purpose intended by nature. The list of plants bearing coloured fruits includes the following, which are British : — berberry, bittersweet, spindle-tree, strawberry, rose, hawthorn, currant, rowan, dogwood, honeysuckle, whortleberry, cranberry, bearberry, holly, daphne, arum, asparagus, lily of the valley, yew, alder, sloe, bramble, elder, bilberry, crowberry, juniper, misletoe, and snowberry ; besides these, may be mentioned the orange, tomato, fig, date, olive, and mango. The colours of fruits arc less varied than those of flowers. Possibly this may arise from the circumstance that wliile it is of importance, as regards fertilisation, that insects should be able to recognise and distinguish dirtereut species of flowers, there is no necessity for birds to distinguish difl'erent fruits, or to conliue themselves to one kind of fruit, as insects restrict themselves for a time to one species of flower. Although never variegated like flowers, nuinv fruits under cultivation exhibit a twofold colouration ; thus we have red and green gooseberries, purple and green grapes, red and white strawberries and currants, green and purple plums, &c. [To he contimu'd.) VARIABLE STARS OF THE ALGOL TYPE. By Miss A. M. Clerke, AiUlivr of ".1 Popular History oj A.itronoini/ durini/ the Xinett-'ent/i Century" and " Tlw System of the Stars." TEN stars of the Algol type are now known — ten stars, that is to say, which vary in light not so much physically as geometrically, through the accident of our point of view. They are, to begin with, very rapid binaries ; but other binaries equally rapid shine with sensible constancy. It is only when the orbits of the revolving stars lie so nearly edge- wise to the earth as to involve mutual occultations, that the peculiarity of a sudden loss of light at brief intervals is added to the peculiarity of composition into abnormaUy close systems. This has been spectroscopically demon- strated as regards Algol ; and the other members of the class copy its phases with such fidelity as to leave no doubt that they too are genuine " eclipse stars." To argue the point would be to enfoneer une porte ourertc. But this is not all. There are residual phenomena not amenable to explanation, simply by the recurring transits of a semi-obscure mass. Eclipses beyond question in all cases occur, and produce their due efi'ects ; yet compUcated with others owning a different origin. Slight as these often are, their investigation offers perhaps the most promising clue to the labyrinth of stellar ///ii/.v/(V(/ varia- bility. For their evident connection with certain calculable phenomena of eclipse defines clearly the conditions under which they occur, and strongly suggests their origin through some form of mutual influence by closely re- vohing bodies, demonstrably of low average density. More- over, the residual variations of Algol stars are of a nature tending to bridge the gap separating them fi-om other variables. That is to say, the irregularities of light-change in the two orders show a very ciuious inverted correspondence, as if the same causes which produce darkening in the one set of objects produce brightening in the other. This unlooked-for circumstance can scarcely fail to become the guide to some important truth. For eliciting it, however, observations both more de- tailed and better assured than those yet obtained are urgently needed ; and it seems unhkely that they will be available until in this, as ah'eady in so many other de- partments of astronomy, the retina is superseded by the sensitive plate. The eye is nowhere more subject to illusion than in following the course of rapid liuninous fluctuations ; and its disabilities are not removed by any kind of auxiliary apparatus. Its very powers of adapta- tion, indispensable to it as a living organ, serve to impair its usefulness as a photometer. The stars, then, must register their own changes, and the method of photo- graphic trails appears eminently suitable for the purpose of inducing them to do so. Professor Pickering has shown that comparative measures of different stars made in this way are reliable to about one-tenth of a magnitude ; and discriminations based upon the varying width and in- tensity of successive sections of the same trail might be expected to reach a still higher grade of precision. Some practical ditliculties would certainly have to be met, but probably none that would prove insuperable. Thus, an arrangemoiit might be contrived lor automatically, at fixed 54 KNOWLEDGE. [March 2, 1891. intervals, moving the telescope in right ascension by the width of its own field, while the plate was simultaneously shifted ^O" or 30" in declination. A series of parallel trails would result, exhibiting with absolute fidelity the gradations of loss or gain of light by which an Algol star traversed a critical stage of its minimum. Although ex- posures covering the whole of any one minimum could rarely be obtained, the comparison of trail-pictures of various sections of successive minima would be almost equally instructive. The realization of this plan would seem to be of considerable importance for the study of variable stars, and may safely be left to the ingenuity of celestial photographers. The eclipse-theory of stellar Ught-ehange possesses little elasticity. Its explanatory powers are well defined, and incapable of extension. In the first place, the progress of the variations which it can account for must be along a smooth curve. There can be no stoppages or interrup- tions. Again, the amount of change must be invariable. High and low minima might, indeed, very well alternate in the same star, although they have not yet been found to do so ; but capricious deviations from the assigned measure of obscuration are inadmissible. They seem, nevertheless, occasionally to occur. S Cancri and U Ophiuchi have each been once observed to lose far more than the usual proportion of their light ; and M. Duner recorded, at Upsala, November 2-5 and December 7, 1890, two abortive minima (as they might be called) of Y Cygni, when the star dropped to the extent of scarcely five, instead of eight tenths of a magnitude.* Besides these anomalies in the measure, there are anomalies in the mode of change, which are equally per- plexing and more persistent. The curves graphically representing it are unsymmetrical in at least seven of the Algol stars.! Their light, in other words, varies at a dif- ferent rate before and after minimum. This is obviously incompatible with the progress of an eclipse by a body mo\lng in an approximately circular orbit. And marked ellipticities are impossible (as Professor Pickering long ago pointed out in the case of Algol) where the conjoined stars are in such proximity as to leave no room for con- siderable oscillations about a mean distance already perilously small. But indeed no amount of eccentricity in the paths tra- versed could satisfactorily account for the observed pecu- liarity. To begin with, the retardation does not advance continuously ; in three or four of the stars a pause is indi- cated, followed by a resumption of progress. Moreover, the observed irregularities are of an invariable type ; they take the form of a delay in recovery after minimum. It * The exceptional minima of all these three stars have been re- corded on excellent authority. TJ Ophiuchi is No. G, 1G2 of Schjel- lerup's Copenhagen Catalogue, and was suspected by him of variability, on tile ground of his careful observation of it, June 9, 1863, as of 7'7 magnitude, while Lalande had put it at G, Bessel at 7 magnitude. The regular course of change of the star, since ascer- tained by Mr. Sawyer, is from G'O to G-7 magnitude once in every 20'3 hours. Of S Cancri the usual range is from 8-2 to 9 '8 magnitude. Nevertheless, Schmidt observed it at Athens, April 14, 1882, to remain stationary for a whole hour at 11-7 magnitude (Aslr. Nach., No. 2,491^. In his determinations of Y Cygni, Duner used Ch.andler's comparison-star /), of 7-8 magnitude in the Durch- musteruny, and exempt from any suspicion of change. At all the minima oi)served by Chandler and Yendell. T Cygni sank decidedly lower than this star ; but on the two occasions mentioned in the text Dunc'r found it to remain two steps (about one-fifth of a magnitude) brighter, and concluded, on apparently strong evidence, its phases to be inconstant {Astr. Nach. No. 3,011). t These are: Algol, S Cancri, 8 Libnc, X Tauri, U Cephei, U Ophiuchi, and U Coronac. S Antli.-c will probably be added to the list ; and we are unacquainted with particulars as to the phases of Y Cygni and R Canis Majoris. is always the ascending branch of the curve which is lengthened.; In order to explain this remarkable circum- stance on gravitational principles, we should need the wholly unwarrantable assumption that nil the stars in question passed periastron before falling under ecUpse. Such a concurrence of coincidences is of course highly improbable. Look, besides, at the minimum curve of U Ophiuchi de picted in Fig. 1, from the mean of 295 observations by Mr. Chandler. haq T-7-1 1 1 1 i 1 1 1 r 0^ / Z J ^ s- Fig. 1. — MiNiMDM of U Ophiuchi. From 295 Observations by Mr. S. C. Chandler. The singular inflection of its ascending line is vouched for, as an objective reality, by the independent determina- tions of Messrs. Chandler and Sawyer {Astninumk-al Journal, No. 177), and often appeared more conspicuous in individual phases than as it emerged from the average of many. The possibility of regarding it as an effect of orbital retardation is at once excluded by the fact that, on the whole, there is no delay. Accelerated progress before and after the pause is so exactly compensatory that the duration of recovery just equals the duration of decline, notwithstanding irregularities in the rate of one as com- pared with the rate of the other. Here, then, evidently, we have a physical cause of obscuration co-active with the geometrical one, and tra- velling in its train. Conjectures as to its natiu-e hence naturally associate themselves with the enormous tidal strains necessarily prevalent in systems of such peculiar construction as those of Algol and its congeners. From these extensive deformations of figure must result in both members of each revolving pair ; but the effects upon light-change are not easily unravelled, and, indeed, depend to some extent upon what we know nothing about, the mode of axial rotation of the stars concerned. On this point the simplest, and perhaps most probable, hypothesis is that they have none relatively to each other. If this be so, they move as if spitted together ; there is no tra- velling tidal wave, but each body has the permanent form of an elhpsoid with three unequal axes, the longest cen- trally directed towards the companion-star. The widest expanse of luminous surface would, under these circum- stances, be presented to our vision a quarter of a revolution before, and a quarter of a revolution after each eclipse, when slight maxima should occur, with corresponding intermediate minima. And the matching of these theo- retical by actual effects in X Tauri, and perhaps also in Algol, is suggested by some recent observations of il. Plassmanu, needing, however, to be confirmed before J Although the curve of U Cephei (.see Fig. 2) shows a slight pause heforc minimum, the whole time of recovery considerably exceeds that occupied by the decline in light. March 2, 1891.] KNO^A^LEDGE 55 much stress can be laid upon them. He, too, has recourse in a general way to the tidal rationale ; and — what is more siginificant — ranks A. Tauri as a transition instance between Algol and (3 Lyra\ adding the remark that spectroscopic measures of its radial movements may help to elucidate the still imfathomed mystery of "short-period" varia- bility. {Asti: Nad,., No.' 3,016.) A cause tending further to complicate tidal phenomena in sun-like bodies has been adverted to by Wr. Eanyard. It is this. A photosphere is probably a region of con- densation, or the hottest region where matter can exist in a non-gaseous form. Consequently the temperature of the photospheric region is fixed. It may be regarded as an isothermal surface changing its level with local varia- tions of heat. The photospheres, accordingly, of two adjacent radiating masses should bulge out somewhat, one towards the other. Deformations arising in this way in the Algol stars might be expected to become sensible to our perception — if at all — after a similar fashion to tidal deformations, namely, by maxima of lustre at elongations, minima at conjunctions.* Neither source of disturbance, however, connects itself naturally with the enigmatical pause in recovery charac- teristic of this class of variables. And the late M. Klinkerfues's supposition of an atmosisheric tidal wave following in the wake of the satellite, and bringing about * If we suppose the larger star to have given birth to the smaller eclipsing star, in a manner similar to that suggested by Prof. Geo. Darwin with regard to the birth of the moon from the earth, we should expect to find the larger star rotating on its axis faster than the smaller star completes a revolution about it: and the longest axis of the tidal ellipsoid would also, as in the case of the earth's tides, travel in advance of the line joining the centres of the two stars. Thus the larger star would present its minimum area before the time of inferior conjunction or central eclipse. O But there is another possible cause of variation in the light derived from the eclipsed star, which was not over- looked by Prof. E. C. Pickering in his remarkable paper on *'~* the " Dimensions of the Fixed Stars, with special reference ^ to Binaries of the Algol type," published in the Proceedini/s .5P of the American Academy, Vol. XVI., viz. the probable de- '" crease of the brightness of the discs of stars towards their ^ edges. Prof. Pickering says : '• The presence of lines in g stellar spectra leads to the belief that the stars, like our j sun, are surrounded by an absorbing atmosphere. They also, therefore, probably resemble it in presenting a disc brighter in the centre than at the edges, owing to the greater thickness of the atmosphere and consequent greater absorption at the edges." Prof. Pickering seems to have assumed that the decrease of brightness would be similar at both limbs, but with an egg-shaped star with the longer axis inclined to the line of sight the rate of increase of thickness of the absorbing layers would bo different at the two limbs, and, under the conditions assumed above, we should have the decrease of light towards the preceding limli A more rapid than towards the following limb B ; consequently the light of the larger star would recover its brightness more slowly just after central eclipse than it decreased before central eclipse. According to my theory, the photosphere of a binary star would be intermediate in form between an isothermal surface and a surface of equilibrium, for, as explained in a former paper, wo cannot suppose the photospheric clouds to bo floating in an atmosphere. Tho particles must bo falling under the action of gravity retarded but slightly, if at all, by gaseous friction, such as tliat which retards the fall of the particles composing a cloud in our atmosphere, but they would be retarded by tho backward kicks of molecules evaporated towards the heated centre. Such falling pari ides would bo finally evaporated at a level which would depemi on the temperature of the region, as well as on their rate of falling : and since tho acceleration of gravity would be similar at all places on a surface of equilibrium, and tho temperature similar at all places on an isothermal surface, we should expect to find tho falling particles glowing most vividly before their final dissolution in a stratum which would extend around tho star as a thin shell intermediate in form between an isothermal surface and a surface of equilibrium. — A. C. RANVAur>. partial obscurations through increased absorption, receives no countenance from the spectroscope. The light of U Cephei, it is true, turns ruddy as it fades ; but not, it may safely be asserted, owing to this cause. The variations of its spectrum offer a tempting and hitherto unexplored field of study. Indeed, the star has of late in every way, especially in this country, been too much neglected. It is remarkable for a prolonged minimum, originally explained by Professor Pickering as due to a total eclipse by a large, semiobscm-e satellite. But Mr. Chandler's observations showing variations of about two-tenths of a magnitude during the supposed totality, seem to compel recourse to some other hypothesis, if not to replace, at any rate to supplement the first. Two periods of the star being nearly equal to five days, only every second minimum can be followed at the same season of the year. Those of which the average course is represented in Fig. 2 occurred in the autumn. A shorter spring series of observations, also by Mr. Chandler, giving almost a dead level of least light, of close upon two hours' duration, claimed an inferior degree of authority (Astyo- nomical Jijiirnal, No. 199). There is probably no real distinction in character between the alternating phases. ^V /^ i 8f 9v ^ f Fig. 2. — Minimum of U Cephei. From 159 autumn observations bv Mr. S. C. Chandler. The vicinity of this object to the pole renders it par- ticularly suitable for '• trailing" experiments, which might definitively settle the interesting question as to the true form of its light-curve. ^ 67 1 6? ^ 77 C^ID ifO 6C So t>c no IV M)C 'fO 200 13£ i^ i^<> :&■ SCO Fig. 3. — Provisional MiNiMCM-CnEVE op S Astli-e (Yendell). Since tidal effects grow, ctrterix ptirilms, in the inverse proportion of the cube of distance, they ought, so far as they intluence luminosity, to be most apparent in variables of the shortest periods, since those are proved by the proportionate length of their eclipses to be made up of the most closely contiguous pairs. But there is no sign that the subsidiary changes of Algol stars obey any such law. They are especially striking in S Cancri, with its relatively long period of nine and a half days. 66 KNOWLEDGE [March 2, 1891. They are only doubtfully traceable in S Antlia?, notwith- standing the extreme swiftness of its revolutions. Mr. Yendell's provisional light-curve for the latter star, shown in Figure 3, regains its original level with scarcely percep- tible retardation. Professor Paul, of Washington, the discoverer of this stellar prodigy, refrains for the present fi-om pronouncing upon the reality of its suspected anomalies. Indications were, however, caught by him of a lagging after minimum, in the manner of U Ophiuchi and S Cancri, and he also records his impression of con- siderable inequalities both in the duration and intensity of its separate phases, a long, shallow curve occasionally replacing an undulation of wider amplitude and quicker accomplishment,* while both the loss and the gain of brightness appeared to i^roceed by accesses, rather than by an equable flow {Astronomical Journal, Nos. 21.5, 234). The period of this star is by far the shortest known, either for a binary or a variable. According to Mr. Chandler, it retains its maximum brightness of G'7 magni- tude during 4h. 30m., sinks in about Ih. 40m. to 7-3 magnitude, and recovers with nearly equal rapidity ; the whole period being of 7h. 46m. 48s. (Astronomical Journal, No. 218). Mr. Yendell's determinations, on the other hand, assign .5h. 10m. to the phases ; but an eclipse extending over more than half the period of revolution is a manifest absurdity, only to be got rid of by doubling the latter, t and assuming the occurrence in each circuit of two mutual eclipses by equally bright stars. The reduc- tion of light by about one-half at each obscuration renders this a plausible expedient, the adoption of which in nature can be tested by spectrographic means. A more powerful telescope than that at present in use at Potsdam would, however, be required to disclose the periodical doubling of spectral lines due to the possibly two-fold origin of the light we receive from S Antlise. A system is at any rate here presented to our considera- tion such as the boldest imagination could not beforehand have conceived. Even with a doubled period, the occult- ing twin-suns must revolve (if the data suppHed by Mr. Yendell be accepted without modification) in so narrow an orbit relatively to their bulk, that the distance from sur- face to surface amounts to no more than yLt_ of the dis- tance from centre to centre. By reducing the time of light-change in accordance with Mr. Chandler's observa- tions, a free space would be aflbrded of still much less than half the orbital span. The subsistence of such an arrangement cannot easily be reconciled with known mechanical laws ; yet it seems undeniable. NOTES FROM CAMBRIDGE. ■ By E. B. Johnson. ANATOMY IN THE OLDEN DAYS. THE turbulence natural to medical students and the popularity of Professors Macalister and Humphry combined to transform the new anato- mical lecture-room into a scene of loul-voiced and inspiriting enthusiasm at Professor Macalister's opening lecture. He was commemorating the comple- tion of the new buildings by giving a resume of anato- mical teaching in Cambridge from the days of the medieval stwlium ijcncralc to the present time of elaborate sub-division. • The well-known correlation of short with sharp sun-spot maxima offers a curious analogy with these significant indications.' t As suggested by Mr. Backhouse in the Oliservatmy for October 1890. " The earliest record of a school of Physics at the University is in 1421, but the first definite provision for anatomical teaching was made by John Caius somewhat later in the same century. He was followed by W. Hardy in the sixteenth and by a brilliant galaxy of anatomists in the seventeenth centuries, of whom one instructed New- ton, and another tried his hand at writing plays. From the time of Caius we were intimately connected with the Corporation of Surgeons in London, who sent us a scholar receiving £40 a year for his maintenance and £3 a year to provide himself with books. In order to qualify as a prac- titioner in those days it was necessary to have attended three dissections at which a body was opened, and " the physicians present discoursed at random concerning the interior." The first separate professorship of Anatomy was founded at Cambridge in the year 1707, but the immediate effect of endowment appears to have been a cessation of all interest in the subject. It was the time of the Resurrec- tionists, however, and we read of the watchmen being allowed to search in Emmanuel for a missing body. This was illegal, be it remarked, and really an act of coercion, as may be seen from the following tale. A giant once died in Dublin, thereby exciting the desires of an ana- tomical pirofessor and his students, to whom he said : " Gentlemen, I understand that your feelings are excited towards the seizure of this body, against which I must certainly counsel you. But in case your zeal should overcome your discretion, I will tell you the exact case of the law, which is, that you may take the body, but that for the removal of the least rag or shred of covering thereon you may be hanged. Therefore, if you shmihl remove the body, be careful that it is utterly unclothed." Needless to say, that Professor was given the opportimity of experimenting upon that giant. A more melancholy anecdote is associated with the memory of our own Professor Collignon, who once invited two friends to the dissection of a body, in which one of them recognised the features of an acquaintance. It was the body of Lawrence Steme, "whose final return to his University formed a tragic ending to the sentimental journey of his life." Professor Haviland made the first collection of anato- mical specimens, while the first museum was foimded by his successor Professor Clark, who raised it to be the first in the world. We have entered upon a goodly heritage, and, in the stimulating presence of Sir George Paget and Sir George Humphry, may we not learn to penetrate yet farther into those regions of knowledge where the unknown still far exceeds the known ? ARTIFICIAL COLD. By Vaughan Cornish, B.Sc, F.C.S. WITHIN the last twelve years the production of artificial cold has become an important in- dustry. The principle of the methods employed has long been known, but it is only recently that the great practical difficulties of the problem have been overcome. The requisite im- pulse was given by the need of finding means for preserving meat in a fresh condition during its passage from foreign countries. For such purposes as this the freezing machines of Carrd, w^hich still figure in the ordinary text-books on Physics, are wholly inadequate. The problem was first practically solved by Coleman by the construction of the Bell-Coleman air machine, an apparatus so well thought out and perfected that in its first trial a cargo of meat of a value of £8,000 was transported across the Atlantic in a perfectly fresh condition. From 1879 the industry of Mabch 2, 1891.] KNOWLEDGE. 57 refrigeration has rapidly increased in importance as new ajjplications have been perceived, and as further improve- ments in machinery have lieen effected. The subject has engaged the attention of many able engineers, and some three hundred jjatents have been taken out in connection with it. At the present time the production of low tem- peratures plays an important part, not only in the meat trade, but for the preservation of other perishable articles of food, as fish, eggs, and butter, in the brewing industry, and in the production of ice. New applications are being found every day, among which may be instanced the preparation of preserved fruits and similar processes, where crystallization from solution has to be effected. The im- portant problem of the cooling of theatres is engaging attention at the present time, and will no doubt soon receive a satisfactory solution. The principles involved in refrigeration present many interesting features which are scarcely touched upon in the ordinary works on heat. For the production of hiifh temperatures it is usual to employ the force of chemical affinity ; chemical combination in the process of combus- tion being attended with an evolution of heat. On the other hand, many chemical compounds are formed with alisurption of heat ; but these can only be produced in an indirect manner, and their formation cannot be employed for the production of low temperatures. It is a curious circumstance that in oixler to understand the rationidc of the refrigerating process it is necessary to consider, in the first place, the means of attaining high temperatures and the working of heat engines. By the burning of fuel in the furnace steam is produced in the boiler of a steam-engine, and by the changes of volume of the irorkimi xuhsttinci' (steam) a portion of the energy of heat is transformed into mechanical power. In other words, the energy which formerly consisted in that motion of minute particles which constitutes heat, is in the steam- engine converted into the form of energy which consists in the motion o[ a large mass of matter (<'.//• of the piston or the fly-wheel of the engine). Briefly, in heat engines, of which steam-engines form one class, a calorific efi'ect is converted into mechanical power. In refrigerating machinery, on the other hand, mechanical power is so employed as to yield a calorific effect ; but in this case the calorific efiect is negatire, and the final result is the pro- duction of a low temperature. The refrigerating machine is not in itself a complete apparatus, since it requires to be diiirn by a steam-engine. In order, therefore, to attain logical precision in our view of the process of the artificial production of cold, it is necessary to consider as one complete system the combination of the steam-engine and the freezing machine. In this dual arrangement we start with the production of a higli temperature in a fur- nace, and finally attain a very low temperature in the freezing chamber. The working parts of the freezing machine are very similar to those of the steam-engine. In both tliero is a system of cylinders, pistons, and valves, and a working substance which undergoes alternately compression and expansion. In the Bell-Coleman machines the working substance is air. The process begins with the compression of air by the stroke of a piston m the roiiijire.ssidii ri/lindcr. The power which drives this piston is obtained directly from the piston of the steam-engine. The compression cylinder is surrounded by a jacket in which cold water constantly circulates. The heat generated by the com- pression of the air is almost entirely taken up by the cold water. Thus we obtain air very little above the ordinary temperature, but under a high pressure. When the pressure is released the air expands. If the expansion be allowed to take place into a vacuum, then — as Joule first proved — no change of temperatui-e takes place. But if the expansion takes place under such conditions that mechanical power is developed, the mechanical work is done at the expense of the heat of the expanding air, which consequently is chilled. This is what actually takes place in the exjumxion cylinder. The air, in expanding drives a piston which is connected with the cylinder of the steam-engine in such a way that it aids the back stroke of the piston in the steam cylinder. Thus the frigorific efiect is obtained in the refrigerating machine by an action wliich lightens the work of the driving engine. By means of this expansion the air is readily cooled to — ■50'^ Fahr., or, if desired, to a still lower temperature. It was here that a great practical chfficulty came in. Atmospheric air con- tains water- vapour, and at such low temperatures this was deposited m the form of hoar-frost. This fi'ost or snow choked the valves and otherwise hindered the working of the machine. It was not found practicable to remove the moisture entirely before the admission of the ak to the machine ; and till the invention of Mr. Coleman the snow diflSculty appeared to condemn the use of air as the work- ing substance. This difficulty was overcome by the device of allowing a partial expansion of the air before it entered the expansion cylinder. This preliminary partial expan- sion is effected in sloping tubes placed in the reft-igerating chamber itself. Under these conditions, the aqueous vapour deposits not as snow but in a mist or ram, and the moisture is run oft' by suitable taps placed at the bottom of the sloping tubes. The air thus freed from moistm-e enters the expansion cylinder to undergo the second and greater expansion by which the principal part of the frigorific efi'ect is obtained. The cold air fi-eezing machines are those employed on board ship for the transport of meat from Australia, New Zealand, and America, The meat is placed in large chambers, the walls of which are double, the interspace being filled with wood charcoal as a non-conducting material. A jet of intensely cold air is delivered into the chamber at each stroke of the piston of the expansion cylinder, and the temperature of the chamber is thus kept at or near the freezing point during the whole voyage. There is another important class of freezing machines, of which the ammonia machines are the most important type. In this second class the working substance is not a permanent gas such as air, but a substance (such as ammonia) capable of being condensed to a liquid by pres- sure, even at the ordinary temperature of the atmosphere. In these machines the frigorific effect is due in the first place to the heat absorbed by the vaporization of the liquefied substance ; and secondly, as in the air machines, to expansion of the vapour, ^'olume for volume, the working substance exercises a much greater cooling effect in the ammonia machines than in the air machines. Consequently the machinery is more compact and more economical of fuel. Au important point of difterence between these two types is that whereas the air machines work with an oiien ci/clc, drawing in a fresh supply of material at each stroke of the piston, the ammonia ma- chines work in cloned ci/clc, the same working material going through the same round of changes over and over again. It will readily be perceived that this circumstance necessitates very different arrangements in the freezing chamber to those which have been described above, where the working substance itself is delivered from the machine and is the direct cooling agent. The refrigerating cham- ber connected with an ammonia machine is generally cooled by the circulation of a cold liquid in pipes, on a system similar to that employed in heating by means of 58 KNOWLEDGE, [Maboh 2, 1891. hot-water pipes. The liquid is some sohition having a very low freezing-point, such as a solution of calcium chloride in water, hriiw being the term generally applied to such solutions. In the ammonia machines a special cylinder for expan- sion is not required, the expansion being allowed to take place in long coils of tubing, which are placed in a bath in which the brine is kept circulating. From this bath the cold brine is driven by pumps through the system of tubes. An important advantage possessed by the ammonia machines is the fact that there is no moisture to be re- moved, and their construction is in consequence con- siderably simplified. Except on board ship they have undoubtedly an advantage over the air machines, and are coming daily into more general use. For marine ijistalla- tinns — to use the trade term — the air machines are still preferred, owing principally to the fact that in case of accident the working substance could not be removed in the case of ammonia, the escape of which, owing to an accident in rough weather, would, moreover, be highly inconvenient. An interesting application of cooling by means of brine has lately been made in mines. One of the greatest difficulties which can occur in the operation of sinking a shaft is that presented by a stratum of sand saturated with water. In more than one case this difficulty has been overcome by freezing the sand and water into a firm mass and then continuing the sinking operations as if the material were solid rock. The shaft ha\dng been simk to the upper surface of the quicksand, a number of small bore-holes are made to the bottom of the stratum, and in these are placed tubes closed at the bottom, through which cold brine is circulated from a tank at the surface, which is cooled by an ammonia machine. In the course of a few days the quicksand is frozen to a solid mass, and the boring can be proceeded with. It will thus be seen that the production of artificial cold is an industry which, though still in its infancy, has already attained considerable importance. It appears likely that the next ten years may see a development scarcely less rapid than that of the last decade. Bv W. Montagu Gattie, B.A.Oxon. T HE following is an elementary explanation of the play of the hand published in the February number of Knowxedge. For convenience of reference, the distribution of the cards is here repeated. D.— Kg., 5, 3, 2. C— 0, 8. 2, H.— 10, 7, 4, 2. S.— 10, H. D.— 8, 7, i. C— Ace, G, 5, 8. H.— Kn., '.), C, 5. S.— 6, 2. Z turns up g the King of j^ Diamonds. I).— Ace, Qn., 9. C.-Qu., Kn.,7,4. H.— Kg., 8, 3. S.— Kg., Qn., 5. 1).— Ku., 10, 6, C— Kg., 10. H. — Ace, Qn. S.— Ace, Kn., 9, 7, 4, 3. Trick 1. — A opens his longest suit, and, having four only, leads the lowest ; Y, holding king and another. passes the trick ; V> plays his highest card, and Z his lowest. Trirk 2. — B, by opening with a small heart, shows his partner four at least of that suit. He might return a club ; but this would not be quite prudent, and would also be likely to mislead A, inasmuch as the immediate return of a partner's suit is usually interpreted as a re- quest for a third round on which to make a small trump. Z plays his lowest heart, and A his highest ; and Y of course wins the trick with his ace. Trick 3. — Guided by considerations which have been explained already, Y leads a trump, and, having three only, opens with the highest, so as to assist his partner {who has turned up the king) as much as possible. Z gathers that Y has not more than three trumps ; for he would not lead knave from a long suit unless he held the four honours, or king, queen, knave, and two others, and both these cases are precluded by Z's holding the king. Z therefore finesses the knave, and at the same time takes occasion to commence an " echo " to the trump lead by playing the three instead of the deuce. When the deuce falls at trick 5, four trumps at least are marked in Z's hand. Trick 4. — A continues with the queen of clubs in order to clear the suit. He knows that (unless the ten of clubs was the beginning of a call for trumps ) Y has either the king single or no more ; but in the latter case Y would pass a small card led (for, B having played ace on the first round, the king must then be with Z), and Z might win with a small card, retaining the command of the suit. B's three of clubs shows that A led from four cards ori- ginally ; for, the deuce having fallen already, the four must have been A's lowest club, and, with five of the suit, he would have led the lowest but one. Z plays his lowest card, and, as this is the eight, it follows that the only other club he can hold is the nine (the knave, of course, being marked in A's hand). Trick 5. — Y continues with his next best trump, Z completes his " echo," and the ten draws the ace from A. Trick 6. — A is reluctant to enable Y to make a small trump on the clubs, and therefore returns the hearts. Holding two only, he returns the higher, and, as B and Z play sis and four respectively, Y concludes that the three is in A's hand. He notices also that B, who led the five at trick 2, now plays the six, and therefore can only have had four hearts originally ; so that, as A can have but one (the three), Z must hold the other two. Trick 7. — After this third round of trumps, Y counts the hands, from inferences already drawn, thus : — Z's " echo " at tricks 3 and 5 has shown that he has the long trump ; he has two hearts, from trick 6 ; and not more than one club, fi-om trick 4. Therefore he must have at least two spades. A has the knave of clubs and one other (tricks 1 and 4), and the three of hearts ; therefore he must have three spades. There remain for B two hearts, and either two clubs and two spades, or three clubs and one spade, according as Z has the nine of clubs or not. Trick 8.- — Z's proper lead is obvious enough. It would be fatal to lead up to Y's tenacc in hearts, and he cannot do better than give his partner the best spade he has. A, holding king, queen, naturally puts on the queen to draw the ace and make his king good ; but, looking at the great strength in spades declared in Y's hand, it would probably be better play to pass the ten, and that course would cer- tainly save the game, whether Y jiiiesscd or not. A's play, however, is quite orthodox. Y's couji has already been fully explained. Its merit consists in his seeing that, ex- cept in the improbable case of Z's holding the best and Makch 2, 1891.] KNOWLEDGE, 59 second-best hearts, the game cannot be won, and may be lost, if Z has the lead after becoming exhausted in spades. It should also be noticed that, while B and Z know per- fectly well how the hearts are divided, A and Y are in the dark on this point. It is this uncertainty which deters A from leading a heart at trick 10, although he would thereby not only save but win the game, if B should be found with the best and second-best hearts. The maxim " Simplify the game as much as possible for your partner," has a scarcely less important correlative, " Place your opponent, whenever possible, in a difficulty." Y achieves both purposes in this instance by foregoing a single trick. Ctjcss (JToIumn. By C. D. Locock, B.A.CJxon. Pboblkm bt T. Tavern ek. Black i7 picrcs). White (10 pieces). White to play, and mate in two moves. The above beautiful problem is taken from the Liverpool Wei Lly Mercury. For the benefit of any who may find it too diiBoult, the following puzzle is given as an easier task. Intending solvers need not be dismayed by its length : it is only necessary to go straight ahead. There are no v.ariations, all Black's moves being forced. Dedivitled to Wordsicort/i Douis/horpe, C/uimjjivn Stale-mater of the World. »..sj ^ ^ White (10 pieces). White to play, and .itale-mate /i/.s- own King in fifteen moves. CllKSS FALL.XCIKS. I. (Legal) That it is unlawful for a player to Castle on the (,^>ueen's side when his tilt square andQKt siiuare are commanded by opposing pieces. This is a delusion under which many fairly experiouood players are known to labour. The law merely says that the King in castling must not do so from, over, or ioto check. II. That a Rook and Knight are stronger than two Bishops. Many games have been lost through this fallacy. If the position is an open one with Queens on the board, the two Bishops if favourably posted will often win. III. That the Queen is worth two Rooks and a Pawn. On the contrary, it can be proved that, when there are no other pieces on the board, two Rooks are nearly worth a Queen and Pawn. For, pro- vided the K be secure from perpetual check, the two Rooks can double to attack the weakest Pawn, which can only be defended by the King and Queen. The two Rooks can then be exchanged for the Queen and Pawn. IV. That P to R3 is a harmless " waiting " move. As a matter of fact, there is no such thing as a harmless waiting move in the earlier part of the game. The move P to KR3 is doubly disadvantageous. In the first place, the Pawn becomes a mark for the opponent's Queen's Bishop. And secondly, it makes it inadvisable afterwards to move the KBP, on account of the " hole " created at KKt3 V. The disadvantage of P to QR3 is a somewhat subtle one. Sup- pose, for example, the moves 1. P to K4, P to K4 : 2. Kt to KB3, Kt to QB3 : 3. B to B I, B to B4 ; 4. P to B3, Kt to B3 ; 5. P to Q3. Black now makes the "waiting" move PtoQR3? White replies G. B to K3. In positions of this sort, if the QRP were unmoved, Black would now retire the Bishop to Kt3. For if White exchanges. Black gets .in open Rook's file. But in the present case, if he play B to Kt3, White exchanges with advantage. Or if he retire to K2, White gains two moves by taking it. leaving either the Kt or the R out of play. Black, therefore, is compelled either to exchange, and present White with an open KB file for his KR, or to play P to Q3, leaving White to exchange when it suits him.. CHESS INTELLIGENCE. The Steinitz-Gunsberg match ended in a victory for Steinitz by C games to i. with no less than 9 draws. The large proportion of drawn games seems to indicate a harder fight than the Steinitz- Tschigorin match of 1889, which the former won by 10 games to 6, with only 2 draws. On the whole, however the result of the match is a confirmation of previous form, as shown in the recent drawn match between Tschigorin and Gansbcrg. It is pos- sible that Mr. i^teinitz might have won both matches, had he chosen, by a somewhat larger majority. His invariable habit of adopting unsound defences undoubtedly caused the loss of several games in both matches. At the same time, it should be remembered that the intrinsic badness of his novelties is to a certain e.'iteut balanced by his greater familiarity with them. For these novelties are not played on the spur of the moment. On the contrary, they have generally been in Mr. Steinitz's note-book for many months before the match begins. The Steinitz-Tschigorin Correspondence games have now been resumed. The following moves have been made since the publication of the Diagram in the January number : — White (Tschigorin), 18. B to R3 19. QR to Qsq 20. B to B4 21. Kt to Q5 Evans Gambit." Black (Steinitz). P to QB4 Kt to B3 B toB3 Present Position. Ul-ACK. 60 KNOWLEDGE [Makch 2, 1891. ' Two Knights' Defence." White (Steiiiitz'. 19. B to Kt2 20 Q to B2 21. K to Bsq Black (Tschiporiii\ PtoBo QxP PtoBG Present Posilii Black. s ^\ 1 i k i' '^ k ■^ w i i \-M% ^ Mr. Gimsberg is expected to return before the end of February, but not in time to edit the Chess Column for JIarch. There are rumours of a match between Mr. Steinitz and Dr. Tarrasch of Xuremberg, who won the last two International Tourna- ments without losing a single game in either. The German amateur has signified his willingness to plav; but it takes two to make a match, and Jlr. Steinitz's consent is not always easy to obtain. Con- siderable self-denial in the matter of terms is essential on the part of anyone who wishes to be his opponent. The match would be interesting as a contest between master and pupil ; for Dr. Tarrasch is an exponent of that " modern school " of which Mr. Steinitz claims to be the founder. On that very account it is probable that, if the younger player should lose the match, he would be defeated by a more decisive majority of games than players of the opposite school, such as Tschigorin and Gunsberg, who attack Mr. Steinitz sometimes in a style of which he strongly disapproves, instead of waiting to be slowly attacked themselves, in accordance with Mr. Steinitz's principles. 'I'he following game, played in the Manchester International Tournament of last year, is given, for want of a better, as a specimen of Dr. Tarrasch's style. ' RuY Lopez.' White (C. D. Locock). 1. P to K4 2. Kt to KB3 3. B to Kto 4. B to R4 5. B to Kt3 G. P to Q4 7. Castles (c) 8. KtxP 9. P to QB3 10. PxKt 11. R to Ksq (/•) 12. P to QKt+ ! (.). It is called the prothallus. On its under surface are two kinds of organs, which are of great im- portance in the life-history of this fern. These are the archegonia (Fig. I. h., arch., and rf.), or female organs, and the antheridia, or male organs (Fig. I. h., an., and c). The archegonia are flask-shaped. The base of the flask, which is embedded in the prothallus, contains an egg or ovum, the female reproductive cell. The anthe- fhrxoL Fig. I. — a. Transverse section of leaf of a Fern (As/iidiuui filix 7nas), showing sporangia. /'. Under surface of prothallus ; arrh., archegonia ; an., antheridia. c. Longitudinal section of antheridiam (much magnified). (I. Ditto of arohegonium. ridia are globular in form. Each one contains numerous lively specks of protoplasm (irpoiros first, and 7rAao-/u,a form, the linng part of the plant-cell, by whose activity the plant is built up), which move about with great agiUty when the antheridia burst. They then make their way (if moisture be present) to the neck of the archegonium ; one of them enters it, and pierces the ovum. Thus impregnation is eftected." The result of fertilization is a fern-plant that during its early period of existence sends out an organ called a foot into the tissue of the prothallus, to absorb therefrom the food-material that the plant is as yet tmable to obtain independently for itself. In the meantime it sends roots into the soil and a stem into the air, and when the pro- thallus is exhausted, it is ready to commence life on its own account. In Etjukctuw, the Horse-tail, an ally of the fern, the proces.=es are essentially similar, but the male and female organs (the antheridia and archegonia) are borne on separate prothalli, although the spores from which these arise are all alike. In a higher branch of Vascular Cryptogams differen- tiation of male and female is carried back a further stage, for two kinds of spores are here produced. Sclugimlhi, so common in our greenhouses, may be selected as a typical • Prothalli are often found growing in the crannies of the wall of a greenhouse in which ferns have been standing, but the non-possessors of a greenhouse can easily procure prothalli by sowing spores in a pot of light soil, carefully watering them, and covering the pot with a bell-jar. The length of time the spores take to germinate depends on the species of fern from which they have been derived. Suppose that a prothallus has been found, that the little root-hairs on the under surface have been freed from particles of soil by careful manipulation under water with a camel-hair brush, and that it has been mounted in water on a glass slide, under-side uppermost, and covered with a cover-slip. It is now ready for examination under the high power of a microscope. By gentle pressure of the cover-slip the spermatozoids may he ejected from the antheridia. and m.iy be seen wriggling through the water. 62 KNOWLEDGE [April 1, 1891. example. The male spores are much smaller than the female ; hence thi'ir respective names, microspores and macrospores (/ttxpos small, /xuxpos large). The sporangia which contain these are termed microsporangia and macrosporangia respectively (Fig. II. n.). When the macrospore (iim. sp.) germinates, the protluillus does not come out of the spore, but remains as a mass of tissue, witliout green colouring-matter inside it, and in addition there is a nourishing material called endosperm, which later on becomes divided up to form a tissue of cells (Fig. II. /).). The male prothallus also remains inside the microspore. It consists of only one cell, and has no chlorophyll. A peculiar organ, termed the suspensor, develops from the fertilised egg, as well as the true embryo plant. It pushes the embryo into the endosperm, avckeojpnxo. Fig. II. — a. Longitudinal section of apex of sporangium bearing shooi oi Sclac/ijiel/a; sp., developing sporangia ; iiii. .'c/j. , microspores ; 7iia.sj}., macrospores. 0. Diagrammatic section of germinating ma- crospore. c. Ditto of archegonium (much magnified.) so that it may feed on it. It is noteworthy that the gi-owth of the embryo takes place iiimle the spore, not outside, as in the two former cases. The cone of I'iniis (e.g. Pinns si/lvestris, the Scots Fir), is a collection of leaves that have become modified to bear ovules, which afterwards are termed seeds. The ovule is a macrosporangium which, however, differs from that of SelagineUa in that it possesses a covering or integument (Fig. III. /(., //(.). The whole of the interior of the ovule is occupied by the prothallus. The male spore is familiarly spoken of as the pollen-grain, and the microsporangia as the anther-lobes or pollen-sacs ; they are borne on the under surface of the stamens (Fig. III. a., st., p.) The pollen-grain is provided with two bladders or floats, and is carried by the wind to the ovules which lie exposed on the upper surface of the carpels or modified leaves on which they arise. The integument does not quite enclose the ovule, but leaves a small aperture, the niicropyle (fjiiKfxii small, and ttuXt; a gate) for the reception of the pollen-grain. There the microspore (pollen-grain) enters and rests on the surface of the macrosporangium, germi- nates, and sends a tube (Fig. III. c. d.,f.; and /-., p.) into the microspore, where it comes into contact with the ovum, in one of the archegonia developed in the prothallus. There is no endosperm in Pinus, as in SelagineUa, but the important points to be noted are that not only does the embryo develop inside the macrospore, but the macro- spore remains inside the macrosporangium that is still attached to the parent plant, from which it derives suste- nance ; for after the developing embryo has used up all the nourishment in the prothallus, fresh nutriment is poured into the macrospore from that source. When the tube of the pollen-grain, which we may com- pare to an autheridium, touches an ovum in one of the archegonia, it sends part, at least, of its contents into it. As a result the ovum divides up to form a young plant (Fig. III. c), that is provided with a long suspensor. The embryo is so placed that its root lies towards the micropyle. The mature ovule (macrosporangium) with its coat is the ■■urd, and the collection of seed-bearing leaves which we find form what is commonly called a flower. The Angiosperms iayytiov a vessel, and a-Ktpp.a a seed) are so called from the fact that their seeds are enclosed by the leaves (carpels) on which they are borne ; and in this they ditier markedly from the Gymno- sperms lyu/ni'os naked), such as the Pine, in which these are quite exposed. The majority of our familiar garden shrubs and forest trees belong to the large group of Angiosperms. A carpel may bear one or many ovules, which later on develop into seeds, and the carpel . itself undergoes, as a rule, a characteristic change to form what we know as the fruit. The pollen-grains are found in sacs (anther- lobes or pollen-sacs)" situated on the upper portions of the stamens. They are very similar to those of the Pine ; but instead of having balloons they often possess warts or prominences by means of which they may adhere to the various animals that carry them to the stigmas of the carpels on which they must alight in order that they may be in a position to accomplish their role in life. ^^'e have reserved until this stage a minute examination of the macrosporangium, or ovule — the organ that is of such vital importance in connection with the repro- duction of the plant ; the reason being that it is best to take for this purpose familiar examples such as may be easily procured by anyone desirous of making the examination of Fig. III. — a. Diagrammatic longitudinal section of male cone of Pinus (Scots Fir) Only two of the pollen-sacs are represented con- taining pollen-grains (microspores), p. ; St., stamen, with pollen-sac on under surface, h. Ditto of ovule of Pinus ; ;;., pollen-grain germi- nation ; Hi., micropyle; in., integument (coat) of macro-sporangium (oTule); sp., WctII of macrosporangium. r. Pollen-grain; _/'., cell ■which will develop into pollen-tube d. The same, wit^h cell (/") de- veloped as pollen-tube. c. Diagrammatic representation of develop- ing egg ; there ought, in reality, tc be four embrj^os figured arising from these ovules. the object for himself. These are best found in the butter- cups and daisies, the hyacinths and lilies of our fields, woods, and waysides. In all these cases the ovule is con- tamed within the carpel or carpels, and the pollen -grain * See article on " Some Curious Modifications to Prevent Self- fertilization." — Kxowi.KDGE, Feb. 18fll. April 1, 1891.] KNOW^LEDGE. 63 can only effect an entrance to it by way of a tube fin many cases) in the style which opens to the exterior, in the stigma, and communicates below with the cavity of the ovary or o\iile-containing portion of the carpel. The ovule is built up on the same plan as that of the Pino, but instead of being furnished with one integument, it has two, both of which completely enclose it with the excep- tion of an aperture, the micropyle, so that the pollen-tube may be enabled to reach the macrospore. Fig. IV. a. shows a vertical section of an ovule of the Hyacinth (SrUht nutiinx) as it appears before fertilization ; on the outside are seen the integuments, enclosing the wall of the macrosporau- gium. The part by which it is attached to the carpel is called the stalk, or funiculus (./'. ) ; m. is the micropyle. The macrospore is known as the embryo-sac ; towards its micropyle end lie the ovum {., antipodal cells; sn , secondary nucleus. 6. Diagram illustratinjj development of embryo- sac (macrospore). c. Germinating Bean {ad. luit.). d. The same at a slightly later stage; r.. cotyledons;.?., young stem bearing ordi- nary loaves (<«/. nat.). e. Diagrammatic section of portion of seed of Grass. the prothallus stage of its growth. The central cell is the secondary nucleus. The remainder of the macrospore is filled with nourishing material. It will be interesting to note how these cells have origi- nated. We will go back to that stage in which the embryo-sac (macrospore) appeared as a single cell, when it was essentially tlie same as the Fern spore. All cells contain a nucleus, which is probably a part of its proto- plasm that luis become denser in structure, and per- haps changed in some other way. The nucleus is an important body, as in the division of cells it first divides up, and then becomes surrounded with protoplasm. The nucleus of the ciiibryo-sac divides into two. Tlie two thus formed similarly divide, and so do the resulting four nuclei. The positions they assume in each stage are shown in Fig. IV. I>. Then one nucleus from each end of the macrospore travels to the centre. There they fuse to form the secondary nucleus. This stage is represented in the fourth diagram of Fig. I\". //. The pollen-grain, when it has alighted on the stigma, commences to germinate, and sends a tube down the style, just as that of Pinus does ; only here germination takes place on the stigma, whereas in Pinus it is effected on the macrosporangium (ovule) itself. The contents of the tube having fu.sed with the egg, the latter di\-ides up to form the embryo. At the same time the secondary nucleus splits up, and so on until the whole of the embryo- sac is filled with a tissue — endosperm, a mass of nourish- ing material. The developing embryo is furnished with a suspensor, as was that of Selaginella and Pinus, and, as in the latter case, development takes place in such a way that the root is directed towards the micropyle, and the first leaf or leaves, as the case may be, in the opposite direction. The reason of this arrangement will soon be obvious. All plants containing green colouring-matter (chlorophyll) obtain a large proportion of their food (at least the whole of their carbon) from the air. But when chlorophyll is absent the process of carbon assimilation. that is, the breaking up of the carbon dioxide of the air and taking up of the carbon and part of the oxygen, can- not go on, so the plant starves. This anyone can test for himself by growing plants in the dark ; then chlorophyll will not be formed, what was previously there will disap- pear, the plant will assume a miserable, starved appear- ance, and will soon die, unless again brought to the light. However, place a potato in a dark, moist cellar (most cellars appear to possess these qualifications), and see what happens. A long, lanky plant will be produced. This will appear to contradict the statement just made ; but a little consideration will show that it only apparently does so, for the potato is a storehouse of nutritive material on which the developing plant has been feeding. \Yhenever this store is exhausted, the plant dies. The ovule partakes in a great measure of the characteristics ascribed to the potato tuber. It is a reservoir of nourishing matter, in which the young plant is bathed at the commencement of its existence ; this material it absorbs before it quits the seed. For the examination of a mature seed we will take the common Garden Bean. It shows outside a scar or hiUim that indicates the position of the short stalk which joined it to the carpel, and near the hilum is a small o])ening. the micropyle. Take a penknife and cut the seed-coat, and the contents will then fall out, and probably divide into two thick fleshy lobes, on one of which there is a knob-like process. This small process is the young plant, and the two fleshy lobes (Fig. II. rima fucie, the higher a moun- tain range is, the less time it has been subject to this vvashing-away process, and, therefore, the younger it is as regards relative age. It might, indeed, be objected to this that the mountains that are now the highest have always been the highest ; and that at the beginning of all things their original height as much exceeded their present height as the latter does that of the smaller ranges. In this \-iew, however, their original heights would have had to be so stupendous as to be almost inconceivable, and probably much greater than is compatible with the physical conditions of the globe. This hypothesis may, therefore, be dismissed as untenable ; more especially as there is direct evidence of a totally different kind, which is conclusive as to the truth o"f the alternative view. This evidence is afforded by fossils, and more especially by a particular kind of fossil, which, from its abundance and the restricted geological epoch in which it is found, is of more than usual value in inquiries of the present nature. If any of our readers have ever examined the Tertiary clays and sands of Barton, in Hampshire, or of Bruckle- sham, on the Sussex coast, they will probably have met with numerous disc-like objects, the larger of which are somewhat more than an inch in diameter, while the smallest are scarcely bigger than a pin's head. When split or cut, these objects are found to contain a number of minute chambers, separated from one another by thin walls arranged in the form of a spiral, as shown in the figure. Technically they are known as nummulites, and belong to the very lowest division of the animal kingdom — lower even than the sponges, wliich some people cannot be persuaded to believe are animals at all. Now these nummulites are exceedingly interesting to those who study the growth and formation of mountain ranges, for the reason that they occur, in any quantity and of large size, only through the greater portion of the Eocene or lowest division of the Tertiary (latest) geological period, although not reaching down to the London Clay ; and also because they were very widely distributed in the seas which then covered a large part of our existing continents. If, then, we should find rocks containing great numbers of large nummulites on the flanks or tops of a mountain range, we should be assured that such range was younger than the Eocene period, at which date its component rocks were being formed as mud at the bottom of the sea. Now, although in England the aforesaid nummulites only occur in soft beds of clay and sand in the low clifis of the southern coast, when we cross to the Continent we find them forming the greater part of a massive limestone, known as the Nummulitic Limestone. This very charac- teristic rock is more massive and more widely spread than any other Tertiary deposit, and, in its thickness and A XcMMUI.ITE, VIKWKD FROM AnOVE. ANI> HoIil/.dXTALI.Y Bisected. identity of structure over large areas, recalls the Mountain Limestone of the Palaeozoic epoch. It is, indeed, abso- lutely one mass of nummulites, of which sections are displayed on every fractured surface ; and it was probably an open sea deposit, which must have taken incalculable ages for its formation. It occurs in Southern Europe in both the Alps and Pyrenees, attaining a thickness of several thousand feet in the former, and occurring at elevations of more than 10,000 feet above the sea-level. In the Pyrenees it forms a beautiful white crystalline marble. On the south of the Mediterranean, Nummulitic Limestone is found again in the mountains of Algeria and Morocco, in Eastern Europe it reappears in the Carpathians, and thence may be traced into the Caucasus and Asia Minor. All travellers to India are familiar with the Mokattam range of bare mountains on the western shore of the upper part of the Eed Sea, which are likewise almost entirely composed of this same limestone. It is, indeed, a common belief among the Egyptian peasantry April 1, 1891.] KNOWLEDGE 65 that the larger disc-like nummulites are lentils left by the builders of the pyramids, and subsequently turned into stone. From the Caucasus and Asia Minor the Nummu- litic Limestone may be followed into Persia, Baluchistan, Sind, the Punjab, and so into the Himalaya. Thence it continues into Assam and Burma, and reappears in the Andaman and Nicobar Islands in the Bay of Bengal. It is, however, in the inner Himalaya that the oceiir- rence of Nummulitic Limestones and certain overlying Tertiary rocks is of more especial interest, since it is there that they attain a greater elevation tlian in any other part of the world. It is in the upper Indus Valley, in the neighbourhood of Leh in western Tibet, that these nummulitic rocks occur ; running some distance down the Indus to the west of Leh, and to the eastward of that town extending into Chinese territory. There is good evidence to show that the arm of the sea in which these nummulitic rocks were deposited communicated with the ocean to the eastward in the Bay of Bengal, instead of foUowing the course of the Indus in a westerly direction to the Arabian Sea. Moreover, in some parts of this area the rocks which overlie, and are, therefore, newer than the Nummulitic Limestone, are raised to the stupendous elevation of more than 21,000 feet above the sea-level. We have, therefore, before us decisive evidence to show that those parts of the earth's surface which at the present day form some of the highest peaks in the Himalaya were, at the period when the London Clay was deposited, below the level of the sea ; and consequently that the elevation of that part of the Himalaya has taken place entirely since that epoch, during a period when the physical features of England have altered only to a comparatively slight degree. There is, moreover, equally conclusive evidence to show that the elevation of the Himalaya was not completed until a much later epoch of the earth's history, since on the southern flanks of this mighty range we find beds of sandstone containing remains of mammals which lived during the Pliocene, or later Tertiary epoch, raised to a height of several thousand feet above the sea- level. The elevation of the Indus Valley in the heart of the Himalaya could not, therefore, have commenced until the Miocene, or middle Tertiary epoch, while that of the outer Himalayan ranges could not have been completed till far into the Pliocene period, and, for all we know to the contrary, may still be in progress. Not only so, but the same endence likewise tells that the Alps, Pyrenees, Carpathians, the Caucasus, and the Egyptian Mokattam range, as well as the moimtains of Algiria, have all attained their present elevation since the latter part of the Eocene period, when at least a considerable portion of their area was submerged. And we accordingly learn that many of the most striking physical features of the Old World are of comparatively modern origin. When, however, we turn to mountains like those of the Lake District and Wales, which only attain moderate elevations, and in which the rocks belong solely to the Palipo/.oic, or oldest geological epoch, it is evident that we have to do with elevations of an extremely remote date. There is, indeed, satisfactory proof that these old moun- tains were once vastly higher than they are at present ; their diminished altitude being due to the long ages during which they have been subjected to the wear and tear of the elements. To such mountains the proverb to which we have already alluded is, therefore, strictly applicable ; but in a geological sense the phrase " everlasting hills " can be applied neither to the oldest nor the yomigest mountains. DISSEMINATION OF SEEDS. By Theodore W. Dicker. THE dispersion of seeds over the wide surface of the globe, which has been of so much importance in the distribution of vegetable life, has been accom- plished by adaptations as marvellous as they are oft'ective. In these methods we find another proof of Nature's firm determination to carry on the race. Fhst we have the astonishingly la^•ish manner in which seeds are produced. Eight thousand have been coimted in a single capside of the White Poppy, whilst it has been estimated that a single Tobacco-plant can produce 860,000. How multitudinous, too, are the microscopic spores of the Flowerless Plants. It has been calculated that a single frond of Spleenwort could produce a million spores, and it is necessary to only shghtly kick a mature Puff-ball (Lycoperdon) to drive the spores out in a small cloud. Why, then, it may be asked, with all this tremendous re- productive potency, is not the earth overrun to a most inconvenient extent by plant-life ? The possibiUty of over- production is checked in many ways, among which are the unsuitability of position, the destructive struggle for existence which goes on among crowded plants, and by the great consumption of seed by men and the lower animals. In addition to the exuberance of production we must take into consideration the power which seeds and fruits possess of resisting injiny. They are less perishable than any other part of the flowers producing them, and are well adapted to retain their vitality, even through great changes of temperature, for a length of time. Some wheat which Sir George Nares brought from the Arctic regions, where it had been left by the crew of the i'ularis two years before, was found to still possess its germinating power ; and Dr. Trimen states that some seeds of ^felumbium in the herbarium of Sir Hans Sloane, who died in 1753, germinated in 1866. In the distribution of seeds we find three kinds of agencies concerned, sometimes acting independently and sometimes in concert. First, there are the remarkable efl'orts which plants themselves make to disseminate the products of fructification ; secondly, there is the powerful instrumentality of two inanimate forces without, viz. wind and water ; and, lastly, there is the unconscious but in- terested action of animal life. Let us examine first the methods by which plants them- selves seek to insure the proper disposal of their seed. Dissemination generally beguis at the close of life in annual plants, and at the " period of rest " in woody plants. It is then, except in the case of succulent fruits, that the fruit attains the degree of dryness necessary for the lil)eration of the seed. Indeed, fruits may be roughly divided mtodry and succulent. As succulent fiuits generally exhibit no particular mechanical efl'orts in themselves at dis- semination, it is with the former, or dry fruits, that this part of our article is concerned. Dry fruits, again, may be separated into the tle/iisvent, or those in which the peri- carps, or seed-cases, open to permit of the escape of the contained seeds, such as the Pea-pod, and the imhltistttit, or those in which the pericarps do not open. Taking first the ileliisceut fruits, we find that they usually consist of a number of seeds enclosed in tough pericarps, as in the Poppy or the Vetch. As such fniits present no special attraction to animals, the seed-cases must of necessity open to permit of the exit of the seeds ; for whei-e the seeds are numerous it would manifestly be to their disadvantage if the fruit merely fell to the earth and they escaped only through the rotting of the seed-case, as this would 66 KNOWLEDGE [April 1, 1891. set up a struggle for existence in which only the most capable would survive. Fruits of this kind therefore split in a regular and distinctive fashion in order that the seeds may escape. And not only do the pericarps prevent a crowded planting by thus splitting, bi;t they frequently still further carry out this im- portant object by ejecting the seeds with considerable force. The methods by which this is achieved are most curious and interesting. The legume of the Pea splits along its two margins, the two halves falling away from eai-h other and throwing off the seeds in various direc- tions. The seed-cases of the Pansy and of the Violet explode, scattering the seeds forcibly. In the Gorse and the Broom a sudden burst of the pods and a sjiring-like twist of their two halves effectually disperse the contents. On sunny -July days the cracking sounds produced by the bursting pericarps may be distinctly heard. The mature fruit of F.chdIUum elaterium separates from its stalk and ejects its seeds with great rapidity through the orifice left by the rupture. The sporangia of many ferns (Bracken) have an elastic ring which is probably intended for the energetic dispersal of the spores. In certain pines the scales of the cone, when thoroughly dried by the hot days of the summer following that of its production, open with a jerk, forcibly ejecting the winged seeds. Frequently a number will burst together, and then the sound may be heard at a great distance. In the expulsion of the seeds of the Balsam (Impatiens) the contact of some outside object is of advantage. The seed-case consists of one cell with five valves, and, if touched by accident when ripe, it at once bursts open, the valves coiling themselves violently, and, springing from the stalk, scatter the seeds in all directions. In the Poppy and the Snapdragon a stOl larger share of the work of releasing the seeds falls to an outer agency, for here the pericarp consists of a capsule which opens along the top by valves that leave small pores through which the seeds fall out when the capsules are shaken by the wind. In all of these various methods of the expulsion of seeds it would seem that they are due to mechanical causes, and depend in most instances (/»(- jmtuns excepted) upon a certain condition of dryness in themselves, and upon the state of the surrounding atmo- sphere. Passing from the modes in which dry ft'uits, consisting of a number of seeds enveloped in tough pericarps, effect dissemination, we have to consider next the means which obtain among dry fruits whose seeds are not collectively enclosed in a strong seed-case. Here, too, we find the forcible ejection of seeds. Those of the Oat are scattered with such energy that on a fine, dry day the snapping thus caused is distinctly audible. But the most curious pronsion possessed by seeds of tbis class for self-dissemi- nation is the hygroscopic awn. In the Wild Oat {Avena fatua), for example, there is attached to the glumeUa (a small leafy structure connected with the seed), a spiral awn covered with numerous fine hairs, and this awn has the power of expanding when moist, and of contracting when dry. Thus the attached seed is constantly on the move with the changes in the weather, the hairs clinging to any object met with, until germination or destruction puts an end to its motion. The seed of Barley, too, is provided with a similar awn, which is furnished with minute teeth that point towards its apex. The seed, when lying on the ground, naturally expands with the moisture of the night, and contracts with the dryness of the day ; but, as the teeth prevent its mo^•ing towards the point of the awn, all motion must be in the direction of the base of the seed, which wiU thus travel many feet from the parent stalk. As a ready proof of tbis, an ear of Barley will, if placed seed uppermost in the coat-sleeve in the morning, be found to work up to the arm-pit during the day. A still more remarkable provision exists in Erodium, a genus belonging to the Geranium order, by which the seed buries itself. The fruit splits into five cone-shaped seeds, at the base of which is a long awn or filament. As the seed lies on the ground the awn remains straight so long as it keeps moist, but when it gets dry one side of the awn contracts, forcibly causing the upper end to form a curve which brings its point against the ground, and the apex of the conical seed downwards. The lower part of the awn now commences to contract into a spiral, causing the cone to rotate and to enter the earth where the hairs which it bears, and which point upwards, hold it fast. The spiral portion also enters the ground, forcing the seed dowTiwards. Moisture now, instead of reversing the effect produced by dryness, only continues it, for the spiral coils, in trying to straighten themselves, are held fast by hairs, and the result is that the seed is driven deeper into the groimd. It is a notable thing, as Mr. Francis Darwin has pointed out, that these burying con- trivances are all of a similar nature, though belonging to plants of widely separated orders. Having considered plants which possess special facilities in themselves for dissemination, we come to those which depend to a gi-eat extent upon outside agencies for their dispersion. Of these agencies, the all-pervading instru- mentality of the wind may be taken as naturally next in order to the power of self-distribution. The exceeding smallness of many seeds, not to speak of spores, admits of their ready transport by the wind. In addition to tbis, certain fruits are evidently intended for dissemination by this agency, for they are furnished with downy tufts or with wings which support them on the breeze. When ripe for dispersion, the light, flossy seeds of the Dandelion and the Thistle may be seen floating in considerable quantities on the softest wind. These special appendages, though designed to serve the same purpose, and though often similar in appearance, vary greatly in their origin. There are three kinds of wing-shaped processes which, while the fruit is developing, take their rise from different parts of the flower. The wings on the seeds of certain species of the Pine Order arise from an outer layer of the tissue of the scale ; those on the seed of Bhinonia muvh-uta from the coat of the ovule, and those on the samara; of the Elm and the Maple are developments from the pericarp, which, of course, in simple fruits is the matured ovary. Again, the silky tuft of hairs, or pappus, of the CompositiB and of kindred orders, is a peculiar development of the calyx; whilst the coma of the seeds of Asclepias and of the Willow is a hairy growth from the testa. Aided by these special formatims on seeds and fruits, the importance of the wind in the work of dissemination is difficult to over- estimate. Frequently the wind acts in conjunction with another outside agent of dissemination — water. The wind strips the vegetation of a district of its fruits and carries them into neighbouring streams, to be caught perhaps by the bend of a bank where they form a cjlony. Plants growing by the banks of rivers will thus be distributed along the course of the stream. Curiously enough, it will sometimes happen that an Alpine plant will in this manner be brought into a lowland district where the climatal con- ditions are not favourable to its growth. It may flower, but cannot produce seed, and it is only by the continual renewal of the seed by the current that the species is able to maintain its occupation of the uncongenial localitj-. Certam seeds will, however, be borne by the current right out to sea, where, with others which have been carried April 1, 1891.] KNOWLEDGE. 67 direct to the ocean by the wind, they may probably flourish on some remote island. Necessarily such seeds must be well protected against outer injury, whether from friction or from the action of salt water. Dr. Hooker found in his examination of a large number of the floras of islands that the LeguminosiP, to which order the Pea, the Vetch, and the Bean belong, contained more species common to other parts of the world than any other order. The preponderance was due to the characteristic form of the fruit, its strong pericarp being well adapted for preserving the seed, whilst its shape enabled it to float on the water. Of course, it is only fruits of a certain lightness and buoyancy that admit of transport by wind and water. Those that are too heavy for this method of distribution, such as pulpy fruits, depend upon the agency of animal life for dispersion. There can hardly be any doubt that the bright, succulent, and edible coverings of fruits are specially intended to attract the attention of birds and other animals. In order to produce this attractive exterior we find not only the ovary — afterwards the pericarp proper — specially developed, as in the Orange or the Grape, but various other parts of the flower. Thus, by structural developments adapted to take ad- vantage of the means of transport existing in the forces of wind and of water, and in the surrounding animal life — afibrding another proof of the interdependence which exists in Nature — have plants been spread over the Earth. " The real difficulty," says Sir Charles Lyell, " which must present itself to everyone who contemplates the present geographical distribution of species, is the small number of exceptions to the rule of the non-intermixture of different groups of plants. Why have they not, suiJiJosing them to have been ever so distinct originally, become more blended and compounded together in the lapse of CALCITE AND ARAGONITE IN SHELLS. By Vaughan Cornish, B.Sc, F.C.S. IF different materials have the same chemical compo- position, they are generally regarded as being essentially identical, and are looked >ipon as varieties of the same substance. Carbonate of Ume is a familiar example ; chalk, limestone, marble, Ice- land spar, and aragonite are all composed of carbonate of lime, and are spoken of as different varieties of carbonate of lime. This does not, however, represent the view of the mineralogist. Chemical composition is only one among several criterions considered in the definition of a mineral species. It often happens that minerals differing fundamentally in their crystalline form, and in the in- ternal structure which is connected with the external form, have the same chemical composition. These are regarded by the mineralogist as distinct species, notwith- standing the identity of chemical composition. Funda- nu'Utal difference of crystalline form is the basis of differentiation among minerals of which the composition is identical. We will endeavour to make clear the principles on which it is decided whether a difference of form is to be regarded as fundamental. In mineralogical collections, ranged side by side with the well-known rliomb of Iceland spar, may be seen a vast variety of crystalline forms of carbonate of lime. In general appearance they dift'ei' greatly from one another ; yet the mineralogist will tell one that there is no fiiiiiliniitntul difference in these forms, whicli are all intimately related to that of the rhomholu'dron. This relationship is a matter of geome- try, which we must he content to state merely in a general manner. A crystal is a body bounded by certain plane surfaces — the faces of the crystal. The arrange- ment of a system of planes is best understood by con- sidering how their position is related to three lines intersecting at a point, these lines being termed aaxa. A crystalline form is defined, first, by the position of these lines ; secondly, by the manner in which the position of the planes is related to that of the lines. All the various forms which, in the mineralogical collection, are placed in proximity to the rhomb of Iceland spar, are forms which can be built up on the same system of axes, and the positions of the planes or faces with respect to these axes are all related to one another according to a simple geometrical law. All these specimens are, therefore, reckoned as belonging to one mineral species, to which the name calciU' is given. In the next compartment of the mineralogical collection will be found another set of crystals, also composed of carbonate of lime. These, however, are members of another mineral species known as (iiai/diiite. Their forms are related among themselves by a simple geometrical law, but the plan of construction is radically different from that of the calcite forms. The system of planes representing the faces of the crystals cannot be built up on the same three axes as those of the calcite forms, and the law con- necting the positions of the planes themselves is different in the two cases. For the mineralogist, carbonate of hme comprises two mineral species — calcite and aragonite — and all the difl'e- rent varieties are classed under one of these two names. The question may be asked. Is there not something fanciful in basing a classification of material substances merely on certain abstract ideas of symmetry"? Calcite and aragonite are composed of the same kinds of stuff' or matter ; if our minds were not gifted or encumbered with abstract notions about symmetry, should we discover any difference of properties between these two mineralogical species '? As a matter of fact, the properties of crystalline substances furnish a striking example of the real and inti- mate relation of oui- ideas of symmetry with the actual con- stitution and properties of matter. Every property of a crystalline substance is related to the particular symmetry of its form. Thus, take the case of the action of the sub- stance upon liglit. A ray of light is affected in the same way by its passage through any crystal of calcite : all speci- mens of aragonite behave alike in their action on light ; but the mode of action is entirely different in the case of aragonite from that of calcite. For exhibiting these differences of behaviour in the most distinct manner an elaborate instrument is employed, the stauroscope, in which iKihiriu'il light is used. We cannot enter here into the method of using the instrument, but in most text-books of mineralogy will be found plates showing the different intcrt'firmr phenomena afforded by a crystal of calcite and one of aragonite. .\ fragment of a crystal shows the phenomena characteristic of its species, which do not depend upon the specimen possessing crystalline faces. The action upon liglit depends upon the actual structure of the material of which the crystal is composed, which, as the above example shows, is intimately related with the crystalline form. We see, then, that the phy- sical properties justify the mineralogist in sorting the varied crystalline forms of carbonate of lime into two classes, and in characterizhig every member of each class by one of two names — the names of two mineral species. We have said that . 70 KNOWLEDGE [April I, 1891. pylons are covered with battle-scenes, representing the Syrian campaign of Eameses II., including the battle under the walls of the city of Kadosh on the Orontes. In the interior of the temple, in addition to the seated colossi already mentioned, eleven gigantic standing statues in red granite have already been unearthed, and there must be three more beneath the floor of a mosque which still occupies the south-western corner of the temple. These, on accoimt of the religious prejudices of the people, cannot, for the present at least, be imearthed. The mutilation of the faces of the figures is probably due to the fanaticism of the early Christian hermits of the Thebaid, who regarded them as idols. Fortimately there is no such danger from the Moslems, who, though icono- clasts, do not regard the statues as images or idols, but believe that they are the bodies of their own ancestors, who, as a punishment for their sins, were turned into stone by Allah. The other day one of these statues was imearthed, and the next day at early dawn three Arab women were found solemnly walking round it, and per- forming suitable funeral cei'emonies, as if around the body of one of their own dead. The following extract from a translation of a private letter addressed by M. Grebaut, director-general of the excavations, to his learned predecessor, Professor G. Maspero, of Paris, was printed in the Times of March 2 : — " Ha%dng found, in situ, at Deir-el-Bahari, a royal sarcophagus of a queen, and seeing that the surrounding ground had not been disturbed, I thought it worth while to make further excavations on the spot. " At a depth of 15 metres we came upon the door of a rock-cut chamber, in which were piled, one above the other, 180 mummy-cases of priests and priestesses of Amen, together with a larger number of the usual funerary objects, including some fifty Osirian statuettes. Of these, we at once opened ten, finding a papyrus in each. " There are a great many enormous wooden sarcophagi, C(mtaining mummies in triple mummy-cases, aU very richly decorated. Among these we have found a priest of Aah-hotep. These sarcophagi are of the time of the 21st dynasty. What we have found is, therefore, a ' cache ' of the same period as that of the royal mummies discovered in 1881, and made by the same priests of Amen. " Notwithstanding that the soil has remained untouched for 3,000 years, some of these sarcophagi are broken, and manj' of the gilded faces of the superincumbent efSgies are injured. The way in which they are piled up, their damaged condition, and the general disorder, point to a hurried and wholesale removal, as in the case of the royal mummies. We find, for instance, a mummy-case in- scribed with one name, enclosed in a sarcophagus inscribed with another, while probably the inner cases may prove to belong to a mummy with a name diil'ering from both. May we here hope to find some royal miimmies for which there was not space in the vault discovered ten years ago ? I scarcely dare to hope it. " At a first glance it would seem as if the high priests had abstained from burying the mummies of their more humble predecessors with those of royalty. Everything must, however, be opened and studied. " About midway in the shaft now open may be seen the door of an upper vault ; and, to judge by certain indica- tions, there is also probably an intermediate vault ; had we, however, only the 180 sarcophagi contemporary with, or anterior to, the 21st djmasty, it would be a magnificent haul, the greater number of the sarcophagi being really splendid and in perfect preservation. There are also some charming things among the minor objects. "The name has been purposely erased, or washed off, from several of the large sarcophagi, and the place left blank, as if the scribe had not had time to fill in that of the new occupant ; but we may probably find the names of those later occupants on their inner mummy-cases. One of the largest of these sarcophagi is surcharged with the name of the High Priest of Amen, Pinotem. " As soon as we have cleai'ed the lower vault I shall attack the upper chamber, or chambers." ILcttcrs. [The Editor does not hold himself responsible for the opinions or statements of correspondents.] PERPETUAL CALEXD.A.RS. To the Editor of Knowledge. Sir, — I was much interested in Mr. Prince's calendar, inasmuch as I designed one myself on much the same lines a few years since. Mine, however, seems to have some advantages for finding the days of the week in past centuries (especially in the Old Stjde). I therefore en- close a copy and the rules for using it, in case j'ou should think it of sufficient interest to reproduce for the readers of Knowledge. — Your obedient servant, Akxold S, Hansakd. Rules for Using the Table. I. — The numbers in the ring next within the names of the months are the last two figures of the years ; the numbers in the ring next inside this are the days of the month. The numbers on the movable disc refer to the first two figures of the years {i.e. when the given date is within the years 1700 and 2099 N.S.). II. — To "find the day of the week of any given date (N.S) where the first two figures of the year are given on the movable disc ; firstly, bring that number opposite to the last two figures of" the given year ; secondly, note which day of the week is thus brought imder the small arrow at "the top of the movable disc, and bring that day April 1, 1891.] KNOWLEDGE 71 of the week under the required month. The days of the week are now opposite their proper days of the month. III. — If the year is given in thick figures it is a Leap Year, and tlie -tanuary and February in thick letters must be used ; in other cases the plain .January and February must be used. IV. — The table may be used for any other centuries (N.S.), the calendar being repeated every fourth centixry. Thus 1600-1699 is identical with 2000 ; 2100 with 1700 ; 2200 with 1900, &c. V. — For Old Style dates, in the first motion of the disc, the day of the week given in the following table must be set opposite to the given year ; the second motion being the same as in New Stj'le dates : — andreds (Old Stylo). — 18 11 — 17 10 — 16 9 — 1.5 8 Division of Disc. Sunday Monday Tuesday Wednesday — 14 20 13 19 12 7 &c. Thursday Friday Saturday N.B.— That the years 1600, 1700, 1800, &c., are all leap years, O.S. ; but only every fourth of them, e.y. 1600, 2000, 2400, &c., are leap years according to N.S. THE MAGIC SQUARE OP FOUR. To the Editor of Knowledge. Dear Sib, — For the sake of accuracy, I should like to point out a mistake in my estimate of the number of varieties of type D. The types A, 1> and D are mutually convertible by a few simple transpositions, and therefore must have the same number of varieties. Now it is mathematically demonstrable that there can be only 48 varieties of A and B ; hence there must be just 48 of D. How it happened I wrote 96 I do not know. On the other hand, Mr. Cram tells me he can make 56 each of G, I, .J, and L. Consequently, we are still 32 short of Freniele's total of 880. T. S. Barrett. To the Editor of Knowledge. Dear Sir, — In reading Mr. -J. Pentland Smith's very interesting article on " Contrivances for the Cross-Fertili- zation of Plants," , in Knowledge, Feb. 2,1891,1 have been completely puzzled by the following problem : In speaking of the case of Aspidistra elatior, Mr. Smith, either in his own words or quoting Dr. Wilson, says in effect : — (I.) There is no access to the pollen until the stigma is fertilized. (II.) Fertilization cannot be effected until pollen has been deposited on the stigma. >Vluit I want to know is : How is the first flower fer- tilized, so as to commence the process ? Yours faithfully, F. .]. Pkovis. Coleford, Gloucester, 16th March 1891. [Until the decay of the stigma the slugs cannot get to the pollen. One can easily imagine that sooner or later the stigma of the first flower of the season will decay, whether pollenated or not, and that then access can be obtained to the pollen below. Pollenation, that is the resting, and ultimate germination of the pollen on the stigma, precedes fertilization in all Angio-sperms or plants wliicli have their seeds enclosed by the carpels. — J. P. Smith.] STELLAR SPECTRA. By E. W. Maunder, F.E.A.S. {Assistant superintendiiu/ the Spectroscopic Department of (ireeninch Observatory). WHEN the publication of Dr. Elkin's determina- tion of the parallax of Arcturus rendered it probable that we must class this star as one of the most distant of its magnitude, it became clear to me, as I tried to show in the February number of Knowledge, that it must be of most gigantic size, and must move with most amazing swift- ness. But a fiu'ther point for inquiry also suggested itself. If Arcturus be, as would appear to be the case, the star which actually gives the most light of any we know of at present, then its spectrum should be typical of the largest and hottest stars, whereas it has been customary to regard it as of a markedly lower class. The subject of the classification of stellar spectra has been occupying special attention of late ; it may, there- fore, be worth while to see if any further light, however feeble, can be thrown on the matter from the point of view suggested by the magnitude of Arcturus. The earliest classification of stars was effected by Sir W. Herschel, who grouped them according to their colours ; the only arrangement possible at a time when the spectroscope was still undreamed of, but a real step, never- theless, towards the more delicate discrimination which that instrument renders possible. Fraumhofer, in his en- deavours to solve the secret of the spectrum, noted the strongly marked diflerences between the spectra of diflerent stars, and drew the important conclusion that the dark lines which crossed them were due to something in the stars themselves, and not to any effect of our own atmo- sphere, or any absorption of light in space. But the first spectroscopic classification of stars was due to Rutherford in America, and Secchi in Em-ope. The latter, as was inevitable in beginning so new a research, made several alterations from liis first scheme ; but his final classification divided the stars into " types " of spectrum as follows : — Type I. — The white and bluish white stars, like Sirius and Vega. The spectra in this type show the four lines of hydrogen intensely dark, broad, and with diffused and shaded edges. Metallic lines are faint and narrow, and not easily seen. The principal stars of Orion form a variety of this type, in which the hydrogen lines are much less marked, and much narrower than in other stars of the first type. Type II. embraces the yellowish stars, such as our Sun, Arcturus, and Aldebaran. The hydrogen lines are well seen, but narrow and fairly sharp ; the entire spectrum is full of well-marked metallic lines, some of which are more pronounced than the lines of hydrogen. The stars of Type III. arc mostly orange in hue ; o Ononis and a Herculis are the best examples. The hydro- gen lines are faint, or no longer seen ; but a succession of dark bands, dark and sharp towards the violet, and shading away into nothingness towards the red, makes this type of spectrum the most strongly marked and the most beautiful of any. Type IV., the stars of which are mostly red, also shows a banded spectrum, but the bands fade off in the opposite direction to those of Tj-pe III. Secchi further called attention to the existence of a couple of stars showing briijlit lines in their spectra, the forerunners of a fifth type ; and, a little later, the dis- covery by MM. Wolf and Rayet of a curious group of stars in Cygiius added a sixth type. Secchi's classification was purely an observational one, and it was independent of theoretical considerations as to 72 KNOWLEDGE [April 1, 1891. the iis|iritivc ages in the evolution of a normal star which the diUereut types might represent. For it was naturally felt that there must be growth and development amongst stars as amongst animals and plants. A star must have its birth, its periods of growth, full vigour, and decay, closing in the — Last scene of all That ends this strange, eventfnl history, a dark, cold body, incapable of giving light and heat to other worlds, or of sustaining life upon its own surface. And naturally the attempt was made to connect these different types of spectrum with the various stages of stellar life-history. Zollner seems to have been the first to suggest that the white stars were the hottest, and that the yellow colour of the stars of the second type showed that they had advanced some way in the process of cooling down. Angstrom suggested that the shaded bands of the orange stars indicated the formation of compoimd bodies in their atmospheres, consequent on the lowering of tem- perature ; and Lockyer, a little later, expressed the same views still more definitely. " The hotter the star, the simpler its spectrum," he said ; " and the older a star, the more does the free hydrogen disappear from it." Vogel, more recently, being dissatisfied with Secchis mode of grouping stellar spectra, devised a more elaborate one, the principal change from Secchi's system of Types being that \'ogel makes Types 111. and IV. varieties of the same Class 111. The leading thought in this new classification was that all stars have at one time or another been of the first or Sirian Type, all will pass through the second or Solar Type ; but after passing this stage the star may either show a spectrum hke that of a Herculis, or like that of the small red stars. The road diverges here ; the majority follow the path which Antares, Betelgeuse, and the btcidn of Hercules have taken ; but a few, especially the stars in two small groups on the Jlilky Way, prefer to gi\e spectra in which the bands are sharpest to the red, and shade off towards the violet. It was well objected to this scheme that it made no pro\-isiou for a period of increasing temperature in a star. Stars are certainly not brought forth from nebulie, like Pallas Athene from Jupiter, fully developed and equipped with their whole armoury of light and heat. There is evidently a time during which the surface brilliancy in- creases, and this probably corresponds with a time during which the mean temperature must be increasing. Besides, the place assigned to the red stars was a perfectly arbitrary one. We know that the First and Second Types are con- tiguous stages, whichever be the earlier ; for stars hke Procyon, Rigel, Spica, Polaris, a Cygni, and others, supply examples of almost every possible gradation, from the unmistakable Sirian to the complete Solar form. So, again, Aldebarau, Betelgeuse. and many others form a series of links connecting the Second and Third Types ; but until recently the Fourth Type stood alone. There are no instances of stars whose spectra leave us in doubt as to whether the Fourth Type or some other is the more strongly represented ; there are no intermediate forms. It is therefore a pure assumption to assert that this pai-- ticular kind of spectrum is either the next stage to the Solar Type or that it is an alternative stage to the a Herculis Type. The most recent classification is that of Lockyer, and he certainly avoids one of the objections to which Vogel's is open. The Sirian Type is still taken as that of the hottest stars, but he breaks up the Solar Type into two groups ; the one showing rising, and the other falling temperature. The course of evolution, according to his plan, is : Group I., the nebular stage ; Group 11., the orange star, or a Herculis stage ; Group HI., the a Cygni stage, including some spectra of Secchi's Type 11. ; Group IV., the Sirian stage ; Group V., the Solar stage, including the rest of Secchi's Type II. stars ; Group VI., the red star stage; Group VII., the dark stage. The position assigned to the red stars is, of course, as much a matter of assumption on Lockyer's plan as on Vogel's. The former has, however, this advantage over his predecessors, in that it corresponds to the probable stages of growth as well as those of decay. The Sirian stars, which he, in common with almost every theorist," regards as the hottest and largest, mark not only the commencement of a fall in temperature, but the conclusion of a rise. We are saved the difficulty of assuming the Sirian phase to be that in which all stars were originally created, and from which they have only changed by degradation. But in all these systems the supremacy of the Sirian Type is assumed, not proved, and it has been well pointed out that it is quite possible to read the record the other way, and to argue that the ruddy stars are the hottest, and that the orange, yellow, and bluish tints are o\-idences of a progressive decline in temperature. It is a question, therefore, of much importance to see if any positive information can be given us on the subject. Two circumstances have greatly operated to the present view. Firstly, that a solid body raised to incandescence first glows with a ruddy hue, and then, as the tempera- ture increases, so the colour changes to orange, yellow, white, or blue ; and it was very natural, though scarcely scientific, to extend the analogy to the stars. For a stellar spectrum shows us by the continuous band of colour, in- terrupted by dark bands, that the light we receive is not the whole of the Ught the star emits, but that it has sufl'ered absorption in the atmosphere of the star itself ; and it is m the difi'erences of the quality and amount of this absorption, and not in the differences of the original light of the star, that we find the tests for distinguishing one type from another. That is to say, it is by the dark lines or bands, and not by the continuous spectrum, that we classify the stars. The difference, therefore, between the Sirian and Solar stars lies not in their photospheres, but in their absorbing atmospheres. For Sirius such ab- sorption is almost confined to hydrogen, the influence of which is excessively marked ; but for the Sun, Arcturus, and their congeners, twenty or thirty elements have im- pressed the spectrum with the evidences of their presence. Given that two stars of these two Types are at the same distance from us, and that they appear to shine with the same amount of light, surely the star which displays the * In this, as in other departments of science, the inductive method is the only safe one, and a few observed facts are preferable to any number of theories founded on assumed conditions. The physical connection of the trapezium stars with the Orion nebula, and the stars of the Pleiades cluster with the Pleiades nebula, can hardly be doubted : and if the nibular stage is the first one in a star's history, we have evidence that three diflferent classes of spectra are exhibited by stars involved in nebulous matter. In all three the hydrogen lines, or some of them, are conspicuous, but the spectra are considerably more complicated than those of stars usu.ally ranked as belonging to Secchi's First Type. The spectra of the trapezium stars appear to be crossed with bright lines similar to. but more intense than, the bright lines of the Orion nebula around them ; the hydrogen lines are not hazy and diffused as in Secchi's First Type, but comparatively narrow and sharp. The two classes of spectra in the Pleiades gi-oup each include stars of various magnitudes ; and if we may assume that all the stars of the Pleiades group are of the same age, we must conclude thiit the two classes of spectra do not correspond to different stages of cooling. The star which appeared in the Andromeda nebula in 1885 seems to have had a spectrum terminating abruptly at the red end, as well as, according to some observers, very faint bright lines, which are asserted to exist in the Andromeda nebula spectrum. The ifacts brought together by Mr. Maunder in this paper should check, too precipitate theorists. — A, C. Ranyaiu>. Ai'EiL 1, 1891.] KNOWLEDGE. 73 greatest indications of absorption in itS spectrum must be actually emitting the greatest amount of light from its photosphere. ■■ And, to say the least, it is arguable that the fuller development of the metallic spectra in stars of the Second Type shows a higher temperature, not a lower one. It is conceivable, not to put it more strongly, that an intenser heat may in these stars keep metals in the state of absorbing gas, and at a higher atmospheric level, which in Siriau stars are precipitated at or below the photosphere, and so give no sign of their presence. At all events, we can feel well assured that the temperature of the Solar stars is very high, for not only do we find the metallic lines in the visible spectrum, but we tind them strongly marked and numerous far in the ultra-violet, a proof that even in the reversing layer the temperature is high enough to compel the metals whose gases compose it to give out radiations of even the shortest wave-lengths, and to give them out strongly and unmistakably. The other circumstance that has led to the belief that the white stars are the hottest, the red the coolest, is that whilst more than half the stellar giants are of the first type, there are only two Ist-magnitude stars of the third type, and the brightest of the fourth-type stars is not so bright as the 5tli-magnitude. But, again, a closer con- sideration of the facts leads us to a different conclusion. Surely we have no right to assume that the stars are equally distributed amongst the various Types. If they really mark different stages in stellar evolution, some may be much more quickly passed than others ; or it may be that but few stars are yet old enough to have reached the most advanced stage, or else that but few are so young as not to have passed through at least one phase. There is, however, a simple test which we can apply. If the orange or ruddy stars are fainter on the average than the white and yellow, then the further down in brightness we go the larger will be the proportion of such stars observed. But this does not appear to be the case. If we take those stars of the Oxford Uranometria which are above the 5th magnitude, and have been classified by Secchi, we find them thus divided : — Type I. Typo II. Type III. Above 1st mag. ... ... 5 2 1 Between 1st and 2nd ... 11 -1 1 „ 2nd and 3rd .20 17 4 Srdand-tth ... 50 54 2 4th and 5th ... 85 29 2 121 lOG 10 The stn.rs of (hicm and of tlie Pleiades which have spectra a little differing from the normal type, have never- theless been included under Type I. Excluding these, and such stars as were outside the general Oxford limit of North Polar Distance (100°), and were only observed on account of their special brightness, we find that for the * If the stars are all composed of similar materials (as has been, perhaps, too hastily assumed), and their photospheres are clouds of incandescent particles. The temperature of their photospheres could not exceed the liighost temperature at which the most refrac- tory materials would he driven into vapour, and all photospheres would shine with equal brightness. That there are differences in the apparent brightness, area for area, of stars can hardly bo doubted from tlie facts wo have already learnt witli regard to the masses of double stars ; such, for example, as Sirius and liis companion, and the binaries of the Algol type. From tho facts we know with regard to our own sun we cannot suppose that tho matter of gaseous stars is stratillcd at different levels, as some theorists have too hastily assumed. For on the sun tho continuous eruption of matter from below the photosphere would sulliciontly mix the gaseous matter by transfer in mass, if we could conceive of it as not mixed by diffusion. Any apparent stratilication can only be duo to some vapours continuing incandescent at lower tem- peratures than others. — A C. U.^nvaku. stars north of 10° S. Dec, and above the 5th magnitude, the numbers would run : — Type I. Type II. Type III. Above 1st mag. ... ... 2 2 1 J5etween 1st and 2ud ... 8 4 0 2Qd and 3rd ... IH 17 4 ,, 3rd and 4th ... 45 54 2 4th and 5th ... 33 29 2 lOG lOG y It would seem then that, within these Hmits, the first and second types are about equally numerous, and each about twelve times as abundant as the third. , Comparing these numbers with the results of Vogel's and Konkoly's spectroscopic surveys, which were carried down to the 7i mag., we tind that they give out of 6,073 stars examined the numbers for each type as follows : — Tvpe I. Type II. Tvpe III. Tvpe IV. 3,145 2,105 " 375 " 12 besides 14 stars of the Orion variety of Type I. and 422, that could not be properly classified under any of the above heads. The comparison shows that, so far as these observations go. Type I. has a small preponderance over Type II. for the higher magnitudes, but that this preponderance ceases between the 3rd and 4th magnitudes to become much more marked as fainter stars are included. Three con- clusions seem to be fairly deducible from this result. First, that Sirian stars are more numerous on the whole than Solar stars. Secondly, Solar stars are on the average rather brighter than the Sirian stars, or else rather nearer to us. Thirdly, that the average difference in the bright- ness of the stars of the two Types is not by any means so great as we should expect if either Type marked a stage of very greatly superior temperature to the other. Of course the materials I have used are very incom- plete and can only supply indications, and not proofs. Still, it may be worth while to take the question a stao-e further, and see what light paraUax determinations have to throw on the question. Taking the table of parallaxes given in the appendix to Miss Clarke's Systcin of the Stars — a book as valuable and instructive as it is charming in style — we find 20 stars the parallaxes of which are given, and which are found in Secehi's lists of star Types. Adding Arcturus we have 21, of which nine are First Type, and 12 Second Type stars. Employing the Oxford magnitudes and computing the absolute light-giving power of each star, takmg Sirius as our standard, we obtain the following table : — Sirian Stars. Solar Stars. /3 Cassiopeia . 0-29 a Cassiopeiie . 1-41 a Persei . . 1-90 rj Cassiopeia' . t)-12 Sirius . . 1-00 y8 Andromeda' . 0-98 Procyon . . 0'56 Polaris . . 4-45 Kegulus . . 2-55 a Arietis . . 1-39 a Lyno . . 48-35 Aldebarau . . 1-68 a Draconis . 0-04 Capella . . 514 a Aquilffi . . 0(51 Pollux . ;-j-!)2 a Ce^jhei . . 1-GO >/ Herculis. . 0-15 TT Herculis . 0-19 € Cygni . . 0-50 Arcturus . . 147-00 It will be seen at once that two stars stand out from all the rest ; \'ega amongst the Sirian stars benig noarlv six times us bright as tho other eight taken together : and Arcturus, amongst the Solar stars, more than seven times as bright as all tho eleven others taken together. In both cases tho parallax adopted is that of Dr. Elkin, which for these two stars, and especially for \'oga, differs 74 KNOWLEDGE [April 1, 1891. considerably from the results obtained by other observers. The mean of seven other faii-Iy accordant detenninatious of the parallax of Vega would give its intrinsic light- giving power as 1'92. In any case the two stars are evidently exceptional, and, as what we are seeking for is an average i-esult, may well be left on one side, and then the remaining stars do not differ extravagantly in bright- ness. The mean Sirian star would then have a light- giving power of 1'07; the mean Solar star of 1*8 ; a result which I think may at least warrant us in saying that the supposed superiority of First Type stars receives no support from it. Yet another mode of attacking the problem is open to us. Binary stars, the orbits of which have been deter- mined afford a means, as Mr. Monck has pointed out, of forming some idea of their relative brightness, if we as- sume that all the stars in question are spheres of equal density, and Mr. Gore, in his recent " Catalogue of Binary Btars," has computed this relative brilliancy per unit of surface for most of the fifty-nine stars whose orbits he gives. The result is a curious one. All the stars are, as Mr. Gore himself remarks, either First or Second Type, and there is a well-marked and unmistakable superiority of the First over the Second.''' Assuming all the stars of equal density, the Sirian are about six times as bright, surface for surface, as the Solar. From this we may infer that the slight superiority in total radiating power of the Solar stars is not due to greater extent of photosphere in proportion to their mass, but that the very reverse is the case ; so that the Solar stars do not merely emit more light than the Sirian, but they are superior to tiiem in a yet higher proportion, both in size and density. If so, we may regard theorists as probably right when they have placed the Second Type stars as belonging to a later stage that the First ; but as wrong when they have re- garded the Sirian stars as occupying the apex of the curve, and stars like our sun as being well advanced on the road to decay. * Except in the case of one star, y Leonis, which is clearly by far the brightest star, surface for surface, on the assnmption men- tioned above. A PERPETUAL CALENDAR. In addition to the rules given in the last number for finding the day of the week corresponding to any given date New Style, we might have added some simple rules to extend the use of Mr. Prince's table and calendar to dates previous to 2nd September 1752, when the Old Style of reckoning came to an end. The change of style was effected in England by dropping the eleven days between Wednesday the 2nd September 1752, and Thursday the nth September 1752. If the eleven days had not been dropped, the 14th of Sejitember would ha\e been on a Monday ; therefore, in passing backwards from New Style dates to Old Style dates, Thursday becomes Monday and one jumps forward four days in the week, or backwards three days. To find the day of the week on which an event happened in the last century after the change of style, the rule given in the last number was- — find the day of the week for the corresponding day in this century, and go forward two days in the week. From the beginning of the century to the 2nd September 1752, you must find the day of the week for the corresponding day in this century and go forward six days, which is equivalent to going back one day in the week. Events which happened in the 17th century occurred on the same day of the week as that on which the bicentenary of the event falls in this century ; thus, Evelyn mentions that Ash Wednesday in the year 1661 was on February 27th. Turning to the table in the last number, w^e find that the Dominical Letter for 1861 was F, and that the 27th February 1861 was also on a Wednesday. To go back to preceding centuries of Old Style reckoning we go forward one day in the week for every century. Thus, events in the 16th century which happened on a Sunday, have their tercentenaries in this century on a Saturday. Mr. E. Er.skine Scott has sent us a Perpetual Almanack and Calendar published by him in 1850, which, besides a table for finding the day of the week corresponding to any day of the year when the Dominical Letter is given, gives a table with the Dominical Letter for every year, from the Christian Era onwards, reckoning by either Old Style or New — a table which will be found convenient for determining the days of the week corresponding to dates in foreign countries as well as in England. The Gre- gorian or New Style was adopted in Rome in 1582; in Paris, by taking ten days off' the Calendar, 15th December 1582. In Russia, Old Style is still in use. It now dif- fers from the New Style by twelve days ; thus, the lath of April 1891 in England corresponds to the 1st of April in Russia. TABLE I. Me. Ekskine Scott's Table for finding the Dominical Leiter OR Letters for any Year, Old Style or New. l\t\o «tnlc. Hunds. of Years. (Dlti ,ft!)lc. 100 200 lioo m) 600 900 000 70o! 800 100011001200 Hundreds of Years. 100 211(1 :;ii(i Km' ."iil( (1 1300 1400 1500 1(;(XI 700 800 90(1111(11! 11(1(1 12ooi:Ji(i 1700 IW'Oll'OO 20(1(1 210O22(M)'i-;0()24(»l 1400 •'KKI ]50o[l600:i700J1800 2200.2300 2400 2500 1900 2000 2600 2700 Years above C E G !BA Hundreds. DC ED FE GF AG BA CB B D F G 1 ■•'I B C D h F G A A i; F, K 2 30 58 86 A B C D E F G G B D E 3 31 59 8/ G A B C 1 D E F FE AG CB DC i 32 60 88 FE GF AG BA CB DC ED D V A B a X^ 61 89 T> E F G A B a c K G A fi :u 62 90 ('■ 1) K K (J A B B D F G 35 63 91 B C D E F G A AG CB ED FE 8 36 37 64 65 92 93 AG F BA "g~ CB A DC B ED FE D GF E F A C T> P E (} B C 10 38 66 94 k; K G A B C 1) D F A B 11 39 67 95 D E i' ^ A B C CB ED GF AG 12 40 68 96 CB A DC B ED FE GF E AG F BA G A r. E F 13 41 69 97 G B 11 E 14 42 70 98 a A B C D E F F A C D 15 43 71 99 F G A B C D E ED c GF E BA CB 16 U 72 ED FE GF AG BA CB DC G A 17 45 73 c D E F G A B B D F G IS 4fi 74 K C D E i F G A A 0 E F 19 47 75 A B C D 1 E G GF BA DC ED 20 48 76 GF AG BA CB DC ED FE E G B C 21 49 77 E F G A B C D D F A B '». ,50 7» 1) K Jb' G A C E G A 23 51 79 80 — C BA D CB E DC F ED G FE A GF B AG BA DC FE GF 24 52 G B D E 2,1 ."iS 81 G A B C D E F F A C n 2fi M 82 k' (i A B C D E E G B 0 27 55 83 a i' G A B C D DC FE AG BA 28 56 84 Dt ED FE GF|AG BA CB Directions. — Look for the given year at the top of the himdreds contained in the Table, on the lelt for New April 1, 1891.] KNOWLEDGE. 75 Style, and on the right for Old Style ; then below this point, and on a line with the given year of the century in tlie centre of the Table, you will find the Dominical Letter for the year. TABLE II. For Finding tue Days of the Wekk corrksponding to the Days of the Months; the Dominioai, Letter for the Year BEING ascertained BY TABLE L Note. — The donhU Ultevs in tich ctnitpfirtmeut refer to hap years, the ^tithjle to JANUAEY A AGB BAG CB|D DC EED F FE|G GF FEBEUAKY D DC E EDF FEG GF A AG B BAG CB MARCH DEDE FEP 6PG AG A BA B CBC DC APRIL G AG A BA B CB C DC DED E FE P GF MAT B CBC DC DEDE FE P GF G AG A BA JUNK E FE P GF G AG A BA B CB C DC D ED JULY G AG A BA B CB C DC D ED B FE|F GF AUGUST C DC D ED E FE F GP G AG A BA B CB SEPTEMBER P GF G AG|A BA B CB C DC DEDE FE OCTOBER A BA B CB C DC DED E FE F GF G AG NOVEMBER D EDE PEP GP G AG A BA B CBC DC DECEMBER F GF G AG A BA B CB C DC DEDE FE 1 , 8 ' 15 22 1 29 Sun. |Sat. iFri. Thur.Wed. Tues. Mon. 2 9 1 16 23 30 Mon. jSun. Sat. Fri. iTliur. Sat. iPri. Wed. !Tues. 3 4 10 17 11 18 24 31 25 ... Tues. Mon. Sun. Thur. Wed. Wea. 'Tues. jMon. jSun. Sat. Fri. Thur. 5 6 12 19 13 20 27 1 ... Thur.Wed. iTues. [Mon. Sun. Fri. Tliur. Wed. |Tues. Mon. Sat. San. Fri. Sat. 7 U 1 31 28 ... Sat. Fri. Tbur.'Wed. Tues. Mon. Sun. Directions. — Tlie Dominical Letter answering to the given year being found by Talilc L, find tliis Dominical Letter in the above Table on the same horizontal line with the given month, and under it, in the lower part of the Table, are the days of the week, corresponding with the days of the given month in the same horizontal line on the left-iiand side of the Table. EKRATUM. In the Article on the Milky Way in the Southern Hemisphere, in the last number of Knowledge, it was by mistake stated that one of the two clusters at tlie bottom of Mr. Barnard's plate of the Sagittarius Region of the Milky Way was entirely wanting in Mr. Russell's photo- graphs. This is not the case, though there is ample evidence of the variation in brightness of many other stars shown upon the plates. Only one of the clusters is shown in the plate from Mr. Russell's photograph ; the other, or preceding cluster, is just outside the field. OUR INVISIBLE FOES, OR BACTERIA IN AGRICULTURE. By Miss A. W. Buckland. Tlli'i first question now asked whenever an epidemic attacks either man or the lower animals is, Is it caused by germs or liacilli floating in the air, or conveyed by water, milk, or any other medium. Tlic germ theory of disease, at present so popular, may be said to have originated in the successiul experi- ments made by M. Pasteur for the cure of the dreadful disease known as splenic fever in sheep, and the import- ance of the subject to the agriculturist and merchant, as weU as to the medical profession, may be best understood and appreciated by reference to a few facts. During the year 1888 more than eleven hundi-ed head of cattle were slaughtered in Dublin, because they had been in contact with a few suflerLng from pleuro-pneu- monia, whilst the Commission appointed to investigate the best mode of preventing and curing this and simOar diseases, recommended tlie continuous slaughter of all animals which might have been exposed to infection, adding to the report, however, a clause to the effect that, should experiments in inoculation be deemed advisable, such experiments should be carried out only with the most stringent precautions. Meanwhile the Government of India, as the result of experiments made, has ordered the inoculation of all the valuable elephants in the Government stables, for the prevention of a disease by which they have hitherto been decimated. M. Pasteur, as is well known, proi)osed to exterminate the millions of rabbits which have become such a pest in Australia and New Zealand, by introducing among them by inoculation the disease known as chicken- cholera, deadly to fowls and rabbits, but harmless to other animals and to man. But although the Australasian Governments approached the matter in a scientific spirit, and gave every facility for properly conducted experiments, under the supervision of Dr. Katz, bacteriologist, employed by the Linnean Society, — (1) to test the commuuical)iUty of chicken-cholera to rabbits, the possibility of spreading the disease from rabbit to rabbit, and the readiness and channels by which such commimication could be procured ; (2) to ascertain whether the disease is transmissible fi'om infected rabbits to other domestic animals — mammals and birds ; (3) to ascertain whether the infectivity of the disease is weakened by repeated transmissions from rabbit to rabbit, — the experiments do not api^ear to have been successful, for although the rabbits inoculated die, they do not apparently convey the disease to others. Nevertheless it seems to be demonstrated beyond dispute, that certain forms of bacteria invariably accompany certain diseases, and reproduce similar diseases when introduced by inocu- lation into the bodies of men or animals. These iiiicro-oiytniisms, so exceedingly small as to be absolutely invisible to the naked eye, have yet been so carefully observed microscopically, and so faithfully re- produced and enlarged by photography, that they can be studied in all their wonderfully varied forms ; and the difl'erences between them are sufficiently marked to be appreciated even by the non-scientific observer. Some resemble dots in various groups ; some are twisted spirals ; some look like chains ; others resemble small bags, with strings attached ; some look like branches of trees, whUst others are simply rods crossing each other. If we regard them as animals, they do not appear to possess any bodily parts, neither head nor tad, neither heart nor stomach ; whilst if they are vegetables, they have neither roots nor branches, although abounding in spores. That they are very much alive cannot be doubted, nor the fact that they multiply with the most astonishing rapidity. The growth of one which occurs in sugar is so rapid that 49 hectolitres of molasses were converted into a gelatinous mass in twelve hours. Micro-organisms can be cultivated in various media, and wUl still retain their identity, but they cannot all be cultivated in the same media. . Dr. C'lookshauk says : •' Some species cannot be cultivated artificially, others wUl only grow upon blood- serum ; many grow upon nutrient gelatine, but some species only if it be acid or alkaline 76 KNOWLEDGE. [April 1, 1891. respectively. Though the comma baciUus of Koch, like the majority of organisms, grows best on an alkaline medium, yet the surface of a potato is acid, and on this it is well known to flourish at the temperature of the blood." Those bacteria are everywhere, in the air we breathe, in the water we drink, in the ground we tread on, but hapiiily some are innocuous ; and the noxious mvrst find a suitable soil in which to develop their evil nature, other- wise the human race must have been exterminated by them long ago, and the whole of the animal and vegetable world must have become simply putrefactive media for the propagation of micro-organisms. We cannot pretend in this article to go into any scientific description of the numerous bacteria which, thanks to the researches of Koch, Pasteur, and many other zealous workers on the Continent, have become as well known as creatures of larger growth ; but we will endeavour to point out some of the points of interest to the general public in this new science, as brought before us in the Manual of Bacte- rioloi/!/ of Dr. Crookshank, one of our chief English workers in this branch of science, who established a bacteriological laboratory at King's College, in which many elaborate investigations are carried on daily. WtsMamial is primarily for the use of students, and therefore deals largely with the methods of cultivation, and preparation for the microscope, of the various species of bacteria, all the necessary apparatus being elaborately illustrated. The study of bacteria may be considered to be quite recent, yet, as Dr. Crookshank points out, " Leeuwenhoeck, two hundred years ago, recognised and described microscopic organisms in putrid water and saliva, which probably correspond -nath organisms such as vibrios and leptothrix of modern times." The article upon " Medicine " in the Emi/clojxedia Britannicu also points out that Schiinlein "made in 1839 one discovery apparently small, but in reality most suggestive, namely, that the contagious disease of the head called favus is produced by the growth in the hair of a parasitic fungus." In this may be found the germ of the startling modern discoveries in parasitic diseases ; and it seems that even as early as 1773 JMiiller suggested a classification of these microscopic organisms ; but even to the present day their exact place in the economy of nature has not been determined. " Existing as they do," says Dr. Crookshank, " upon the very borderland of the vegetable and animal kingdoms, not only have they been transferred fi-om one to the other, but even the question has been raised whether the smaller forms should be con- sidered as lidng beings at all." But he says: "The gradual improvements in the means of studying such minute objects, the methods of cultivating them artificially, and of studying their chemistry and physiology, and the ever-increasing revelations of the microscope, have resulted in establishing these microscopic objects as members of the vegetable kingdom, ranking among the lowest forms of fungi." After showing the various classifications of these fission-fungi. Dr. Crookshank divides them, after Zopf, into four groups, and each group again into genera and species. He then gives a long list of each, classifying them according to their association with disease in man and animals, and adding to thelist such asare unassociated with disease. Glancing at these lists, we are struck by the fact that in some of the groups almost all the species are associated with disease, whOst some forms are common to men and animals. In Sirtjitoiomts, for instance, there are seventeen species traceable to disease in man, eleven belonging to disease in animals, two common to animals and man, and only four unassociated with disease. In Sarnjia, on the contrary, all the species appear to be innocuous. In other groups the hurtful and innocent species are more equally di\'ided. In the genus Muio- cocciis, to which belongs the much-dreaded germ of rabies, and also that of scarlatina, measles, and whooping-cough, there are ten species belonging to human disease, five to animals, one to plants, and eighteen which are harmless. In the Bacteriaceffi the hurtful and innocent species seem also to be pretty equally divided ; bitt to this group belong some of the most dreaded of disease-germs, such as that of pneumonia, diphtheria, chicken -cholera, the disputed comma bacillus of Asiatic cholera, the bacilU associated with typhus fever, with anthrax, with tuberculosis, with malaria, with swine fever, &c. &c. The yeast-fimgi and mould-fimgi, some of which are so destructive to vegetable life, appear to be allied to the bacteria or fission-fungi, but are nevertheless quite distinct. The moulds of various kinds, which form on almost everj-- thing eatable, especially in damp weather, belong to these, but they also include the potato-blight (PeronoKjiam infi'stinis), grape-disease (Oiflium), the mildew, smut, and other wheat-diseases, the salmon-fungus, and the silk- woiTn disease ; all of which have had disastrous eft'ects upon the prosperity of mankind, although they have not been inimical to human life in the same way as the Bacteria. It would seem as though these micro-organisms were Nature's favoured weapons of destruction — her tiny poisoned arrows, with which she shoots hither and thither continuously, and against which all living things, whether animal or vegetable, require to be rendered more in- vulnerable than Achilles. Is there to be found any Styx wherein mankind ni'iy be rendered invulnerable to the attacks of these invisible foes '? Pasteur is supposed to have discovered the means of depriving some of these arrows of their deadly power by extending to other diseases the system of inoculation, introduced first in connection with small-pox, and afterwards modified by -Jenner into vaccination, long before the discovery of Bacteria as the constant accompaniment, if not the actual source, of disease. The two diseases, with the cure or prevention of which the name of Pasteur will be always associated, are rabies or hydrophobia, and anthrax, known also as splenic fever or wool-sorter's disease ; the former is, without doubt, one of the most terrible of maladies, and the latter, although less generally known, has caused the cruel death of mul- titudes who have been brought into contact with it. Both diseases are commimicated in the first place from animals to man. The mode of prevention adopted by M. Pasteur is inoculation with the bacillus of the disease, thus re- sembling the old inoculation ior small-pox rather than vaccination, which is the communication of an allied animal disease rather than the human form of that disease. But M. Pasteur does not, as in the old inocula- tion , give the disease in its full force ; but he takes the bacillus, cultivates it in different media, and only intro- duces it into the animal or human body after it has been attenuated and its full malignity destroyed. Speaking of anthrax. Dr. Crookshank says: " By cul- tivating the bacillus in neutralized bouillon at 42°-43° C. for about twenty days, the infecting power is weakened, and animals inoculated with it are protected against the disease." To obtain a still more perfect immunity, they are inoculated a second time with material which has been less weakened. The animals are then protected against the most virulent anthrax, but (nily far a iiiiii\ From such a culture, however, new cultures of %arulent bacilli can be started, and a culture that is "vaccin" for April 1, 1891.1 KNOWLEDGE 77 sheep, kills a guinea-pig, and then yields bacilli that are fatal to sheep. Exposure to a temperature of 55° C, or treatment with -5 to 1 per cent, carbolic acid, deprives the bacilli of their virulence. The virulence of the bacillus is also altered by passing the bacillus through different species of animals. The bacillus of sheep or cattle is fatal when re-inoculated into she^p or cattle ; but, if inoculated in mice, the bacilli then obtained lose their virulence for sheep or cattle ; only a transitory illness results, and the animals are protected for a time against virulent anthrax. The possibility of mitigating the virus depends upon the species of animal ; rodents cannot be rendered immune by any linown " vaccin." The same process is employed by M. Pasteur in his now celebrated inoculations for hydrophobia. In the course of his expe- riments some very curious facts have come to light ; it has been discovered that " passing the virus through various animals considerably modifies its properties. By inoculating a monlcey from a rabid dog, and then passing the virus through other monlieys, the virulence is dimi- nished ; but by inoculating a rabbit from the dog, and passing the virus from rabbit to rabbit, the virulence is increased." In swine-erysipelas Pasteur and Tliuillier discovered that "by passing the virus through pigeons the wulence was increased, but by passing it through rabbits it was progressively diminished. Thus a virus was obtained from a rabbit, which produced only a mild disease in pigs, and after recovery complete immunity.'' To the non-professional observer, these facts seem pregnant with deep meaning ; they appear to point to the change from the old inoculation for small-pox to the vaccination of Jemier, in which a similar but less virulent disease may be communicated from a lower animal to man, producing immunity from the graver disease ; and as we look down the long lists of bacilli, some of deadly vu-u- lence and some innocuous, yet all belonging to the same group of germs, we wonder whether eventually it may not be foimd tliat a cultivation of innocent germs may be made to supplant the more malignant forms ; and this opens up the whole question of immunity, which forms one of the most interesting portions of Dr. Crookshank's book. Immunity may be natural or acquired. We all know that certain individuals are much more subject to infec- tious diseases than others, even of the same family. In some diseases one attack renders the person impervious to the same disease ; but this is not always the case, some- times after a time the protective influence of the first attack ceases, and the individual succumbs to the disease a second time. In certain diseases one attack predisposes to a recurrence of tlie disease, as for example erysipelas ; and again, " the occurrence of one disease is stated to induce a liability to others; small-pox and typhoid fever are regarded as predisposing to tuberculosis." When Pasteur first began to try to mitigate the virulence of anthrax, he found that by cultivating the microbe in chicken broth, and allowing it to remain for several months before carrying on successive cultivations in fresh media, " the new generations which were then obtained were found to have diminished in virulence, and ultimately a virus was obtained which produced only a slight dis- order ; and on reco\ery the animal was found to be proof against inoculation by virulent matter." This change in the quality of the virus M. Pasteur attributed to a pro- longed contact with the oxygen of the air, and he shows that if the cultivation of these germs is carried on in sealed tubes, admitting very little air, the virulence is retained. Heat also has been found to diminish the viru- lence of the bacillus of anthrax, and the same has been brought about by chemical means, carbolic acid in minute quantities, and bichromate of potash added to a cultivation, " gave after three days a new growth, which killed rabbits, guinea-pigs, and half the sheep inoculated; after ten days rabbits and guinea-pigs, but not sheep ; and after a longer time even guinea-pigs were unaffected." Tin discussing the question of what constitutes immunity, Dr. Crookshank gives some very curious and suggestive facts. He says ; " Kaulin has shown that Axinrtiillus niijer develops a substance which is prejudicial to its own growth in the absence of iron salts in the nutrient soil. Pasteur has suggested that in rabies, side by side with the living and organized substance, there is some other substance which has, as in Raulin's experiment, the power of arresting the growth of the first substance. If we accept the theory of arrest by some chemical substance, we must suppose that in the acquired immunity afforded by one attack of an infectious disease this chemical sub- stance is secreted, and, remaining in the system, opposes the onset of the micro-organism at a future time. In the natural immunity of certain species and individuals we must suppose that this chemical substance is normally present." Passing over two other theories, each of which presents certain difliculties, we find the curious fact that in some cases the white blood-cells appear to have the singular power of destroying bacteria. " If anthrax bacilli are inoculated in the fi.-og, the white blood-cells (leucocytes) are observed to incorporate and destroy them until they entirely disappear, and the animal is not aflected. But if the animal, after inoculation, is kept at a high tempera- ture, the bacilli increase so rapidly that they gain the upper hand over the leucocytes, and the animal succumbs. In septicipmia of mice the white blood-cells are attacked and disintegrated by the bacilli in a similar way. It is, however," adds Dr. Crookshank, " difficult to accept any explanation of immunity from these observations — to suppose, for example, that immunity depends upon the micro-organisms being unable to cope with the leucocytes in certain species. It is difficult to conceive that the leucocytes in the blood and tissues in the field-mouse are differently constituted ft'om those in the house-mouse, so that they form an effectual barrier in the one case, though so readily destroyed in the other." Hence we imderstand that field-mice are exempt frorc the septictemia which is fatal to house-mice and sparrows, the representative bacilli of the disease being found most commonly in the interior of the white blood-corpuscles. Pei'haps the immunity of field-mice may result from some chemical secretion or the difference in their mode of hfe and in their food. This is a subject still open to investigation. In anthrax "a drop of blood from an aficcted animal, or a minute portion of a cultivation, introduced under the skin of a mouse or guinea-pig, causes its death, as a rule, in from twenty-four to forty-eight hours. Sheep fed upon potatoes which have been the medium for cultivating the bacillus, die in a few days. Goats, hedgehogs, sparrows, cows, horses are all susceptible. Rats are infected with difficulty. Pigs, dogs, cats, white rats, and Algerian sheep have an immunity fi-om the disease. Frogs and fish have been rendered susceptible by raising the temperature of the water in which they lived." In this list we find the same difference with regard to sheep as in the two species of mice. To the common sheep the disease is fatal, whilst the Algerian sheep is immune. This immunity of certain species has been seized upon by agriculturists, who, when their flocks and herds suffer from a certain disease, have found it beneficial to change the breed. At the Cape of Good Hope, for instance, many 78 KNOWLEDGE [Apbil 1, 1891. years ajjo, when the Angora goat was introduced, it was found to be less liable to scab than the common goat. The same thing has followed from great blights in the vege- table world. The disastrous potato-blight caused the intro- duction of many new varieties found by experience to be capable of resisting the disease ; and the European vines affected by phylloxera are now being replaced by different kinds brought from America and other parts of the world. There can be no doubt that in time this immu- nity will cease, and the newly introduced variety will require to be again replaced, unless some means should be found of destroying the micro-organisms, which, like the newly introduced animals or vegetables, will in time adapt themselves to their surroundings, and perhaps acquire fresh virulence thereby. When the investigations into disease-germs began, it was thought by many that all infective diseases might be prevented by inoculation, but at present the various expe- riments made have not confirmed this idea except in anthrax, or splenic fever, rabies, and the new remedy for tuberculosis"' ; it seems, however, probable that some day pleuro-pneumonia may be added to the list. For many years past this disease has been successfully treated at the Cape of Good Hope, and in Australia, by inoculation. Happily, it seems that the wide-spread infection, which at one time was supposed to be likely to follow the burial of an infected animal through earth-worms bringing the bacilli to the surface, is not so common as was believed. " Klein has pointed out that if mice and guinea-pigs which have died of anthrax are kept unopened, the bacilli simply degenerate and ultimately disappear " ; therefore Ur. Crookshank thinks that free access to oxygen is necessary to develop the spores. " Contamination of ground in which diseased animals have been buried must result, therefore, from bodies in which a x)ost-mortem exammation has been made, by which the blood and organs have been freely exposed to the air, or from animals which have not been examined, owing to their hides being soiled with excretions, and with blood which issues from the mouth and nostrils before death." One of the most prominent uses of the science of bac- teriology is the power gained by it of examining the water, air, and soil of any place, and thus determining the num- ber and character of the bacteria in any given spot. By this means, places particularly subject to any given disease may be avoided by those peculiarly liable to such disease, and it may be, also, that eventually a means may be found of destroying the pestilential bacilli, and rendering spots formerly unhealthy fit for human habitation. Before concluding this paper, we ought to point out the numbers of bacteria which have been observed to be present in the air at different times and places. Miquel, who has made this a special study, finds " the average number per cubic metre of air for the autumn quarter at Montsouris to be 142, winter quarter 49, spring quarter 85, and summer quarter 10-5. In air collected 2,000 to 4,000 metres above sea-level, not a single bacterium or fungus spore was fur- nished ; while in ten cubic metres of air from the Rue de Kivoh (Paris), the number was computed at 5.5,000. By an apparatus known as ' Hesse's,' twenty-five htres of air from an open square in Berlin, gave rise to three colonies of bacteria and sixteen moulds ; whilst two litres from a schoolroom just vacated by the scholars, gave thirty-seven colonies of bacteria and thirty-three moulds." The won- der is that with all these sources of disease and death con- stantly with us, anyone should escape ; nevertheless, it is * Dr. Koch's inoculation differs from that of Pasteur in the injec- tion of dead instead of living bacilli. an established fact that none of these micro-organisms are ever found in perfectly healthy blood. The reason of this is not plain. It is certain that the healthy and unhealthy ahke must inhale or swallow these germs ; why should they be deadly to the one and innocuous to the other '? Is it because in health the white corpuscles of the blood are in such a state of chemical activity as to be able to absorb and consume these micro-organisms, as in the recorded case of the frog ? And is it, as in the same case, only when the temperature becomes raised by fever, that the germs develop too rapidly for natm-al elimination '? This would appear a possible exiilanatiou, but more is wanted. Why, if these germs are everywhere, should we not more frequently hear of the spontaneous outbreak of disease, instead of finding it generally traceable to one especial source '? THE FACE OF THE SKY FOR APRIL. By Herbekt S.\dler, F.E.A.S. THE number of sun-spots and faculw on the solar disc continues steadily to increase. The zodiacal light should be looked for during the first ten days of the month. Conveniently observable minima of Algol occur at 7h. 14m. p.m. on the 4th ; Oh. 7m. a.m. on the 22nd ; and 8h. o6m p.m. on the 24th. The following are the times of minima of some of the Algol type variables aUuded to by ]Miss C'lerke in the March number of Knowxedge, and which may be con- veniently observed at the present time. The places are for 1890. U Cephei (Oh. 52m. 32s.-H81° 17'). Max. 7-1 mag.; min. 9-2 mag. Period, 2d. llh. 49m. 45s. April 14th, Ih. 53m. A.M. ; April 19th, Ih. 32m. a.m. ; April 24th, Ih. 12m. A.M. ; April 29th, Oh. 52m. a.m. E Canis Maj. {7h. 14m. 80s. -16° 11'). Max. 59 mag. ; min. 6-7 mag. Period, Id. 3h. 15m. 55s. April 2nd, 6h. 49m. P.M. ; April 8rd, lOh. 5m. p.m. ; April 19th, 7h. 46m. P.M. ; April 28th, 9h. .52m. p.m. S Cancri (8h. 37m. 39s. -H9° 26'). Max. 8-2 mag.; min. 9-8 mag. Period, 9d. llh. 37m. 45s. April 19th, Oh. 36m. A.M. 8 Libne (llh. 55m. 6s.— 8° 5'). Max. 5-0 mag. ; min. 6-2 mag. Period, 2d. 7h. 51m. 23s. April 2nd, 8h. 5:^m. P.M. ; April 9th, 8h. 28m. p.m. ; April 10th, 8h. Im. p.m. ; April 23rd, 7h. 36m. p.m. ; April BOth, 7h. 12m. p.m. U Corona- (16h. 13m. 43s. 4- 32° 3'). Max. 7-5 mag. ; min. 8-9 mag. Period, 3d. lOh. 51m. 8is. April 6th, Ih. 5m. A.M. ; April 12th, lOh. 47m. p.m. ; April 19th, 8h. 29m. P.M. A maximum of S Coronse (6-1 mag.— 7-8 mag. at max. ; 11-9 mag. -12-5 mag. at min.), which follows U Coronse 3m. 12s. in E.A., and is 17'-3 south of it, is due on April 5 th. Mercury is very well placed for observation dm-ing the greater part of April. On the 1st he sets at 7h. 22m. P.M., or 52m. after the sun, with an apparent diameter of oi" and a northern declination of 8*^ 2'. At this time he will appear about as bright as Aldebaran, about f'^^f of the disc being illuminated. He gradually increases in bright- ness, setting on the 7th at 8h. 9m. p.m., Ih. 29m. after the sun, with an apparent diameter of 6", and a northern declination of 13° 20'. At this time he is considerably brighter than an average first magnitude star in the same position, rather less than eight-tenths of the disc being illuminated. On the 11th he sets at 8h. 87m. p.m., Ih. 50m. after the sun, with an apparent diameter of 6|", and a April 1, 1891.] KNO^VLEDGE 79 northern decimation of 16° 18'. His theoretical bright- ness is now about equal to what it was on the 1st, but, owing to his being considerably farther fi-om the sun, he will probably appear brighter. About /^ of the disc is now in sunlight. On the 17th he sets at 9h. 3m. p.m., 2h. 6m. after the sun, with an apparent diameter of 7^", and a northern declination of 19° 2.S'. He is at his greatest eastern elongation (19° 50') at 7h. p.m. on the 18th. On the 21st he sets at 9h. 10m. p.m., 2h. 7m. after the sun, with an apparent diameter of 8-4", and a northern decli- nation of 20° 40'. He has now decreased very perceptibly in brightness, about three-tenths of the disc being illumi- nated. On the 27th he sets at 9h. Im. p.m., Ih. 46m. after the sun, with an apparent diameter of 9f", and a northern declination of 21° 5'. He now does not exceed a .5th magnitude star in brightness, about ^[^ of the disc being illuminated. During the month Mercury passes through Pisces on to the borders of Aries and Taurus, being foimd at the end of the month near the group t,, r, 63 and 65 Arietis, but without approaching any conspi- uous star very nearly. Venus is a morning star throughout the month, but is too near the sim to be well seen. On the first sh? rises at 4h. 27m. A.M., Ih. 11m. before the sun, with an apparent diameter of 16-0", and a southern declination of 11° 36', She is near .Jupiter on the mornings of the 7th and 8th. On the 30th she rises at 3h. 39m. a.m., 57m. before the sun, with an apparent diameter of 13J", and a southern declination of 0° 2'. About seven-tenths of the disc is illuminated on the 1st of April, and nearly eight-tenths on the 30th, when the theoretical brightness of the planet is only one-third of what it was at the beginning of January. On the morning of the 15th Venus will be very near the 4th magnitude star <^ Aquarii. During the month she moves from Capricornus through the greater part of Aquarius. Both Mars and .Jupiter are in\'isible for the purposes of the amateur observer. Saturn is well placed for observa- tion, rising on the 1st at 3h. 17m. p.m., and setting at 5h. 3m. A.M., with a northern declination of 9° 10^-', and an apparent equatorial diameter of 19^'' (the major axis of the ring system being 441", and the minor 3f"). On the 80th he rises at Ih. 24m. p.m., and sets at 3h. 14m. a.m., with a northern declination of 9° 37', and an apparent equatorial diameter of 18,V" (the major axis of the ring system being 42^", and the minor 4-0"). Shortly before 8 P.M. on the 3rd Titan is 17" south of the planet ; and on the evening of the 5tli lapetus will be about 45" « a little // Saturn. Early on the evening of the 17th Titan will be seen about 20" south of Saturn, and on the 22nd and 23rd lapetus is near its western elongation, and at its brightest. Shortly before Saturn sets on the 30th a 9'5 magnitude star will be seen about 70" north of the planet. During April Saturn describes a short retrograde path in Leo, but he does not approach any naked-eye star. Uranus is an evening star, rising on the 1st at 8h. 5m. P.M., with an apparent diameter of 3f", and a southern declination of 11° 0'. On the 30th he rises at 6h. 4m. P.M., with a southern declination of 10° 33'. He describes a short retrograde path to the E.N.E. of 86 Virginia. He is in opposition on the 19th, when he is about l,623i millions of miles distant from the earth. A map of his path up to the beginning of September will be found in the F.wilixh Mcrliaiiii- for February 6th, 1891. Neptune is, for all practical purposes, invisible. Shooting stars are fairly plentiful in April, the most marked shower being that of the Lyrids, with a radiant point in 181i. Om. K.A. and -|-33' decl. The radiant point rises on the nights of the 19th and 20tb, when the maximum occurs, at 6h. 27m. p.m., and souths at 4h. 8m. A.M. The moon enters her last quarter at 6h. 30m. a.m. on the 2nd ; is new at 8h. 57m. p.m. on the 8th ; enters her first quarter at Ih. 40m. a.m. on the 16th ; and is full at 5h. 5m. A.M. on the 23rd. She is in perigee at lOh. a.m. on the 7th (distance from the earth 223,850 miles), and in apogee at llh. 30m. a.m. on the 19th (distance from the earth 251,920 miles). The greatest western libration is at 4h. 64m. a.m. on the 13th, and the greatest eastern at 5h. 44m. P.M. on the 27th. 2Mt)ist Column. Bv W. MoNT.\Gu Gattee, B.A.Oxon. The Management of Trumps. WE believe it was the late .James Clay who once facetiously remarked that there were twenty thousand young men going about in rags in America because they would not lead triunps from five to an honour. There are, neverthe- less, many cases in which it is desirable to play a waiting game, even though favoured by fortune with great strength in trumps. A curious instance of the success of Fabian tactics is furnished by Hand No. 16 (Knowledge for December last), in which the original leader persistently avoids leading trumps, although holding six to two honours. Such cases are for the most part peculiar, and scarcely admit of generalisation ; but perhaps it may safely be laid down that, when the leader's score is 4. he should almost always hesitate to open trumps unless he holds winning cards in the plain suits. A typical case is that in which the hand contains, besides the trumps, numirical strewitli only in one of the plain suits, so that two or even three rounds will probably be required in order to establish it. The advantage, under such circumstances, of opening the plain suit in the first instance, is well illustrated by the following hand, for which we are indebted to Mr F. S. Hughes : — Hand No. 19. Z's Hand. Score— AB, 2; YZ, 4. Z turns up the six of hearts. Note. — A and B are partners against Y and Z. A has the first lead ; Z is the dealer. 'The card of the leader to each trick is indicated by an arrow. Trick 1. yVias— AB, 1 ; YZ, 0. ^ Y 0 0 0 0 0 0 0 O 0 Trick >. Y /^ O 0 0 0 A i 0 0 0 0^ z Tricks— XB, 1 ; YZ. I. 80 KNO^VLEDGE [Apbel 1, 1891. H 4* 1 4. 4. 4. 4. n 4. 4. 4. 4. 4, \ 4. 4. Z ¥^ © ♦ ♦ '/ricks— AB, 2 ; TZ, 1. rnci-s— AB, 3 ; YZ, 1. Note. — Trick 3. — YZ being at the score of 4, Z de- termines not to open trumps, and leads his fourth-best chib. Tkick 5. Trick 6. Tricks— XB, S ; YZ, L'. Tricks— AB, 3 ; YZ, 3 Note. — Trick 5. — Z's discard shows five chibs originally, and enables his partner to count his hand. Trick 6. — The four of trumps is now marked in Y's hand, and the three best trumps clearly lie between A and B. Tricks— AB Note. — Trick 7. — Z therefore continues the trumps ; for. if the adverse trumps are all in one hand, AB must' win the game in any case, since they will make three tricks in trumps, and one, at least, in clubs. Accordingly, Z plays on the assumption that the adverse trumps are divided. As the cards happen to lie, he would win the game equally by continuing the club suit ; but this would be dangerous, as AB might be enabled to make their trumps separately. Tkick 10. Y 1 "•rick ct. Y ^ + 4. 4. 4. 4. Wj^ 4. 4. ma \ I4. 4.^ Z rricks- -AB, 0 ; YZ, 4 ♦ 0 0 ♦ ♦ * 9 's? Trickf—AB, f. ; YZ, 4. Tricks 11 to 13. — A leads ace of diamonds, on which Z plays his last trump, and YZ then make two tricks in clubs. YZ Score the Odd Trick and win the Game. A's Hand H.— Kn, 10, 9. S.— Qn, 5, 3. D.— Ace, Kg, Qn, 10, 2. C. — Ace, Qn. Y's Hand. H.— 7, 4. S.— Kg, Kn, 8. D.— 9, 7, 6, 5. C— Kn, 9, 7, 3. B's Hand. H.— Kg, Qn. S.— Ace, 10, 9, 7, 4, 2. D.— Kn, 8, 3. C.-Kg, 4. Z's Hand. H.— Ace, 8, 6, 5, 8, 2. S.— 6. D.— 4. C— 10, 8, 6, 5, 2. Remarks. — Trick 2. — If Z intended to lead trumps, he woidd trump with the five and lead the three ; but for the moment he is not anxious to expose his strength. Trick 3. — If Z leads a trump, AB make at least the odd trick. B wins with the queen, and returns the knave of diamonds. If Z rulis and continues with the ace of trumps and then a club, A wins with the queen of clubs, and leads the knave of trumps and then the ten of dia- monds ; if Z ruii's and opens clubs at once, A wins with the qlieen, and leads the ten of diamonds and afterwards (however Z plays) the ace of diamonds ; and, if Z dis- , cards his spade on trick 4, B leads the ace of spades, and Z cannot save the game. To retiun to the actual game, we may observe that those players who adopt the " plain- suit echo " would, in Y's place, play the seven of clubs instead of the three. Trick 4. — Mr. Hughes remarks that " A leads a spade, and not a diamond, as he does not know whether Z is strong or weak in trumps." We think, nevertheless, that, as A has command of the clubs and some protection in spades, and as YZ are four up and Z is rirffing diamonds, the correct lead is the knave of hearts. This, however, would not save the game imless YZ played badly. Trick 6. — Y counts three clubs and five trumps re- maining in his partner's hand, and therefore leads a trump. Trick 9.— The beginner should note that even at this point Z would lose the game by continuing the trumps instead of clearing his clubs. Contents of No. 60. PAGE On the Form of the Milky Way. By John Eichard Sutton, B.A.Cantab 41 Giant Birds. By R. Lydekker, B.A.Cantab 43 The Magic Square ot Four. By T. Squire Barrett, F.S.S 45 A Perpetual Calendar 47 Note on the Orbit of the Double Star 2 2. By S. W. Bnrnham 48 Letter :— E. W. Maunder 49 The Milky Way in the Southern Hemisphere. By A. 0. Ban- yard 50 PAGE Notices of Books 51 Birds and Berries. By the Eev. Alex. 3. WUson, M.A., B.Sc. . . 52 Variable Stars of the Algol Type. By MissA.M. Gierke.. 53 Notes from Cambridge. By B. B.Johnson 56 .Artificial Cold. By Vanghan Cornish, B.Sc, F.C.S 56 Whist Column. By W. Montagu Gattie, B..\.Oxon 58 Chess Column. By C. D. Ijocock, B.A.Oxon 59 TERMS OF SUBSCRIPTION. " Knowledge " as a Monthly Magazine cannot be registered as a Newspaper for transmission abroad. The Terms of Subscription per annum are there- fore altered as follows to the Countries named ; s. d. To West Indies and South America 9 0 To the East Indies, China, &c 10 6 To South .Africa 12 0 To Australia, New Zealand, &c 14 0 To any address in the L'nited Kingdom, the Continent, Canada, United States and Egypt, the Subscription is 75. 6d., as heretofore. Communications for the Editor and Books for Review should be addressed Editor of "Knowledge," care of David Stott, BookseUer. 67 Chancery Lane, W.C. May 1, 1891.] KNOWLEDGE 81 ^^ AN ILLUSTRATED "^i^ MAGAZINE OF SCIENCE SIMPLY WORDED— EXACTLY DESCRIBED LONDON: MAY 1, 1891. CONTENTS. The Artificial Reproduction of Rubies and other Precious Stones. By Vauguan Cornish. B.Bc, F.C.S. 81 The House Cricket. By E. A. Butler 82 Clustering Stars and Star Streams. By J. E. Gore, F.R.A.S 85 What is a Volcano ? By the Rev. IT. N. Hutchinson, B.A., F.G.8 87 Notices of Books 89 The Pleiades Cluster, and its Probable Connection with the Milky Way. By A. C. Ranvard 91 Letters :— E. E. Barnard ; Rout. W. D. Christie ; W. H. S. MONCK 93 The Face of the Sky for May. By Herbert Sadler, F.R.A.S 96 Whist Column. By W. Montagu Oattie, B.A.Oson. ... 97 Chess Column. By C. D. Locock, B.A.Oxon. 99 THE ARTIFICIAL REPRODUCTION OF RUBIES AND OTHER PRECIOUS STONES. By Vaughan Coenish, B.Sc, F.C.S. IN speaking of the artificial reproduction of precious stones, it must be understood that we are dealing with processes wliicli have nothing in common with the iwitiition of gems. Ingenuity and skill, and even a certain amount of scientific knowledge, have been exercised in imitating diamonds, pearls, and so forth ; but the art is merely one of counterfeit, the mate- rials produced at most deceive the eye, and they possess neither the chemical composition nor the properties of the natural objects which they simulate, except the qualities of colour and lustre. In these two points the counterfeit is often sufficiently good to deceive any save a practised eye ; but it must be borne in mind that the intrinsic value of a gem, apart from the fictitious value due to i-arity, depends not solely on beauty of colour and histre, but on the hardness of the material which pre- serves, for instance, a cut ruby from deterioration for centuries. It is the character of permanence which gives to precious stones their pre-eminent, value among other beautiful objects. Ikit the ruby may not only be imitated more or less suc- cessfully by colouring a dense and highly refracting kind of glass ; it can also be irjinnlKcol, that is to say, the thing itself can be prepared in the laboratory. Such a product is termed an artiiinnl ruby, and the common acceptation of the word appears to carry with it a prejudice, as if it were intended to convey that the object would be a ruby were it not tliat rubies are formed naturally, whereas this was produced through the intervention and contrivance of man. So much is this the case that if, as may well happen, rubies should prove to be produceable of sufficient size for the purposes of the jeweller, there will certainly be a feeling against wearing the stones so produced as ornaments, due to the idea that the jewel is in some sort a sham. This is a natural but mistaken conception. A mineral — the rnby, for instance — is a body having a certain chemical composition and other equally important characteristics, such as those of its crystalline form, specific gravity and hardness. The body is formed through the operation of certain laws of chemical combination and of crystallization. Whether the opportunity for the operation of these laws occurs in the bowels of the earth or in the crucible of the chemist, cannot be rightly held to afi'ect the identity of the body produced. The reproduction of minerals has been carried on for the last forty years, chiefly among a small school of French chemists, and is to be regarded as a part of the great work of chemical STOtbesis. Synthetical or constructive work only begins at an advanced stage in the study of an experimental science, and the synthesis of minerals was necessarily preceded by many years of analytical investigation. In the first decade of the present century, the laws which regulate the proportions in which the elements enter into chemical combination were already established. At this time the art of chemical analysis was being rapidly developed, and its methods were applied to the examination of minerals. It was found that the elements they contained were present in those particular, definite proportions which bad been found to be characteristic of chemical combina- tion. It was during this epoch also that the laws of crystallography were first established. The chemical composition and the crystalline form were recognised as the two most essential characteristics of each mineral species, although other properties were duly taken account of, as, for instance, specific gra\-ity, hardness and colour. Thus mineralogy was put on a sound footing as a classifi- catory and analytical science ; but the next step in advance, the introduction of synthesis, the building up of the minerals, appeared to be beyond the power of the experimentalist. It was found that substances prepared in the laboratory, having the same chemical composition as natural minerals, did not possess their other charac- teristic features. Thus Heavy Spar has the same chemical composition as the sulphate of barium produced in the laboratory ; but whereas the first is a hard, well-erystal- lizcd body, the second is formed as a fine powder, destitute of coherence and of crystalline form. Again, silica occurs in nature as the well-known Kock Crystal, but in the ordinary chemical process it is obtained as a gritty powder. The silicates, a class of substances comprising many well-crystalli/.od gems, such as the garnet, could only be reproduced artificially as ylasses, transparent indeed and coherent, but without crystalline structure. Such failures gave rise to the impression that there was some special intluonco or force at work in nature in the production of minerals which could not be com- manded by the chemist, just as it was supposed that the substances produced in the vegetable and animal kingdoms needed the action of the so-called riud /'on,-, and were incapable of reproduction in the laboratory. The belief in this ii'(<(/ tone was dispelled when the advance of chemistry solved the problem of the synthesis of organic 82 KNOWLEDGE [Mat 1, 1891. bodies. Similarly it was found that by modifyiug the ordinary methods of the chemical laboratory so as to imitate more closely the conditions olitaiuiug in the for- mation of rocks and of mineral veins, compounds could be produced, ha\ing not only the chemical composition, but the other characteristics of the natural minerals. For instance, in the case of barium sulphate, the material is produced in the laboratory by the interaction of a solution of a barium salt and a solution of a sulphate. It was found that if special devices were adopted so that the two solutions only came in contact with extreme slow- ness, the forces of crystallization came into play, and the barium sulphate separated out with the form, hardness, and other characteristics of the natural mineral. The processes previously employed had been too rough and hasty, and had not repiroduced the conditions of Nature's laboratory. Water plays a part in most of the ordinary chemical processes, but under the usual con- ditions water cannot be raised to a temperature above 100^ C, since it is then converted into steam. In the depths of the earth great pressures come into play, and when there is at the same time a high temperature, water, kept by pressure in the liquid state, acts imder very special conditions. By heating silicates, such as glass, with water in strong steel vessels, so that a high tempera- ture and great pressure are obtained, it is found that the silica is separated in the form of quartz, in crystals reproducing in the most complete manner the minute peculiarities, the surface markings and striations, of the natural mineral. For the production of corundum, a jiiu- is employed, i.e. a substance which fuses at a moderate temperature and in which the alumina dissolves, to separate out on cooling in the crystalline form. The colour of the ruby — one of the varieties of corundum — is due, not to the substance of which it is mainly composed, but to a very small proportion of a colouring matter. By the addition of a small amoimt of a suitable material the red colour is obtained in the product of the laboratory, and by varying the colouring material sapphu-e and oriental emerald have been obtained. So far the size of the specimens has been small, one-third of a carat being about the maximum for rubies. The carat is equal to four grains. A cut ruby weighing a grain would be suitable for one of the smaller stones of a ruby ring. In the process of cutting, however, the weight is generally reduced by one half, so that the largest specimens yet produced are not adapted for employment as ornaments. They are, however, used in the jewelling of watches. The details of the method employed at the present time in their production are as follows. The chemically precipi- tated amorphous alumina is heated with barium fluoride, or a mixture of the fluorides of the alkahne earths, which acts as a flux, and a trace of bichromate of potash is added to impart the red colour. The addition of carbonate of potash, which renders the fused mass alkaline, furthers the formation of larger crystals. The heating is kept up for several days, at the end of which time a plentiftd crop of crystals is obtained. Although the aggregate weight obtained in one operation amounts to some pounds, the individual crystals are, as has been said, small in size. It is frequently contended that the fact of reproduction is the only essential point, and that the size of the crystals produced is of httle importance fi-om the scientific point of view. It must, nevertheless, be allowed that the interest of this work will be much increased when products are obtained wliich will compare in size and beauty with those occiu-ring in nature. Of other gems, some — as the garnet and the spinelles— have been prepared ; others, as the emerald, have hitherto pi'oved less tractable. In the case of turquois, the arti- ficially prepared substance has the chemical composition and the appearance of the natural stone ; but inasmuch as the laboratory product behaves diflerently under certain conditions, as, for instance, when heated, it must be con- sidered as an approximate reproduction only, if not looked upon as a mere imitation. The pearl is formed of aragonite, a mineral readily reproduced by evaporating a hot solution of carbonate of Ume. The peculiar beauty of the pearl is, however, due to the structure resulting from its mode of growth. It would be rash to hazard an opinion as to whether this structure could be imparted by methods at the disposal of the chemist. But the great problem in the artificial production of gems is the preparation of the diamond, and this problem is still unsolved. Popular prejudice has relegated the attempt to the same category as the endeavour of the alchemist to transmute the baser metals into gold. The aim of the alchemist was once a legitimate object of scien- tific research. In the light of modern ideas on the nature of chemical elements it is so no longer. The endeavour to obtain the element carbon in that transparent crystal- line form in which it is found in nature, has certainly nothing in common with the work of the alchemist. Yet the light in which the attempt is viewed by the majority is still that so graphically described by Balzac in his inge- nious novel. La Beclwrche de FAbsolu. Balthazar Claes devotes his life to the endeavour to reproduce the diamond, and " people would scarcely speak to him — a man in the nineteenth century seeking the philosopher's stone. They called him an alchemist, and said he might as well try to make gold. As he passed by in the street people pointed hiin out with expressions of pity or con- tempt." The want of success which has hitherto attended the efforts of the Balthazars of real life is perhaps scarcely to be wondered at. In the case of other minerals the successful reproduction has generally been achieved only after the minute study of the mode of natural occurrence, and this has afl:brded guidance as to the best means of imitating the natural process of formation. It is only of recent years that the diamond has been found in its original matrix, so that materials have been wanting on which to base experimental methods. The chemical nature of the body, a combustible substance, is so difl'e- rent from that of the ruby and most other gems, which are oxides or oxidized materials, that the methods to be employed for its production will probably involve the application of difl'erent principles. There is no reason, however, to regard the problem as insoluble. When sufficient guiding data have been obtained, skill will not be wanting to imitate in the laboratory the conditions under which Nature has worked in the formation of this most beautiful product of the mineral world. THE HOUSE CRICKET. By E. A. Butler. FEW domestic insects have succeeded in inspiring such widely difierent sentiments in the minds of then- hosts as the House Cricket. To most people it is far better known by the evidence of the ears than of the eyes. Its shrill chirping, prognosticatory, according to popular belief, of cheerful- ness and plenty, reveals the performer's presence when no trace of its person can be discerned ; and hke the similar soimd made by its near relative, the grasshopper, it is one which there is great diificulty in localising or tracing to its origin. Distinct and intensely penetrating May 1, 1891.] KNOWLEDGE. 83 tbongli this " shrilling " is, yet most people find it a perplexing task to decide exactly from what quarter it proceeds. This constitutes an element of mysteriousness, and it is not surprising that the invisible minstrel should have been credited with occult influences. The feelings with which the sound has been regarded have accordingly varied with the disposition of the hearer, from super- stitious reverence to downright dislike and extreme irritation. While to Milton, for example, " the cricket on the hearth " seemed no unsuitable accompaniment of thoughtful solitude, when the devotee of " divinest Melan- choly " retires to Some still removed place . . . Where glowing embers through the room Teach light to counterfeit a gloom, on Gilbert White, the naturalist of Selborne, the chirping of crickets had quite an opposite effect. Speaking of the Field Cricket, which is in most respects much like its cousin of the house, he remarks : " Sounds do not always give us pleasure according to their sweetness and melody ; nor do harsh sounds always displease. We are more apt to be captivated or disgusted with the associations which they promote than with the notes themselves. Thus the shrilling of the field-cricket, though sharp and stridulous, yet marvellously delights some hearers, filling their minds with a train of summer ideas of everything that is rural, verdurous, and joyous." If poet and naturalist do not agree here, still less are they in accord in other instances ; if to the former the cricket is "Little inmate, full of mirth," "always har- binger of good," one whose song is "soft and sweet" (!), to the latter it is a "garrulous animal," keeping up a " constant din," " a still more annoying insect than the common cockroach, adding an incessant noise to its ravages." And while the simple and easy- going rustic life of olden times might tolerate and even enjoy this incessant clatter, the state of nervous tension at which so much of present-day life is lived will no doubt lead most people to agree with the naturalist here, rather than with the poet, and vote the cricket a household nuisance. The noise upon which such different views ha^•e been held is apparently a love-call, and is accordingly pro- duced only by the males, the female crickets being, in fact, through the absence of the requisite machinery for chirping, absolutely dumb. To the cause of the noise we shall recur pre- sently ; meanwhile, we may consider the zoological position and the structure of the insect. As a family the crickets enjoy a wide distribution, and in this country five species have been met with, though for some reason best known to themselves, only one has domesticated itself. The family is called (in/lliihr, and is closely allied to those of the grasshoppers and locusts, forming with them one of the great divisions of the order Orthoptera, viz. that of the " leapers." To another sec- tion of the same order, viz. the "runners," it will be remembered, the cockroach belongs. Our English domes- tic species (Fig. 1) is called (iri/lliai iloiiicxtirm. At first sight a cricket strikes one as being not unhke a grass- hopper in general form, the resemblance being caused Fig. 1. — House Cricket (^Gryllus doinesticus). chiefly by the great proportionate length and elevated position of the hind legs. In body, however, it is broader and flatter than a grasshopper, and in other respects is sufficiently distinct to be regarded as the type of a different family. The mouth organs bear a close resemblance to those of the cockroach, as a comparison of the accompanying figures with those of Knowledge, vol. xii., p. 218, will testify. As one looks in the insect's face, the greater part of the mouth organs is concealed by a not very stout flap, hinged above and shaped like a cheese-cutter ; this is the liihniiii, or upper lip. On lifting it, like the visor of a knight's helmet, there is disclosed a pair of stout, dark brown, horny, toothed jaws (iiiandililcf:, Fig. 2), which are used not merely to divide the food, but also as excavating implements, to hollow out retreats into wliich the insects can retire in the day-time or when alarmed. These mandibles again, when closed, completely cover the rest of the mouth organs ; on their removal, the second- ary jaws, or maxilla., come into view (Fig. 3) ; these are very much like the cockroach's, the inner lobe {bicinia) being tipped with two sharp teeth, and received for pro- tection's sake into a groove of the outer (i/alai), and they are furnished with a pair of five-jointed palpi. Beneath, or rather behind them, is the lnhiuni, showing again a similar structure to that of the prototype, and equally obviously composed of a pair of jaws which have co- alesced, i.e. have become imited into a single organ in their Fio. -'. — Mandibl Cricket. Fig. n. — JIouTH Organs of Cricket. «i, maxillae ; mp, maxill.irv jjalpi : /, labium ; //<, labial palpi ; t, tongue. basal portion ; this, too, carries a pair of palpi. The chief difference between the two insects is to be seen in the appendage to the labium in its centre, which is called the liw/uhi, or " tongue." lliis is a most marvellous and exquisite structure, and deservedly a great favourite with microscopists. As shown in the figure, it is pressed out of place. On opening the mouth it will be seen on the floor, rising into a grooved, hollow, fleshy eminence. When flattened out it is found to be a kidney-shaped, leaf-like expansion, strengthened throughout by radiathig fibres of chitinous material, which, when highly mag- nified, show a beautiful mosaic structure. Kitchen refuse of various kinds constitutes the food of these creatures, and a good deal of moisture as well seems to bo necessary for their well-being. No doubt this curious tongue helps them in drinking. They have been accused of gnawing 84 KNOWLEDGE. [May 1, 1891. holes in stockiugs hung before the fire to dry, in order to satisfy their cra\-ings for moisture. Hence, also, it is not an infrequent experience to find them drowned in pans or jugs of liquid. The House Cricket is more or less of a pale brown colour throughout, and, unUke the cockroach, it is fully winged in both sexes, and, therefore, has uo need of man's agency to supplement its powers of locomotion. It flies with an imdulatory motion, making long rising curves in the air, and dropping at regular intervals. The wings are extremely beautiful objects ; in fact, the house cricket contains so many exquisite and deUcate structures, that anyone who has a few hours to spare and can devote them, with a good microscope, to the dissection of the insect, will find ample material for interesting study and observation. There are two pairs of wings, the upper pair being more or less horny and exceedingly different in males and females ; and the under pair thin and mem- branous, and similar in both sexes. When closed, the right upper wing partly overlaps the left, and the under wings project in the form of long, tapering, rod-like pieces beyond the tips of the fore wings, extending about half as far again as these. The fore wings are much broader than a casual glance would suggest, seeing that only about two-thu-ds of their width lies flat along the back, the other third being bent down at right angles to the rest, and Ijiug close along the side. Those of the female are very regularly veined, there being two systems of nervures proceeding in oppo- site directions, one on each side of the stout ridge at which the wing is bent. But the wings of the male (Fig. 4) are extremely peculiar, and it is in them that the power of chirping resides. There is the same division into Fig. i. — Right Fore wing of JIale Ckicket. a, line of bending ; 6, file ; c, drum. two areas as in the female, but the hinder section, i.e. the one that lies on the back, has its veins distributed very irregularly. A stoutish nervure runs straight across this near its base, and then beyond it a large clear triangular area is left almost devoid of nervures. At the apex of this, nearer still to the tip of the wing, is another similar, but smaller and four- sided, patch, with a single, pale, delicate nervure rimning across it, and the rest of the wing is covered pretty closely with a network of nervures. If, now, these wings be turned over and examined beneath, it will be found that the straight nervure aforesaid is crossed transversely by a large number of little hard ridges, gi\ing it the appearance of an extremely fine file. These are much too small to be seen with the naked eye, but a moderate magnification coupled with careful focus- sing soon brings them into view. When the chirping is to be produced, the insect bends the fore part of the body shghtly downwards, and then slightly raising the fore wings, rubs them rapidly across one another ; durmg this motion, the file of one rubbing against the surface of the other produces a creaking ^-ibration, which is greatly in- tensified by the clear, open plates above-mentioned, w'hich are therefore called " drums." It wiU now be evident why the females are mute ; they have neither " file " nor " drum," and hence are physically incapable of " singing." It is clear from the above that the chirping is in no true sense of the word either a voice or a song, being quite unconnected with the respiratory organs ; it is a purely external and mechanical sound, comparable, as a means of expressing sentiments, rather with the human device ot clapping the hands, or flipping the fingers, than with the utterance of sounds with the mouth. Of course it is not to be expected that an insect should make any noise with its mouth other than that produced by eating, since the mouth does not, as is the case with us, commimicate with the breathing organs. The entrances to these are in the cricket, as in aU other insects, along the sides, and any sound that might be produced in them by the passage in and out of the air would be more strictly comparable with the voice of vertebrate animals ; some insects, as for example, the common bluebottle-fly, are able to produce a noise in this way, and may therefore be truly said to possess a voice. But that is by no means the rule, and the soimds insects produce are in general the restilt of the friction of external parts upon one another. The hind wings of the cricket are exceedingly delicate, and are each strengthened by about fifty nervures radiating fan-wise from the base. As about half these neirvures are weaker than the rest, the weak ones being placed alter- nately with the strong ones, the whole wing cau be folded up lengthwise like a fan, and this accounts for its pointed form as it protrudes from beneath the upper wing. It is this jjeculiar method of straight, longitudinal folding that has caused the name Orthoptera (N/c'/iV/Zif-winged) to be given to the order. Of course the power of chirping implies the power of hearing. It is only natural to suppose that the male crickets would long ago have abandoned the habit of serenading (if, indeed, they had ever perfected it) if their mates had not been able to recognise their attentions. It is rather curious, however, that this insect, notwithstand- ing its hving in our houses, and the con- siderable cm'tailment of its field of quest for partners consequent thereupon, should have preserved almost as strongly as its out- door relative this power of chirping ; one cannot help feeling a suspicion that, if this vigorous minstrelsy be merely of an amatory nature, either the gentler sex in the cricket world have become extremely coy, or else there is a vast deal of wasted energy on the part of their swains. However that may be, as the power of recognition of this call seems as though it must be an important matter in cricket economy, we naturally look about for some special apparatus suit- able for the detection of soimds, of a much more indubitable character than is generally met with in insects. .\nd the search is soon rewarded. It is only necessary to examine the tibia, or shank, of the fore legs, just below its jimction with the thigh, to find an organ to which it is diiiicult to assign any other function. Here, on the flattened outer edge is a long, oval, transparent, membranous disc, stretched over a corresponding aperture in the walls of the leg (Fig. 5), and exactly opposite it, on the other side of the leg, there is a sunilar, but roimd and much smaller disc ; between these two. in the centre of the hollow shaft of the leg, is a bladder-like expansion of the main breathing-tube of the leg. Numerous curiously shaped neiTe- endings, having the peculiar form of those May 1, 1891.] KNOWLEDGE 85 of special sense, are distributed at this spot, and the action of the complex apparatus seems to be such that the membranous disc, vibrating in response to the chirping of some distant mdividual, communicates its motion to the air within the breathing-tube, which in its turn affects the neighbouring nerves, thus enabling the insect to perceive the sound. Projecting from the hinder part of the female's body is a long ovipositor, consisting of a double boring im- plement, used in depositing the eggs in suitable situa- tions. Large numbers of eggs are laid, and the course of development is similar to that of the cockroach or bed- bug, the eggs yielding small, active, six-legged creatures, something like their parents in form ; after a series of moults, these attain by progressive changes, but without any pause in their activity or suspension of their fimc- tions, the adult size and form, acquiring wings only at the last moult. The metamorphosis is thus incomplete. Two long, unjointed, tapering appendages, pointing back- wards, project from near the extremity of the abdomen in both sexes. They are furnished abundantly with very fine hairs, and are probably sense organs, possibly giving notice of impending danger from behind. Crickets are pugnacious insects amongst their own kind ; notwithstanding similarity of habits, however, they are often found inhaliiting the same houses as cockroaches. But it seems probable that the steadily advancing armies of the latter insect will, in the course of time, either exterminate them, or compel them to take to an out-door life. This latter they are not averse to doing in the sunnner time even now. But from the way in which they hug the kitchen ;iire, it seems as if artificial warmth is essential for them in the winter. CLUSTERING STARS AND STAR-STREAMS. By .J. E. Gore, F.K.A.S. THE general tendency of the stars to gather into groups, more or less marked, is perhaps indicated by their ancient division into constellation figures. In the Northern Hemisphere we have the well- known groups of the " Plough " (Ursa Major), " Cas- siopeia's Chair," the " Sickle " in Loo, Corona Borealis or the Northern Crown, and Orion ; and in the southern hemisphere the Southern Cross, Scorpion, Corvus, &c. The " Dolphin's Rhomb," the head of Hydra, and the group near the binary star 70 Ophiuchi also form ex- amples of this clustering tendency. That in some of these groups, at least, the connection is real and not merely apparent is shown by the com- munity of " proper motions " discovered by the late Mr. Proctor in the five stars of the " Plough," /?, y, S, e, and ^''' — a connection afterwards verified by Dr. Huggins's spectroscopic observation of their motion in the line of sight. We have a similar case in " Cassiopeia's Chair," where several of the stars in this well-known group seem to be moving in the same general direction through space. Among the lucid stars, the most remarkable examples of this clustering tendency are found in the smaller groups, such as the Hyades and Pleiades. In the latter cluster — perhaps the most remarkable group of stars in * Dr. Auwer's subsequent determinations have, however, shown that in throo of those stars, p, y, and o, the " proper motion " is small ami doubtful. We have, however, a i|uintuple system in €, f, Alcor, and the telusuupic and spectroaoopic eumpuuious uf ^. the heavens — six stars are visible to ordinary eye-sight, but some persons gifted with keener vision can see a larger number.* There is a tradition that seven stars were originally visible to average eyes, but that one disappeared at the capture of Troy. With reference to this supposed disappearance of the "lost Pleiad," Professor Pickering has recently discovered that the spectrum of Pleione (which forms a wide pair with Atlas) bears a striking re- semblance to that of P. (34) Cygni, the so-called " tem- porary star of 1600." The similarity of the spectra shown by these two stars suggests that Pleione may — like the star m Cygnus — be subject to occasional accessions of light, which may, perhaps, account for its possible visi- bility to the naked eye in ancient times. Examined with a telescope the Pleiades show an enormously increased number of stars — even with an opera-glass a considerable number may be seen — and in a photograph of the group, taken at the Paris Observatory with an exposure of three hours, no less than 2,326 stars can readily be counted in a space of about 3 square degrees. In this remarkable picture, smaller aggregations of stars are \'isible ; for instance, Alcyone, the brightest of the whole group, forms one of a small cluster of some ten stars, and Maia and Merope have several faint stars near them. A common proper motion in many of the brighter stars'of the Pleiades shows that here also we have a family of stars traveUiug through space together. The Hyades also form a remarkable naked-eye group, with the brilliant red star, Aldebaran, as their leader, but the component stars are not so closely crowded as in the Pleiades group. I am not aware whether the Hyades have yet been photographed. Another well-known cluster is the Priesepe, or the "Beehive," in Cancer. The stars composing it are, how- ever, scarcely perceptible to the unaided eye, and in ancient times this|cluster, from its nebulous aspect, was pro- bably ranked as a nebula, and perhaps placed in the same class with the great nebula in Andromeda, which was also known to the earlier astronomers. Coma Berenices is another example of a scattered cluster. Here the stars are brighter, and may be well seen with an opera-glass. Among clusters a little beyond the hmits of naked-eye vision, there are many interesting examples of star clus- tering which may be seen with a binocular or good opera- glass. One of the most remarkable of these surrounds the star 5 Vulpeculie. I give two drawings of this curious little asterism, one (Fig. 1) as seen by myself with a 2-inch telescope, and the other (Fig. 2) as drawn by Mr. Espin, with a reflecting telescope of 17:^ inches aperture. The tendency of the brighter stars to run in lines will be noticed, and the curious grouping of fainter stars towards the left of the larger diagram is also remarkable. This group should be photographed. It is surroimded by Milky Way light, accordmg to both Boeddicker and Heis. About 2j degrees preceding the bright star Pollux I see a small cluster of stars, of about the 7th and 8tb magnitudes, which, with a binocular field-glass, very much resembles the Pleiades as seen with the naked eye. The stars 10, 11 and 12 Geminorum (north preceding /x * Miss Airy is said to have seen 12, and Mostlin (according to Kepler) no loss than 14, 86 KNOWLEDGE [May 1, 1891. Geminorum) also lie in a small cluster of stars, which may also be well seen ■nnth a binocular. The well-kno\vn double cluster x Persei may be seen with an opera-glass, but a telescope is necessary to see the component stars, and the larger the instrument the greater the number visible in these wonderful objects, which, like many somewhat simDar clusters, lie in the Milky Way. This twin cluster has been well photographed at the Paris Observatory, and also by Mr. Roberts. On the Paris photograph^ — at least, in the paper print in my possession — the clusters are clearly resolved into stars with no trace of outstanding nebulosity, suggesting that the component stars are probably at nearly the same distance from the earth. The cluster 39 ilessier, between tt' and 71 Cygni, may be well seen with a binocular, in which it somewhat resembles the Pleiades as seen with the naked eye. Another fine open cluster will be found a little north, following /3 Ophiuchi. Between fi and y Ophiucbi is a remarkably blank spot. On August 15, 1800, I failed to glimpse the faintest star with binocular in a clear, moon- less sky, a striking contrast to the rich region north of /3. A similar blank space will be found just north of the stars IT and Aquilie (north of Altair). On September 3, 1886, I could only see glimpses of very faint stars with the binocular in a sky clear and moonless, a remarkable vacuity so close to a region of bright stars, and a good example of an interesting stellar feature, namely, rich and poor regions in close proximity. I may here mention that a region of considerable extent, remarkably barren of bright stars, will be noticed with the naked eye in the northern hemisphere. This comparatively poor region, which contains no star brighter than the 4th magnitude, is bounded by Cepheus, Cassiopeia, Perseus, Auriga, Gemini, Ursa Major, Draco, and Ursa Minor, and forms a conspicuous feature in the north-eastern portion of the sky in the early winter evenings. It will be noticed that the bounding constellations all contain conspicuous stars. Examined with a telescope, the heavens aflbrd numerous instances of stellar aggi'egatiou. The Milky Way forms, of course, the most remarkable example, on a great scale, but among comparatively isolated groups there are numerous interesting objects. Of these, the cluster known as 35 Messier — a little north of the variable star tj Geminorum — is visible in an opera-glass, but a telescope is required to see the component stars. A very beautiful photograph of this cluster has been taken at the Paris Observatory. A well-marked clustering tendency is visible among the brighter stars of the gi-oup, two, three, four, and sometimes five stars being grouped together in subordinate clusterings. In the southern hemisphere a splendid cluster of small stars surrounds the star k Crucis. Sir John Herschel charted 110 stars to the 7th magnitude and fainter. Some of the component stars are coloured with red, greenish, and bluish tints, which, he says, " give it the aspect of a superb piece of fancy jewellery." It lies near the northern edge of the well-known " Coal-sack," and Dr. Gould says of it : " The exquisitely beautiful cluster k Cruciti contains a large number of stars of various tints and hues, con- trasting wonderfully with each other, when viewed with a telescope of large aperture." A drawing by Mr. Russell of this cluster, made in 1872, shows some well-marked star- streams. Just north of ^ Scorpii is a bright cluster which I found \-isible to the naked eye in the Punjab sky as a hazy star of about 4i magnitude. With a 3-inch refractor the components were well seen. The so-called "globular clusters" form excellent examples of the clustering tendency, but here the com- ponent stars lie so close together that their physical connection cannot be doubted. Among groups of stars not usually classed as clusters there are many examples of this aggregating tendency \-isible on the stellar photographs taken at the Paris Observatory. Photographs of portions of the Milky Way in Cassiopeia, Gemini, and Lyra show the small stars to be in many places not scattered uniformly, but with a marked tendency to cluster into subordinate groups ad- joining comparatively starless spaces. This is especially noticeable on a photograph of a portion of the constella- tion Gemini (R.A. 6h. 10m., N. 20° 20 ), a little south of 7] Geminorum. On these photographs many cases occur in which three, four, or more stars are grouped together, often in a straight line, or nearly so, and to all appearance comparatively isolated from their surrounding neighbours. On a photograph of a rich MUky Way region in Cygnus (R.A. 19h. 45m., N. 35° 30') taken by Mr. Roberts at Liverpool, with an exposure of 60 minutes, on which no less than 10,200 stars may be counted (in an area of about 4 degrees), similar features are noticeable. In his observations of the Milky Way in the southern hemisphere Sir John Herschel says : " Here (R.A. 17h. 50m., S. 33°-36°) the Milky Way is composed of separate, or slightly, or strongly connected clouds of semi -nebulous Ught ; and as the telescope moves, the appearance is that of clouds passing in a sciul, as the sailors call it." " I could fill a catalogue with the clusters of the 6th class which are here. The Milky Way is like sand, not strewn evenly as with a sieve, but as if flung down by handfuls (and both hands at once), leaving dark intervals, and all consisting of stars 14 . . . 16 . . . 20m. down to nebu- losity, in a most astonishing manner." No. 2,908. " Cluster 7th class. The second of two stars 9m. which may be considered the leading stars of the very large and fine cluster of the Nubecula Major, which fills many fields, is of all degrees of condensation and much broken up into groups and patches. . . . The field full of grouping stars." The tendency of the stars to rim in streams is pointed out by Proctor in his Unircrse mul the Coiiiiiu/ Transits (first two chapters). Among the lucid stars the most re- markable instances of this stream-forming arrangement are found in Pisces, Scorpio, " the river Eridanus," the streams in Aquarius, and the festoon of stars formed by rj, y, a, 8, and /x Persei. The stream forming the constella- tion Eridanus was noticed by the ancients (as the name " river " implies), but in this case the stars are so far apart that the connection is probably more apparent than real. Perhaps the same may be said of the streams form- ing Scorpio and Pisces, but still they are sufficiently well- defined to attract the eye of even a casual observer. Other examples of the kind may be seen in Corona Borealis, May 1, 1891.] KNOWLEDGE 87 or the Northern Crown ; in Corona Austrahs in the southern hemisphere ; and also among fainter stars visible to the naked eye, or w-ith an opera-glass. But it is among the still fainter stars — those visible only with a telescope or revealed by photography — that we find the most striking examples of this stream-forming ten- dency. In these cases the small stars composing the streams are comparatively close together — at least, ap- parently so — and for this reason the evidence in favour of a real physical connection is proportionately stronger. Webb says* : " A little n. ji. /x Sagittarii xviih. 57m., S. 18° 50' is a spot referred to by Secchi as exemplifying in a high degree the marvellous structure which the great achromatic at Eome shows in the Galaxy. The remarks of this accomplished astronomer on the successive layers of stars are very curious : first he finds large stars and lucid clusters ; then a layer of smaller stars, certainly below 12 mag. ; then a nebulous stratum with occasional openings. But what he says startled him, and all to whom he showed it, was the regular disposition of the larger stars in figures ' si geometriques qu'il est impossible de les croire accidentelles. La plus grande partie sont comme des arc de spirale ; on pent compter jusqu'a 10 ou 12 ctoiles de la 9me. a la lOme. grandeur. . . . Se sui- vant sur une meme courbe comme les grains de chapelet ; quelquefois elles forment des rayons qui semblent diverger d'un centre commun, et co qui est bien singulier, on voit d'ordmaire que, soit au centre des rayons, soit au com- mencement de la branche de la courbe, on trouve une etoile plus grande et rouge. II est impossible de croire que telle distribution soit accidentelle.' " I have already noticed that on the Paris stellar photo- graphs many cases may be seen of three or more stars placed in a straight line, or nearly so. Sometimes a comparatively bright star seems to draw a train of fainter stars after it, like the tail of a comet, and occasionally a stream of stars of nearly equal brightness may be traced for some distance from their source. In the photograph of the cluster 38 Messier, this stream-formation is well marked among the brighter stars. Webb describes it as " a noble cluster arranged as an oblique cross. "+ Observing with a 3-inch telescope in India, in July 187-1, I noticed a beautiful cluster of stars about ■L° north of \ and V Scorpii, resembling, in shape, a bird's foot, with remarkable streams of stars. This cluster is visible to the naked eye as a star of 5 or 5s magnitude. Sir WiUiani Herschel, speaking of the compressed cluster H. vi. 25 in Perseus, says, " the larger stars arc arranged in luaes like interwoven letters"; and, Webb Bays, " it is beautifully bordered by a brighter fore- shortened pentagon." From the close proximity of the component stars — of some at least of these clusters — the reality of a physical connection between them seems beyond dispute, and from analogy we may conclude, I think, that " streams " and " sprays " of stars in otlier portions of the heavens are, in some cases at least, due to a real and not merely an apparent connection. From a telescopic examination of the Milky Way, Professor Holden finds numerous star - streams, and also arrangements forming "small definite ellipses" of stars, often all of the same size. ... In certain parts of the sky, the arrangement is so intricate that no single pattern can be discovered. In most regions a little atten- tion will show that there are several patterns, one for * Celestial Ohjects, Fourth Kdition, p. 3S5, foot-note. i Ibid., p. '2il. each of the fainter magnitudes of stars " (Monthly y(jtices, E.A.S., Dec. 1889). In a paper in the Monthly Xotices, R.A.S., for April 1890, Mr. Backhouse calls attention to the " straight lines and parallel arrangements of pairs, lines, and bauds of stars, and also of irresolvable wisps " observed by him in a portion of the Milky Way included between the .stars 15, 13, 8 Monocerotis, a Orionis, ^ Tauri, and 5, fj., ^ Gemi- norum, and " besides the parallehsms " he notes " a most wonderful case of radiation of .stars and 'visps in a fan-shaped group, 08 Orionis being approximately the centre." He finds a preponderance of the groupings "at an average delation of 15° from the direction of Gould's Galactic Equator, viz. at a position angle of 345° with that great circle, and more nearly parallel with a Galactic Equator derived from Proctor's chart of the DunhiiiuKtenuuj stars, and be adds : " One conclusion derived fi'om the in- vestigation is that the stars and wisps in parallel lines are probably in the same region of space ; and therefore that the majority of the stars — at least of those down to the 9th or 10th magnitude — in extensive tracts of the area examined are really near one another." An examination of Dr. Boeddicker's beautiful drawing of the Milky Way seems to show that the Galaxy itself is — at least, chiefly — composed of "star-streams" and " star-sprays " and clustering groups of small stars, and does not represent a " cloven " flat disc, as was originally supposed. Mr. Proctor pointed out that " the nebular system also shows the most marked tendency to stream-formation." Li the great nebular region in Virgo and Coma Berenices, he finds that " the stars are not arranged imiformly over either region, but to some degree clusterLngly with inter- spersed spaces relatively vacant. Now no nebula appear in the more vacant spaces, nor do nebula appear chiefly where the stars are more clustered. It is on the borders of star-clusterings, and in the breaks of star-streams, that the nebuhe show themselves, precisely as though they had taken the place of stars where star-matter began to fail." This fact, considered in connection with Laplace's Nebular Hypothesis, is very remarkable and suggestive. The nebulie seen in the streams may possibly represent stars in their initial stage. WHAT IS A VOLCANO? By tue Rev. H. N. Hutchinson, B.A., F.G.S. IN old days volcanoes were regarded with superstitious awe, and any investigation of their action would have been considered rash and impious in the highest degree. A certain "burning moimtaiu " in the Lipari Isles, called Volcano, was considered to be the forge, or workshop, of Vulcan, the god of Fire. And so it comes about that all " burning mountains " take their name from this island in the Mediterranean. In the present paper it will only be possible to consider two aspects of the subject of volcanoes, which may, perhaps be more suitably presented in the form of ques- tions, viz. (1) WItat t.s a rokano .' (8) Wliat (or tht' chiif phenomena of rolcanic action ! In the first place, a volcanic mountain consists of alter- nating sheets of ash and lava, mantling over each other in an irrogiUar way, and all sloping (or " dipping," as geologists say) away from the centre. In the centre is a pit, or chimney, widening out towards the top so as to resemble a funnel or a cup. Hence the name " crater," which means a cup. In the centre of the cone there is fi-equently a little minor cone. As oiu' readers will pro- 88 KNOWLEDGE [May 1, 1891. bably be aware, many of the lunar volcanic craters also possess these little minor cones, which are well seen in some of the larger photographs of the moon's surface. A number of cracks, or fissures, radiating from the central orifice, intersect the volcano. These get filled with lava welling up from below, and from what are called " dykes," which may be regarded as so many sheets of igneous rock — basalt or felsite, as the case may be — that have, while in a molten condition, forced their way in among the layers of ash and lava. The word " ash " is used by geologists in a special sense; and volcanic ash is not, as might be supposed, a deposit of cinders, but mostly of dust of various degrees of fineness ; and sometimes it is very fine indeed. It is synonymous with the word "tuff." Pieces of pumice-stone may be embedded in a volcanic tuff, but they only form a small part. How these volcanic tuffs are formed we shall explain pre- sently. Dykes strengthen the mountain and tend to hold it together when violently shaken during an eruption. But notwithstanding, it sometimes happens that the whole structure is blown to pieces by some unusually violent out- burst. The shape and steepness of a volcano vary with the nature of the materials ejected. The finer tije volcanic tuff' the steeper and more conical is the mountain. The formation of a volcano may not be inaptly illustrated by the little cone of sand formed in an hour-glass as the sand-grains fall. The latter settle down to a certain slope, or angle, at which they can remain in their place. This is known as the " angle of repose." When the materials are coarse the angle is less. When they are fine the angle is greater. The district of Auvergne in France contains a number of very interesting extinct volcanoes, some of which were formed principally of a thick and viscous lava which slowly welled up from below, and in so doing formed round and dome-shaped little hills such as the " Puy de Dome." Vesuvius, Teneriffc, .Jorullo in Mexico, and Cotopaxi in the Andes, are examples of steep volcanoes built up principally of volcanic tuff. Others, more irregular in shape, such as Kilauea in the Sandwich Islands, are largely built uj) by successive lava- Hows. Little minor cones are frequently developed on the fiauks of a volcano, which during eruptions give rise to small outbursts on their own account. They are easily accounted for by the dykes wliich we mentioned just now ; for when the molten rock forces its way through the fissures, it sometimes finds an outlet at the surface, and, being full of steam, as soda-water is fidl of gas, it gives rise to an eruption. The central orifice, with its molten lava, is, as it were, a great dyke which has reached the surface and so succeeded in producing an eruption. The opening of a soda-water bottle not infrequently illustrates a volcanic eruption ; for when the pent-up carbonic acid cannot escape fast enough it forces out some of the water, even when the bottle is held upright. Lastly, every volcano is built up on a platform of stratified rocks, or strata, laid down in the usual way under water, and at some period subsequent to their formation molten matter came up from below, and found its way through them to the old land-surface which they formed. Earthquake shocks preceding the first eruption probably cracked up the strata, and so facilitated the uprise of the lava with its imprisoned steam. The main point which we wish to emphasize is that volcanoes are never formed by upheaval. They must not be regarded as blisters due to the swelling or upheaval of strata, but, as we have endeavoured to explain, they are gradually built up from below, and may be compared to rubbish heaps, which grow by gradual accumulation. But in the case of volcanoes, the rubbish comes from below. It is not necessary to suppose that the subterranean reser- voirs from which the molten rock is supplied, exist at any very great depth below the original land-surface on which the volcano grows up. Indeed, the eddence we at present possess, from the denuded areas of volcanic action, goes to show that this is not the case. The old "upheaval theory" of the formation of vol- canoes, once advocated by certain geologists, instead of being based upon actual evidence, or reasoning from facts, as modern scientific theories are, was a mere guess. Moreover, if the explanation we have given should not be sufficiently convincing, thei-e is the proof furnished by the case of a small volcano near Vesuvius, whose formation was actually witnessed. It is called Monte Nuovo, or the New Mountain. This mountain is a little tufl'-cone, 430 feet high, on the bank of Lake Avernus, with a crater more than a mile and a half wide at the base. It was mostly formed in a single night, in the year 1538 A.n. We have two accounts of the eruption to which it owes its existence, and each writer says distinctly that the moun- tain was formed by the falling of stones and ashes. One witness says : " Stones and ashes were thrown up with a noise like the discharge of great artillery, in quan- tities which seemed as if they would cover the whole earth ; and in four days their fall had formed a mountain in the valley between Monte Barbara and Lake Averno of not less than three miles in circumference, and almost as high as Monte Barbaro itself — a thing incredible to those who have not seen it, that in so short a time so consider- able a mountain should have been formed." Another says : " Some of the stones were larger than an ox. Tlie mud [ashes mixed with water] was at first very liquid, then less so, and in such quantities that, with the help of the afore-mentioned stones, a moimtain was raised, 1 ,000 paces in height." These accounts are important as showing how, in a much longer time, a big volcano may bo built up. They are examples, or little epitomes, of slow and vast processes which Nature vouchsafes to us, and which enable us to comprehend her actions when they are on a larger scale. We must now consider briefly the second question. The following are the chief phenomena of a great eruption : — • Its advent is heralded by earthquakes, afl'ecting the moun- tain and the whole country round ; loud subterranean explosions are heard, resembling the fire of distant artil- lery. The vibrations are chiefly transmitted through the ground ; tue mountain seems convulsed by internal throes due, no doubt, to the efforts of imprisoned vapours and liquid rock to find an opening. These idications are accompanied by the drying up of wells and disappearance of springs, since the water finds its way down new cracks resulting from the explosions. When at last an opening has been effected, the eruption begins, generally with one tremendous burst, shaking the whole mountain down to its foundations. Frequent explosions follow with great rapidity and increasing violence, generally from the crater. These are indicated by the globular masses of steam which are to be seen rising up in a tall column like that which issues from the funnel of a locomotive. The elastic gases in their violent ascent hurl up into the air a great deal of solid rock from the sides of the crater, after first blowing out the stones which previously stopped up the orifice. Blocks of stone falling down meet with others coming up, and so a tremendous pounding action takes place, the result of which is that great quantities of volcanic dust are produced, generally of extreme fineness. Winds and ocean currents transport these light materials for long May 1, 18!J1.] KNOWLEDGE 89 distances. Eecent researches show that fine volcanic duat is universally distributed over the sea. The darkness so frequently mentioned in accounts of eruptions is caused entirely by clouds of volcanic dust obscuring the daylight. The red clay deposits in the deepest and most remote parts of the ocean are now considered to be chiefly com- posed of oxidized volcanic dust. Portions of liquid, or semi-liquid, lava are caught up by the steam and hurled into the air. These assume a more or less spherical form, and are known as " bombs." At a distance they give the appearance of flames. And here we may remark that the flaring, coloured pictures of Etna or Vesuvius in eruption, which frequently may be seen, are by no means correct. The huge flames shooting up into the air are imaginary — another case of a popular fallacy — but probably suggested by the glare and bright reflection from incandescent lava down in the crater. But there is another way in which a good deal of fine volcanic dust, or ash, is produced ; and it is this— the lava is so full of steam intimately mixed up with it that the steam, in its violent escape, often blows the lava into mere dust. This might be illustrated by the cloud of spray seen for a moment after a soap-bubble has burst ; and we can well imagine that something like this takes place in a boiling and seething mass of lava in a crater during eruption. The steam, we ought to mention, is not dissolved in the lava, but absorbed by it, and is said to be "'occluded" (hidden away). When lava-flows take place the lava does not always come from the crater, but often issues firom the side of the volcano. This marks the crisis of the eruption, and now a gentle decline sets in. The volcanic forces have done their worst, and the lava-column begins to sink. Explosions decrease in violence, less ash is ejected, and finally cinders choke up the orifice ; and so the volcano, as it were, chokes up itself. So great is the force of the pent-up steam trying to escape that it frequently blows a large portion of the top of the volcano bodily away, leaving only a truncated cone ; and, in some cases, a whole mountain has been thus blown to pieces. Finally, torrents of rain follow or accompany the upthrust of so much steam into the air. Vast quantities of volcanic ash are caught up by the rain, and in this way large quantities of mud are washed down the sides of the moimtain. Sometimes the mud-floes are formed on a large scale, and, descending with great rapidity, bury up a whole town. It was in tliis way that the ancient cities of Herculaneum and Pompeii were buried up by the great Vesuvian eruption of a.d. 79. The Italians give the name lava d' acqun, or water-lava, to flows of this kind, and they are greatly dreaded on account of their very rapid flow. An ordinary lava-stream creeps slowly along, so that people have time to get out of the way ; but in the case of mud-flows there is often no time for escape. Into the question of the cause of volcanic phenomena we cannot enter now ; but we shall have more to say in a second pajjer. Notices of Boofts. The lloney-Bee: Its Natural History, AHaU»iuj, and Physioloriy. By T. W. Cowan, F.L.S., etc. (Iloulston &. Sons.) This little manual, which, though consisting of upwards of 200 pp., is scarcely larger than pocket-size, forms the natural supplement to the author's numerous works on Bees and Bee-culture. The subject is handled in an exhaustive and thoroughly scientific manner, and the book, which is written in a cominendably concise style, and contains upwards of seventy figures, teems with rehable information. The labour of compilation must have been great, and the author deserves the thanks, not only of ajsieulturists, but of all who are interested in the anatomy and physiology of insects in general, for having put into such a comiJact and inexpensive form so much of the detailed results of recent scientific research. Authori- ties are constantly cited throughout, and the references to the copious bibliography appended supply the reader with all that is necessary to guide him in pursuing the subject further. Taking a look into a hive at the height of its activity, we are introduced to the queen " mo^dng slowly over the combs, surrounded by a number of workers, which are constantly touching her with their antennte, and offering her food. She stops at an empty cell, examines it by putting her head inside, then, hanging on to the edges of the comb, inserts her abdomen, and deposits at the base of the cell, to which it is attached by a glutinous secretion, a little bluish-white oblong egg." The position of the egg in the cell is altered day by day, till, sloping gradually from the upright, it eventually Ues in a horizontal direction, as shown at A, B, C, in the accompanying figure of a brood-comb. Here also are shown the growing grub, the remarkable crater-like open- ings of the royal cells, drone colls at K, and at N cells containing workers, some of which are just nibbling their way out through the cappings of the cells. Mr. Cowan considers that bees generally confine their honey- and pollen-collecting expeditions to within a radius of about two miles from their hives, except when food is scarce, when they will fly as far as four or five miles. By his own observations he has proved that the rate of flight may be at least as much as twelve miles an hour, i.f. for un- weighted bees, the heavily-laden ones returning from a foraging expedition, of course travelling more slowly. Great pains have been taken to give a clear exposition of the mechanism and method of action of the sting. 90 KNOWLEDGE [May 1, 1891. ■which is much more complex than might have been imagined. The accompanying figure shows the long tubular poison-gland which passes its secretion, consisting chietly of formic acid, into the large reservoir at the base of the sting ; the two lancets the latter contains may move either simultaneously or alternately, and at each stroke the Bee's Sting asd Poison-Gland. poison is forced into the woimd with considerable energy through canals in the lancets themselves, and out at the openings between the barbs. Though the queen rarely stings a human being, yet the writer's experience shows that she can do so if necessary. He states also that she can withdraw her sting more easily than the workers, by mo%-ing round and giving the barb a spiral motion ; this, Dorsal Vessel or "Heart" of Bee. he maintains, the worker could do also, but that she is in such a hurry to get off that she does not give herself time, but tears herself away, leaving the sting and its appendages behind her. Mr. Cowan has adopted the striking and effective device of showing different systems of organs separately in .situ on the dark background of the body ; one of these illustrations, e>diibiting the dorsal vessel, or " heart " of the bee, is here appended ; the small explanatory diagram added shows how the blood enters by the side openings of this valvular tube, and is propelled towards the head. No subject IS more debateable than the functions of antennae, and hence much interest attaches to the chapter dealing with the researches that have been made into the structure and function of the tactile hairs, and of the curious sensory pits in these organs in the bee, which have by some authors been considered to be smell hollows, and by others an auditory apparatus. The accompanying Salivary Glands. figures of the salivary glands of the bee will give an idea of the neatness with which the histological illustrations are executed. Mr. Cowan has made many measurements of the cells of the comb, with the view of testing the accuracy of commonly-received notions as to their extreme regularity, and he finds that frequently considerable devia- tions fi-om the normal size and shape of the ceUs occur. Following Miillenhofi', he maintains that " the complexity and apparent accuracy of the structure is not in the least owing to the development of a mathematical instiact in bees, or artistic dexterity, but simply to physical laws dependent on their method of work," the cells behaving " mutually like soap-bubbles, which when isolated are round, but, if touching each other, where imited the film forms a perfectly flat w-all." One or two misprints occur in the technical terms, as e.ij. " vasa il if-ierentia, " for " rfc-ferentia," and " vesiculfe seminal-(.s " for " semi- nal-es." Celestial Motiona : a Handy Book of Astronomi/. By W. T. Lynx, B.A., F.K.A.S. Seventh Edition. (London: E. Stanford.) We are pleased to welcome a new edition of Mr. Lyun's very handy little manual, the sixth edition of which was reviewed in Knowledge for Jime 1889. In the present one the information appears to have again been carefully brought up to date, reference being made to Schaparelli's results with respect to the rotation of Mercury and Venus, and to the identity of the comet dis- covered by Brooks in .July 1889 with what is generally known as Lexell's comei of 1770. No notice, however, is May 1, 1891.] KNO^VLEDGE 91 taken of the " spectroscopic binaries " discovered at Harvard and Potsdam. There are very few misprints in the work, but we must demur to the statement on page 9 that the resulting mean distance of the moon fi-om a parallax of 57' 2" is 237,300 miles. As a matter of fact the mean distance of the moon is about 238,840 miles, the average distance is not the mean of the maximum and minimum values of the distance, and a parallax of 57' 2" would answer to a distance of about 238,900 miles. — H. S. THE PLEIADES CLUSTER, AND ITS PROBABLE CONNECTION WITH THE MILKY WAY. By A. C. Ranyard. THE Pleiades lie a httle to the south of the MUky Way, in a Ime with the Hyades — the three great stars in the Belt of Orion, and Sirius, the brightest star in the heavens. This striking chain of jewels lies nearly parallel with the Milky Way, just outside its southern border. It forms part of a great belt or stream of bright stars first noticed by Sir John Herschel,* and subsequently more closely studied by Dr. B. A. Gould,+ which appears to gh-dlc the heavens very nearly in a great circle that intersects the Milky Way at an angle of about 20°, crossing it near the margin of the Southern Cross, and in the northern hemisphere again crossing the Milky Way in Cassiopeia. This stream of bright stars, like the stream of milky light it crosses, is more striking in the southern hemisphere than in the northern, and one can hardly doubt its intimate connection with the stream of smaller stars with which it appears to be associated. Of the twelve brightest stars in the heavens which rank as of the first magnitude or brighter than the first magni- tude, seven he in this brilliant girdle of stars, and three are intimately associated with it, being situated only just on the opposite border of the Milky Way. Taking the stars Ln their order of brightness according to Professor Pickering's photometric catalogue, they stand thus : — 1. Sirius, ranked as of the — 1'4 magnitude; 2. Arctuni,s, O'O magnitude, that is, one magnitude brighter than the first magnitude ; 3. Cdpella and Fi'//", both ranked as of the 0-2 magnitude ; 5. yS Orionis, OS magnitude ; 6. Cuno- * Sir John Herschel says of it, in hla Kesu/ts of Astronomical Ob- xervations made at the Cape of Good Hope, p. 385 : — " The medial line of the Milky Way may be considered as crossed by that of the zone of large otars which is marked out by the brilliant constellation of Orion, the bright stars of Canis Major, and almost all the more conspicuous stars oi Ar Leonis . 4Cfi f Scorpii .. .'.-70 02 20 . . 9-77 •fi Ursffl Maj. 21-20 A Ophiuchi 29-54 U Ononis ■4-09 Y Virginis 4-92 ti Braconis 4-21 12 Lyncis 14-01 25 Can. Ven. 7-28 C Sa^ttarii 2.-t-04 Sirius ... 6-35 ^ Coronse Bor. 1-40 « Cygni . 31-29 Castor :«12 /i2 Bootis 2-74 3 Delpliini (!-85 f Canon 2!l(i Y Corona! Bor. 22 10 ,\ Cygni 11-01 Solar Stars. S 30132 0-fi8 42 ComlE 2-46 2 2173 ... 0-8S 1} CassiopeiiB , . 0-33 2 17.17 0-37 T Ophinchi 7-35 .'») Audromedffl . 6-23 5 181» 0-95 70 Ophiiicbi 0-:!O 2 228 M7 a Centauri 1-31 Y Coronie Aust. 1*22 OS U9 . 1-07 J Bootis ... 0-34 02 •■!«7 - . 2-46 S 1037 ISJ 44 Bootis 207 OS 4a- un-liiii-. 104 KNOWLEDGE [June 1, 1891. state in which many of its remains are preserved, to have accumulated with considerable rapidity. Fishes are found with their scak's undisturbed, cidarids with their spines in situ and so forth, showing that they were entombed in material solid enough to support them before the destruc- tion of their soft parts was accomplished. There is also reason to think, from the absolutely amorphous state of much of the calcareous matter, that some of it was of chemical or mechanical origin ; that is, it is either a invcipitate from solution or else detritus from pre-existing limestones. Dr. Sorby considers it impossible for calcite shells to form such a substance by their destruction, though aragonite ones may do so. Such are the principal arguments which have been adduced m denial of the theory that the Chalk was an earlier equivalent of the Atlantic Ooze. If, as geologists are becoming more inclined to hold every day, that theory is untenable, what shall we put in its place ? According to Dr. A. R. Wallace, conditions almost identical with those under which the Chalk was formed exist at the present time in the northern part of the Gulf of Mexico. The researches of Pourtales show that the ocean bed is there covered with a fine white mud, closely resembling Chalk in composition, and which consists chiefly of the impalpable detritus of the coral-reefs which fringe the numerous islands, together with the skeletons of the foraminifera abounding in the warm waters of the region. Coral-reefs exist in the Chalk of Maastricht and Faroe, but with these exceptions they are almost unknown in the formation. Prof. Prestwich also discusses the subject at considerable length in his " Geology." He thinks that much further investigation will be required in order to set the question at rest. In the meantime, he is of opinion that the Chalk was formed under conditions which have passed away, or at any rate are nowhere exactly realised at the present time. The stratigraphy indicates that it was deposited in a nearly enclosed sea of no great depth. The rivers flowing into this sea brought down a very exceptional amount of soluble silica, though not so much as in some- what earlier times : some of the Upper Green-sand beds contain as much as 72 per cent. In the presence of solid silica (of which sponge spicules, Ac, are made) or of organic matter, this substance was precipitated, and formed the flints which so often enclose remains of sponges, or occupy the tests of echinoderms. WHAT IS THE CAUSE OF VOLCANIC ACTION? By Kev. H. N. Hutchinson, B.A., F.G.S. IN our previous paper we endeavoured to explain the structure of a Volcano, and described briefly the chief phenomena of an eruption. " Is it possible," the reader may ask, " to form any conclusions as to how volcanic eruptions are brought about ? " — in other words, to find out what is going on underneath, and so to obtain some idea of the cause or causes of these strange manifestations of subterranean activity. It must be confessed at once that, in the present state of scientific knowledge, no full and complete explanation is possible. Geologists and others are as yet but feeling their way cautiously towards the light which, perhaps before long, will illumine the dark recesses of this mysterious subject ; but nevertheless, since volcanic action was first carefully studied by Mr. Scrope, Sir Charles Lyell, and others, such valuable material has been collected, that we are getting much nearer to a true theory now that the ground has been somewhat cleared. Others, among living geologists, have carried on researches of very great value, and so have thrown valuable light on the subject. It will, perhaps, hardly be necessary to point out that the main difficulty is our ignorance of the interior of the earth. If wo could penetrate subterranean regions to a sufficient depth, and find out the physical conditions prevailing far below the surface, there would be little difficulty in finding out how Volcanos are worked. But since direct knowledge is impossible, the problem must be attacked indirectly. We are somewhat in the position of a medical man diagnosing a difficult case ; only medical science has the great advantage of knowing accurately the internal structure of the human body. The earth, unfortimately. is a body the internal anatomy of which is unknown. Of its epidermis, or skin, we have learned a good deal, but beyond that all is speculation. Looking upon volcanic action as a curious disease from which our patient the world occasionally suffers, it may not be unprofitable to see if some rough sort of diagnosis of the case is possible. For this purpose it will be necessary to consider volcanic action a little more generally. We must not confine our attention to any one outbreak of the disease, or to any one Volcano, but look at the subject as a whole, putting our- selves, as it were, in the position of the physician who judges of any one "case" from the experience he has derived from the study of a great many " cases." Now the first thing to remark is that volcanic action goes through phases, of which there are three. First, there is the state of permanent eruption — this is not a dangerous state, because the steam keeps escaping all the time the safety-valve is working, and all goes on smoothly. The second state is one of moderate activity, with more or less violent eruptions at brief intervals — this is rather dangerous ; the safety-valve is at times jammed. And thirdly, we have paroxysms of intense energy alternating with long periods of repose, sometimes lasting for centuries. These eruptions are extremely violent and cause widespread destruction ; the safety-valve has got jammed and so the boiler bursts. No Volcano has been so carefully watched for a long time as Vesu\'ius. Its history illustrates the phases we have just mentioned. The first recorded erup- tion is that of A.D. 7S, a very severe one of the paroxysmal type, by which the towns of Hereulaueum, Pompeii, and 8tabi» were buried up. We have an interesting account by the younger Pliny, whose uncle lost his life through remaining too near the scene of action, partly for the sake of rescuing those in danger and partly because he wished to observe the strange phenomenon. Before this great eruption took place Vesuvius had been in a quiescent state for 800 years, and if we may judge from Greek and Iloman writings was not even suspected of latent possibilities in the way of volcanic eruptions. Then followed an interval of rest till the reign of Severus, the second eruption taking place in the year 203. In the year 472, says Procopinus, all Europe was covered, more or less, with volcanic ashes. Other eruptions followed at intervals, but there was com- plete repose for two centuries, i.e. until the year 1306. In 1500 it was again active, then quiet again for 130 years. In 1631 there came another paroxysmal outburst. After this many eruptions followed, and they have been frequent ever since. Vesuvius is, therefore, now in the second stage of moderate activity. But geologists can take a wider view of Volcanos than this ; their researches into the volcanic action of remote geological periods have yielded important results, which may be briefly indicated here. They can sum up the history of a volcanic region, and the result seems to be somewhat as follows : — There is a regular cycle of changes ; June 1, 1891.] KNOWLEDGE. lU.j the invasion of any particular area of the earth's surface by the volcanic forces is heralded by subterranean shocks causing earthquakes. A little later on, fissures are formed, as indicated by the rise of saline and thermal springs, and the issuing of carbonic acid and other gases at the surface of the earth. As the subterranean activity becomes more marked, the temperature of the springs and emitted gases increases, and at last a visible rent is formed, exposing highly heated and incandescent rocky matter below. From the fissure thus formed, the gas and vapours imprisoned in the incandescent rocks escape with such violence as to dis- perse the latter in the form of scoriie and volcanic ash, or to cause them to pour out in streams or lava flows. The action generally becomes concentrated at one or several points along the line of action — that is, the line of fissure and dislocation. In this way, a chain of Volcanos is formed, which may become the seats of volcanic action for a long time. When the volcanic energies are no longer able to raise up the fluid materials so that they shall flow out of the cones which have been built up, nor to rend their sides and form parasitic cones, fissures with small cones may be formed in the plains around the great central Volcanos. Later on, as the heated rocky matter below cools down, the fissures become sealed up by con- solidating lava, and the Volcanos fall into a condition of quiescence, after which they begin to suffer from the effects of exposure to the atmospheric agencies of decay, and thus become more or less worn away or " denuded." But still the existence of heated rocky matter at no great depth below is indicated by outbursts of gases and vapours, the formation of geysers, mud-volcanoes and ordinary thermal springs ; gradually, however, even these manifesta- tions become more feeble, and thus all v-isible signs of volcanic energy die away in the district. Such a cycle of changes may require millions of years, but by the study of Volcanos in every stage of their growth and decline, it is possible to reconstruct this outline of their life history. That Volcanos are built up along lines of fissure in the earth's crust does not admit of any doubt. The present distribution of Volcanos over the earth is a striking proof of this, and, moreover, we have further evidence derived from the study of old volcanic areas, which have been, as it were, dissected and so brought to light by long-continued erosion or denudation. Let us look a little more closely at the present distribution of Volcanos on the earth's surface, for it reveals some interesting facts which nnist be borne in mind in forming any conclusions with regard to the possible cause of volcanic action. One rule wo have already observed, viz., that Volcanos arc mostly distributed along lines. Secondly, they seem to follow or coincide with great mountain chains, such as the Andes, Eocky Mountains, or the ranges of C!entral America. Thirdly, there is some kind of connection between Volcanos and tiie coast lines of continents. Fourthly, they are always near some liody of water (j.c, when in the active stage). Fifthly, they are situated in regions of the earth which are undergoing slow H])huaval, and are absent from regions where subsidence is taking place. In framing any conclusions with regard to the problem under consideration, we must renu-niber that volcanic action depends mainly on two things — (1) a high temperature below the region of activity, (ii) the presence of steam at a high pressure. Superheated steam evidently plays a very important part, and the force which raises masses of molten lava to the surface may be that due to the expansive power of steam. Volcanic eruptions, then, are essentially gigantic explosions, such as are faintly imitated in the bursting of steam boilers. This is good as far as it goes, but we cannot take it as an explanation of volcanic action ; for we require to know the source of the steam, and of the lava, as well as the reason for the high temperature necessary for the production of both. Where does the heat come from ? and what is the source of so much steam ? Sir Humphry Davy, discoverer of the metals of the alkalies and alkaline earths at the commencement of the present century, showed that the metals potassium and sodium when touched by water develop a great deal of heat ; in fact they burn on water, decomposing it and uniting with the oxygen. This led him to throw out the idea that if pure metals exist far down in the earth's interior, the access of water and air might give rise by oxidation to a large amount of heat, sufficient in fact to produce volcanic phenomena. But later on he confessed that this chemical theory of Volcanos was unsatisfactory. If it were true, enormous quantities of hydrogen gas would necessarily be emitted during volcanic action, but this is not the case. It will readily be perceived that all explanations of volcanic action resolve themselves finally into the question of the condition of the earth's interior, with regard to which we can at present only speculate ; hence the absence of any complete and consistent explanation of the volcanic problem. Certain facts undoubtedly tend to establish the idea, once firmly maintained, that the whole of the earth's interior is in a highly heated state, but they do not prove it. The well-known increase of temperature as we descend mines, which is about 1'^ F. for every 50 or GO feet, is not sufficient proof, for the nitc af incnu.sc does not seem to be maintained as we descend to the greatest depths, and it is possible that the centre may be cold." Still, astronomers tell us that the earth has been for ages a cooling globe, so that it would seem natural to suppose that there are still vast stores of heat within ; but they may be more or less local. It has even been argued, at one time, that the whole interior of the earth is in a molten condition, with only a thin crust of solid matter forming a kind of shell or outer * It is conocivablo, though it is not probal)lt', thiit tlic central portions might not l)e wanner tlian the regions which liave been already explored; but it is impossible that, after the lapse of ages, they should remain cooler than the exterior layers. The sun was formerly supposed by Bode, Sir .lolin Iferseliel, and other distin- guished astronomers to be a cool body surrounded by two atmospheres, the inner one a partially opaque lieal-ahsorbini atmosphere, an. in., promycelium ; i/., promycolinl gonidia. gonidium may still be visible. Tlioso are also gonidia, but by reason of their structure are better fitted to withstand the rigors of winter than those produced in the earlier part of the season. They are the last gonidia to appear on the niycelimn, so they have received the name of tclcuto- gonidia (tcXcutos " last "). All this time the fungus has been preying upon its host, and preventing the elaboration of sap for the building up of its seeds. Its attacks are thus dreaded by the farmer. This stage of the fungus, which was not known until recently to have any connection w'ith the preceding, re- ceived the name of Puccinin ijniiiiinia. The mildew, or blight, was known as far back as the time of Shakespeare. In AV;;// Lear, Act III. so. iv., we read that " the foul fiend Flibbertigibbet mildews the white wheat." " The fungoid nature of the mildew was not known, however, until the latter half of the last century, for TuU, writing in ITHH, attributes it to the attack of small insects, ' brought (some think) by the east wind,' which feed upon the wheat, leaving their excreta as black spots upon the straw, ' as is shown by the micro- scope.' ! " ■■ The teleuto-gonidia remain on the decayed leaves all winter, but in the spring they throw oft" their dormant state, become active, and germinate. Each di\nsion sends out a small tubular body (Fig. II. r.,p.iii.) which divides up into three or four cells that still retain organic connec- tion with one another. From each cell is thrown out a short process, whose tip develops into a minute bulbous swelling (Fig. II. c, //.). The two tubes produced from the teleuto-gonidia are called promycelia, and the swellings just mentioned the promycelial gonidia. These last are produced in immense numbers, and are carried about by the wind. It was noticed many years ago that in the vicinity of Barberry bushes (lierhrriK vulijiiris) the wheat in a wheat- field presented the rustfil appearance which we now know to be due to the presence of teleuto-gonidia, while in neighbouring parts the wheat retained its normal appear- ance. Many accomits were given of the connection between the Barberry and mildew on wheat, but no one knew why this connection should exist. So convinced were farmers of the harmful nature of the Barberry that almost all these bushes have been uprooted from our hedges ; and in 1760 an Act was passed in Massachusetts enforcing the destruction of these apparently harmless shrubs. The promycelial gonidia, one would naturally imagine, would germinate on the wheat-leaves, but experience tells us that this does not take place. They will only develop when they fall on the Barberry, or its ally the Mulmnia ilu-ifoUa. In the leaves of the former plant, and in addition on the berries of the latter, they develop a myce- lium in no way diftering from that seen in the leaves of the wheat. The hyphie or threads of the thallus insinuate themselves between the cells, and absorb nourishment from them. Its presence on the Barlierry would probably have passed unnoticed were it not that during the early summer reproductive cells arise from the mycelium. Then it is seen that the under surface of the leaves are infected here and there with circular yellow blotches. The aid of a pocket-magnifier shows each blotch to be composed of a zone of small holes, from which a yellow powder issues. On the upper side of the leaves minute apertures are present, arranged likewise in a circular manner. If we examine a section of the leaf under the microscope, the yellow patches will show themselves to be composed of cup-shaped bodies. livery cup is tilled with bright yellow cells (Fig. 111.. ". .V'-) arranged in linear series, and each series arises from the down- turned end of a hypha. A distinct wall surrounds each cup or tn-idiniii (Fig. III., eetles, where, as we have already seen, it is the first pair of wings which takes no part iu flight. In the Cicadas and Bugs (Fig. 1), constituting the order Khynchota, the wings, when present, arc tour in number, ^it the first pair may be converted into horny wing-covers, as in the Beetles. Like those of the next order, all the members of this group difl'er from the insects mentioned above in that they do not undergo a complete metamorphosis before attaining their final perfect state. The last order that we have to notice is the Orthoptera, in which are grouped the Cirasshoppers, the Cockroaches, the Karwigs. the Dragon- flics, etc. Except in a few parasitic and some other Fio. 1. — Enlabged View of a Flt- «G Bug, with the Wings closed. 114 KNOWLEDGE. [JlNE 1, 1891. forms, all these insects are furnished with two pairs of wings, which dififer, however, greatly in structure. Thus, while in the Dratjon-llios, wliich in this respect may be regarded as tlio more generalised representatives of the order, both pairs of wings are large and membranous ; in the Grasshoppers, Cockroaches, and Earwigs the front pair are leathery, and serve as wing-covers to the hinder pair, which are folded beneath them in a beautiful, fan- like manner. Whereas, however, in the Cirasshoppers the first pair of wings still take some small share in fiigbt, in the Earwigs they are extremely small, and serve solely OS covers. The Earwigs, tlicrcforc, which many people believe to be incai)able of flight, represent the extreme of wing-specialisation in this group of Insects. This closes the list of flying creatures found among the Invertebrates, and we pass, therefore, to the Vertebrates, where we find our first examples of flight among the class of Fishes. In this group, however, in spite of assertions to the contrary, there is no instance of true flight; such fishes as are able to fly at all merely doing so after the spnrious manner. The longest flights are made by the about 7 inches. Its sides, limbs, tail, and head are furnished with loose expansions of skin which, becoming inflated with air, act as a parachute in the long, flying leaps which the creature is able to take from tree to tree. The true Flying Lizards, which range from India to the Philippines, have their parachutes constructed after a totally different fashion. In these creatures the last five or six ribs arc greatly elongated to support an expansion of the skin of the flanks, which forms a fan-like wing on either side. The late Prof. Moseley described tliese lizards m the Philippines as flying so rapidly from branch to brancli that the extension of their parachutes could scarcely be observed ; and also states that some kept on board ship were in the habit of flitting from one leg of the table to another. Since the extinct Flying Dragons or Pterodactyles of the Mesozoic epoch, wliich are the only reptiles capaljle of active flight, have been described at length in a previous article, our allusion to ihcm will here be brief. These extraordinary creatures, as shown in Fig. 3, were fur- FiG 2.— The Flying Fish 0 — Uj:stoi;4.tiiin ur a Long-Tailed PxEiiOUAcTVLii. {After Marsh.) Itli Xalural Size. well-known Flying Fishes (Fig. 2) of most of the warmer seas, in which the flrst pair of fins are greatly elongated for this purpose. These fishes rise from the water with an upward impulse made by the sides of the body and fail, and tliey may remain above the surface for a distance of 200 yards. They do not usually reach a height of more than a few feet above the water, although they occasionally spring so high as to alight on the decks of ships. There are few more beautiful sights than to watch from the bows of a large ocean steamer a shoal of Flying Fish as they rise one after another, witli their quick meteor-like flight, and then as suddenly disappear beneath the dark waters. Flying Fish, it may be observed, are first cousins of the common Herring. The only other Fish endued with the power of flight are the Flying Gurnards, which belong to a totally different group, and of which there are three kinds inhabiting the Mediterranean and most tropical seas. All of them are larger and heavier than the true Flying Fishes, although they fly in the same manner. It has been stated that a Frog from the Malay region uses the large webs on its feet as a kind of parachute in its descent from the trees on which it dwells to the water, but later researches do not lend countenance to this idea ; and our next examples of flight must accordingly be drawn from the class of true Reptiles. Among living Rep- tiles there is no instance of true flight, although two groups are endowed with the power of spurious flight. The first example of this is the Flying Gecko, a small lizard, belonging to that peculiar group so well known in tropical climates from their habit of nmning up and down the walls of dwelling-houses. The Flying Gecko is an inhabitant of Borneo, Java, Ac, and attains a length of nished with tliin membranous wings, which were supported in front by the arm and forearm near the body, and at their extremities by the greatly extended joints of a finger corresponding either to the ring or little finger of the human hand. The membranous expansion was con- tinued down the sides of the liody to embrace the legs and the upper part of the tail ; while in at least some of those species in which the tail was long, its extremity was fur- nished with a racket-shaped expansion of membrane (as in Fig. 2), probably used as a kind of rudder during flight. Some of these creatures were of enormous dimensions, having an expanse of wing estimated at upwards of 2.'j feet. That they were endowed with the power of true flight is perfectly evident from their general structure ; as is especially shown by the strong ridge developed on the breast-bone for the attachment of the muscles neces- sary for the down-stroke of the wings. Their mode of flight was probably very similar to that of Bats, which they appear to have resembled in their wing-membranes, although the support of these membranes, as we shall subsequently see, was arranged on a totally different plan in the two groups. It is, perhaps, superfluous to add that any resemblances existing between Pterodactyles and Birds are solely due to then- adaptation to a similar mode of life, and that there is not the remotest genetic con- nection between them. We come now to the Birds, in which true flight has attained the fullest development, and the whole organiza- tion is profoundly modified to suit the exigencies of a more or less completely aerial mode of life. It is true, indeed, that certain birds, such as the Ostrich, Cassowary, and Penguins, are totally incapable of flight ; but this June 1, 1891. KNOWLEDGE 115 incapacity is certainly an acquired one in the last-named bird, and there is a considerable probability that it was liicewise so in the two former. The great peculiarity whereby Birds differ from all other animals is iu the presence of their external covering of feathei-s. A feather, as we all know, is one of the most iieautiful objects in nature ; and its structure, which we may, perhaps, explain in a later article, is an admirable instance of adaptation for a particular purpose. The uses of feathers are two-fold. In the first place; the small ones with which the body is clothed form the most perfect covering that can be imagined to ensure the main- tenance of the high bodily temperature so essential to the active existence of a bird. Then, again, the larger and stronger feathers of the wings are the most efficient instruments for obtaining the utmost advantage from the resistance of the air to their strokes during flight. The peculiar nature of tlie wings of Birds may be summarised by the statement that whereas all other animals Hy by means of expansions of the skin itself, these alone tly iiy means of sejiarate outgrowths or processes developed from the skin. (To be continued. ) ilcttcvs. [The Editor does not hold himself responsible for the opinions statements of correspondents.] photographer must be naturally an experimenter, his difficulties must be thought out and conquered as they arise. He will soon find the exposures necessary to obtain the best ell'ects. For the Jloon, .Tupiter and Saturn, in the principal focus, only a fraction of a second is necessary, depending on the aperture and focal length of the telescope, as well as on the altitude of the object above the horizon and the clearness of the uiglit. Hence, these objects, as well as the Sun, can be photographed without a driving clock. Dr. von Konkoly'sl book on Astronomical Photography contains a good many woodcuts of instruments and apparatus, but they are not such diagrams that a reader who did not know what was represented could construct an instrument from. This book is also four years old, and Astronomical Photo- graphy has made great progress since that time. I would advise any intending astronomical photographer to thoroughly read some book on geometrical optics, and then to think out his difficulties for himself. — A. C. Ran YARD.] To the Editor of Knowledge. Mackay, Queensland, March 21st, 1801. Sir, — Is there any Kmilisli work treating of Astronomical Photography '? In ti. L. C'hambers' " Handbook of Astronomy," Vol. II., 1800, p. 116, a footnote mentions a German work, Konkoly's, published by Halle, 1887, as the only work on the subject. People who live iu the centres of population can, no doubt, get vied riM-e instruction ; those in distant parts of the world have to depend upon books, and there seem to be none on this subject. I am one of those who deeply regretted the cessation of Answers to Correspondents in 1885, and of Gossip in 1888, which alone were worth, to me, twice the money paid for Knowledge. I liked the genially caustic pen of the late lamented R. A. Proctor, and his way of making personal friends of his readers. Your obedient servant, J. GwEN Davidson. [We have not at present, as far as I am aware, any book in Isnglish on Astronomical Photography. A very charm- ingly illustrated little French book on the subject was issued in 1.SK7 by Admiral Mouchez,- the Director of the Paris Observatory, but it is devoted to giving an account of what has been done, rather than to answering the questions which I imagine Mr. Davidson would like to ask. The photographic difficulties which the astronomical photogi'apher will encounter arc dealt with in a legion of text-books. The astronomical dillicullies involved in the accurate mounting of his equatorial, and the accurate driving of his clock, cannot, I think, be dealt with hy any copy-book rules. To succeed, the astronomical * " liii rhiitdfiraiiliic Aslroiiciiii M. Ic ('.Mitr.'.Aiiiinil K. Mciu-luv dew Umiuls-.\ujriistiii, JSST. (|110 !l rOl.S.'VVll INu-is, (iiiulli .lircdr Paris." I'nr rn\i liars, .'55, tjimi To the Editor of Knowledge. Dear Sir, — Whilst grateful to you and your reviewer for pointing out the mistake in the last edition of my Celextial Mutiona (1 might, perhaps, demur to some of the remarks, but do not propose to do so at present), allow me to call your attention to an error in the same number of Knowledge itself (p. 01), which may puzzle many readers. The passage runs : " He [Michell in I'hil. Tntnx. for 1767] concludes that there must be some physical connection between the numerous double and triple stars which had already l)een discovered by Sir WilUam Herschel . . . ." Michell makes no mention in his paper of HerschePs discoveries, nor could he for a similar reason to that which prevented a distinguished personage from seeing a Spanish fleet. It was not in sight; and HerschePs discoveries had not commenced in 1767, the year after he was appointed organist in Batli. Yours faithfullv, P.lackheatli, May (ith, iSOl. W. T. Lynn. [Michell's reference to the double and triple stars dis- covered by Herschel, is in ^ paper published in the I'hit. Trans, for 1781. The fact to which I wish to call atten- tion is that Michell's remarkable papers were written before Herschel's discovery that several close pairs of stars were moving round one another. The boldness of Michell's conclusion that there must be a physical connection be- tween close double stars is rendered more remarkable by the fact that, at the date of his first paper, 1767, less than a hundred of such pairs of stars were known. Michell's words in his first paper are well worthy of being quoted at length. Ho says, at p. 217 of the Vint. Trans, for 1767, after speaking of certain stars which appear double to the naked eye — " If, besides these examples that are obvious to the naked eye, we extend the same argumeui to the smaller stars .... which appear double, treble, &c., when seen through telescopes, we shall find it still infinitely more conclusive, both in the particular instances and in the general analogy arising from the frequency of them. We may from hence, therefore, with the highest probability, conclude (the odds against the contrary opinion being t " PTOktisrlio .Viileitung zur Iliminelsphotognvpliio ncbst oilier kurgefassteii Aiiloitiiii!; zur nuHlornpii pboUigniptiiselu'ii Oponitiou und dor spoctrul pluilograpliic ini oabiiiot von Niooluus von Koiikoiy. Uallo, 1SH7. 110 KNOWLEDGE [June 1, 1891. many millions to one) that the stars are really collected to_G;etber in clusters in some places, where they form a kind of system, whilst in others there are either few or none of them, to whatever cause this may be owing, whether to their mutual gravitation, or to some other law or appointment of the Creator ; and the natural conclusion fioni hence is, that it is highly probable in particular, and next to a certainty in general, that such double stars as appear to consist of two or moi-c stars placed very near together do really consist of stars placed near together, and under the influence of some general law." Herschel subsequently greatly enlarged the list of telescopic double stars which he sought for and measured in the hope of finding some in which the distance and position angle might vary in the course of the year, indicating a parallax as the earth moves round its orbit. Dut instead of finding a yearly oscillation in the distance and position angle as he expected, he found to his surprise, in many cases, a regular progressive change which indicated that one of the stars was slowly describ- ing a regular orbit round the other. This discovery was annoimced in Herschel's paper in the L'liil. Trans, for lKO;-i and 1804. In speaking of this discovery Herschel said that ho " went out like Sanl to seek his father's asses, and found a kingdom," the dominion of gravitation extending to the stars. .\ dominion which, it should be noted, the Eev. -Tohn llichcll had six-and-thirty years before prophesied would be found to exist, and which in his paper of 17S1 he bad still more coufideutlj' asserted must exist. — A. C. Ixanyaed.] STAlfdNAKV RAinATIiiX OF MRTKORS. To thf EiUtar of Knowledge. Sir., — I note some remarks in your current number, bearing on the Stationary Radiation of Meteors. The difficulty of reconciling this feature with theory is well known, and the question has been debated whether the fixed radiants cannot be explained by successive showers accidentally placed in nearly the same apparent points of the firmament. After uivestigating the observational part of the subject as fully and carefully as circumstances allowed, I found that, allowing for tiivial errors in determining positions, the showers occurred from identical centres, and coi-tainly could not be ascribed to chance grouping. A large proportion of the observed radiant points are of this fixed and long-enduring character. As a rule their individual meteors move with great velocity when the radiants are near the earth's apex, but, with increasing distance from it, their speed sensibly moderates, and they finally become slow, and very slow. Thus my stationary radiant at 47° -f 4-1° yields rcni snift streak-leaving meteors in .July and August, while in November and December they are venj shnr. But this peculiarity is not exemplified in all cases, for there is a shower at 01°+ 41)'' which discharges very swift meteors at the end of November and early in .January, whereas in September I have recorded them as Hifift. This is, however, an exception, and the rule appears to be that the showers meeting the earth give swift meteors, whUe those overtaking it give slow ones. It is clear from the varied phenomena observed both in the major and minor systems, that one and the same explanation will not suffice to explain them all, for every possible diversity of meteor shower may exist and display radiation in the firmament. We may find sporadic meteors of great velocity, and coming from distant space. There may be hyperbolic, parabolic, and elliptical streams, also meteors comparatively isolated, and forming the remnants of past groups dismembered by planetary perturbations, for the vicissitudes which these small bodies encounter must be very considerable. Some of the elliptical streams are very wide, and of this the August Perseids, with their shifting radiant, afford a prominent instance. The apparently stationary shower which I have seen at various times, coinciding in position with that of the Perseids on August 10th, is, of course, entirely different in character to the cometary shower, and needs a different explanation. The latter presents a vastly richer display as well as a moving radiant, and these features readily distinguish it from contemporary showers. We require a vast amount of additional observation in this field. If an energetic observer, living in a finer climate than England, took up the subject, and watched the sky assiduously for several years, he would undoubtedly obtain sufficient data to clear up some of the features which now present such difficulties. I do not tlsink the results of past observation would be controverted, but that the new evidence might enable satisfactory theories to bo formed. As to the accuracy with which radiant points may be determined, I believe that observers of long experience are likely to be the best judges of this. The probable error is different in difl'erent cases, for scarcely any two observers exhibit the same degree of skill. Training would never make some individuals accurate in this difficult branch of work. It takes fully two years of habitual observation before anyone can acquire desirable proficiency in record- ing meteors, and confidence in assigning their radiants. Speaking for myself, I believe my positions are within 2°, and frequently within 1", of the real centres. I should regard 2 as a lanjc error in ascribing the radiant of a well-defined meteor shower. The Andromcdes of Novem- ber 27th, with their widely-difi'used radiant, form a very exceptional shower, from which it would be unsafe to judge of the character of others. Many of the minor systems exhibit contracted and sharply-defined radiants which may be accurately determined by the careful observer. Yom-s faithfully, Bristol, Mav 20th, 1S!J1. W. F. Dexnixg. i[KTF.0R-EADIAXT8. To the Editor of Knowledge. Sir, — I am afraid that I cannot throw any light on the limits of error as regards the determination of meteor- radiants. It would be interesting if three or four practised observers would make their observations on the same night, at the same place, and then compare their results. But whatever the hmits of error may be, I do not see that errors would, on the whole, produce a greater clustering of meteor-radiants than if the positions were accurately known. I should add that Mr. Dennmg's catalogue contains only positions determined by observations on a single night. But he has a column entitled " Other nights of observation," i.e., other nights on which meteors were observed as coming fi-om the radiant thus deter- mined, which I used in my previous letter. The number of meteors used in determining the radiant is in each case mentioned in bis catalogue. I did not intend to maintain that these stationary or long-enduring radiants are in all cases active throughout the year. The evidence, at present, at least, does not go that far. But the reasons for not obsernng meteors from particular radiants at certam seasons of the year are pretty evident. We cannot expect to trace such meteors when June 1, 1891.] KNOWLEDGE. 117 the radiant point is below tlie horizon or near the horizon at the usual hours of observation ; and as Mr. Denning tells us that he made nearly all his observations looking East, meteors from radiants in the West would naturally be passed over. Further, I do not think that where the radiant is of this long-enduring or stationary character, the shower is of uniform intensity throughout. On the contrary, so far as I have traced, the maximum of each long enduring shower occurs nearly at the same date in successive years. The showers appear, moreover, to be more intense in some years than in others. I wish to state iu conclusion, that I never disputed in any way the accuracy of Mr. Denning's observations. I only dilfer from him as to the classification and arrangement of some of them. Truly yours, 10, Earlsfort Terrace, Dublin. W. H. S. Monck. THE FACE OF THE SKY FOR JUNE. By Herbert Sadler, F.R.A.S. THE increase in solar activity still continues. During June there is no real night in the British Islands. There will be an annular eclipse of the Sun on the afternoon of the Gth, which will be visible as a partial eclipse at Greenwich. At that station the eclipse begins at 5h. 2.2m. p.m., the first contact taking place at an angle of 88° from the vertex towards the west, reckoning for direct image ; the middle of the eclipse being at 5h. 'l(5'7m. r.ai. ; and the last contact taking place at Gh. 23'()in. P.M., at an angle of 5° from the vertex towards the west ; the magnitude of the eclipse being 0-2IJ8. Witli the exception of an exceedingly small eclipse on the morn- ing of March 2Cth, 1895, the next solar eclipse visible at Greenwich will not take place till June 8th, 1899. The following are conveniently ol).servable times of minima of some Algol type variables (c/. " Face of the Sky " for April and May) : U Cephei. — June 2nd, lOh. 29m. P.M. ; June 7th, lUh. 9m. p.m. ; June 12th, 9h. 49m. P.M. ; June 17th, 9h. 28m. p.m. ; June 22nd, 9li. 8m. p.m. S Cancri. — hme 11th, lOh. 22ui. p.m. 8 Libra\ — June 14th, Oh. 2Cm. a.m.; June iHth, midnight; June 27th, llh. H.'im. P.M. U Coronie. — June 20tli, llh. 49m. p.m. ; June 27th, 9h. 31m. p.m. U Ophiuchi (17h. 10m. 57s. -f 1° 20').— Max., G-0 mag. ; min., G-7 uuig. ; period, Od. 20h. 7m. 41-60s.— June 4th, lOh. 17m. p.m. ; June 9th, llh. 3m. P.M. ; Jime 14th, llh. 48m. p.m. ; June 15th, 7h. 5Gm. P.M. ; June 20th, 8h. 41m. p.m. ; Jime 25th, 9h. 28m. p.m. Y Cygni (20h. 47m. 47s. 4-34° 15').— Max., 7-1 mag.; min., 79 mag. ; period, Id. lib. 5Gm. 48s. — June 2nd, lOh. Gm. P.M. ; June 5th, lOli. Im. p.m. ; June 8th, 9li. 5Gm. P.M. ; June 11th, 9h. 51m. p.m. ; June 14th, 9h. 45m. P.M. ; June 17th, 9h. 40m. p.m. ; June 20th, 9h. 34m. p.m. ; June 23rd, 9h. 28m. p.m. ; June 2Gth, 9h. 23m. p.m. ; June 29th, 91i. 18ni. P.M. Variable, of short period, not of Algol type. t; AquiliB (19h. 4Gm. 52s. + 0" 43). Max., 3-5 mag. ; min., 3-7 mag. ; period, 7d. 4h. 14m. Os. June 27th, 9h. P.M. Maximum of R Hydra) (rf. " Face of the Sky " for February, 1889) on June 1st. The lines of hydrogen in the spectrum of this star appear bright near maxinuuu. Mercury is a morning star throughout June, but owing to his proximity to the Sun and the strong twilight pre- vailing he is not very favourably situated for observation. He rises on the 1st at 3h. 13iii. a.m., or 38m. before the Sun, with a northern declination of 13' 2G' and an apparent diameter of 84", just three-tenths of the disc being illumi- nated. On the 16th he rises at 2h. 48m. a.m., or 56m. before aimrise, with a northern declination of 18° 53', and an apparent diameter of 6|", six-tenths of the disc being then illuminated. On the 30th he rises at 3h. 9m. A.M., or 38m. before the Sun, with a northern declination of 23° 54'. and an apparent diameter of 5j-", yy^j of the disc being then illuminated. He is at his greatest western elongation (23|'^) on the evening of the 5th. During the month he passes from Aries throughout the whole length of Taurus into Gemini, but without approaching any con- spicuous star very closely. Venus is also a morning star this month, but her observation is rendered difficult by the same conditions which militate against the visibility of Mercury. She rises on the 1st at 2h. 45m. a.m., or lb. 6m. before sunrise, with a northern declination of 13° 47' and an apparent diameter of ll.V", /..'o of the disc being illumi- nated. On the 30th Venus rises at 2h. 24m. a.m., or Ih. 23m. before the Sun, with a northern declination of 22° 1' and an apparent diameter of lOV', ^Vif o( the disc being then illuminated, and the brightness of the planet being only one quarter of what it was on January 8th. During the month she passes from Aries into Taurus. Mars is invisible. The minor planet Vesta (<;/'. " Face of the Sky " for January, 1890) comes into opposition on the 23rd, and but for her great southern declination would be excellently placed for observation, as, with one exception, this is the closest approach to the earth that she has made during the last thirty years. Her distance from us at opposition is about lOG, 655,000 miles, and she is visible to the naked eye during the whole of June, though the proximity of the nearly full Moon at the actual date of opposition will interfere with naked eye observation. At the present opposition she attains to the 6*0 magnitude, and it is to be hoped that search will be made with powerful telescopes in the South of l*;urope and the I'nited States, both by means of photography and by eye observations, for a pos- sible satellite. On the day of opposition she souths at midnight with a southern declination of 20^ , her apparent diameter being about 1 J". A map of the path during the month will be found in the KinjUsli MirlHinir for May 8th. As Jupiter does not rise till llh. 9m. p.m. on the last day of the mouth, and as none of the satellite phenomena are visible at Greenwich till' after midnight, we defer an ephemesis of him till July. Saturn is an evening star, but is nearing the west so rapidly that he should be looked for as soon as possible after sunset. He sets on the 1st at 3h. 9ni. a.m., with a northern declination of 9^ 27' and an apparent ecjuatorial diameter of 174' (the major axis of the rmg-system being 40|" in diameter, and the minor 3|"). On the 30th he sets at llh. 13m. p.m. with a northerly declination of H^y, and an apparent equatorial diameter of IG'G" (the major axis of tlie ring-system being 38j" iu diameter and the minor 3"). On the 4th lapetus is near his greatest eastern elongation, where he is faintest. On the evening of the Gth Titan is eclipsed by the shadow of Saturn, the middle of the eclipse taking place about 7h. 30m. P.M., and the satellite is again eclipsed on the evening of the 22nd, the middle of the eclipse being at about Gh. 45m. P.M. lapetus is about 3G" north of Saturn on the evening of the 23rd. Saturn is in quadrature with the Sun on the 1st, and describes a short direct path in Leo during June, but does not approach any conspicuous star. Uranus rises on the 1st at 3h. 52m. p.m., with a southern declination of 10° 11' and an apparent diameter of 3-0". On the .SOth he ri.ses at Ih. 55m. p.m., with a southern declination of 10° r, and an apparent diameter of 3-G". He describes a very short retrograde path to the N.N.E. of 86 Virginia during the month. Neptune is invisible. 118 KNOWLEDGE [June 1, 1891. There are iio very woll marked showers of shooting stars in June. The Moon is now at 4h. 2Gm. p.m. on the 0th ; enters her first quarter at Oh. 34m. p.m. on the 1 1th ; is full at rih. llim. A.M. on the 22nd; and enters her last (juarter at llh. IGm. p.m. on the 2Hth. She is in apogee at midnight on tlie IHtli (distance from the earth, 251,225 miles) ; and in perigee at 5h. a.Ai. on the 2Gth (distance from the earth 228,850 miles). The greatest western libration takes place at 3h. Om. p.m. on the 7th, and the greatest eastern at 3h. 17m. a.m. on the 20th. mxinnt Column. l!y W. Mu.NTAGu Gattie, B.A.Oxou. Declining to Dkaw the Losing Trump. THE situation in which it is bad play to draw the losing trump is usually defined m the text-books as that in which one adversary has a long suit established, while his partner holds a card of that suit and also the losing trump. Another and somewhat mure complicated case arises when the holder of the losing trump, although void of tbe estabhshed suit, can lead another suit in which his partner has a card of re- entry. This is illustrated by the following hand — Hand No. 21. Score — Love all. Z turns up the seven of hearts. Note. — A and B are partners against Y and Z. A has the first lead ; Z is the dealer. The card of the leader to each trick is indicated by an arrow. TliICK 1 Z o o Tricks- 0 0 ^^ Y -AH, 1 : YZ, 0. Tricks— AB, 2 ; YZ, 0. Note.— The only diamond Z can have is the eight ; A has the rest, unless B has begun a call for trumps. Thick 4. YZ, ]. Note. — Trick 4. — With trumps declared against him, and an adverse suit already established, Y prefers not to open with his fourth best spade. The fall of the cards shows that Y has the knave of spades. Tricks— AH, i; YZ, 1. Tricks— AB, 5 ; YZ, 1. Thick s. Z Tricks— AB, 5 ; YZ, Tricks— AB, U ; YZ, ?. Note. — Trick 8. — Y retains his trump to ruff the diamonds, in case A should have the ace of spades. After this trick it is clear that A can only bring in the diamonds by winning a trick in clubs. z Thick Hi. Z /' 1*7^ \±I*\ 4> ^ 0 o Tricks -AB. 6; YZ, 3. Tncks—AB. 7 ; YZ, 3. Note. — Trick 10. — If Y now draws the Irump, and A should afterwards be found with the best club, he will make that and the queen of diamonds, and A15 will win the game. Z's only possible spade is the eight ; and, as he can only have one diamond, he must have four clubs, of which one must be either knave or ten. Thick II. Thkk 12. Z ^ Z **^ 4. + [+_ + Y B 4. 0 <> 9 Kt3 would also lose speedily. (r) Preventing KtK2. After 30. . . . RK5; 31. KtK2, KtQ5 ; 32. KtxKt, QR x B ; 33. KtKG, RxP ch ; 34. KKtsq, KRBG : 35. QR4, Black has to waste time in freeing his Bishop. (»•) For QKtS see note (x\. If 31. B x P, PxB; 32. QQ7 eh, EK2 ; 38. Q x Kt, RKKtsq wins, as pointed out in the Daily Neirs. (.,■) 32. QKt8 loses hy PKKt4 ; 33. BBsq ! (otherwise KtB4 followed by PKt5 wins at once), 33. . . . KtB7 ch winning the exchange. (//) Not QxRP on account of ... . RKtu, 34. rB8, BQG ch, and 35. . . . RKt4. (j) Shutting out the Queen for the remainder of the game. Mr. Tschigorin judiciously reserves the capture of the KBP. After the exchange of pieces Black has only one check, for the Queen could sacrifice herself for two Rooks. (1) 35. PQR3 is useless on account of KtB3 (not Kt x KtP ; 3G. P x B, R QRsq. ; 37. Q x R, etc.) (2) A beautiful and unexpected move, which forces a win in a few moves. (8) QKtG is the only move to save the Queen. Black would then mate in six moves. Mr. Tschigorin's play throughout could hardly be im- proved on. The Evans Gambit was also resigned by Mr. Steinitz at the same time. Only one move on each side was made since the publica- tion of the diagram in the May number, viz., 3G. . . . K to Ktsq. ; 37. P to QG. IHiKjrain aj the final position. Black (9 pieces). ■\Vbite (10 pieces). Black ivxii/ns, [For if 37. . . . Q to B5 ; 38. R x P cb, B x R (K x R leads to the loss of the Queen in four more moves) ; 39. Q X R ch, K to R2 ; 40. Q to R5 ch, BR3 (otherwise the Pawn goes to Queen) ; 41. Q to B5 ch ; and 42. Q to K3, winning easily. [ Mr. Steinitz has put his two most recent eccentricities to a crucial test, with an unsatisfactory result. The two defences are not only purposeless, but, as pointed out in the Chess Mimthltj, inconsistent with each other. In the one case Mr. Steinitz moves a piece to a bad square in order to be attacked; in the other case he does the same thing in order not to have the piece attacked. In each case the defence is made more difficult than is necessarv. Theory of the Chess Openinys. By G. II. D. Gossip. (Messrs. W. H. Allen & Co.) This, the author's third treatise on the subject, is the latest contribution to English chess literature. The book is of prepossessing exterior, the brilliant colour of the binding being rendered still more brilliant by a diagram of what is variously described in the introduction as " Mr. Gossip's historically magnificent performance," or, more briefly (but in larger t}^e), Gossip's Brilliant Matk. TTliis is a position taken from a game in the American Tournament of 1889, which, in Mr. Gos.sip's opinion, should have taken the brilliancy prize.] The author has adopted, for the first time, tho column arrangement of variations. The experiment is not altogether a success : the columns appear to have been arranged regardless of natural sequence, and in at least one case have been repeated word for word. The analytical portion of the work is satisfactory on the whole. Perhaps Mr. Steinitz has been too unquestioningly fol- lowed. The author might certainly " venture to ditfer " more often than he does. The work is mainly, as it pro- fesses to be, a compilation from all the modern sources, but much of it is the author's own. Especially noticeable is the adequate treatment of the Vienna opening, several branches of which have been hitherto strangely neglected. The book teems with personal controversy, more entertain- ing than instructive, vindication of capability being the main topic ; but, judged simply from a chess point of view, it is of undeniable value, being exhaustive and thoroughly up to date. The price is extremely moderate, and the printing and binding excellent. Contents of No. 67. The Artificial Keprodnclion of Rnbies antl other Precious Stones. By Vausrban Cornish, B.Sc.,F.C.S The House Cricket. By E. A. Butler Clustering Stars and Star Streams. By J, £. Gore, P.E.A.S What is a Vo'cano ? By the Bey. H. N. Hutchinson, B.A,, P.G.S Notices of Books The Pleiades Cluster, and its Probable Connection with the Milky Way. By A. C. Eanyard Letters.— E. E. Barnard, Eobt. W. D. Christie. W. H. S.Monck The Face of the Skv for May. By Herbert Sadler. F.R. AS Whist Column. By W. Montaifu ttattie, B.A.Oxon Chess Column. By C. I). Locock, B.A.Oxon TEEMS OF SUBSCniPTIOX. •' KNOWI.EDGE " as a Monthly Magazine cannot be reeistored as a Newspaper for transmission abroad. The Terms of Subscription per annum are there- fore altered as follows to the Countries named: 8. d. To West Indies and South America 9 0 To the East Indies, China, &c 10 G To South Africa 12 0 To Australia, New Zealand, &c 14 0 To any address in the United Kingdom, the Continent, Canada, United States, and Egypt, the Subscription is 7s. 6d., as heretofore. Communications for the Editor and Books for Review should he addressed Editor of "Knowledoe," care of DA\'n) Stott, Bookseller, fi7, Chancery Lane, W.C. July 1, 1891.] KNOWLEDGE 121 AN ILLUSTRATED MAGAZINE OF SCIENCE SIMPLY WORDED— EXACTLY DESCRIBED LONDON: JULY 1, 1891. CONTENTS. PAGE Gnats. Midges, and Mosquitos. By E. A. Butler 121 On the Plan of the Sidereal System. By J. R. StTTOx, B.A.Canhih 123 The Experimental Method in Geology. l?y Vmgban C.iTiNi^ii, B.Sf.. F.C.S. 12.5 Flying Animals. By R. I.tpkkkkh, B.A Cantiib. 127 The Companion to ,i Ursa; Majoris ip 1077i. B\ S. \V. Btknhaii 12ii Astronomy as taught by Academy Pictures I2li Birds and Berries. Bv tin- Ri'v. Ai.k.\. .s. \Vu..--mn. M.A.. B.Sc ' VM) Notices of Books . 132 Letters: — W. H. S. Moxck ; E. W. Mauxdeb ; C. LtMi; H. Christopher; H. y, HrTCHixsox; R. C'hahtres 133 The Potato Fungus. By .1. Pentland Smith. M.A.. B.Sf., &<•. 13.-) The Face of the Sky for July. By Herbert Sadler, F.R.A.S 137 Whist Column. By W. JIontago Gattie. B.A.Oxoii. 1.3,S Chess Column. By C. D. Locock, B.A.Oxon 139 NOTICE. " KNowLEiKiF. " is now published from its own oftic-o, :V2V\ llif,'h Holborn, W.C. (nenr to the rml of I'luniceni Lam'). Cheques and Postal Orders should be made payable to Messrs. Witherby & Co., at the above address, to whom all communications with respect to advertisements, sub- scriptions, and other business matters should be addressed. GNATS, MIDGES AND MOSQUITOS.-I. I'.Y !',. A. lirTI.RK. UNDER these names are included a variety of small, delicately constructed flies, the very types, in the insect world, of slenderness, grace, and fragility, lint fairy-like elegance of form is no guarantee of gentleness of disposition, and it is united, in the case of •«*»'(' of these insects, with n persistence and hardi- hood in attack, and a bloodthirstiness of nature, that make them some of the most intolerable of pests. In this country, it is true, we are now, for reasons which will appear later on, tolerably free from annoyance on their part ; but as they are world-wide in distribution, ranging from the tropics to the Arctic zone, there are many less- favoured lands, in which they still exist in countless myriads, and in which their extermination would be bailed, whether justifiably or not, as an unmixed blessing. They form a sub-section of the enormously extensive order of Diptera, or two-winged tlies, an order which is probably responsible for the infliction of a larger amount of suffering and annoyance upon human beings and other vertebrate animals than can be charged upon any other. At least two very distinct types of Diptera may be recognised ; on the one hand, there are stout-bodied and comparatively short-legged flies, with minute and curiously shaped antennae like those of the blow-fly, and on the other, slender-bodied exceedingly long-legged flies, with antenna; of ordinary size and of less extraordinary shape. To the former division (/>'/v;(7i//cf;r( = short-horns) are referred the house-flies and allied insects discussed on a former occasion in our papers on " House-flies and Bluebottles," as well as hosts of others less familiar ; while to the latter {Xt'tnocera = thread-horns) belong a weak-limbed and fragile gi'oup, the daddy-long-legs or crane-flies, together with the numerous kinds of gnats, mosquitos, midges, merry- dancers, &c. (though not the equally, or even still more, fragile May-flies or day-flies). It is with the section Nemocera, therefore, viz. the "thread-horned" flies, that we are now concerned. There is amongst the members of this group a striking variety, both as to habits and life-history. Some, in their early stages, lead an active life in the water ; others, of a more sluggish temperament, inhabit fungi or rotten wood ; others, again, like the notorious Hessian fly, are parasitic on plants, producing gall-like excrescences within which they reside ; while yet others, hke the daddy-long-legs, whose larvfe are the detested '-leather-jackets" of the gardener, live underground, devouring roots of plants as well as vegetable refuse. It might be expected that, with such diversity of habits, there would be correspondingly great differences of form in the adult insects. Such, bow- ever, can scarcely be said to be the case, and thus many that are superficially similar in the adult condition may have passed through their preliminary stages under totally different circumstances. This fact, coupled with the fragile and easily damaged structure, and consequent difficulty of preservation, the obscure colours, and the com- paratively unmarked characters of the perfect insects, makes the nice discrimination of species a very diihcult task, and it is not surprising that the popular judgment has declined this task, and has seen in all these different creatures but varieties for which three or four names at the outside will suffice. Our first business, therefore, must be, as is usually the case in dealing with insects under their popular names, to define our terms, and to say what insects we include and what we exclude, and in what sense we use the terms " gnats, midges, and mosquitos." Without in the least attempting accurately to distinguish species, it may suffice to say that, when we speak of gnats and mosquitos as household pests, we do not by any means refer to all gnat-Uke creatures, nor even to all which would commonly bo called gnats, but only to such as belong to one particular family, the Ciiliridtr, and which, by their blood-sucking propensities, trouble mankind indoors, either in this country or elsewhere. Nor shall we draw any definite line of distinction between gnats and moscjuitos. It is often imagined that mosquitos are creatures confined to warm climates and having nothing to represent them in this country ; but the fact is that the difl'erence between a gnat and a mos(iuito is little more than one ot name. To an entomologist they are practically the same thing ; both are members of the same genus, ( 'itlix. and the difference 122 KNOWLEDGE, [July 1, 1891. is, at the outside, not more than that between closely allied species. It is true that the virulence of the " bite " of these creatures in tropical countries is much greater than it is here ; ;nid, when one remembers the frightful effects that are sometimes produced on the human body by these little pests, and the strenuous efforts that are made, and the elaborate precautions that are taken, whether in the way of oily unguents, of curtains and nets, or even of burying the body in the sand, to guard against their attacks, it is no doubt disappointing to discover that after aU there is nothing so very remarkable in the creatures, and that they can hardly be distinguished from insects ^nth which we are familiar at home. Nevertheless, it is a fact, which we must constantly bear in mind, that the insects to which these names are applied are to all intents and purposes identical both in structure and in life-history, and we are therefore justified in making no distinction here. Moreover, there is no doubt that, even in the matter of virulence, our own gnats vary a good deal, both according to season and to the temperament and sen- sitiveness of the person attacked. "We must not, however, fail to note that there are other flies, belonging to difierent families, that are also blood-suckers, and in some cases are ahnost as troublesome as the true gnats and mosquitos. This is specially the case with the small flies called Simvlia, which are closely allied to the family Culiridn-, and are, it w^ould appear, sometimes called mosquitos in America. Such insects, however, are not referred to here, and what we have to say about " gnats and mosquitos '' concerns only the family CuliriiUe, and, in fact, the genus Cith-.r. Of the term " midges " it is somewhat more difficult to fix the application ; it is indiscriminately used of at least two types of flies, quite distinct from one another, one, in most respects except persecuting powers, similar to the gnats and mosquitos, the other very different in appear- ance, and at first sight more like tiny moths than flies ; but it appears also to be popularly used in a loose manner for small and annoying insects of whatever kind, without any definite conception as to the actual form intended. It is obvious, therefore, that when the entomologist hears people talking vaguely of gnats and midges, it is not always easy to understand exactly what insects are being referred to. With these preliminary precautious, and bearing in mind that not every small, long-legged, fragile fly is a gnat in the sense in which the word is here used — i.e., a blood- sucking gnat — we may now proceed to consider first what sort of being a blood-sucking (jnat or iiios(]>titii really is, referring afterwards to those which seem to be more cor- rectly called iiiidi/is. The photogi-aphs on the accom- panying page will give a pretty good idea of the general form of a gnat. A small head, a considerable portion of which is occupied by the compound eyes, is attached by means of a short neck to a huge globular thorax, so dis- proportionately large as to give the insect, when viewed sideways, a hump-backed appearance. Behind this the trunk is completed by a long, slender, cylindrical abdomen. A long, straight, beak-like appendage, carrying the mouth oigans, points forward from the head, and a pair of more or less tufted, thread-like antennae fonn an excellent head- gear, counterbalancing this above. From the upper part of the thorax spreads at each side a single membranous wing, exquisitely delicate, and gi-acefuUy fringed along its hinder edge ; the place of the customary second pair is taken by the " poisers," long knobbed stalks, as ah-eady described in the other di\-ision of flies, but proportionately much larger than in those. From the under surface of the thorax start the three pairs of inordinately long legs, upon which, when at rest, the body is, as it" were, slung up off the ground, as if on springs. Though the legs consist only of the ordinary parts, yet the divisions seem at first sight to be more numerous than usual, by reason of the great proportionate length of some of the parts, and particularly of the tarsi, or feet, which in the hind pair constitute more than half the entire length of the leg, the leg itself becoming nearly three times as long as the abdo- men. The insect is beautified by the addition, on various parts of the body, of minute iridescent scales (Fig. 1), similar to those of butterflies and moths ; rows of them adorn the wings, especially along the Fig- 1- nervures. A marked difference appears between the sexes. The male can be distinguished by the extraordinary development of the antenn;e, which, as frequently in insects of that sex, are. if one may judge from their structure, far more deUcate organs of sense than those of his mate. The antennre of the female consist of a string of cylindrical joints like long beads, each provided with a circlet of fine hairs of no very great length. Those of the male, however, while similarly constructed, have the brushes much longer and more thickly set, especially at the base, for the extreme tip is almost bare. In the photograph the hairs of the female are indistinct through their extreme tenuity, and the charming symmetry of form and arrangement which those of the male naturally exhibit is unfortunately destroyed because the insects have been preserved in balsam, and it is impossible then to ensure that appendages so dehcate should be spread out with all the hairs in proper position ; no conception, therefore, of their great beauty can be formed fi'om a specimen so preserved. The greatest interest, of course, attaches to the pro- boscis, for herein are contained the weapons of attack. In this, again, the sexes difi'er greatly, and it is against the female only that the charge of blood-sucking can be substantiated. The male is an inoffensive creature, and usually remains in his native haunts, not invading our apartments ; for it must be remembered that these flies, like those treated of before, pass their early stages out of doors and enter our houses only when fully grown. The straight, cylindrical spike projecting from the head, though itself no thicker than a hair, is a tube, or rather trough, terminated by two small fleshy lips, the dwarfed represen- tatives of the two large folding leaves which terminate the proboscis of the blow-fly. This tube represents the labium of the normal insect's mouth, and concealed within it lie the much finer picrciiii/ organs ; for the so- called " bite,'' like that of the bed-bug, consists really of a boring and sucking operation. Along by the upper slit of the trough lies a long bristle-shaped organ, which represents the labrum, or upper lip, and of course all the rest of the mouth organs, except the palpi, he between this and the labium, i.r., in the trough of the latter. The mandibles and maxilla?, which in insects that feed on solid food are efficient biting weapons, are here, as in the bed-bug, replaced by fom- fine-pointed, needle-like bristles, the maxillie being further barbed at the tip like a savage's spear, and the mandibles slightly broadened into a lancet- shaped tip. Besides these, another piercing bristle is found, which is an appendage of the labium itself. Thus there are no less than six boring organs, all contained within a sheath which is itself almost of hairlike fineness. The sheath itself, like so many other parts of the body, is beautifully ornamented outside with abundance of battle- dore-shaped scales. At its base are two short jointed JrtU^ y" Female G-nat oe Mosquito, magnificil almul five diameters. The rod-like projection from the he-nl ix ll:r hiliinm.from irhicJi one of the stiilcts^jyrolMhlii thetahriim.issij>fi,nh,l hinentli ; the other piercinff orr/ans lie within it. The nn',i>i/r .muil Im-ii pirlpi run l/e seen at the //rise of the labium as tiro little ih'rk sirfihs. mi:' nhore.the other heloio. The nervures of the trii/t/s look Ihirk tnni rlitmli/ hecaiise of the senles that lie aloni; them. Tins insert "hites" i.e., siirhs hloud. Male G-xat, magnified about five diameters. The rod-liJce labium is seen as in the female, but the maxillari/ palpi are enormously elongated, and are broadened and f ringed at the tip lii-e twq flubs, above and below the labium. The nntennre are deeply fringed. This insect does not " bite." Lauva of G-xat, magiiilied alunil toi; diametors. The broad head and thorax- are followed b;i the cylindrical liody. in which the dark dii/exlire tube is seen. At the lower end (tail) n branch projects at an angle, carrying within it the main trachea or breathing tube, the entrance to which is at the ex-treme lip on the left. Pvv.\ OF (jXAT, magnified about ten diameters; The tail is furnished with two transparent .steering and swimming ptddle.i, and from the back of the thorax- arise, as two horns, the two :>/)enings to the breathing apparatus (thoracic tpiracle.i). Legs and ii-inqs can be seen folded up under the thin transparent sfrin of th^ lhora.r. MALE AND FEMALE GNAT OR MOSQUITO, with Larva and Pupa, from photographs lent by Newton & Co., of Fleet Street. July 1, 1891.] KNOWLEDGE 123 organs, the maxillary palpi, representatives of the two iinjointed red clubs which are such conspicuous appendages of the mouth of the blow- fly. This straight, unjointed spike is, at first sight, as different as could well be imagined from the elbowed, broad-tipped apparatus with which the house-fly and the blow-fly sip their hquid nutriment ; jet both are but extreme modifications of the same plan, the rasping and sucking elements being carried to the summit of perfection in the one case, and the boring or piercing ones in the other. Many intermediate forms may be seen, as in the drone-flies, breeze-flies, wasp- flies, and others which have no popular names, and a very interesting series showing the gradations might without much difticulty be prepared. Now how is this collection of weapons used ? The little insect drops gently and daintily down on to the spot it has selected for its attack, and the descent of so light and airy a being is likely to leave the victim unconscious of its presence, unless he has actually seen it settle. Then the proboscis is pointed downwards, and the tiny lips that form its tip pressed against the flesh. The bristles withia the gutter-like sheath, being then pressed together into one solid boring implement, their common tip is forced down on the flesh, and as they enter the wound, the trough in which they were lying separates from them in the middle, and becomes bent towards the insect's breast, the two little lips all the while holding on tight. The greater part of the length of the stilettos is then plunged into the victim's flesh, and the blood is drawn up the flne interstices of the composite borer. The wound, though six instruments are concerned in making it, is extremely minute. 8o far, our description has concerned the proboscis of the female gnat or mosquito only. That of the male is somewhat different. There is still the straight stick-like labium, but the palpi are greatly elongated, running along by the sides of the tubular proboscis as far as, or even beyond, its tip, and tufted at the end. A fine rod-like organ may be separated from the labium, but whatever else the insect may have in this way, it does not use for sucking blood, being in fact perfectly harmless. In their earlier life these insects inhabit ponds and stag- nant water generally. The larva and pupa are shown in the accompanying photograph. The former, an odd- looking, big-headed, wriggling creature, swims about head downwards, devouring all sorts of organic refuse in the water, coming to the surface to breathe through the opening at the end of the tail-branch. The pupa also swims about, but with its head upwards, and though active, it takes no food. It requires to come to the surface occasionally for air, which is taken in at the two little projecting horns on the thorax. Fuller details of these early stages and of the entire life-history must be reserved for our next paper. {To be continued.) ON THE PLAN OF THE SIDEREAL SYSTEM. By J. R. Sutton," B.A., Cantab. ANY lines of circumstantial evidence goto show that the Milky Way is a ring-shaped formation, roughly circular in section, one of the most important depending upon the almost obvious connection between the lucid stars lying on or near the galactic belt and the nebulous looking matter of M • Mr. Sutton is at present in South Africa. Hi Kiniburley with a letter iu which ho apuh>Ki/os fn in the ul.acnrc of books of reterem-o. lli-i i.liM> tion of tho belt of i^eut stars with the Milky indeiwudeutly and before he had seen my paper iV 1 jiaper was forwarded from ■ wiifinif ou such a subject wilh regard to the flssocia- NN'iiy were formed eutirely tho May number. — A.C.R. which it consists. It scarcely needs demonstration that all these lucid stars are not necessarily ijidm-tii- (under which term we include all stars actually within the stream, or which, though outside it, are so near as to influence it to an appreciable extent), nor is it Ukely that the relation when it does exist will always be made out. Nevertheless, in many, perhaps the majority of cases, so far as the (optically) extra-galactic stars are concerned, the problem is not a diflicult one for any person ou whom the shadow of -John Michell's mantle has fallen. When- ever, for example, a star or group of stars lies opposite or inside a gap in the profile of the Milky Way ; or whereve. any of its numerous branching lateral offsets terminate in the immediate vicinity of a bright star or star-group, we are entitled to assume, if the doctrine of chance has any credit at all, that these stars are intimately associated with, if they are not the agents which have determined the conformation of the stream, and they may therefore be considered a part of it. When we come to deal with the stars optically upon the stream the problem is not quite so simple. Such stars may be either within the stream or without it, and, if the latter, may or may not be galactic. We know that the parts of the sky traversed by the Milky Way contain very many more bright stars than would be the case if the stars were uniformly distributed over the whole celestial sphere ; and Probability interprets this to mean that the chances are enormously against a general dissociation between the two. This, however, is not exactly the same as provini/ a relationship. If it were, it would mean that all, or nearly all, the stars so situated are galactic. On the contrary, although the statement may be true in general, it is not possible to indicate at random any star or star-group as therefore forming part of the Milky Way. Such details have to be decided independently, from particular and not from general considerations. The only instances we can be tolerably sure of are those (1) in which a stream of lucid stars and a nebulous streamer branch out together from the main course of the Galaxy, and turn to the right or left up to the apex of either with- out parting company ; (2) in which a star or star-group lies in the midst of a small dark space surroimded by fields of normal brightness ; and (8) in which stars are seen significantly mixed up with clustering aggregations of nebulous matter. In all cases of this nature there is no reason to doubt that the Galaxy and the lucid stars are mutually dependent. There is no necessity just now to discuss these points at any greater length ; that has been done elsewhere. They have been introduced, in brief, simply to indicate the principal lines of evidence made use of in the attempt to prove the rmg-fonn of the Milky ^^'ay, and to avoitl con- tinual repetition iu the course of this tliscussion. It is clear that some of the clusters in the Milky Way might be streams of stars seen in projection. Suppose an observer to select some star-group lying at the extremity of a straight galactic streamer, and then to take up such a position iu space that his line of sight should pass through the group and along the axis of the streamer. If the streamer be supposed dinded into sectional lamime of the same thickness, these, taken singly, would be of the same intrinsic brightness however far off they might be ; and in the case of a cylindrical stream their apparent size would vary inversely as the square of their distance from the observer. Hence the streamer would have, from the assigned position in space, the characteristics of a close globular cluster, its brilliancy decreasing gradually but rapidly towards its edges. Moreover, the lucid star-group at its apex would be pro- 124 KNOWLEDGE [July 1, 1891. jected into it, anil so help to increase the impression of its beiuK globular. The obvious inference is that we are unable to decide oft'-liand whether any single chister is really a cluster or a drift of stars. But such a theory with regard to the many clusters lying on the Milky Way would involve the existence of many straight streamers radiating towards our sun. If the Milky Way is a ring, and the sun occupies a central position, this might be possible, and the theory is supported to some slight extent by the behaviour of those apparent clusterings in the field of the Milky Way, whose brightness increases not towards their centres but from one side to the other, the magnitudes of the larger stars upon them following the same order. This is exactly what should happen in the case of a spicular projection diijhth/ inclined to the line of sight. Other instances having the same tendency will readily occur to the student. But if any of the apparent clusterings are streaming appendages seen in perspective, we are met at the outset by the ditliculty that none of them are so bright as we should expect; reasoning merely from first principles, their brightness is evidence enough that their length (if length they have) is small in comparison with the great arm stretching from Cygnus to Ophiuchus. The nebulous clouds in Aquila would cer- tainly be darkness itself contrasted with the condensed brilliancy which would be exhibited by the spur in Scorpio to an observer situated on its produced major axis. In- deed the conspicuous cluster in the sword handle of Perseus offers the only possible comparable example, and not altogether a good one either. It is necessary, then, to give up the assumption that any great galactic drifts lie within the space enclosed by the Milky Way, and pointing towards us. This may tend to shake our faith in a ring-form theory of the Milky Way — indeed in any of the present theories of its structure based on its streamy nature, such as Proctor's spiral theory ; furthermore, according to ths same reasoning, it seems probable that the great branch reaching to Ophiuchus, and the meanderings in Scorpio, are what they give the im- pression of being, namely, at approximately the same distance from us, and therefore parallel to the main course through Aquila and Sagittarius. We shall, however, have presently to consider this matter in another light when speaking on the probable position in space of the great appendages in Perseus and Cepheus. And incidentally we shall have reason to point out that the Milky Way is by no means obviously a stream of stars nf all si-e.s. Any theory which could account for the extraordinary evenness of outline of the Milky Way would have much in its favour, and this a ring theory has, as well as the spiral stream theory. It is curious that the assertiveness of the Milky Way among the stars has always been tacitly recognized as a sign of its importance. Thomas Wright thought that its brilliancy represented the greater depth of the universe in its plane ; and the two Herschels followed suit with different degrees of scepticism notwithstanding John Michell and his mathematical formul*. Proctor thought that the Milky Way was a stream of stars of all sizes, all those scattered over the rest of the sky being in a sense sporadic, and not of any particular moment in modifying what he thought to be the architecture of the universe ; and it must be admitted that his reproduction in one photograph of Argelander's forty charts might well seem to be very substantial grounds for the idea. But although it is true that the Milky Way is richer in lucid stars than any area of equal size outside it, it is not true that it is the richest ijieat-cinnlnr hdt of the sky. That distinction is claimed by a belt arranged about a gi'eat circle through Cygnus, Perseus, Taurus, Orion, Crux, and Scorpio. Besides, the stars lying within it offer the clearest example of a star-stream it is possible to conceive. That it is a real star-stream is suggested first of all by its undeviating direction. A person standing under Orion will have overhead a most imposing arch of stars, springing with perfect symmetry from the horizon on either hand in t'rux and Perseus without anything that can be called a break. Moreover, it passes across an exceedingly dark part of the sky. Below the horizon on the one hand it can be distinctly traced as far as £ and !; Ophiuchi, where it seems to end, on the border of an empty space, sending out, meanwhile, a small arm from Crux, along the main course of the Milky Way as far as u Sagittarii. In the same way, and as easily, we can trace the other continuation of the arch through Perseus, Cassiopeia, Cepheus, Cygnus, and Lyra almost or quite to a Ophiuchi on the other side of the empty space mentioned above. This end also sends out an arm in the direction of Aquila apparently as a feeler for the star. In one respect the great star-belt offers a curious analogy to the Milky Way : both are cut completely across, one in Ophiuchus, the other in Avgo ; and both spread out fan- wise on either side of the respective gaps, and to complete the resemblance, just as the nebulous magellanic clouds lie off, though having no defined connection with the gap in Argo, so do the apparently free star-groups of Ursa Major and Hercules lie off' the gap in Ophiuchus. Still these facts only suggest, and do nothing to prove, that the great star-belt actually marks the course of a real ring of stars in space. But there is a class of facts, well worth examination, which seems to place the matter beyond doubt. First, then, if we trace the course of the Milky Way from Auriga through Monoceros we shall find it the most tame and unexciting object imaginable. It is as monotonous as an unvarying brightness can make it. With the solitary exception of /3 Tauri, no star of any magnitude occurs until we come to Argo, in which constellation the Milky Way and the great star-belt intersect at a very acute angle, so that the two are prac- tically in company for a considerable space. Here there is a sudden metamorphosis : from being regular and unbroken the former becomes torn up into indescribable confusion — torn into ribbons so to speak, and it is pretty- clear that the stars are the agents effecting the disrup- tion, as we have shown elsewhere. For here we get all the associations referred to in the first two paragraphs of this article. Parting company with the stars (in Sagit- tarius) the Galaxy resumes very nearly its even outline and untroubled aspect until it intersects the star-belt again in Cygnus. Here the same phenomena of disrup- tion recur. Furthermore, there is not a galactic off"-set of any size worth mention, whose shape, direction, and aspect are not determined by the stars in the great star-belt. The streamer in Perseus lies directly along, and that in Cepheus, across it. Those in Ophiuchus and Scorpio bend equally towards it. Indeed, the Milky ^^'ay itself, between Cams Jlajor and Sagittarius, seems to have a decided double -warp of the same nature : curving round from either constellation perchance to come sooner into the plane of the star-belt. The spreading finger-shaped pro- jections, facing each other across the gap in Argo, illustrate very forcibly the predominance of the latter in this respect. Lastly, the area covered by the Milky Way is rich in lucid stars, because it crosses the richest parts of the star- belt. The conclusion seems to be emphatically forced July 1, 1891.] K N O ^A/^ L E D G E . 125 upon us that the great-star-belt is a genuine girdle of stars in space ; in which, also, the foundations of the sidereal system are laid, the MilUy Way being an appendant to it, of lesser rank. In short, the most noteworthy arrange- ment in the architecture of our universe seems to consist of a great ring of large stars intersecting an equal ring of small ones at the extremities of a common diameter. Let us recapitulate the evidence : To start with, we have the probability — shall we say certainty '? — that the Galaxy is a ring-shaped structure, having, as we sought to show, no great branches in its own plane. Next, we have the significance of an almost entirely isolated, symmetrical belt of bright stars (stars singularly uniform in magnitude and distriliution) encircling the whole heavens, and cutting the Milky \\'ay in two exactly opposite parts. Then we have the striking suggestiveness of the disturbed state of the Milky Way in these parts, coupled with its evenness both in outline and aspect elsewhere. Lastly, we have the evidence derived from the aflfiuity between the Milky Way and the stars in the belt ; the galactic off-set in Perseus lying along the direction of the belt, the stellar off-sets from Cygnus to Aquila, and from Crux to Sagittarius, lying along the Milky Way ; the galactic streamers, more- over, in Ophiuchus and Scorpio, nay, even the main stream of the Milky Way, turning aside to the star-belt just where the greatest angular distance separates them. The double-ring structure enunciated above dovetails in with all these points ; indeed, it seems the only logical deduction from them. Both Sir William Herschel's hypothesis of an even distribution of stars throughout our stellar system, and Proctor's spiral theory, fail utterly to account for the fact of a zone of bright stars associated with, but differentiated from, a zone of small ones in the manner observed. Further than this, the theory of a double-ring furnishes us with a rational explanation of the conspicuous absence of streamers round the interior face of the Galaxy, for it tells us where a powerful extraneous force is to be found counteracting altogether the action of the Milky Way upon itself. THE EXPERIMENTAL METHOD IN GEOLOGY By Vaughan Coknish, B.Sc, F.C.S. THE record of the investigation of a geological problem may generally be divided" into two parts, the descriptive and the explanatory. A rock, for instance, is described according to its mode of occurrence, structure and mineralogical composi- tion ; then follow deductions as to the epoch at which it was formed, and the mechanism of the actions by which its particular characters have been produced. This, as a rule, marks the limit of the geologist's investigation of such a problem ; seldom, far too seldom, are the conclu- sions submitted to the decisive test of experimental methods. This lack of the confirmatory evidence of experiment makes a large part of the literature of Geology very unsatisfactory reading, the deductions being too often either indefinite or inconclusive. In the present article \vc give a sketch of some of the efforts which have been made to raise Geology to the rank of an experimental science. In the last years of the eighteenth century a controversy raged between the schools of Huttoii and of Werner as to whether heat or the action of water had been the dominating influence at work in the formation of the rocks of the earth s crust. By wliat agency, for example, had chalk been converted into limestone or marble ".' How can this have been effected by heat, said the school of Werner, since heat decomposes carbonate of lime, expelling the carbonic acid ? The answer to this question was furnished by the experiments of Sir James Hall, " ()n till' iictii/n of livdt IIS iiiiiilijicil III/ pressure." Chalk was heated in a gim-barrel, the end of which was firmly closed. Under these conditions, the pressure in- creasing as the temperature is raised, the carbonic acid is not driven off from the carbonate of lime, the change induced being not chemical but physical, the powdery non-coherent chalk being converted into a compact crystal- line mass, having all the characters of limestone, or of marble. Hall also investigated another problem connected with the same controversy. Hutton maintained the purely igneous origin of those rocks which have characters similar to the modern lavas. It had, however, been noticed that if a piece of a crystalline rock were melted in a crucible it was not reproduced on cooling, but that an uniform glassy mass was formed. By a judicious com- bination of the methods of observation and of experiment, Hall obtained important evidence as to the conditions of crystallisation of rocks. He observed during eruptions of lava that a great part of the crystallisation of the con- stituent minerals took place slowly, and by degrees, during the gradual cooling of the mass of molten rock. Basing a method on this observation, he melted various rocks in graphite crucibles, and maintained the materials in a state of fusion for a long time, taking care that the temperature should be somewhat above that necessary to melt the glassy mass. Crystals gradually formed, and a crystalline rock was reproduced, of which the melting point was higher than that of the glass formed in previous experiments, where the cooling had been rapid. Similar experiments were conducted about the same time (1804) by Gregory Watt. They were on a larger scale, a reverberatory furnace being employed in place of a crucible. The molten material was only allowed to cool with extreme slowness. From time to time samples were withdrawn and examined after solidification. Those in which the anueaUng process had 1 continued longest were the most perfectly crystalline, and i possessed the highest specific gra%'ity, just as a natural crystalline rock, such as granite, is denser than a glassy rock (('.;/. obsidian) of the same chemical composition. These early experiments elucidated several important points with regard to the processes which have taken place in the formation of the eruptive rocks. The products obtained were, however, at most very imperfect reproductions of the natural rocks, and the methods for the determination of mineral species were at that time too rough to allow of the identification of the small and imperfect crystals obtained. Before the date (18(56) of the next important experimental research on the formation of rocks by igneous fusion, the application of the microscope in petrological work had effected a revolution in this respect. A slice of rock, so thin as to be transparent, reveals to the microscope the outline, and even the internal structure, of the minute crystals which form its groundworli or /'"«•. The crystal of each mineral species shows its characteristics of form, the particular angles at which its faces are inclined to one another, and the lines developed in the process of grinding the thin section which indicate the directions of cleavage. Not less important in identification are the optical characters which determine the tints which different parts of the field of view assume according as the polarised light passes through the plate of one or other of the minerals of which the rock is composed. The refinements of optical analysis enable the identification of the species to be made with certainty even in crystals of microscopic size. .\t the date to which we have referred, M. Daubree published his experi- 126 KNOWLEDGE [July 1, 1891. raeuts on the reproduction of the roclcs of a certain class of meteorites. The meteorites being melted and kept for some time in the liquid condition, the constituent minerals befjan to crys' illise out, and finallj-, after slow coolin,<,', a rock was produced having the same constituent minerals as the original meteorite. Almost the only difference between the meteorites and the artificial products was the absence in the latter of that hreccititcil structure which IVccjucntly characterises an eruptive rock which has under- gone violent mechanical strains. By the employment of the modern refinements of microscopic and of chemical analysis, Daubree was able to establish the absolute identity of the minerals contained in his artificial products with those of the meteorites. The class of meteorites for which the method of reproduction was found successful were those containing the smallest proportion of combined silica, characterised by the presence of olivine and augite and by the absence of the feldspars. Except for the presence of metallic iron, the mineral composition of these meteorites is very similar to that of what are termed the ultra-basic rocks, i.e., those the analysis of which shows the smallest proportion of silica. Many basalts and other lavas come under the category of ultra-basic or basic rocks. Observational evidence appeared, however, to favour the view that these rocks had not been produced by the purely igneous method employed by Daubree, but that the action of water had played an important part in their formation. It was in 1878 that MM. Fouque and Levy commenced the celebrated research in which they showed that the more basic eruptive rocks can be reproduced in every detail of mineral composition and structure by the action of heat alone without invoking the aid of pressure, or the inter- vention of water or any other substance not forming a constituent of the rock. To appreciate the details of their method it is necessary to make clear the guiding data which were furnished by the study of the minute structure of rocks. Some eruptive rocks are entirely composed of an aggregate of perfectly crystallised minerals. One or more of the constituents (in granite, the quartz) may not show crystalline faces; they have presumably solidified last and have been compelled to mould themselves round the crystals already formed, but their structure is completely crystalline, as is shown by their action on polarised light. Other rocks differ from the holocrysfalline in that the crystallised minerals are imbedded m a vitreous or glassy matrix which scarcely affects polarised light. These rocks are classed, from the character of the ground mass, as glassy rocks. The most common structure of eruptive rocks is that of the third class, of which the ground mass has begun to crystallise before solidification, but the crystallisation has only gone as far as the produc- tion of iiiicniUths. These are crystals of small size, most frequently microscopic, which are so far developed that the determination of their species is readily effected. They are seen to be grouped round the larger crystals of the rock in a manner plainly indicating their later formation. It appears reasonable to suppose that the microliths are formed during and after the welling up of the rock, whilst the formation of the large crystals may be referred to a previous epoch before the disturbance of the fluid mass from its subterranean position, when a condi- tion of calm fusion favoured their growth and develop- ment. The temperature at which they were produced must be supposed to be higher than in the case of the microliths. Between these two epochs of crystallisation comes the eruption, during which the older crystals may be rounded, worn, or broken by shock. Hall had shown that to obtain a crystalline structure instead of a glassy mass, it was necessary to keep the material at a temperature slightly above that of the melting point of the glass ; but if, as appeared probable, the minerals of the different epochs of crystallisation did not possess the same degree of fusibiUty, it would bu necessary in order to reproduce this association of minerals to maintain the materials at a series of tempera- tures successively decreasing. The result of the final opera- tion might be expected to be the solidification of a mass of microliths of the more fusible minerals cementing together the larger crystals already formed. Such was the method employed by Fouque and Levy, and the result was in com- plete accordance with their expectations. As an example of their work, we will describe the reproduction of a basalt precisely similar in character to certain basalts found in the Department of Auvergne. A mixture of substances pre- pared in the laboratory of the same chemical composition as the rock was placed in a platinum crucible, which was maintained at a white heat for forty-eight hours. A sample taken out at the end of this time, and allowed to cool rapidly, showed on solidifying crystals of olivine imbedded in a brown coloured glassy matrix. At the end of the first forty-eight hours the position of the crucible in the furnace was changed so that the temperature was lowered to that corresponding to a bright red heat, at which it was kept for a second period of forty-eight hours. The product obtained at the end of this time showed the crystals of olivine as before, but imbedded not inaglass but inamatrix composed of microliths of augite and of soda-lime feldspar. Among the other rocks reproduced was a leucite-lava, the crystals of leucite having rounded angles just as in the natural rock, showing that this pecuUarity is not necessarily due, as had been supposed, to the effects of disturbance after the first epoch of crystallisation. The rocks produced by the methods we have described are of the same character as those formed in the volcanic eruptions of the present time, which belong to the class of the more basic rocks. The more siliceous rocks, such as granite, which contain free silica in the form of quartz, do not appear to be formed under the conditions obtaining in the eruptive processes which geologists have been able to observe in actual operation. When the materials of the acid rocks are subjected to the processes above described, the minerals which crystallise out are not those of the original rock, but are of different crystalline form, even when they have the same chemical composition. The excess of sihca remains in the imcombined state, but has characters resembling those of the variety Iniown as tridymite rather than those of quartz. The acid rocks and their characteristic minerals (as quartz potash- feldspar and soda-feldspar) have doubtless been formed by processes radically different from that of simple fusion. The minerals above mentioned have been reproduced by the reaction of suitable materials in the presence of water, at a high temperature and pressure. Hitherto it has not been found possible to produce the compacted associa- tion of these minerals which constitutes an acid rock. Sufficient data have, however, been obtained to justify the belief that at no distant date the jiroblem of the mode of formation of this class of rocks will be solved by the experimental method. One of the most important contributions to experimental geology during recent years, is the discovery of Spring, that pressure is capable of inducing chemical change independently of its effect in raising the temperatm-e of bodies. This discovery has a direct bearing on the phe- nomena of mctaiiwrphism, or the bodily conversion of sedimentary rocks into others of a completely different character. Spring has sho'wn, that by the application of great pressure, chemical combination is induced, in cases where the comijound occupies a smaller volume than the components, and conversely that a decomposition is brought July 1, 1891.] KNOWLEDGE 127 about by pressure, when the volume of the bodies formed by decomposition is less than that of the compound. Briefly, pressure brings about such chemical changes as are accom- panied by a contraction. The apparatus employed in these experiments consisted of a small steel chamber, in which the substances were placed, furnished with a piston worked by a powerful lever, provided at the end with a heavy weight. If the piston were forced down rapidly the substances would be heated, and it would be impossible to discriminate between the changes due to rise in temperature and those due to increased pressure. In Spring's apparatus the lever is lowered very gradually, its descent being regulated by a finely cut screw. The steel chamber is surrounded by water, in which is placed a dehcate thermometer, and the descent of the piston is operated so gradually that there is practically no rise of temperature. These experiments aflbrded the first example of the direct conversion of mechanical work into chemical energy. As a last example of the application of experimental methods in Geology, we will deal with some of the problems presented by mineral veins. The cracks and openings by which rocks are traversed are in some cases unfilled, in others they contain debris of the rock itself, and lastly, they are sometimes found filled with foreign minerals, and are then known as mineral Veins. Most of the fine well- crystallised minerals which adorn museum collections come from mineral veins, or from ca\dties in rocks, known as " geodes." Tin veins, for instance, contain the oxide of tin, cassiterite, in large well-formed crystals. Others contain oxide of iron, also well crystallised ; and another class con- tain the metallic sulphides, such as galena, the common lead ore found in Derbyshire and elsewhere. The processes by which these minerals have accumulated in the veins, and the mode m which their crystallisation was induced, long remained a mystery. In studying the characters of tin veins, Daubree was struck by the constant presence of minerals, such as apatite, topaz and tourmaline, which contain the elements chlorine and fluorine. It is known that the chloride and fluoride of tin are volatile, and that these compounds are decomposed by water, the hydrogen of the water forming hydrochloric or hydrofluoric acid gas and the oxygen combining with the metal. Experiment showed that if the vapour of water be brought in contact with that of chloi-ide of tin at a fairly high temperature the oxide of the metal is formed in crystals, having all the chara//., claw of thumb; m.c, metacarpus; /j/i", L'lul. ord, 4th, and oth fingers. relatively slender and considerably more elongated than usual. The thumb remams comparatively small, and ends in a claw ; but all the other fingers — more especially the third or middle one — are enormously elongated, so that the third, fourth, and fifth, which have no claws at the end, are absolutely longer than either the fore-arm or the arm. Between these elongated spider-like fingers the wing-membrane is stretched, the whole structure per- mitting of the wing being folded, when at rest, in the manner familiar to all. A comparison of Fig. 3 with Fig. 2, or, still better, with the figure of the skeleton of a Pterodactyle, given in the article on Flying Dragons, will .show how essentially the wing of a Bat difi'ers from that of a Pterodactyle. As we have said, the single finger sup- porting the wing-membrane of a Pterodactyle corresponds either with the one marked i or tliat marked rt in Fig. 4 (probably the latter), and it may therefore be said that while a Pterodactyle files with one finger, a Bat fiies with its whole hand. Equally marked is the ditt'erence between the wing of a Bat and that uf a Bird ; the latter having only the first three fingers of the Bat's wing developed, and all of these being strangely modified from the ordinary form, while the chief elongation has taken place in the bones of the arm and fore-arm, instead of in those of the fingers, and Hight is efiected by the aid of feathers instead of by a membrane. This completes our survey of the various modes of Hight obtaining in the aiiiuiiil kingdom. In it we have indicated the dilVercnce between spurious and true flight, have shown how the former is but an extreme development of the long leaps taken by arboreal animals, and liave suggested how it may have gradually passed onwards into true Hight. AVe have also seen liow the wings of the Invertebrate animals differ in tuto from those of tlu' \'ertehrates ; while among the Vertebrates true Hight luis been independently deve- loped in three distinct groups — Pterodactyles, Birds, and Bats — on totally ditt'erent structural lines; the latter instance thus allbrding us an excellent example of the way in which difi'erent groups of animals may be variously modified to occupy the same position in the realm of nature. The supersession of the Pterodactyles by the THE COMPANION TO « URSvE MAJORIS (/8 1077). By S. W. BURNHAM. THE close companion to a Ursiie Majoris, which was found with the 30-incb refractor in the early part of 1889, has now been measured each year since that time. These observations show clearly that the companion is moving round the principal star in a retrograde direction, and that the two form a physical system. The proper motion of a is not large (0'144" in the direction of 240-.5°), but it is sufBcient to show in the measures of so close a pair, even in the two years covered by the observations. The following are the measures down to this time : — 18H9-19 32G-1° 0-91" ^3 4n. lK90-2(i 320-1° 0-87" ft 4n. 1891-3() 31()-H° 0-80" ft 4n. It is not unlikely that it may prove to be a rapid binary, and that the distance is now about maximum. In that case a more rapid change in the angle may be looked for soon. It is easily measured with the large telescope when the conditions are good, but with a distance of one-third, or even one-half that given in the measures, it would probably be a severe test for the SG-inch. So far as I know it has not been seen anywhere else, though some of the large refractors ought to show it. I hope to measure it regularly each year for some time to come. Lick Observatorv, Jiotc 2,n