give bey ty g peat THO A shew ANS, fi ia virat gt q «3 RGR, Satan a6} Ve yn bene ne Mee | Sta T PAA SNe atta %. SORA SN hie CN i A i se why \ * te 4 oe 408 \ Were ty ee he Aes a) : ny Sais Ove y a bn ‘, M Sis P atitwt BA ersivetr ts Sh i * Nave Seton ae tee Peters i Steichen Bee ans oé Shee kas . oh 8 az a apt hy aot SOO aeaa ews ty BORER om sees estas PT Rea pisos ake Se ocaes ISSN ER anion ante : ae iat 7 ‘pater ae asm eae Sek She EAN = aor NaS, gg nk WSO ON te Someries Fer rea eet Se he PIAA AY oy peatate Met he oni Te peg OS cant i ak ot Har PE Se ee ars ! eae Le IIEh Rene ie rae one | imei ir ie pep Me pager ig ay ropes we ees hae pe AaaY aantee Feit ALAN e ioe $ a airy = Beans pl 1 se : ¢ } shila aera eer. ¥ hrncnrere Re ak Renta Se gan ee oF vey : oP eed han 6a ; EES STE oper eree Vee; on, f } : ai honb PBEEE. toe Plier Von ee wees Snguncnrey, SOT E Fier hae Me 2G 2% aFh be eA Tae nie eet Poetic’ ou Une PALF ae Bite toes aor sabes A bce Piha Sepee wkeryt eae f , ae MN z 1 * eS Sea Wego i ¢ opie ob ee Te eee mH ‘ r F / ey Fred “r Pit tet anes Tey freer nee i é ; fae 5 © PE cope Pen ee, a6 oe ‘ traci mis a gla Bhat g ta seee renee aE rar aon Atel nego g MP eS (ar rites Pwr ka 4 ie elena ; ise sae a done yer veer iy Pe Death : iptcirteraia ne yh +t ty ny Fe rf ie" Oe Lae eee Digitized by the Internet Archive in 2009 with funding from University of Toronto http://www.archive.org/details/transactionsO1camb th > TRANSACTIONS CAMBRIDGE \~ PHILOSOPHICAL SOCIETY. ESTABLISHED Novemser 15, 1819. —<—— VOLUME THE FIRST. CAMBRIDGE: PRINTED AT THE UNIVERSITY PRESS, AND SOLD BY DEIGHTON & SONS, AND NICHOLSON & SON, CAMBRIDGE; AND T. CADELL, STRAND, LONDON. M.DCCC.XXII. 613407 Ae SS OFFICERS ann COUNCIL OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY, ELECTED May 22, 1821. PATRON : His Royal Highness the Duke or Gioucester, Chancellor of the University. VICE-PATRONS - The Eart or Harpwicxe, K.G. High Steward of the University. The Vice-CHANCELLOR. a PRESIDENT: The Very Rev. J. Woop, D.D. Master of St. Jolin’s College, and Dean of Ely. VICE-PRESIDENT: | Rev. E. D. Cuarxe, L.L.D. Jesus Coll. Professor of Mineralogy. TREASURER : Rev. B. Brince, B.D. Fellow of Pet. Coll. SECRETARIES : Rey. G. Peacock, M.A. Fellow of Trin. Coll. J.S. Henstow, M.A. St. John’s Coll. ORDINARY MEMBERS OF THE COUNCIL: Rey. R. Gwarxin, M.A. Fellow of St. John’s Coll. F. Toacxeray, M.D. Emmanuel Coll. W. WHewe t, M.A. Fellow of Trin. Coll. Rey. J. Cummine, M.A. Trin. Coll. Professor of Chemistry. Rey. S. Lez, M.A. Queen’s Coll. Professor of Arabic. Rey. T. Hughes, M.A. Fellow of Emmanuel Coll. Rey. T. Cuevatuier, M.A. Fellow of Catharine Hall. THE COUNCIL. VICE-PATRON, elected Nov. 26, 1821. His Royal Highness the Duke oF Sussex. VICE-PRESIDENT, elected March 25, 1822, in the room of Dr. E. D. Ctarxe, deceased. Rey. T. Turron, B.D. Fellow of Catherine Hall, Lucasian Professor of Mathematics. ADVERTISEMENT. Tux Society as a body is not to be considered responsible for any facts and opinions advanced in the several Papers. which must rest entirely on the credit of thew respective Authors. XIII. Il. XII. CONTENTS OF Vot. I. Parr I. —-_ - ON Isometrical Perspective: by Professor FARISH..-............--. 1 On certain remarkable Instances of deviation from Newton’s Scale in the Tints developed by Crystals, with one Axis of Double Kefrac- tion, on exposure to Polarized Laght: by J.F.W. Herscue., Esq. 21 On the Rotation impressed by Plates of Rock Crystal on the Planes of Polarization of the Rays of Light, as connected with certain pecu- liarities in its Crystallization: by J. F.W. Herscuen, Esq. ...... 43 On the Chemical Constituents of the Purple Precipitate of Cassius: by Dr. E. D. CrarKe. " 58 Observations on the Notation employed in the Calculus of Functions: pC ao PABBMEm, KESAT m... < cROLYS Nase aeRO UIE ies oe 63 On the Reduction of certain Classes of Functional Equations to Equa- tions of Finite Differences: by J. ¥.W. Herscuet, Esq. ......... 77 On the Physical Structure of those Formations which are immediately associated with the Primitive Ridge of Devonshire and Cornwall: by they-' Proiesor SE DG WIER® 0292 MY Sey. & al OMe oc 89 On the Laws according to which Masses of Iron influence Magnetic INebdtes bgt Ss. EV te Hk Stee Eglo \5. Ae Yas He Se. ..1 147 An Account of some Fossil remains of the Beaver, found in Cambridge- SE 0a SOOKE, VESTS No So Ae, OEE ie oot UR, 5 175 On the Position of the Apsides of Orbits of great Excentricity: by Wi Wither ok, Pisq nae ae oe od SNS SOT aah 179 On a remarkable deposit of Natron found in cavities in the Tower of Stoke Church, in the Parish of Hartland, in Devonshire: by Dr SEA Ae rset eee, Me ee esses mc gmeds 193 Vou. I. Parr If Analysis of a native Phosphate uf Copper from the Rhine: by BESOIN Ny) ESCpmeMes Fact bart) Siren es cass Se de cin clasc's ss fataalees 203 Upon the regular Crystallization of Water, and upon the form of its pranary crystals: ‘by Dr. E. D.CLARKE...... 000000000 c0scene 209 XIV. XVI. XXXVI. XXVILI. XXVIII. Contents, Vou. I. Parr II. PAGE On the Application of Hydrogen Gas, to produce a moving Power in Machinery; with a description of an Engine which is moved by the Pressure of the Almosphere upon a Vacuum caused by Explo- sions of Hydrogen Gas and Atmospheric Air: by Rev. W. Ceci . 217 On a remarkable Peculiarity in the Law of the extraordinary Refrac- tion of differently coloured Rays exhibited by certain varieties of Apophyllite: by) Jee-aVVin tl BES CHET Esa ferso sie ae. se a 241 Notice of the Astronomical Tables of Mohammed Abibeker Al Farsi, two copies of which are preserved in the Public Library of the Uni- versity of Cambridge: by Rev. Professor LEE.....--.--.... .+---. 249 On Sounds ercited in Hydrogen Gas: by Professor LESLIE .......... 267 On the Connexion of Galvanism and Magnetism: by Rev. Professor CUMING? 25) Seer Ser ae eee eee nee nays fer ane Pn 269 On the Application of Magnetism as a Measure of Electricity: by Rev. (erofesson CUMMING 265). is foe ae ae RS eee ss 281 A Case of extensive solution of the Stomach by the Gastric Fluids after IDYRRTGS Un] WONG LEW ARAN) oagSans505 G05 256-6 nao s Oke sa heRe oa 287 On the Physical Structure of the Lizard District of Cornwall: by Rev. Professor SEDG WICK .ais...ssucduoes eee ee eee 2901 On Double Crystals of Fluor Spar: by W. WuEweE tt, Esq......... 331 On an Improvement in the Apparatus for procuring Potassium: by Reve, We MaNiDpEnnhiess.. Sekt es ree. Se SE oy eh 343 Notice of a large Human Calculus in the Tibrary of Trinity College : by Rev. Professor CUMMING <. 00 -- 22 - <3 255092 Se ween nine = on 347 On a Dilatation of the Ureters, supposed to have been caused by a mal- formation of their Vesical Extremities: by J. Oxes, Esq. ........ 351 Geological Description of Anglesea: by J. S. HENsLow, Esq, ...... 359 Some Observations on the Weather accompanied by an_ extraordinary Depression of the Barometer, during the Month of December 1821: Gy) Rev. Joa cuSmOn sacs «noe anes oie fom ie oo eee Oe 455 Extract, from the MinttenBo0k <50/..25 «s\5+ i500 “ly «918 eae ee Tsetiof Donations to the Vabrary cies. «00s «= os «+ «0.00! eeaeeeneets = eee ——————— Museum...... 2... cece cece cece neee 461 Gentriaheditilem sacs cee Re ch ceeds es lo ena 465 PREFACE. A. prier statement of the circumstances which led to the formation of THe Campripce PuxiLosopuicaL Socrery may not perhaps be thought an improper introduction to this first part of its Transactions. The various departments of Mathematical and Philosophical Learning have long occupied a distinguished place in the system of Education adopted in the University of Cambridge; and a successful cultivation of them has on all occasions been rewarded with the highest Academical Honours. Hence, as might naturally be expected, men, eminent for their proficiency in those branches of learning, have never been wanting im this University. Of those who have been thus trained to habits of accurate investigation, not a few have endeavoured to direct the principles of science to practical purposes ;— have applied those principles in the manner in which they might be the most beneficially applied —in strengthening the foundations, and in extending the boundaries, of Physical Knowledge. a2 IV PREFACE. Many productions of persons thus connected with the University have, at different times, been received with approbation. There is, however, reason to believe that many other works — deemed perhaps by the authors of them not sufficiently considerable for separate publication, but yet replete with important information—have been suffered to remain unknown; and that many observations, the result of careful inquiry, have been imperfectly recorded. Under these circumstances, it was thought that great advantages might be derived from the establishment, in the University, of a Society, the main object of which should be the advancement of Natural Philosophy. By the formation of such a Society, new facilities would be presented for the communication of know- ledge: and thus, many ingenious Speculations on Philosophical subjects would, in all probability, be drawn from obscurity; and, by means of the Volumes of Transactions which the Society might occasionally publish, be effectually preserved, and recommended to the attention of the world. When, moreover, it was considered, that there are resident in the University many students, who, after completing with honour to themselves that course of reading which has been laid down for them, have both leisure and disposition for more extensive researches — it appeared highly desirable to excite, among persons so well prepared for mental exertion, a common interest in the advancement of Philosophical Know- ne v bd . > . . ledge. The association of men of cultivated understandings, PREFACE. Vv and of similar pursuits, has a tendency to keep alive the spirit of inquiry, and to direct it to proper objects. Hopes were therefore entertained that, by the co-operation of minds thus accustomed te investigation, some services, not otherwise to be expected, might eventually be rendered to the cause of Science. Such, it was conceived, were the consequences which might reasonably be anticipated from the establishment of a Philo- sophical Society im .the University of Cambridge; but at the same time it must be observed that the plan of the Society was not confined to those parts of Natural Philosophy, which form the more immediate objects of Academical pursuit. It was intended that the proposed Institution should embrace the studies of Chemistry, Mineralogy, Geology, Botany, Zoology, and other branches of Natural Science which have in modern times engaged so large a share of the public attention, and can be cultivated with success only by means of a continued series of experiments, and an unceasing vigilance of observation. Some of these subjects have already been partially illustrated by the application of Mathematical principles, and may perhaps be destined to acquire a still greater portion of the precision and certainty which attend the conclusions of demonstrative science :— others lay claim to regard by the practical value of the results which they present:—and of most of them, it may be justly asserted, that they afford ample scope for the exercise of the intellectual powers, in the methods of reasoning by Analysis and Induction. vi PREFACE. In other points of view, considerable advantages were anticipated from the proposed Society. Many Members of the University, although no longer resident within its precincts, have yet opportunities for observation and inquiry. From them it was confidently believed that very interesting communications would be obtained;— communications which would manifest the utility of a Philosophical Institution in the advancement of Physical Science. Great hopes were also entertained of forming such a connexion with other Societies of a similar kind as might, by means of mutual reports of experiments and observations, continually present new subjects of investigation and afford new motives for exertion. Such on the whole were the considerations which induced a few individuals in the University, well known for their zeal and activity in scientific research, to communicate to some of their Academical friends the plan of a Philosophical Institu- tion. Their sentiments were received with so much approbation, that hopes were speedily entertained of carrying the plan into effect. For the purpose of ascertaining the general feeling which might prevail on the subject, a meeting was soon after held, which was numerously attended by Graduates of the University. At this Meeting, it was unanimously agreed, that a PuiLosopuicaL Society should be formed; and at the same time, a Committee was appointed to make such arrangements as might appear necessary for the completion of the design. PREFACE. Vil At a subsequent Meeting, held on the 15th of November 1819, the Report of the Committee, together with a Code of Regula- tions, was read and approved of, and the Officers and Council of the Society were appointed. From that day, therefore, THE CAMBRIDGE PuILosopHicaL Society dates its Establishment. The first general Meeting of the Society, for the despatch of business, was held on Monday the 13th of December, 1819; at which, after an appropriate address by the President from the Chair, a paper stating the design and objects of the Society, was read by the Professor of Mineralogy, Dr. Clarke. The general meetings of the Society have since been held at stated intervals during each term. To this brief narrative of the origin and progress of The Cambridge Philosophical Society, nothing more needs be added, than that a commodious house has been hired, in which its meetings are held; and in which arrangements have been made for the reception of Books, and of Specimens in the different branches of Natural History. For the specimens which have been already collected the Society is indebted to the liberality of some of its Members*. * A list of donations to the Society will be printed at the end of the first Volume of Transactions. viii PREFACE. The Society takes this opportunity of expressing its grateful acknowledgments to the Syndics of the University Press, for their liberality m taking upon themselves the expense of printing this first part of its Transactions. OFFICERS ann FELLOWS OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. PATRON : His Royal Highness the Duke or GiovecesterR, Chancellor of the University. VICE-PATRONS : The Eart or Harpwiexe, K.G. High Steward of the University. The VicE-CHANCELLOR. ee ( PRESIDENT : The Rey. W. Farisu, B.D. Magd. Coll. Jacksonian Professor. VICE-PRESIDENT: ! Joun Havitanp, M.D. St. John’s Coll. Regius Professor of Physic. TREASURER : The Rey. B. Bripce, B.D. Fellow of Pet. Coll. SECRETARIES : The Rev. A. Sepewick, M.A. Trin. Coll. Woodwardian Professor. The Rey. S. Ler, M.A. Queen’s Coll. Professor of Arabic. ORDINARY MEMBERS OF THE COUNCIL: < *The Rey. I. Mitner, D.D. President of Queen’s Coll. Lucasian Professor of Mathematics. ——— E. D. Cuaxe, LL.D. Jesus Coll. Professor of Mineralogy. ——— J. Cummine, M.A. Trin. Coll. Professor of Chemistry. —— T. Carron, B.D. Fellow of St. John’s Coll. — T. Turron, B.D. Fellow of Catherine Hall. ———— T. Kerricu, M.A. Magd. Coll. Principal Librarian. R. Gwartkin, M.A, Fellow of St. John’s Coll. t> In the place of Dr. Mitwer, deceased; and of Dr. E. D. CLarxe and of Professor CumMING retired by rotation, THE COUNCIL. F. THackeray, M.D. Emmanuel Coll. | Rey. G. Peacock, M.A. Fellow of Trin. Coll.sare now Members of the Council. LW. Wuewe tt, M.A. Fellow of Trin. Coll. N. B. An Asterisk is placed before the names of those Fellows who have died during the passage of this Volume through the Press. b x FELLOWS. FELLOWS : A. Right Hon. the Earl of Aberdeen, St. fobal s, President of the Antiquarian Society, Xe. Andrew Amos, M.A. Fellow of Trin. Rev. Edward Anderson, B.D. Fellow of Queen’s. Rey. Thomas Dinham Atkinson, M. A. Queen’s, Thetford. W. Atkinson, M.A. Trin. King’s Bench Walk, Temple. George Attwood, B.A. Fellow of Pemb. B. C. Babbage, M.A. F.R.S. L. & E. F. Ast. Soc. Pet. 5, Devonshire Street, Port- land Place. Rev. Edward Balme, M.A. F.R.S. Magd. 14, Russell-place, Fitzroy-square. John Barlow, B.A. Trin. William Joseph Bayne, B.A. Trin. John Hawkesley Beech, B.A. St. John’s. Rey. Christopher Benson, M.A. Fellow of Magd. Charles Smith Bird, B.A. Fellow of Trin. Rev. Charles James Blomfield, D.D. Trin. Chesterford. Rey. Henry Blunt, M.A. Pemb. Vicar of Clare, Suffolk. Rev. William Boldero, M.A. Trin. Hall. Carlton Rectory, Cambs. Rey. William Bond, M.A. Caius, Wheat- acre, Norfolk. Rev. John Bransby, M.A. F.A.S. & L.S. M.G.S. St. John’s, Stoke Newington. Rey. John Brasse, M.A. Trin. Stanstead, Essex. Rey. Bewick Bridge, B.D. F.R.S, Fellow of Pet. Treasurer. Rev. J. Brinkley, D.D. M.R.I.A. &c. An- drew’s Professor of Astronomy, Dublin. * Right Rey. the Lord Bishop of Bristol. D.D. Master of Trin. Coll. Edward Ffrench Bromhead, M.A. F.R.S. Caius, Thurlby Hall, Newark, Notts. Charles Ffrench Bromhead, M.A. F. Ast. Soc. Fellow of Trin. Rey. John Brooke, M.A. Jes. Elmstead, Essex. William Brougham, B.A. Jesus. Lincoln’s Inn. Rey. John Brown, M.A. Tutor of Trin. Rey. George Adam Browne, M.A. Fellow of Trin. Rey. R. Buck, M.A. Madg. Agecroft Hall Manchester. Rey. James Bulwer, B.A. F.L.S. Jesus. Dublin. Rey. Edward Bushby, M.A. Fellow of St. John’s. Rey. George Butler, D.D. Sidney, Master of Harrow School. Rev. Samuel Butler, D.D. St. Master of Shrewsbury School. (e The Right Rev. the Bishop of Calcutta, D.D. F.R.S. Pemb. Frederick Calvert, M.A. Fellow of Jesus. Rey. Arthor Judd Carrighan, B.D. Fellow of St. John’s. Rey. Thomas Catton, B.D. Fellow of St. John’s. Rev. William Cecil, MA. Fellow of Magd. William Frederick Chambers, M.D. Trin. Fellow of the Royal College of Phy- sicians, 10, Curzon Street, London. Rev. Robert Chatfield, LL.D. Emman. Vicar of Chatteris. Rev. Temple Chevalier, M.A. Tutor of Cath. Hall, Samuel Hunter Christie, M.A. Trin. Royal Military Coll. Woolwich. John’s FELLOWS. Xl William Clark, M.A. M.G.S. Fellow of Trin. Professor of Anatomy. Rey. Edward Daniel Clarke, LL.D. &c. Jesus. Professor of Mineralogy. Henry Coddington, B.A. Fellow of Trin, The Earl of Compton, M.A. Trin. Presi- dent of the Geological Society, &c. Rev. Joseph Cook, M.A. Fellow of Christ’s. Rev. George Miles Cooper, B.A. Fellow of St. John’s. Rev. George Elwes Corrie, M.A. Tutor of Cath. Hall. Rev. Richard Crawley, M.A. Tutor of Magd. Rev. James Cumming, M.A. F.RS. M.G.S. Trin. Professor of Chemistry. D. James Charles Dale, M.A. F.L.S. Sidney, Glanville’s Wooton, near Sherborne, Dorset. Rey. Whitehall Davies, M.A. Christ’s. Plas Issa, Wrexham. Rev. Martin Davy, D.D. F.R.S. AS. & L.S. Master of Caius. Rey. Richard Dawes, M.A. Downing. Thomas Edward Dicey, M.A. Trin. Clay- brook near Lutterworth. Rey. Aldersey Dicken, M.A. Fellow of Pet. Rey. Richard Duffield, B.D. Fellow of St. John’s. Kenelm Henry Digby, B.A. Trin. Albany, London. Rey. Thomas Dikes, LL.B. Magd. Hull, Yorks. E. James Collett Ebden, M.A. F. Ast. Soc. Tutor of Trin. Hall. Edward Bishopp Elliot, M.A. Fellow of Trin. J. Elliotson, M.B. Jesus. Grafton Street, London. Thomas Flower Ellis, B.A. late Fellow of Trin. John Escreet, B.A. Trin. Stisted near Halstead. Rey. John Eyans, M.A. Tutor of Clare Hall. F, Rey. Fearon Fallows, M.A. F.R.S. F. Ast. Soc. Astronomer Royal at the Cape of Good Hope, late Fellow of St. John’s. Rev. William Farish, B.D, M.G.S. M.S.A, & A. Magd. Jacksonian Pro- fessor. President. Rev. Nicholas Fiott, M.A. St. John’s. John Hutton Fisher, B.A. Fellow of Trin. Rey. Clement Robert Francis, M.A. Fellow of Caius. Rev. James Clarke Franks, M.A. Trin. William Frere, M.A. Searjeant-at-law, Master of Downing, Vice-Chancellor. Vice- Patron, (1820). Gs William Albin Garratt, M.A. late Fellow of Trin. Lincoln’s Inn. John David Glennie, B.A. Trin. Dulwich. His Royal Highness the Duke of Glou- cester, LL.D. F.R.S. Chancellor of the University. Patron. Rey. J. Goodall, D.D. F.L.S. &c. Provost of Eton Coll. William Greenwood, B.A. Fellow of Bene'’t. Rey. John Griffith, M.A. Tutor of Emm. Henry Gunning, M.A. Christ’s. Rev. John Guthrie, M.A. Trin. Newark, Notts. Rev. Richard Gwatkin, M.A. Fellow of St, John’s. H. Rev. John Hailstone, M.A. F.R.S. and L.S. M.G.S. Trin. Trumpington. 52 xi Rev. Henry Parr Hamilton, M.A. F. Ast. Soc. Fellow of Trin. Edmond Glyn Hamond, B.A. Jesus. The Earl of Hardwicke, LL.D. Queen’s Coll. High Steward of the University. Vice- Patron. Richard Harvey, B.A. Cath. Hall. John Haviland, M.D. St. John’s. Regius Professor of Physic, Fellow of the Royal | | Rev. Richard Jeffreys, M.A. Fellow of College of Physicians. Vice-President. Rey. Samuel Hawkes, B.A. Fellow of Trin. Richard Hey, LL.D. Magd. Hartingford- bury, Herts. John Stevens Henslow, M.G.S. St. John’s. John Frederick William Herschel, M.A. F.R.S. L.& E. M-R.S. Got. F. Ast. Soc. Fellow of St. John’s. Rev. John Phillips Higman, M.A. F.R.S. Fellow of Trin. John Hind, B.A. Mathematical Lecturer of Sidney. Joseph Hindle, B.A. Fellow of St. John’s. Rey. Thomas Douglass Hodgson, B.A. Trin. Buckden, Hunts. Rey. John Holme, M.A. F.L.S. &c. Pet. Freckenham, Suff. John Holroyd, B.A. Trin. John Lodge Hubbersty, M.D. Fellow of Queen’s. Henry Hunter Hughes, M.A. Fellow of St. John’s. Rey. Thomas Smart Hughes, B.D. Fellow of Emman. Rey. John T. Huntley, M.A. Trin. Rector of Kimbolton, Hunts. Rey. James Devereux Hustler, B.D. F.R.S. Tutor of Trin. William Hustler, M.A. Tutor of Jesus, Registrary of the University. William Hutchins, B.A. Pemb. John Hutton M.A, Christ’s. Marske near Richmond, Yorks, B. A. E2E:S. FELLOWS. I Thomas Ingle, M.D. Fellow of Pet. Rey. Charles Ingle, M.A. Fellow of Pet. Rev. James Inman, D.D. St. John’s. Professor of Mathematics in the Royal Naval College, Portsmouth. J. Edward Jacob, M.A. Fellow of Caius. St. John’s. Rey. Thomas Jephson, B.D. Fellow of St. John’s. Rev. Richard Jones, M.A. Caius. Brigh- ton. Rey. William Jones, M.A. Fellow of St. John’s. K. Right Rey. John Kaye, D.D. F.R.S. Master of Christ’s, Regius Professor of Divinity, Lord Bishop of Bristol. Edward Curtis Kemp, M.A. St. John’s. Rey. Thomas Kerrich, M.A. F.A.S. Magd. Principal Librarian to the University. Joshua King, B.A. Fellow of Queen’s. L. Rey. John Lamb, M.A. Tutor of Bene’t. John Fiott Lee, LL.D. St. John’s, Col- worth House, Beds. Rey. Samuel Lee, M.A. Queen’s Coll. Professor of Arabic. Secretary. Charles Shaw Lefevre, M.A. F.R.S. late Fellow of Trin. Heckfield Place, Read- ing, Berks. Charles Shaw Lefevre, M.A. Trin. Great Russel] Street, London, John George Shaw Lefevre, B A. Fellow of Trin. Alfred Le Merchant, LL.B. F.R.S. Jes. Gray’s Inn. Rey. William Leeson, M.A. Fellow of Clare Hall. FELLOWS. Rey. John Lodge, M.A. Fellow of Magd. Rey. Francis Wm. Lodington, M.A. Fellow of Clare Hall. Rey. Francis Lunn, B.A. F.R.S. St. John’s, Chesterford. Charles Lutwidge, M.A. St. John’s, Hull. Ralph Lyon, B.A. Trin. M. Watkin Maddy, B.A. St. John’s Benjamin Heath Malkin, B.A. Fellow of Trin. Rev. T. R. Malthus, M.A. F.R.S. Jesus, Professor of History in the East India College, Herts. Rev. Wm. Mandell, B.D. Tutor of Queen’s. Rev. Bennet Michell, M.A. Fellow of Emman. Thomas Mills, B.A. Queen’s. * Rey. Isaac Milner, D.D. F.R.S. and A.S. President of Queen’s, Dean of Carlisle, Lucasian Professor of Mathe- matics. Rey. James Henry Monk, B.D. Tutor of Trin. Regius Professor of Greek. Basil Montague, M.A. Jesus. 25, Bedford Square, London. —Morris, M.D. F.R.S. Pemb. Par- liament Street, Westminster. John Bacon Sawrey Morritt, M.A. St. John’s, Rokeby Park, Yorks. Edward Murray, B.A. Trin. Westminster. John Musgrave, M.A. Fellow of Caius. Tourin, Cappoquin, Waterford. Rey. Thomas Musgrave, M.A. Fellow of Trin. Lord Almoner’s reader in Arabie. N. Cornelius Neale, M.A. St. John’s, South- end near Sydenham, Kent. Hon. and Rey. George Neville, M.A. Master of Magd. \ xii O. Rev. Holt Okes, D.D. Caius. Woodford, Essex. Rey. William Okes, M.A. Fellow of Caius. Rey. John Oldershaw, B.D, Emm, Arch- deacon of Norfolk. 12 The Viscount Palmerston, M.A. St. John’s, M.P. for the University. John Ayrton Paris, M.D. F.L.S. Caius, Fellow of the Royal College of Phy- sicians. Doyer-street, London. Rev. George Peacock, M.A. F.R.S. F. Ast. Soc. Fellow of Trin. Rey. Daniel Mitford Peacock, M.A. late Fellow of Trin. Stainton near Darling- ton, Durham. P Rey. Charles Penrice, M.A. St. John’s. Plumstead, Norfolk. The Right Rey. the Lord Bishop of Peterborough, D.D. F.R.S. St. John’s, Lady Margaret’s Professor of Divinity. Rey. Dan. Pettiward, M.A. Trin. One- house, Stowmarket. Frederick Pollock, M.A. F.R.S. Trin. Bedford-row, London. Stephen Pope, B.A. Fellow of Emman. Charles Porter, B.A. Fellow of Caius. Rev. William Procter, M.A. Fellow of Cath. Hall. Re Marmaduke Ramsay, B.A. Fellow of Jesus. Rey. Richard Relhan, M.A. F.R.S.& LS. Trin. William Blackstone Rennell, B.A. Fellow of King’s. Henry Revell Reynolds, M.A. Trin. Chief Commissioner of the Insolvent Debtors’ Court, &c. Bedford Row, London. Rey. William Richardson, B.A. St. John’s. xiv FELLOWS. Rey. Hastings Robinson, M.A. F. Ast. Soc. Fellow of St. John’s. Edward Rogers, M.A. and L.M. Fellow of Caius. Rey. Joseph Romilly, M.A. Fellow of Trin. Rey. Hugh James Rose, M.A. Trin. Maresfield near Uckfield, Sussex. Rey. Whitworth Russell, B.A. St. John’s Ickford, near Thame, Oxfordshire. Ss. Rey. Adam Sedgwick, M.A. M.G.S. Fellow of Trin. Woodwardian Professor. Secretary. Richard Sheepshanks, M.A. Fellow of Trin. Edward Smirke, M.A. St. John’s. 2, Inner Temple-lane. Rey. John Smith, M.A. Fellow of St. John’s. John Henry Smyth, M.A. Trin. M.P. for ” the University. The Earl Spencer K.G. F.R.S. Trin. * George Stainforth, B.A. Trin. Henry F. Stephenson, LL.B. Trin. Hall. Temple, London. Rey. George Stephenson, M.A. F. Ast. Soe. Fellow of Trin. Hon. Henry Sidney Stopford, M.A. Trin. Hill Street, Berkeley Square. Joseph Studholme, B.A. Fellow of Jesus. aL Frederick Thackeray, M.D. Emman. Thomas Thorpe, B.A. Fellow of Trin. Rey. John Toplis, B.D. Fellow of Queen’s. Hon. and Rey. Henry Townshend, M.A. St. John’s, Brome Eye, Suffolk. Rey. Thomas Turton, B.D. Fellow of Cath. Hall. William Twigg, B.A. Trin. Richard Twopeny, M.A. Fellow of St. John’s. Rey. Edwin Colman Tyson, B.A. Fellow of Cath. Hall. Vie Rev. John Vickers, M.A. Trin. Swannington near Norwich. George Villiers, M.A. St. John’s, Em- bassy, St. Petersburgh. Right Hon. John C. Villiers, M.A. St. John’s, North Audley Street, London. Ww. Weaver Walter, B.A. Sid. Rey. Jonathan Walton, B.D. Trin. Coll. Birbrook, Essex. Thomas Walpole, M.A. Trin. Stagbury, near Tunbridge. Rey. John Warren, B.A. Fellow of Jesus. Thomas Watson, M.A. Fellow of St. John’s. Rey. Thomas Webster, M.A. Queen’s. Oakington, Camb. William Whewell, M.A. F.R.S. Fellow of Trin. Coll. Rey. John William Whittaker, F. Ast. Soc. Fellow of St. John’s. William Wilkins, M.A. F.A.S. Caius. John Hopper Williamson, LL.B. Trin. Hall, Temple, London. The very Rev. James Wood, D.D. Master of St. John’s, Dean of Ely. The Rev, Christopher Wordsworth, D.D Master of Trin. Vice-Chancellor. Vice- Patron (1821). Rev. Francis Wrangham, M.A. F-.R.S. Trin. Archdeacon of Cleveland, Hun- manby near Bridlington. Hall. M.A. HONORARY MEMBERS. M. J. B. D’Andrada, Professor of Mine- ralogy, Lisbon. *Rt. Hon. Sir Joseph Banks, Bart. G.C.B. President of the Royal Society. M. Berzelius, F.R.S. &c. Professor of Chemistry, Upsal. Count De Bournon, Paris. Rey. W. Buckland, F.R.S. M.G.S. Pro- fessor of Mineralogy, Oxford. M. Biot, F.R.S. L.& E. Membre de l Académie des Sciences, &c. &c. Paris. John F. Blumenbach, M.D. F.R.S. &c. Professor of Medicine in the University of Gottingen. D. Brewster, LL.D. F.R.S. L. & E. &c. Edinburgh. M. S. Breislack, Membre de l'Institut Impérial et Royal de Lombardie, &c. &c. Milan. M. Alex. Brogniart, Ingénieur des Mines, &e. &c. Paris. Robert Brown, Esq. F.R.S. &c. London. M. Leopold Von Buch, Member of the Royal Academy of Sciences at Berlin, &e. Xe. R. Chenevix, Esq. F.R.S. M.R.LA. &e. J. G. Children, Esq. F.R.S. L. & E, F. Ast, Soc. &c. M. Le Chevalier Cuvier, Secrétaire per- pétuel de l'Institut de France, F.R.S. Xe. Xe. J. Dalton, Esq. Member of the French Institute, &e. Sir Humphry Davy, Bart. President of the Royal Society, &c. &c. F.R.S. &e. &c. M. Estmark, Professor of Mineralogy, &c. Kongsberg. John Forbes, M.D. Secretary of the Royal Geological Society of Cornwall. G. B. Greenough, Esq. F.R.S. President of the Geological Society. M. Hammer, Oriental Interpreter to the Court of Vienna. M. L’Abbé Haiiy, Membre de I’ Institut, &c. Professor of Mineralogy, Paris. Sir W. Herschel, LL.D. F.R.S. &c. &e. J. Hume, M.D. Hamilton near Glasgow. R. Jameson, F.R.S. E. Regius Professor of Natural History, Edinburgh. James Ivory, Esq. F-R.S. L. & E. &e. M. Kieffer, King’s Oriental Interpreter, Paris. J. Kidd, M.D. Professor of Chemistry, &e. Oxford. C. Konig, Esq. F.R.S. &c. &c. British Museum. W.E. Leach, M.D. F.R.S. &c. &c. Bri- tish Museum. J. Leslie, Esq. F.R.S. E. Correspond- ing Member of the French Institute, Professor of Natural Philosophy, Edin- burgh. M. J. A. H. Lucas, Keeper of Museum of Natural History, Paris. J. Mac Culloch, M.D. F.L.S. &c. &e. Geologist to the Trigonometrical Survey of Great Britain. A. Marcet, M.D. F.R.S. &c. &c. J. Okes, Esq. Cambridge, Rev. W. Pearson, LL. D. F.R.S. F. Ast. Soc. W. Phillips, Esq. M.G.S. &c. London. XV HONORARY Major J. Rennell, F.R.S. &c. M. Reuven, Archeological Professor in the University of Leyden. A. Robertson, D.D. F.R.S. Savilian Pro- fessor of Astronomy in the University of Oxford. M. Le Baron De Sacy, Professor of Ara- bic, &c. Paris. M. Santi, Vice-Chancellor, and Professor of Natural History in the University of Pisa. M. A. Scarpa, F.R.S. &c. Professor of Anatomy in the University of Pavia. S. T. Scemmering, M.D. Professor of Anatomy, Munich. MEMBERS. Sir Robert Seppings, F.R.S. &c. Sur- veyor of His Majesty’s Navy. J. Shuter, M.D. Superintendant of the Botanic Garden at Calcutta. Doctor Slawinski, Professor of Astronomy, Wilna. J. South, Esq. F. Ast. Soc. Dugald Steward, Esq. F.R.S. L. & E. Emeritus Professor of Moral Philosophy in the University of Edinburgh. T. Thomson, M.D. F.R.S. &c. Regius Professor of Chemistry, Glasgow. E. Troughton, Esq. F.R.S. &c. W. Wallace, F.R.S.E. Professor of Mathematics, Edinburgh. REGULATIONS OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. Established—N ov. 15, 1819. Tue Camprince Puiosopnican Society is instituted for the purpose of promoting scientific enquiries, and of facilitating the communication of facts connected with the advancement of Philosophy and Natural History. Sect. I. Of the Constitution of the Society. 1. The Society shall consist of Fellows and Honorary Members. 2. The Officers shall be chosen from the Fellows, and shall consist of a Patron, Vice-Patrons, President, Vice-President, Treasurer, and two Secretaries, who with seven other Fellows shall constitute a Council. Secr. II. Of the Election of the Officers and Council. 1. The Patron of the Society shall be elected for life. 2. The Vice-Chancellor and High Steward of the University (if Fellows of the Society) shall be considered as Vice-Patrons. c XVill REGULATIONS OF THE SOCIETY. 3. The President, Vice-President, Treasurer, Secretaries, and three ordinary Members of the Council, shall be annually elected by ballot from among the Fellows of the Society. 4. The same Fellow shall not be eligible to fill the office of President, or Vice-President, for more than two years successively. 5. The three senior ordinary Members of the Council shal retire annually. 6. No Fellow under the degree of M.A. M.B. or LL.B. shall be a Member of the Council. Sect. III. Of the Election and Admission of Fellows. i. The Fellows shall be elected from such persons only as are Graduates of the University of Cambridge. 2. Every person desirous of admission into the Society, shall be proposed and recommended by three or more Fellows, who shall deliver to one of the Secretaries a paper, signed by themselves, specifying the Christian and Surname of such person, with the name also of his College, together with his usual place of residence ; all of which must be certified from the personal knowledge of at least one of the subscribing Fellows. The following is the Form of the Certiricate required. of ———— Coll. , being desirous of becoming a Fellow of the Cambridge Philosophical Society, we, whose Names are underwritten, do recommend him as a_ proper person to be a Fellow of the said Society. (Signed) This certificate shall be read by one of the Secretaries at the Meeting at which the Candidate is proposed, and remain REGULATIONS OF THE SOCIETY. xIx suspended in the meeting room of the Society till he be ballotted for. 3. The ballot shall take place on the second Meeting after that at which the Candidate is proposed: but all Heads of Houses, Doctors, and Professors, and all persons who have been admitted to Honorary Degrees, shall be ballotted for at the Meeting at which they are proposed. 4. No person shall be declared elected, unless he have in his favour at least two-thirds of the Members voting, and if it appear upon the ballot, that the person proposed is not elected, no notice thereof shall be taken in the minutes. 5. The Vice-Chancellor for the time being, when regularly proposed, shall be admitted a Fellow without a ballot. 6. No person shall be admitted a Fellow, till he has paid his subscription for the current year, or the sum specified in lieu of annual contributions. Sect. IV.. Of Honorary Members. 1. No Graduate or Member of the University of Cambridge, shall be admitted an Honorary Member. 2. Honorary Members shall be proposed by at least six Fellows of the Society, and their mode of election shall be subject to the same regulations as that of the Fellows. Sect. V. Of the Funds of the Society. The annual subscription of each Fellow shall be one guinea, to be paid in advance; or in lieu of annual payments, the sum of ten guineas. c2 = xX REGULATIONS OF THE SOCIETY. Secr. VI. Of the Council. 1. The Council shall have the management and direction of all the affairs of the Society, their proceedings being subjected to the approbation of the general meetings of the Society. 2. The Council shall meet at the house of the Society at least once in every fortnight during full term, and not less than five shall constitute a quorum. Due notice of each Meeting shall be sent to every Member of the Council. 3. All questions shall be determined in the Council by vote, unless a ballot be demanded. The determination of the Council, whether by vote or by ballot, shall at the desire of any two or more members present, be deferred to the next succeeding Meeting. If the number of yotes be equal, the Chairman shall have the casting vote. 4. The Council shall draw up a Report on the state of the affairs of the Society, to be presented at the general annual Meeting. In this Report shall be inserted an abstract of their proceedings during the year. - 5. Nothmg shall be published by the Society, which has not been previously approved by the Council; and, the Council shall be at liberty to call in the aid of any Fellow of the Society, well skilled in the particular branch of science, which may happen to be the subject of any paper, under consideration. Sect. VII. Of the Ordinary Meetings. 1. The Meetings of the Society shall be held on a Monday, once in every fortnight, during full term. REGULATIONS OF THE SOCIETY. XX1 2. The President shall take the chair at 7 p.m. and shall quit it before nine. 3. The business of each Meeting shall be conducted in the following order : 1. The minutes of the preceding Meeting read and approved. ur. Notices of new Motions presented. 11. Members proposed. Iv. Members ballotted for. vy. Motions on the Minutes brought forward and determined. vit. Miscellaneous business. vit. Communications read, and presents acknowledged. 4. Any motion to be submitted to the Society shall be ex- pressed in writing, and signed by at least three Fellows of the Society; it shall be read by one of the Secretaries and if not with- drawn, shall be ballotted for at the next succeeding Meeting. 5. Each Member shall be at liberty to introduce a visitor on delivering his name to the President or Chairman at the time. Sect. VIII. Of the Annual General Meeting. The Annual General Meeting of the Society shall take place on the day succeeding the last meeting of the Society in the Easter term of each year, for the purpose of receiving the Report of the Council on the state of the Society, of auditing the accounts of the Treasurer, and of electing the Officers for the succeeding year. Secr. IX. Of Special General Meetings. 1. The President and Council may at any time call a special general Meeting of the Society. KXil REGULATIONS OF THE SOCIETY. 2. Atleast three days’ notice of such a Meeting shall be given by one of the Secretaries to the resident members of the Society. Sect. X. Of the Duties of the President and Vice-President. 1. The duty of the President shall be, to take the chair at the Meetings of the Society and Council; to regulate and keep order in all their proceedings; to state questions and propositions to the Meeting; to report the result of ballots; and to carry into effect the regulations of the Society. 2. In the absence of the President, the chair shall be taken by one of the Members of the Council in the following order; viz. The Vice-President, Treasurer, or senior ordinary Member of the Council. Sect. XI. Of the Duties of the Treasurer. The Treasurer shall receive all sums of Money due to the Society, transact all its pecuniary affairs, and keep a regular account of receipts and payments, in the mode which may seem most proper to the Council. Sect. XII. Of the Duties of the Secretaries. 1. The Secretaries shall have the management of the corre- spondence of the Society and Council. 2. They shall attend all Meetings of the Society and Council, take minutes of their proceedings, and enter them in books provided for that purpose; they shall transact the business of the ordinary Meetings according to the mode specified in Sect. vir. Rule 3. REGULATIONS OF THE SOCIETY. Xxill 3. They shall have the charge, under the direction of the Council, of printing the Memoirs of the Society and of correcting the press. Sect. XIII. Of the Society’s Property. An inventory of the furniture and other articles im the Meeting Room of the Society, shall be made every year. Cata- logues of the Library, Collections in Natural History, &c. shall also be made for the use of the Members of the Society. Sect. XIV. Of Donations. Eyery person who shall contribute to the Collection or Library of the Society, shall be recorded as a benefactor, his name shall be read at the annual general Meeting, and shall be inserted in the next succeeding volume of the Society’s Memoirs. Sect. XV. Miscellaneous Regulations. 1. All communications, presents, &c. shall be sent to one of the Secretaries, if not personally presented by a Member at a meeting of the Society. 2. The author of any communication, if a Member, shall have the liberty of reading his own paper. + ' 5* / : (are: | iiiiiee anv: snonnisedih= oP ADOT ‘tMhrabse” ay rtiiley> el ens meng fue ys ooF alt lo writs ' : " ak worl aw honve?, fae 1 oP tiee ae oy, . oe iit abit saitte fan oinlinwut of & ye Ww, “1H per apbaisea - el Fisste Wag sr oft ede oa ecole EE Trutnd isi pilostto” } Me a = " sea tt age to vali Wail ‘to - . Pentti ¢ Vo" tress ae a * rumetil “ay “quisvall ,, oil, “i uditians. flewk other Gor S| i aves _pattnds er wotyat ewe a zt balriesst- “od Heda “Afsine aed, y AF ad Usd bine cuties feces fauna ofl pak : ie sunt ne a aft’ hae at lo amor goth sste txoaeds ; : = He Pamareg oie . anoiiplirysst awosan)) ail. : ov x Seat : a ~ om A ; = 4 a = * Wo sho at hipeod Made 24 tae, AAO RMA Rta rcEE A 5, > _- * te moe, os pe i jearemets Jove theweyttiakay eae s ee . thee alt to wink y a ae ne ® . aan Undit ate ati thi jstiai ou ramen = we 7 : thao bat, when Mi 7 = 4 —— : : a = Aas ~~ ix “ , -~ ey ; a i ‘ Neil : % iat . 5 Ye ae? : — mK a ~ eg i ~ . Smee. de eo “ny — onl 7. , ee i @ : ; a . . oe k c + Il. VII. Vill. XI. CONTENTS. Ow Isometrical Perspective: by Professor FARISH....s004.... On certain remarkable Instances of deviation from Newton’s Scale in the Tints developed by Crystals, with one Axis of Double Refrac- tion, on exposure to Polarized Light: by Mr. Herscue....... On the Rotation impressed by Plates of Rock Crystal on the Planes of Polarization of the Rays of Light, as connected with certain pecu- liarities in its Crystallization: by Mr. HERSCHEL... ..eeeeeee On the Chemical Constituents of the Purple Precipitate of Cassius: by Dre QraRKE. eccevcecccee cece *afeliolelelelofolel cl'els} slelelelelerelc Observations on the Notation employed in the Calculus of Functions : by Mr. IESASDIBIAG Eicherciosstet el elcusyenelstelatel cleiel chor ciever ever cieteretercrsiniens On the Reduction of certain Classes of Functional Equations to Equa- tions of Finite Differences: by Mr. HERSCHEL. .....-e+..4.. On the Physical Structure of those Formations which are immediately associated with the Primitive Ridge of Devonshire and Cornwall: by Professors SED GWiECKels el. 1 -leln|s).o:e) ele. 0) s/s) s)lele/o/ ele) s\0) 2) On the Laws according to which Masses of Iron influence Magnetic Needles: by Mr. CurisTiE...-....... bdadeue isielielevel efepelie An Account of some Fossil remains of the Beaver, found in Cambridge- shire: by Mr. OxES....... Aces eh eee eee arehoteh eavelel sre) sr cie ve On the Position of the Apsides of Orbits of great Excentricity: by Wie MVS OID ooo OU bobo OBOE mS Jou S 6dobodoeaH COOOR On a remarkable deposit of Natron found in cavities in the Tower of Stoke Church, in the Parish of Hartland, in Devonshire: by Dr CLARKE... .11- SEstdo SHOE Sodus ocdopoodncoaddodc PAGE 179 193 ADVERTISEMENT. Tue Society as a body is not to be considered responsible for any facts and opinions advanced in the several Papers, which must rest entirely on the credit of their respective Authors. I. On Isometrical Perspective. By WILLIAM FARISH, B.D. JACKSONIAN PROFESSOR, AND PRESIDENT OF THE PHILOSOPHICAL SOCIETY IN THE UNIVERSITY OF CAMBRIDGE. [Read February 21, and March 6, 1820.] Iw the Course of Lectures which I deliver in the University of Cambridge, I exhibit models of almost all the more important machines which are in use in the manufactures of Britain. The number of these is so large, that had each of them been permanent and separate, on a scale requisite to make them work, and to explain them to my audience, I should, independently of other objections, have found it difficult to have procured a ware- house large enough to contain them. I procured therefore an apparatus, consisting of what may be called a system of the first principles of machinery; that is, the separate parts, of which machines consist. These are made chiefly of metal, so strong, that they may be sufficient to perform even heavy work: and so adapted to each other, that they may be put together at pleasure, in every form, which the particular occasion requires. Those parts are various; such as, loose brass wheels, the teeth of which, all fit into one another: axes, of various lengths, on any part of which the wheel required may be fixed: bars, clamps, and frames; and whatever else might be necessary to build up the particular machines which are wanted for one Lecture. These A 2 Professor Farisu on Isometrical Perspective. models may be taken down, and the parts built up again, in a different form, for the Lecture of the following day. As these machines, thus constructed for a temporary purpose, have no per- manent existence in themselves, it became necessary to make an accurate representation of them on paper, by which my assistants might know how to put them together, without the necessity of my continual superintendence. This might have been done, by giving three orthographic plans of each; one on the horizontal plane, and two, on vertical planes at right angles to each other. But such a method, though in some degree in use among artists, would be liable to great objections. It would be unintelligible to an inexperienced eye; and even to an artist, it shews but very imperfectly that which is most essential, the connection of the different parts of the engine with one another; though it has the advantage of exhibiting the lines parallel to the planes, on which the orthographic projections are taken, on a perfect scale. This will be easily understood, by supposing a cube to be the object re- presented. The ground plan would be a square representing both the upper and lower surfaces. And the two elevations would also be squares on two vertical planes, parallel to the other sides of the cube. The artist would have exhibited to him, three squares ; and he would have to discover how to put them together in the form of a cube, from the circumstance of there being two elevations, and a ground plan. This method, therefore, giving so little assistance on so essential a point, I thought unsatisfactory. The taking a picture, on the principles of common perspective, was the next expedient that suggested itself. And this might be adapted to the exhibition of a model, by taking a kind of bird’s-eye view of the object, and having the plane of the picture, not as is most common in a drawing, perpendicular to the horizon, but to a line, drawn from the eye, to some principal part of the object. For example: in taking the picture of a cube, the eye might be Professor Farisu on Isometrical Perspective. 3 placed in a distant point on the line which is formed by producing the diagonal of the cube. But to this common perspective, there are great objections. The lines which in the cube itself, are all equal, in the representation are unequal. So that it exhibits nothing lke a scale. And to compute the proportions of the original from the representation, would be exceedingly difficult, and, for any useful purpose, impracticable: there is equal difficulty too, in computing the angles which represent the right angles of the cube. Neither does the representation appear correct, unless the eye of the person, who looks at it, be placed exactly in the point of sight. It is true that, as we are continually in the habit of looking at such perspective drawings, we get the habit of cor- recting, or rather overlooking the apparent errors which arise from the eye being out of the point of sight, and are therefore not struck with the appearance of incorrectness, which, if we were unac- customed to it, we should feel at once. The kind of perspective, which is the subject of this paper, though lable in a slight degree, to the last-mentioned inconve- nience, till the eye becomes used to it, I found much better adapted to the exhibition of machinery ; I therefore determined to adopt it, and set myself to investigate its principles, and to consider how it might most easily be brought into practice. It is preferable to the common perspective on many accounts, for such purposes. It is much easier, and simpler in its principles. It is also, by the help of a common drawing-table, and two rulers*, * It is unnecessary to describe the drawing-table any further than by observing that it ought to be so contrived, as to keep the paper steady on which the drawing is to be made. There should be a ruler in the form of the letter T to slide on one side of the drawing- table. The ruler should be kept, by small prominences on the under side, from being in immediate contact with the paper, to prevent its blotting the fresh drawn lines, as it slides over them. And a second ruler, by means of a groove near one end on its under side, should be made to slide on the first. The groove should be wider than the breadtli of the first ruler, and so fitted, that the second may at pleasure be put into either of the two positions A2 represented 4 Professor FarisH on Isometrical Perspective. incomparably more easy, and, consequently, more accurate in its application; insomuch, that there is no difficulty in giving an almost perfectly correct representation of any object adapted to this perspective, to which the artist has access, if he has a very simple knowledge of its principles, and a little practice. It further represents the straight lines, which lie in the three prin= cipal directions, all on the same scale. The right angles contained by such lines are always represented either by angles of 60 degrees, or the supplement of 60 degrees. And this, though it might look like an objection, will appear to be none on the first sight of a drawing on these principles, by any person who has ever looked ata picture. For, he cannot for a moment have a doubt, that the angle represented is a right angle, on inspection. And we may observe further, that an angle of 60. degrees is the easiest to draw of any angle in nature. It may instantly be found represented in the plate, fig. 1, so as to contain with the former ruler, in either position, an angle of 60 degrees. The groove should be of such a size, that when its shoulders a and d are in contact with, and rest against the edges of the first ruler, the edge of the second ruler should coincide with de, the side of an equilateral triangle described on dg, a portion of the edge of the first ruler; and when the shoulders 5 and ¢ rest against the edges of the first ruler, the edge of the second should lie along ge, the other side of the equilateral triangle. The second ruler should have a little foot at k for the same purpose as the prominences on the first ruler, and both of them should have their edges divided into inches, and tenths, or eighths of inches. It would be convenient if the second ruler had also another groove rs, so formed that when the shoulders r and s are in contact with the edges of the first ruler, the second should be at right angles to it. For representing circles in their proper positions the writer made use of the inner edge of rims cut out from cards, into isometrical ellipses as represented in the figure ; of these he had a series, of different sizes, corresponding to his wheels. Such a series might be cut by help of the concentric ellipses in fig. 5, but he thinks that it would be an easier way to make use of that set of concentric ellipses as they stand, by putting them in the proper place under the picture, if the paper on which the drawing is made, be thin enough for the lines to be traced through, as by help of them the several concentric circles will go to the representation of one which might be drawn at once. It is difficult to execute them separately with sufficient accuracy, to make them correspond. For this purpose a separate plate of fig. 5, should be had, and one edge of the paper on the drawing table, should be loose to admit of the con- centric ellipses being slid under it, to the proper place, as described, page 9. Professor Farisu on Isometrical Perspective. 5 by any person who has a pair of compasses, and understands the First Proposition of Euclid. The representation, also, of circles and wheels, and of the manner in which they act on one another, is very simple, and intelligible. The principles of this perspective which, from the peculiar circumstance of its exhibiting the lines in the three principal dimensions, on the same scale, I denominate “« Tsometrical,” will be understood from the following detail : Suppose a cube to be the object to be represented. The eye placed in the diagonal of the cube produced. The paper, on which the drawing is to be made to be perpendicular to that diagonal, between the eye, and the object, at a due proportional distance from each, according to the scale required. Let the distance of the eye, and consequently that of the paper, be indefinitely in- creased, so that the size of the object may be inconsiderable in respect of it. It is manifest, that all the lines drawn from any points of the object to the eye, may be considered as perpendicular to the picture, which becomes, therefore, a species of orthographic pro- jection. It is manifest, the projection will have for its outline an equiangular, and equilateral hexagon, with two vertical sides, and an angle at the top and bottom. The other three lines will be radii drawn from the center to the lowest angle, and to the two alter- nate angles; and all these lines and sides will be equal to each other, both in the object and representation: and if any other lines parallel to any of the three radii should exist in the. object. and be represented in the picture, their representations will bear to one another, and to the rest of the sides of the cube, the same proportion which the lines represented, bear to one another in the object. If any one of them, therefore, be so taken, as to bear any re- quired proportion to its object, e. g. 1 to 8, as in my representations of my models, the others also will bear the same proportion to 6 Professor Farisu on Isometrical Perspective. their objects; that is, the lines parallel to the three radii will be reduced to a scale. I omit the demonstration of this, and some other points, partly for the sake of brevity, and partly because a geometrician will find no difficulty in demonstrating them himself, from the nature of orthographic projection ; and a person, who is not a geometrician, would have no interest in reading a demonstration. For the same reason, it is unnecessary to shew that the three angles at the center, are equal to one another, and each equal to 120 degrees, twice the angle of an equilateral triangle; and the angle contained between any radius and side is 60 degrees, the supplement of the above, and equal to the angle of an equilateral triangle. All this follows immediately from Euclid, B. 1V. Prop. 15, on the inscription of a hexagon im a circle. In models, and machines, most of the lines are actually in the three directions parallel to the sides of a cube, properly placed on the object. And the eye of the artist should be supposed to be placed at an indefinite distance, as before explained, in a diagonal of the cube produced. DEFINITIONS. The last-mentioned line may be called the line of sight. Let a certain point be assumed in the object, as for example C, fig. 2, and be represented in the picture, to be called, The regulating point. Through that point on the picture, may be drawn a vertical line, CE, fig. 2, and two others, CB, CG, containing with it, and with one another, angles of 120°, to be called the isometrical lines, to be distinguished from one another by the names of the vertical, the dexter, and the sinister lines. And the two latter, may be called by a common name,—the horizontal isometrical lines. Any other lines, parallel to them, may be called respectively by the same names. The plane passing through the dexter, and vertical lines, Professor Farisu on Isometrical Perspective. 7 may be called the dexter isometrical plane; that passing through the vertical, and sinister lines, the sinister plane; and that through the dexter and sinister lines, the horizontal plane. By the use of the simple apparatus described above in the Note, the representation of these lines in the objects may be drawn on the picture, and measured to a scale, with the utmost facility : the point at the extremity being first found, or assumed. The position of any point in the picture, may be easily found, by measuring its three distances, namely, first its perpendicular distance from the regulating horizontal plane, (that is, the hori- zontal plane passing through the regulating point) secondly, the perpendicular distance of that pomt, where the perpendicular meets the horizontal plane, from the regulating dexter line; and thirdly, of the point, where that perpendicular meets the dexter line, from the regulating point; and then taking those distances reduced to the scale, first, along the dexter line, secondly, along the sinister line, and thirdly, along the vertical line, in the picture. These three may be called the dexter distance of the point, its sinister distance, and its altitude. And it is manifest they need not be taken in this order, but in any other that may be more con- venient to the artist: there being six ways in which this operation may be varied. If any point in the same isometrical plane, with the point re- quired to be found, is already represented in the picture, that point may be assumed as a new regulating point, and the point required found by taking two distances ; and if the new assumed regulating point is in the same isometrical line with the point, it is found by taking only one distance. And this last simple operation, will be found in practice all that is necessary for the determination of most of the points required. Thus any parallelopiped, or any frame- work, or other object with rafters, or lines lying in the isometrical directions, may be most easily and accurately exhibited on any 8 Professor Farisu on Isometrical Perspective. scale required. But, if it be necessary to represent lines in other directions, they will not be on the same scale, but may be exhi- bited, if straight lines, by finding the extremities as above, and drawing the line from one to the other; or sometimes more readily in practice, by help of an ellipse, as hereafter described, page 11. If a curved line be required, several points may be found sufficient to guide the artist to that degree of exactness, which is required. The method of exhibiting the representations of any machines, or objects, the lines of which lie, as they generally do, in the isometrical directions; that is, parallel to the three directions of the lines of the cube, as has been already shewn ; and likewise the mode of representing any other straight lines, by finding their ex- tremities; or curved lines, by finding a number of points. But in representing machines, and models, there are not only isometrical lines, but also many wheels working into each other, to be represented. These, for the most part, lie in the isometrical planes. And it is fortunate that the picture of a circle in any one of these planes, is always an ellipse of the same form, whether the plane be horizontal, dexter, or sinister ; yet they are easily distin- guished from each other, by the position in which they are placed on their axle, which is an isometrical line, always coinciding with the minor axis of the ellipse. This will be obvious from considering the picture of a cube with a circle inscribed in each of its planes, fig. 3, and considering these circles as wheels on an axle. The two other lines (or spokes of the wheel) in the ellipse, which are drawn respectively through the opposite points of contact of the circle with the circumscribing figure, are isometrical lines also; for the points of contact bisect the sides of the circumscribing parallelogram, and therefore the lines are parallel to the other sides. They give likewise the true dia- meter of the wheels, reduced to the scale required. It further Professor Farisu on Isometrical Perspective. 9 appears from the nature of orthographic projection, that the major axis of the ellipse, is to the minor axis, as the longer, to the shorter diagonal of the circumscribing parallelogram, that is, (since the shorter diagonal divides it into two equilateral triangles) as the square root of three, to one ; as appears from Euclid, Lib. I. Prop. 47. And since the sum of the squares of the conjugate diameters in an ellipse, is always the same, if we put J/1 for the minor axis, the ./ 3 for the major, and 7 for the isometrical diameter, we shall have 2? =1+4+3,=4, andi =./2. Therefore the mimor axis, the isometrical diameter, and the major axis may be represented respectively by \/ 1, ./2, \/3, or nearly by 1, 1.4142, 1.7321; or more simply, though not so nearly, by 28, 40, 49. These lines may be geometrically exhibited by the following construction : Let AB, fig. 4, be equal to BD, and the angle at B, a right angle. In BA produced, take Ba = to AD. Draw aD, and produce both it, and «B. Then will BD, Ba, and «aD, be re- pectively to one another, as ./ 1, \/ 2, ./3 by Euclid I. 47. There- fore if a8 be taken equal to the isometrical diameter of the ellipse required, 86 drawn perpendicular to it will be the minor axis, and ad the major axis. The ellipse itself, therefore, may be drawn by an elliptic compass, as that instrument may be properly set, if the major, and minor axes are known. If it is to represent a wheel on an axle, care must be taken to make the minor axis lie along that axle. In the absence of the instrument it may be drawn from the concentric ellipses, fig.5, which may be placed under the paper, in the position above described, and seen through it; if the paper be not too thick, and in this method the smaller concentric circles of the wheel may be described at the same time, as they may be seen through the paper ; or if they should not be exactly of the right size, it would be easy to describe them by hand, between B 10 Professor Farisu on Isometrical Perspective. the two nearest concentric ellipses; and thus also the height of the cogs of a wheel in the different parts of it may be exhibited, longer and narrower towards the extremities of the major, and shorter and wider at the extremities of the minor axis. Their width may be determined from the divisions of the ellipse. In most cases, this may be done with sufficient accuracy from the circumference of the ellipse being divided into eight equal divisions of the circle, by the two axes, and two isometrical diameters, each of which parts may be subdivided by the skill of the artist ; and not only the face of the wheel in front, may be thus exhibited, but the parts of the back circles also, which are m sight, may be exhibited, by pushing back the system of concentric ellipses on the minor axis, or axle through a distance representing the breadth of the wheel, and then tracing, both the exterior, and interior circles of the wheel, and of the bush on which it is fixed, as far as they are visible. Care should be taken to represent the top of the teeth, or cogs, by isometrical lines, parallel to the axle, in a face-wheel, or tending to a proper point in the axle in a bevil-wheel. And nearly in the same way may the floats of a water-wheel be correctly represented. If a series of concentric ellipses, such as are given, fig. 5, be not at hand, it will still be easy for an artist to draw the ellipses with sufficient accuracy for most purposes, by drawing through the proper point in the axle, the major, and minor axes, and the two isometrical diameters, thus marking eight points in the circumference, to guide him. If in any case it should become necessary to represent a circle, which does not lie in an isometrical plane, we may observe that the major axis will be the same, in whatever plane it lies: and it will be the picture of that diameter, which is the intersection of the circle with the plane parallel to the picture, passing through its center. And the major axis, will bear to the minor axis, the proportion of radius, to the sine of the inclination of the line of sight, to the plane of the circle. We may observe further that the diameters of Professor Farisu on Isometrical Perspective. 11 the ellipse, which are to the major axis, as ./ 2 to \/3, when such exist, are isometrical lines*. And the representation of every other line parallel, and equal to any diameter of the circle, may be exhibited by drawing it equal and parallel to the corresponding diameter in the ellipse. If it should be desired to divide the circumference of an ellipse into degrees, or any number of parts representing given divisions of the circle, it may be done by the following method : Let an ellipse be drawn, fig.6, and on its major axis, AG, a circle described, with its circumference divided into degrees, or parts in any desired proportion, at B, C, D, E, F, &c.: from which points, draw perpendiculars to the major axis. They will cut the periphery of the ellipse in corresponding points. It would be difficult, however, in this way, to mark, with sufficient accuracy, the degrees, which lie near the extremities of the major axis. But the defect may be supplied by transferrmg those degrees in a similar way, from a graduated circle, described on the minor axis. In this manner, an isometrical ellipse, may be formed into an isometrical circular instrument, or an isometrical compass, which may shew bearings or measure angles on the picture, in the same manner, as a real compass, or circular instrument would do in nature. It may be often useful to have a scale, to measure distances, not only mm the isometrical directions, but in others also. And this may * We may remark, that if a cone be described, having its vertex at C which lies in the line of sight, fig. 2, and passing through the three radii CB, CE, CG, all the straight lines in the superficies of that cone passing through C, and all other lines parallel to any of them, are iso- metrical, as well as those parallel to the three principal isometrical lines, CB, CE, CG; and no other lines but these can be on the same scale. But though this multiplies the number of isometrical lines infinitely, it is of little practical use: because it is only those, which are parallel to the three principal lines, that can be easily distinguished at sight, to be isome- trical. We may further remark, that if a line be drawn through the point C parallel to any given line whatever, and that line be made to revolve round the line of sight, at the same angular distance from it, so as to describe the surface of a cone, all other lines parallel to it, in any of its positions, will be isometrical, as they respect one another. B 2 12 Professor Farisu on Isometrical Perspective. be done, by a series of similar concentric ellipses, as in fig. 7, dividing the isometrical diameters into equal portions. The other diameters will be so divided, as to serve for a scale, for all lines parallel to them respectively. Thus, in the isometrical squares, exhibited in fig. 2, distances measured on the longer diagonal, or its parallels, would be mea- sured by the divisions on the major axis, those depending on the shorter diagonal, by the divisions on the minor axis. To describe a cylmder, lying in an isometrical direction, the circles at its extremities, should be represented by the proper isome- trical ellipses, and two lines touching both, should be drawn: and in a similar way, a cone, or frustum of a cone, may be described. A globe is represented by a circle, whose radius is the semi-major axis of the ellipse representing a great circle. It would not be difficult to devise rules for the representation of many other forms which might occur in objects to be represented. But the above cases are sufficient to include almost every thing which occurs in the representation of models, of machines, of philo- sophical instruments, and indeed, of almost any regular produetion of art. Buildings may be exhibited by this perspective, as correctly, in point of measurement, as by plans and elevations, under the advantage of having the full effect of a picture. A bridge, or any circular, or gothic arch, consisting of portions of circles lying in isometrical planes, may be represented by portions of isometrical ellipses, which will easily be adapted and drawn, upen the principles already explained, by which wheels are exhibited on their axles. The centers of those circles must be found, with which the centers of the ellipses must be made to coincide, their minor axes lying along the lines drawn from those centers perpendicular to the planes of the circles. The shaft of a pillar consists of a frustum of a cone, and a cylinder united; or perhaps of a cylinder Professor FarisH on Isometrical Perspective. 13 alone, or a congeries of cylinders: and we have already shewn the method of exhibiting these, as well as their bases. And on the same principles, the position, and size of the volutes and ornaments of the capital, may be found, and such guiding points, as will make it easy to trace their forms. Thus the different courts, and edifices of a Cathedral, a College, or a Palace may be correctly depicted ; and even the rooms, and internal structure, though less in the form of a picture, may be exhibited in such a way as to enable an architect, or his employer, to contemplate their situation, their ornaments, furniture, or any other circumstance belonging to their appearance; and to mark down exactly what he would have done, in such a way, as could hardly be misunderstood by an attentive agent, though at a distance. But in thus exhibiting buildings as transparent, and their interior laid open, there is a danger of beimg confused by a mul- tiplicity of lines; which is a difficulty ina building containing many rooms, that would need some address to get over. It is better adapted to exhibit the inside of a single room, of a Cathedral, for instance, the aisles, and transepts of which would not cause any great perplexity. In the same manner a plan of a city might be given, which would not only represent its streets, and squares, as well (by the help of the scale above described fig. 7.) as a common plan, but also a picture of its churches, and public buildings, and even its. private houses, if such were the design contemplated by the artist, as they would almost all become visible, when looked down upon, from the commanding height which this perspective supposes. And such a single exhibition, if well executed, might give a better idea of a distant eapital, than a volume of description. In the instances which have been given, most of the lines are isometrical. But the art is applicable to many cases, where there are few, or none such. It may be necessary, in many of them, to 14 Professor Farisu on Isometrical Perspective. draw isometrical lines, or isometrical ellipses, by way of a guide, to determine the position of certain lines, and poits, to enable the artist to describe with accuracy what he has in view. And there is scarce any form so anomalous, as to preclude the artist from taking advantage of these methods of ascertaining such lines, or points in it, as will give him much assistance, in representing it with precision. If the intention be merely to make a picture, the guiding lines may be obliterated as soon as they have served the purpose designed, or they may be retained, in some cases, and their lengths or diameters noted down in figures, if it be wished, to give ready information. And often, if the artist wishes to provide materials to enable him, at his leisure, to give accurate descriptions, or exact drawings, the rudest exhibition of such lines may completely serve his purpose, provided he notes down on the spot, such measure- ments with accuracy, however unexact the lines may be on which they are recorded. In many cases it may be expedient to take liberties with this perspective, or with the picture, which will make it suit the purpose designed. And this will produce no confusion, provided those liberties are explamed: for mstance, it may often be expedient to make the scale, in the vertical direction, larger, some- times very considerably so, than in the horizontal. It may in some cases be necessary to represent on paper, what is hid in nature. What has been said on the internal structure of buildings, in p- 13, is an instance of this as well as what we shall observe on the exhibition of subterraneous objects. We shall proceed to give some examples of these observations. To give such a representation of an Etruscan vase, as would enable an artist to model it exactly, would be exceedingly easy. Let a vertical line be drawn to represent the axis of the vase, fig. 8, and let pomts be taken in that axis, corresponding to the centers of the principal circles of the vase; through which the horizontal isometrical lines may be drawn representing the radu of those Professor Farisu on Isometrical Perspective., 15 circles, by the help of which the isometrical ellipses representing them are easily drawn. These will become a complete guide to the artist. He may assist himself by looking at the object along the line of sight, and then, if he has any skill in drawing, he will find no difficulty in tracmg the outline from one of these to the other, with sufficient correctness. If he is unskilled in the art, of course he must be at the trouble of finding a larger number of ellipses to guide him. And in a similar manner, any solid, formed by the revolution of a plane figure round one of its sides, may be represented. The laying down the timbers of a ship, or making a picture of one, shall be another example. Let a vertical isometrical plane be conceived to pass through its keel, and to be intersected by the perpendicular planes passing through the ribs, and by planes parallel to the decks. The iso- metrical lines, which are the intersections of these, may be mea- sured in the ship, and represented, with their proper measures noted down, in the picture; which will afford the means of repre- senting the ribs, and laying them down in their proper places. If this should be designed for the purpose of constructing a ship from a given model, it might be sufficient to represent the ribs only on one side; those on the other side being the exact counterparts. If the purpose should be to make use of these lines for a drawing. they need be marked but very faintly, and the artist will have little difficulty, when guided by them, to fill up the representa- tion by hand. In a similar manner, this perspective may be applied to the ex- hibitions of animals, for the illustration of Natural History. All the leading points may be thus accurately designated, and a good artist will find no difficulty in making, by their help, a picture from the animal, which will shew its proportions distinctly. By this means, those agriculturists, who of late years, have so 16 Professor Farisu on Isometrical Perspective. much improved the breeds of our cattle, might explain their ideas with precision, on the points, to which they wish to call the attention of their readers. A regular fortification, which we will suppose to have eight bastions, will afford another example. A person net conversant in such a subject, is in general puzzled with plans, and sections, and has very little idea of what is meant to -be conveyed. But he would easily understand it, if he should see every thing exhibited in a correct picture, especially where he has the view of his object varied, as in a fortification, such as has been proposed. Let an isometrical ellipse be drawn expressing the internal cir- cumference of the place; and another concentric one, which marks the salient angles of the fortification, on the principles already explained. Draw other guiding lines to every necessary point; the lines of the fortification may be easily transferred from a common plan, to the isometrical, by the help of the scale of con- centric ellipses described above, fig. 7, which will serve also to lay down the length of the bastions, and curtains, &c. in whatever direction they lie. Find the elevations of every part on the iso- metrical scale ; and thus the body of the place, the ditches, coun- terscarpe, covered way, glacis, ravellins, and all the outworks will be represented to the eye as they appear in reality, and in every varied position; with the advantage of having all the admeasure- ments laid down with geometrical precision. If the artist should think the vertical lines, in such an exhibition, too small to give a correct idea of all the minute elevations, there would be no harm in his increasing the scale in that dimension in any desired propor- tion. The face of a hilly, or mountainous country, like Switzerland, or the district of the Lakes in the north part of England, will afford another example. Professor Farisu on Isometrical Perspective. 17 Isometrical horizontal lines may be drawn representing lines in the level from which the height of the mountains is to be reckoned, so that vertical lines drawn from the summits of the mountains may meet them, on which the heights may be marked; (as well as recorded in figures, if required). And the mountains themselves may be drawn in their topographical situation. Their bearings may be marked by the help of the isometrical compass described in p. 11. It would be easy to transfer them from a common map to the isometrical plan ; and thus the face of the country might be re- presented, just as it would appear from the commanding height which the isometrical perspective supposes. Yet, as the slopes of hills and mountains are seldom so steep as the line of sight, it might sometimes suit the purpose to represent the height of elevations as twice, or three times the reality, in order that mountains might project an outline on the plane behind ; otherwise, the summit might be projected on the mountain itself: which would in a degree destroy the effect of a picture. This art might be advantageously employed also, for tracing what.is below the surface of the earth, as well as what is above it. it may be applied to geological purposes, and give, not only the order of the strata, but their variations, and their geographicat situations. And for this purpose it might be useful to increase the vertical scale, in a great proportion, above the horizontal. It would be easy to mark the dip, or rise of the strata, as well as of the earth aboye them: to represent their various disruptions, to shew the situation, and extent of fissures, and metallic veins, to mark the boundaries where the upper strata have been swallowed up, or cease to appear; or where the under strata push up towards the day. It would be easy to mark the variations in the thickness of the strata in different places, and to record the result of experiments made at any point, by boring, or sinking shafts: which might be done by drawing a vertical line downward, so as to represent the C 1s Professor Farisu on Isometrical Perspective. thickness of the lammz, which might be marked by different colours. By such a method, the geologist might obtain a map of the country, which might exhibit at one view, the general results of all the experiments, and enquiries, that had been made relative to that science. And the owner of an estate might record in a small compass, all that is known respecting its minerals, and be able, from a comprehensive view of them all, to judge of the proba- bility of success in sinking a shaft, or driving a level. He might also make good use of this perspective, in tracing his shafts, and drifts, in all their windings, elevations, and depressions ; and com- paring them with the surface above: marking also the veins, and strata, in which they run. For if the artist knows what is beneath the surface, he has no difficulty in representing it as trans- parent. He must be careful however not to perplex himself by lines too much multiplied, and take advantage of his being able to paint the lines with different colours, for the purposes of dis- tinction, and he must use a considerable address in throwing out such lines as would be of little use, and in retaining such as will produce the effect of a picture; which should be well preserved, in order to make the exhibition easily intelligible. If he should wish to make a drawing of minerals, or crystals, this perspective would be well suited to the purpose. The point, however, on which the writer of this paper can speak with the greatest confidence, is on the representation of machines and philosophical instruments: having been himself so much in the habit of practically applying to them the principles that have been detailed. And this he has exemplified in the plates. The correct exhibition of objects would be much facilitated, by the use of this perspective, even in the hands of a person who is but little acquainted with the art of drawing; and the information given by such drawings, is much more definite, and precise, than Professor Farisu on Isometrical Perspective. 19° that obtained by the usual methods, and better fitted to direct a workman in execution. The writer of this paper cannot help flattering himself, that what he has delivered in it, may be found of some use, in rendering more clear, and intelligible, communications to societies, such as that, of which he has the honour to be the President. eh nial a "s s eas nem e vers in neh y Save oem tah 2 = | ee eons ith ke ela Nebel wii ingen alan: —wy savin wh. ee pilindedy: Magee | ee rena. thats ero ARO ee en a Rrdiey iei ete cain ; DT eel ie @w Be S ae » sweeper Seat tae a plete soa ie =i . ee ee eae ee ta | at xno —, 5 sagellalt ie ae Neiass Oe a a ch Gree mais Sari Era ae ia gies am ae wy ieee lee earn AR oi Ss ec " de: a eee Bo oi ak RR ae. The ie . * Way Ya Se oe * 3 < € ig * Lowry Fig. 10. Lowry, Se. II. On certain remarkable Instances of deviation from Newton's Scale in the Tints developed by Crystals, with one Awis of Double Refraction, on exposure to Polarized Light. By J. F. W. HERSCHEL, M.A. FELLOW OF THE ROYAL SOCIETIES OF LONDON AND EDINBURGH, AND OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. {Read May 1, 1820.] Tue discovery of crystals which possess two axes of double refraction, which we owe to Dr. Brewster, is perhaps the greatest step which has been made in physical optics since the discovery of double refraction itself by Bartholin, and its reference to an axis by Huygens. It has opened new views on the structure of crystals, and will in all probability be the means of leading us to a more intimate knowledge of the nature and laws of those forces by which the ultimate particles of matter act on light and on each other. When we reflect on the situation of these axes in different crys- tallized media, we cannot fail to be struck by the variety of the angles they include, and of the positions they hold with respect te the prominent lines or axes of symmetry of the primitive molecules, and the question immediately suggests itself, what are the circum- stances which determine their position in the interior of a crystal ? It seems to have been all along taken for granted that, whatever these circumstances may be, the nature of the ray must at least be a matter of indifference; in other words, that a red and a violet ray 22 Mr. Herscuet on the Tints similarly polarized and incident in the same direction on the same point of a doubly refracting surface, will either both undergo or both not undergo a separation into two pencils, without any distinction arising from the place of the ray in the prismatic spectrum. Were this the case, the two axes would be fixed lines within the primitive form, absolutely determined by the nature of the body, as much so as the lines which bound the primitive form itself, and any attempt to substitute for them hypothetical axes coinciding with remarkable lines in the latter figure, however ingeniously devised,*must be re- garded as mere speculation. The fact however is otherwise. In a paper recently presented to the Royal Society, I have shewn that the axes of double refraction in one and the same crystal differ in their position according to the colour of the intromitted ray, a violet ray being separated into two pencils, when incident in the same direction in which a red one would be refracted singly. This re- markable fact, which is almost universal in crystals with two axes places the question in a very different light. It appears that the nature of the ray as well as that of the medium, has its share m determining the position of the axes, and that the imtensity of the action of the medium on the ray is one of the elements involved in this problem. Now it is hardly possible to conceive the neutral axis of a crystal otherwise than as a position of equilibrium, or direction in which the axis of translation of a luminous molecule (if such exist) must be placed, that certain forces may act in opposition, and balance one another; but since forces which balance will lke- wise counteract each other when increased or diminished all in the same ratio, it follows that the partial or elementary forces so held in equilibrium do not observe the law of proportionality when the colour of the meident ray varies. If we suppose then with Dr. Brewster that these partial forces emanate from certain fixed axes coincident with remarkable lines in the primitive form, it will follow that each separate axis has a peculiar specific law which developed by Polarized Light. 23 regulates the intensity of its action on the differently coloured rays, and that each axis, supposing the others not to interfere with it, would exhibit separately a set of circular rings of which the tints would manifest a more or less marked deviation from the New- tonian Scale of Colours, as displayed by they uncrystallized laminee. This view of the subject will be remarkably supported by the facts about to be described, by which it will appear that among crystals with one axis only, there exists the greatest, IT might almost say, the most capricious diversity in this respect, and that probably no two crystals, either with one or two axes, have the same scale of action, or polarize the differently coloured rays with an energy varying according to the same law precisely. To this it may be objected, that from the result of a most elaborate examination of the colours exhibited by sulphate of lime, rock crystal, and mica, M. Biot has concluded that they follow in their action on coloured light, precisely the order and proportions stated in the Table of Newton, for the colours of thin plates of air. This coincidence is certainly extremely remarkable, supposing: it rigorously exact, and antecedent to further experience, would appear to authorize the conclusion, that the proportional lengths of the periods performed by differently coloured rays within crys- tallized bodies depend essentially on the nature of the rays them- selves, and not at all on the interior constitution of the crystal. Indeed in a case very analogous, M. Biot himself has attributed great and decisive weight to a presumption resting on the very same grounds. [ allude to his Memoir on the Rotatory Phenomena exhibited by rock crystal and certain liquids, where having observed that in the former substance, the rotatory velocities im- pressed on the planes of polarization of differently coloured rays, are inversely as the squares of the lengths of their fits; he argues that this relation being independent of any datum involving the 24 Mr. HERSCHEL on the Tints peculiar constitution of rock crystal, ought to be the general law for all other subtances which possess the rotatory property. ‘‘ Ou ** pourrait considérer d’abord que la rotation dans le cristal de roche “ ’étant trouvée réciproque aux carrés des longueurs des accés des ‘« divers rayons simples, cette loi se présente comme une propriété “des rayons mémes, et non comme un résultat dépendant de la ‘nature des corps qui agissent sur eux. Ou doit donc s’attendre, ‘““d@aprés cette remarque, que la méme loi subsistera dans toutes ‘les substances, comme on y voit se maintenir les rapports des ‘“accés mémes dont la seul longueur absolue varie.” However convincmg this line ef argument may appear, and however exactly supported by experiment in the case of the rotatory phenomena, its conclusions are not verified in that of the polarized rings, to which it nevertheless applies with as much or greater force as in the other instance, and this may serve to shew how very cautious we ought to be in our attempts te generalize antecedently to experience in this branch.of optical science. In the paper above alluded to, I have demonstrated that this law of proportionality admits of exceptions, and to the imstances there adduced, I have now to add other still more remarkable ones, which if I mistake not, afford abundant psoof that it has no foundation whatever in the nature of light. Indeed it may be observed, that the last sentence in the passage just quoted, is suflicient to destroy in a great measure the force of the argument in the former part of it: for, since Newton has demonstrated that for rays of a given colour, the lengths of the fits m different media are proportional to the sines of refraction corresponding to a given angle of incidence out ofa vacuum, and since the more recent discovery of the different dispersive powers of substances has proved that media differ very considerably in the proportion of these ses for the different rays of the spectrum, it follows that the proportional lengths of the fits must differ in every different medium. Hence will arise a difference developed by Polarized Light. 25 in the scale of colours which Their laminz of different media should exhibit, and though we may certainly fix on one (that exhibited by a vacuum for instance) as a standard, and call it the Newtonian Scale, yet this, though convenient, is nevertheless in some degree arbitrary, as we know not the nature of the media, with which what we call a vacuum may be filled, nor their action on light. Nor is this cause of deviation so small as to be safely neglected in all cases. In oil of Cassia the difference in the refractions of red and violet rays amounts to no less than =, of the whole refraction, and the colours exhibited by thin or thick plates of this liquid should therefore deviate very sensibly from those in air or in vacuo. Various solids too as chromate of lead, realgar, &c. could they be obtained by any means in sufficiently thin leaves, ought to exhibit a scale of colour differing altogether from that of Newton. The very remarkable succession of colours exhibited by that variety of the Fish-eye Stone (Apophyllite) which possesses a single axis of double refraction, has been noticed by Dr. Brewster, and since shewn in my paper already alluded to, to indicate an action on polarized light very nearly the same for all the colours, being equal upon the red and indigo-blue rays, a little greater for the yellow and green, and a little less for the violet, being the only instance yet adduced in the whole circle of optical phenomena of a maximum taking place between the extreme limits of the spectrum. I was led by this to conceive the possible existence of bodies, in which the law of proportional action should be so far subverted, as to render the periods performed by a red ray, within their sub- stances, actually shorter than those passed through by a violet one ; but certainly did not expect to find any conjecture almost im- mediately verified in the striking manner I am now to detail, and on the very substance which first gave rise to it. By the kindness of my friend Mr. Lowry, (to whose liberality in rendering his invaluable collection accessible to scientific D 26 Mr. Herscuet on the Tints examination, I have every reason to bear honorable testimony) I was provided with a very large, and indeed splendid crystal of Fish-eye Stone, which though not very transparent, owing to air included between its Jaminz, was yet sufficiently so to exhibit the rings of one axis with perfect distinctness, especially after a few days’ im- mersion in oil of turpentine. The character of these rings was however altogether different from that of the rmgs exhibited in the ordinary variety, their tints, instead of being alternately white and black, with a little intermediate shading of lilac and greenish yellow, as described by Dr. Brewster, being those of the following Table, in which the colour of the extraordinary pencil only is given. Taste I. 1** Order. Black, ruddy or yellowish white, white, faint blue, violet. 2° Order. Indifferent pink, orange yellow, dilute imperfect green, blue, purple. 3° Order. Good pink, orange yellow, tolerable green, blue, purple. 4" Order. Fine pink, yellow, green, light blue, indifferent purple. 5" Order. Rich pink, yellow, bluish green, indifferent purple. 6" Order. Pink, pale yellow, pale green. 7° Order. Pink, whitish, pale green. 8'" Order. Pale pink, whitish, pale green. 9g" Order. Ditto, ditto. 10° Order. Very pale pink, very pale green. 11" Order. Extremely pale pink, extremely pale green. 12'° Order. Scarce perceptible pink and green. In this series, the less refrangible rays evidently perform their periods with greater rapidity than those of the opposite end of the spectrum, but the number of alternations is still pretty considerable, and indicates a nearer approach to equality between the extreme red and violet than in the Newtonian Scale. Struck by this cir- developed by Polarized Light. 27 cumstance, a passage in a letter of M. Biot* now occurred to my recollection, in which, speaking of the conclusion I had arrived at by observations on homogeneous light in the ordinary variety of this mineral, he says, “‘ Si vous étes bien assuré de cette anomalie, ‘«je désirerai beaucoup que vous voulussiez bien essayer si elle se “soutient a toutes les épaisseurs, ou si elle éprouve quelque ‘« variation avec la Jongueur du trajet que fait le rayon a travers la “‘ substance cristallisée. Je serais extrémement curieux de savoir “Je quel de ces deux cas a lieu.” To this surmise of a variation in the proportional lengths of the periods depending on the thickness of the plate, or the length of the path traversed within the crystal, all my previous observations had certainly enabled me to answer decidedly in the negative. But so singular a deviation from what I had before observed, led me to suppose that there might be something in this observation deserving a minuter examination, and I resolved to sacrifice this specimen to the enquiry. The result, as will be seen, by a most accidental coincidence, actually verified the suggestion of that acute Philo- sopher, though in a way which he certainly never could have con- templated. The crystal is represented in fig. 13. It was about + inch in its greatest breadth and 0.27 inches in thickness, being a portion of a right prism, the plane angle (bac) of whose base was about 96°. The sides were striated longitudinally, and appeared to have been encased with a thin and highly polished exterior coat, of which a small portion was still adhering+. The structure was perfectly lamellar, the laminze being parallel to the base of the prism. On examining it more narrowly, a remarkable flaw was perceived commencing at f and running along fg, parallel to the lamine. * Dated, Oct. 21, 1819. + The specimen, as I learn from Mr. Lowry was brought from Utoe in Sweden, and was attached to a mass of oxidulous Iron. D2 28 Mr. Herscuet on the Tints On this I set the edge of a knife, and succeeded without difficulty, by a smart blow, in cleanly separating the two portions. The little irregularities in their surface being ground away, and a good polish communicated to them, their thicknesses were taken by the spherometer and found respectively 165900 and 94499 millionths of an inch. On examining them separately in polarized light, I was now much astonished to find the rings exhibited by the two portions, though both circular, yet differing altogether in their characters. Those in the thicker portion were in every respect precisely analogous in the scale of their tints, to those of that variety with one axis, which seems to form the central portion and upper lamina of Dr. Brewster’s Tesselite, and of which I need not here particularize the succession of colours, as it is given at full length in my paper above alluded to. On the other hand, the rings in the thinner portion exhibited a complete inversion of the Newtonian Scale, the red rays being more energetically acted upon than the violet, and that to so extraordinary a degree, that the whole prismatic spectrum was displayed in the very first ring. To obtain a sufficient range of incidence, this plate was enclosed i olive oil, in a proper apparatus for measuring the inclination, and being exposed to polarized light, (the plane of incidence being 45° inclined to that of primitive polarization) the succession of tints and their corresponding angles of incidence were as in the following Table, in which the angles are deduced from two observations of the same tint on opposite sides of the axis. The measures of length in this and the subsequent pages are in millionths of an inch, for the sake of placing in evidence their proportion to the lengths of the fits of easy transmission and reflexion. developed by Polarized Light. 29 Tapre II. Second variety of Apophyllite in olive oil. Index of refraction 1.0497. Thickness of the plate = 94499. Incidence. Ordinary Pencil. Extraordinary Pencil. 0° oO’ | White. Black. White. Sombre orange red. White. Pretty good orange. Very light blue. Good orange yellow. Sky blue. Fine orange yellow. Fine deep indigo. Fine light yellow. 23 35 | Rich dark purple. Pale yellow. Fine crimson. Light greenish yellow. 27° 11’ | Fine pink Fine light green. 28 48 | Pink, somewhat inclining to brick red. |Good bluish green (maximum of contrast), Light pink, inclining to orange. Blue, rather greenish. Pale pink yellow. Dirty and sombre blue. 33 2 | Yellowish white. Dull, indifferent purple. Good pink. Good pink, inclining to brick red. Light yellow green. 36° 48’ | Good bluish green. Dull blue green. Orange pink. Very dull blue green. Yellow pink. 39 41 | Pale purple, almost white. Pale yellow, almost white. 41° 35’ | Pink, inclining to brick red Bluish green, rather pale. Yellow pink. Dull pale blue. 43 55 | White. Very dilute purple. Pale blue green. Pale pink. White. White. 50° 2’ | Very pale pink. Very pale blue. White. White. Beyond this inclination, the colours are no longer distinguishable. The whole series indicates a separation of the colours much more considerable than in the Scale of Newton, but to examine the variation of the polarizing energy for the several simple colours more minutely, we must have recourse to homogeneous light. The requisite measures were taken with every precaution in very fine 30 Mr. HerscuHet on the Tints sunshine, and though owing to the imperfections of the specimen, they do not pretend to great precision, the resulting numbers can scarcely be erroneous to the extent of = or 3, of their own value. I think it necessary to premise this, as the law of action indicated by the following Table of the results is so very surprising and unex- pected, that it was not without scrupulous examination I could persuade myself that no enormous oversight had been committed. The first column expresses the colour of the incident ray, the second the length of the shortest period of alternate polarization it is capable of performing within the crystal, computed by M. Biot’s formula, sin. 6. tan. 6 3 n l=t I in which é@ represents the thickness of the plate, 6 the angle an intromitted ray makes with the axis (supposed perpendicular to the surface), » the number of periods and parts of a period it executes during its passage through the plate, or the order of the ring to which it is referred at its egress, and 7 the length of a period per- formed by the same ray supposed to traverse the crystal at right angles to its axis, or the mmimum length above-mentioned. The third column contains the value of >, which measures the polar- izing energy of the crystal on that particular ray; the last the number of observations employed in computing the values im the pre- ceding. developed by Polarized Light. 31 Taste III. representing the Law of Action of the Second Variety of Apophyllite, on the differently coloured Rays of the Spectrum. Name of Colour. Value of J. Value of Ss . | Number of Observations. Extreme red. 20213 AQ.475 20 Mean orange. 25465 39.270 20 yellow. 30374 32.923 20 green. 38057 26.277 20 blue. 93904 10.649 10 indigo. 250000 + 4.000 — Indigo violet. 250000 + 4.000 — Mean violet. 45992 21.743 Extreme violet. 35043 28.536 By this Table we see that the action of the crystal decreases rapidly, but regularly enough from the extreme red to the blue rays, when it sinks all on a sudden, and throughout the whole extent of the digo and first portions of the violet is so small, that I was unable to obtain a measure even of the first rmg at its max- imum, within the range of incidence my apparatus would admit. It then increases again, more suddenly than it fell, and for the extreme violet has a value intermediate between those for the yellow and green. If we construct a curve roy gbiv, whose abscissas AR, AO, &c. are reciprocally proportional to the lengths of the Newtonian fits, and drawing the line 4rB at an angle of 45° with AV, take the ordinates Rr, Oo, &c. every where proportional to the value of “in this Table, this curve will represent the action of this variety of apophyllite on the whole spectrum, while 7B repre- sents that of a crystal whose tints follow the Scale of Newton, (fig. 14.) This is in perfect agreement with the succession of tints given above, if we cast our eye over it, a deficiency of the indigo rays is perceived in all the scale of the extraordinary pencil, no pure or rich 32 Mr. HerscueEt on the Tints blue occurring throughout its whole extent. In the ordinary pencil on the other hand, the excess of indigo appears immediately in the rich tints of indigo, purple and crimson which occur in the first order. The yellow rays too afford us a numerical verification of the number assigned to them. The maxima and minima of these coincide, as Newton has observed, with the most lumineus, and obscurest parts of the rings, which is a necessary consequence of their great illumi- nating power. Now these occur. at the incidences 23° 35’, 33° 2’, and 39° 41’ respectively, and if we compute the angles of refraction (6) corresponding to these, and take m successively 5, 1, 3, the formula already employed gives by the first maximum - - - / = 29269 by the first minimum - - - / = 29822 by the second maximum - - / = 29370 = 29487 Mean. which differs from the result in the third Table by less than = of its value. , The absolute polarizing powers of the two portions into which the crystal was divided, differed no less remarkably than the characters of their tints. In the thicker plate, by a mean of 20 careful observations made by the interposition of a certain standard red glass, on the rmg of the third order at its minimum (in which the evanescence of the extraordinary pencil was complete, I found 37° 3’ for its apparent semi-diameter in air, and hence we find @=23° 7’, n=3, t=165900, which substituted give 1000000 l and (as is sufficiently evident from the scale of tints in this portion) their value of 7 is nearly the same for all the other colours. Now it is well worthy of observation, that this value coincides almost precisely with the number similarly determined for the variety examined in my paper above alluded to, which I have there found to be 9281. The l = 9269; = 107-886, developed by Polarized Light. 33 difference is little more than ; of the whole, and so exact an agree- ment could hardly have been expected even in plates detached from the same specimen. This circumstance, together with the identity in the scale of tints exhibited by the two substances, esta- blishes not only their exact similarity as individuals, but, what is of much more importance in this case, the definite nature of the variety itself; and at the same time proves that in detaching the two portions from one another, no part of the second variety remained adhering to the first, as it must have become sensible by enfeebling the polarizing power, if not by altering the tints. But the structure of the crystal under examination is yet more compounded than what I have been describing. Dr. Brewster has already, in a highly interesting paper in the Edinburgh Transactions, described the union of our first variety of apophyllite with another, possessing two axes of double refraction, forming regular columnar crystals, consisting of an interior portion of one kind surrounded by a case, or border of the other, &c. The specimen I am now de- scribing, however, presents the hitherto unique combination of no less than three distinct substances, having each but one axis of deuble refraction, unitmg to form a single crystal, and followmg regular geometrical laws of juxta-position. In examining the two plates as above detailed, the portions most transparent and uniform in their structure were selected, and insulated from the rest by fastening them over holes of about an eighth of an inch m diameter in sheets of lead. But when the whole plates were exposed to a polarized beam, each was observed to consist of two distinct portions or com- partments, as represented in fig. 15, where the mterior parts abede are those already examined ; the border ABCDcba being separated from the interior portion by a plane of junction which, in the thicker plate appeared on inclining it, to be marked with a series of pretty broad coloured fringes, whose origin is sufficiently obvious. Con- siderable irregularity appeared in the structure of this border, but, at E 34 Mr. Herscuet on the Tints a perpendicular incidence, or when inclined at any angle in the plane of primitive polarization, or in one perpendicular to it, it had no action upon the incident ray, however turned round in its own plane. Of course it has but one axis of double refraction, and that at right angles to its lamine. The best and most transparent portion being selected and in- sulated as before, the plate was enclosed im the oil apparatus, when the tints developed on inclining it in a plane making an angle 45° with that of primitive polarization, were as follows: Taste IV. Apophyllite, third Variety. Thickness = 94499. Incidence. Ordinary Pencil. Extraordinary Pencil. White. Black. Yellowish white. Sombre indigo. Pale yellow. Indigo inclining to purple. Pale greenish yellow. Pale lilac purple. White, slightly greenish. Very pale reddish purple. Very pale green. Pale rose red. White. White. White, scarce perceptibly tinged | White, scarce perceptibly greenish? with pink? This Table of tints indicates a much more energetic action on the red and violet ends of the spectrum than on the intermediate colours, especially the yellow, and this was fully corroborated by observa- tions in homogeneous light, which gave the values of Z for the several simple colours as in the subjoined Table. developed by Polarized Light. 35 Tasie V. Scale of the Minimum Lengths of the Periods of the dif- ferent simple Rays in the third Variety of Apophyllite, and their Reciprocals. Minimum length of period Polarizing power or value | Number of Obser- Name of Colour. 1000000 ; : of “_ 5 vations. value of /. Extreme red. 43634 : 10 Mean orange. 101238 : 10 yellow. 366620 + 3 10 green. 89646 , 10 blue. 32211 , 10 indigo. 21947 ‘ 10 Extreme violet. 13704 ; 10 The curve representing the values of ; or the polarizing energy of the variety now under consideration, constructed as in the former case is represented in fig. 16. Its ordinate, as we see, decreases rapidly from the red to the yellow, where it is beyond the reach of the present observations, then increases again yet more rapidly, and is greatest of all for the violet rays. For the sake of comparison, fig. 18, represents the curve similarly constructed for the ordinary variety which has a maximum where the variety last described has a minimum. The straight line rB inclined at 45° to the abscissa in all the figures represents the values of > for such crystals as follow Newton’s Scale in their tints. The apophyllite has furnished us then with no less than three instances of remarkable deviations from Newton’s Scale in crystals with one axis. It would certainly be in the highest degree in- teresting to subject them all three to chemical analysis, but as the total weight of the specimen presenting these anomalies did not exceed 60 grains of which nearly one half consisted of the ordmary variety, I have not sufficient confidence in my own chemical dexterity to enter on so very delicate an enquiry, which would E2 36 Mr. Herscuet on the Tints obviously call for a degree of precision attainable only by con- summate masters in the art of mineral analysis. It remains there- fore to be ascertained whether their different actions on light be owing to a difference in composition or merely in their state of aggregation. Meanwhile, as we have seen that the union of two erystals differing in their scale of tints produces a scale differing from either, it may not be irrelevant to enquire whether the alter- nation of amine of two of the varieties above described may not be capable of producing the remaining one. To this end, let ¢, #, t’, &c. be the thicknesses of the 1", 2°, 3°, &e. Jamina so superimposed as to have their axes coincident, and of the same refractive density: 7, U7, l’, &c. the minimum lengths of the periods susceptible of bemg performed by a ray of any colour within these several crystallized plates, and 6 the angle with the axis, at which a similar ray traverses the system. Then, as M. Biot has proved, the number (z) of periods, and parts of a period actually performed by this ray during its passage through the first plate is given by the formula, = 5 -sin. 6 x tan. 6, the Jamin being supposed all of one class (i e. all positive, or all negative) or ¢ being regarded as negative for those of a contrary class. The periods performed by the same ray in traversing the second Jamina will be x sin. @ x tan. @, and so on, and, according to what the same eminent philosopher has proved, the ray will assume at its emergence from the system, the same plane of polarization as if it has executed m+n’ +n’ +&e. periods in one lamina. If then we take nintn’+&e.=N; t4t4+0t'+&c.=—T, developed by Polarized Light. 37 we have N= (45 +— m+ Gc.) x sin. @ x tan. 6 fh : =— x sin. @ x tan. 0, L provided we take Z so that ere. te, Rare TF i r + &ce. Let p, p’, p’, &c. represent the polarizig power of each lamina on the given ray, and P, that of a lamina sua to the com- pound system, and we have, P=; +2 = ; -ic..¥——... sethat = Pt prt .p tit pe + &e. t.p+t.ptt' .p’ + &e. and P= PGS Be: If then P be so assumed, an imaginary plate whose polarizing power is P and thickness that of the compound plate (¢ + t + &c.) will exercise preeisely the same action on the ray as the system so constructed, and it appears from the nature of this formula that it is indifferent in what order the elementary laminz are distributed ; so that all those of the same species may be conceived grouped together and united into one. Now suppose the colour ef the ray te vary, and let e be any quantity whose magnitude determines its place in the spectrum (as for instance, the reciprocal length of one of its fits of easy trans- mission and reflexion in vacuo). Then if we represent as we have done before, the quantity ec by the abscissa of a certain curve, p. (a function of ec) may be represented by its ordinate; p’ (another function of c) by the ordinate of another curve, and so on, and P, the ordimate of a similar curve for the compound plate may be computed by the above formula. 38 Mr. Herscuet on the Tints But it is evident from a moment’s consideration of the forms of the three curves representing the polarizing powers of three varieties of apophyllite, that no one of them can be produced by any combination of the other two according to this law, and we are therefore necessitated to admit each as a distinct variety or at least composed of laminz of not fewer than three kinds. This alter- nation or superposition of lamine of different polarizing powers is no hypothetical case. I have observed its occurrence not only in the instance before us, but in other crystals of perfect regularity in their external forms. Dr. Brewster has also observed phenomena referable to this principle in his paper on the apophyllite. Hyposulphate of lime (formed by the union of that base with the hyposulphuric acid lately discovered by Welter and Gay Lussac, (see Ann. de Chimie, X. March 1819,) affords another imstance of deviation from Newton’s Scale in crystals with one axis of double refraction. This salt crystallizes m bevilled hexagonal tables which have no distinct cleavage, the axis being perpendicular to their broad surfaces. The following is the scale of tints developed by a plate of this salt on exposure to polarized hght: developed by Polarized Light. 39 Taste VI. Hyposulphate of Lime. Thickness =35701. The axis was inclined 5° 12’ to the surface in the plane of incidence. Incidence. 29° 33’ 31° 45’ Ordinary Pencil. White. White. Very pale yellow. Sombre yellow. Sombre pink yellow. Sombre purple crimson. Beautiful rich dark purple. Beautiful deep blue. Bright blue. Fine light blue. Light greenish blue. Light yellow green. Light greenish yellow. Ruddy but pale yellow. Pink, light and approaching to brick red. Fine pink. Pink. Pale purple. Dull blue. Bright greenish blue. Blue green. White. Extraordinary Pencil. Black. Very faint sky blue. Pretty strong sky blue. Very light bluish white. White. White. White a little yellowish. Bright straw colour. Yellow. Yellow verging strongly to orange pink. Fine pink. Sombre pink. Purple. Blue. Bright greenish blue. Splendid green. Light green. Greenish white. Ruddy white. Tolerable pink red. Fine rose red. Dull pale purple. 35° 27° 39° 32’ Ruddy white. . Good Pink red. Dull pale purple. Light blue green. White. Light Pink. White. Extremely pale blue. White. Blue, rather pale. Green blue. White. Pink red. Very pale purple. Very light blue. White. Almost imperceptible pink. White. 40 Mr. HerRscHeEt on the Tints The colours here cease to be perceptible after the fourth order, and the degradation of the tints is evidently much more rapid than in Newton’s Scale. Thus the blue of the first order, which in that scale is scarce perceptible, is here sufficiently strong to influence its complementary tint, depressing it to a pale yellow. The green and its complementary pink of the second order in this Table are fully equal in brilliancy to those of the third in Newton’s Scale, while those of the third are scarcely equal to Newton’s fifth. Accordingly, by a series of measures taken with considerable care in homogeneous light, I found the values of Z for the several simple colours as follows : Taste VII. Scale of the Minimum Lengths of the Periods in Hypo- sulphate of Lime, and their reciprocals. Minimum length of its period, Polarizing power or value | Number of Obser- Name of Colour. 000000 ; or value of 7. of 3 vations. Extreme red. 3241 308.54 38 very exact. Mean orange. |’ 2454 407.45 26 yellow. 2129 469.65 28 green 1861 537.32 20 —— blue. 1058 603.21 20 indigo. 1480 675.83 20 Extreme violet. 1129 885.77 The curve constructed from this Table, as in the case of the apo- phyllites, is given in fig. 18. The rings in this crystal when crossed by a plate of sulphate of lime are affected in the same way as those in carbonate of lime, tourmaline, &e. and the axis is therefore of a repulsive character. The facts above adduced suffice to shew that vast differences exist in the scale of action which a single axis may exercise on the differently coloured rays ; and that, whether we regard the single apparent axis of any of the above crystals as the resultant of two developed by Polarized Light. AL others equal to it in energy but of an opposite character situated at right angles to it and to each other, with Dr. Brewster, or as bemg itself the real axis of polarization. For the resultant axis being the same for all the colours, the partial actions of each of the supposed axes on the former hypothesis, having the same point of com- pensation for all the colours, must be equal to each other and to the resultant force for them all. The mere fact therefore of a deviation from Newton’s scale, however enormous in the tints of any regular crystal with one axis, cannot be regarded as affording of itself any argument for the substitution of two others for it in that particular substance, because each of such axes acting separately would exhibit a scale of tints perfectly identical with that of the axis whose place they supply, and therefore by parity of reasoning should be regarded as the resultant of two others, and so on, ad infinitum. This reasoning appears to me conclusive against any analogy between crystals with one and two axes, founded on a deviation of tints in the rings of the former. But I cannot help regarding the phenomena I have described as affording con- siderable support to the very ingenious theory of the philosopher just mentioned, as applied to crystals with two axes, masmuch as they establish the existence of that diversity in the scales of action of the simple or elementary axes, without which their points of compensation (or the poles of the lemniscates they exhibit in polarized light) must of necessity be coincident for all the simple colours, a coincidence which, as has been already remarked at the beginning of this paper, seldom or never takes place. This I conceive to be the view which Dr. Brewster himself has taken of the phenomena of the deviation in crystals with two axes, and to afford ocular demonstration of the existence of what he has called the different dispersive powers of his elementary axes. J. F. W. HERSCHEL. SLouGH, Feb 19, 1820. thos Pein, a stl iihag ie hy fied as “oon ag eau. aL, THM be orem . Het pe edt: Diy ace iH f Brainy TAP aie ? mem eRe Ga 7] oP WA atid Hone wt idl Oe Plt ae he ee ie ae Won» Sarat 1 AP 1 RES rarest NO pee Nasiera iy Ptiaee te, wih vines ae. Nara et Hse ty "HAS . pe sesetere Vic ‘ tae erie wri mery- ebuni ‘te tous lone he bial iow -hentastie ee et Pt oe Me 1 seedy ie Blaes ealaane partie bd tie te fiw aif awe te (ott SAP” Mie Bib ua a ste “farindy Vi Bebaiics :oh i!) Giaoee j neil P wh byrne baae eet iin * add d iP foibe THAT nnd at! loge ie Ta wongry: : sadvbigtre cm lewheaseedy ‘gw: § : oe ai Hotty ae aponsbinky AM) to vane ct ese eh MTA «bi va MNT NAY ay dee tabi a bar ee ; iret: tO has alt fh hes mm ‘ ax! wilh phe de oaniong Hunky. dvix Wyeniitiree, 7 tasaeie 199 wh Settles vay Yosh wat ge i et legentyae oak Tee gladness é‘ ° mpdth toenelatiiii li aid ean ome P Asie. sans bit L att: gare AOL) gr an “a0 a) | eo a aa Hedy! ore ge ae AH itl dele re ; Wty MHL adi. ; ni + ties naan isis wig Tey wid svud III. On the Rotation impressed by Plates of Rock Crystal on the Planes of Polarization of the Rays of Light, as connected with certain peculiarities in its Crystallization. By J. F. W. HERSCHEL, M.A. FELLOW OF THE ROYAL SOCIETIES OF LONDON AND EDINBURGH, AND OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. [Read April 17, 1820.] Tue phenomena of the developement of colour in plates of Rock Crystal when polarized light is transmitted through them in the direction of the axis of double refraction, and analysed at its egress by a doubly refracting prism, were originally noticed by M. Arago in 1811, and have since been examined in a very masterly manner by M. Biot in two Memoirs communicated to the French Institute in 1812 and 1818. It results from the experiments described in the latest of these, first, that a plate of this substance exposed to polarized light in the manner above described, possesses the singular pro- perty of displacing the plane of polarization of an incident ray, and turning it aside in one invariable direction, through an angle always proportional to the thickness of the plate, so that at its egress, the plane of polarization will assume the same position as if it had revolved in one direction during the passage of the ray through the whole thickness with an uniform angular velocity depending on the nature of the ray. Secondly, that this rotation of the plane of polarization, (for so we may be permitted to call it, though we F2 44 Mr. Herscuet on Polarization by Rock Crystal. know not whether any rotation actually does take place within the crystal, but only that the result is as if it were so) though in- variable in its velocity for rays of the same colour, differs for those of different colours, being greater for the more refrangible rays, and that in the inverse ratio of the squares of the lengths of their fits in vacuo. ? Thirdly, that although the direction of this rotation with respect to the observer (who is supposed to receive the ray in his eye) be invariably the same in the same specimen of rock crystal, whatever be the length of the ray’s path within it, or whichever side of the plate be turned towards him, yet it differs in different specimens ; in some being always from right to left, and in others from the left to the right of the observer so placed. Fourthly, that this smgular property is common to rock crystal with a variety of other bodies, and among the rest with various liquids, such as oil of turpentine, solutions of camphor, sugar, &e. in all which precisely the same law of rotation of the differently coloured rays is observed, the absolute velocity only differing. Many of them carry this property with them into their chemical combinations, solutions, and mixtures with other substances — they preserve it in their solid, fluid, and even gaseous form, with an energy proportional to their actual density, nor can any thing short of the decomposition of their molecules deprive them of it. From these circumstances, as well as from a number of delicate and accurate experiments on the compensation of opposite rotations by the mixture of different liquids, and others which it is not necessary to enumerate here, M. Biot has concluded that there exists a property inherent in the ultimate molecules themselves of certain bodies, independent of their regular disposition in crystalline forms, their state of aggregation or proximity to each other, in virtue of which each individual molecule turns round the plane of polarization of a ray traversing it, through a certain minute but Mr. Herscuet on Polarization by Rock Crystal. 45 determinate angle depending only on the nature of the substance and of the ray. ‘‘Cette propriété consiste dans la faculté qu’ont “les molécules dont il s’agit de faire tourner d’un certain angle, et “dans un certain sens les axes de polarization des rayons lumineux.” Mysterious as such a property may seem and entirely opposing all our preconceived notions of the nature of the ultimate particles of bodies, unless we deny the precision of M. Biot’s experiments, it is hardly possible to refuse our assent to the general tenor of the conclusions he deduces from them. Admitting then, for the present the truth of the inference, we are left to conjecture the cir- cumstances in the intimate constitution of the molecules which can determine an invariable tendency of a ray of light to turn its plane of polarization in one direction rather than another, in whatever way they may be presented to it; and though it seems very difficult to form a definite hypothesis to explain the fact, yet the general impression left on our minds is that of a want of symmetry in the disposition within the molecules themselves, of some of the ele- mentary forces by which they act on light; a thing not incom- patible with perfect symmetry in their external forms, or in the distribution of the more powerful forces which determine the laws of their aggregation in regular crystals. Now so far as the action of crystallized media on light has been examined, there appears to exist an intimate connexion between the crystallographical and optical properties of bodies, and as we have every reason to image that the forces by which the particles of matter act on light and on each other, do not differ essentially in their nature, it is easy to conceive that any deviation from perfect symmetry in the dis- tribution of even subordinate forces of any kind, will m some degree influence the molecules in their mode of aggregation with one another, and however feeble, yet, being a cause constantly in action, may possibly, under favourable circumstances, produce a sensible 46 Mr. Herscuer on Polarization by Rock Crystal. modification and deviation from symmetry in their crystalline form, such as might arise for example, from a preference given to more rapid laws of decrement on some of the angles and edges than on those adjacent to them, though similarly situated with respect to the axis of symmetry of the primitive form. From such laws of decrement would result faces unsymmetrically situated with respect to that axis, and having a bias, or tendency to lean as it were in one direction rather than another. In the variety of quartz to which Haiiy has assigned the name of ‘* Placiédre,” such unsymmetrical faces de in fact occur. One of these crystals is represented in fig. 19, in which we may observe that the faces vw, v, xv, and 2’, 2’, x’, peculiar to this variety, lean or tend as it were, in one uniform direction round the summit A adjacent to them, the angle made by them with the adjacent sides of the prism being greater on one side (the right, for instance) than the other. If we invert the crystal so as to bring the summit a@ uppermost, the plagiedral faces adjacent to this summit observe the same law, and lean in the same direction, nor so far as I know, does any instance oceur of this law being broken, or of faces of this kind leaning opposite ways co-existing on the same crystal*. No inference however could be drawn from this circumstance, were it not for the very remarkable peculiarity of this substance, in virtue of which different specimens of it produce opposite rotations. This, it is evident, furnishes us at once, with a means of verifying or dis- * The faces in question originate in those laws of decrement which Haiiy has called intermediate. The primitive form of quartz is a rhomboid slightly obtuse whose axis is parailel to that of the hexagonal prism. The subtractive molecule by which the decrement on the angles E (fig. 20.) takes place to produce the faces 2, is composed of eight of these rhomboids, its edges consisting respectively of 1, 2 and 4 edges of the primitive rhomboid, and the decrement resulting is represented in Haiiy’s Notation by (£*,D*D'). The alternate faces x’ arise from a different law (as they obviously must, the angles upon which they are produced being differently related to the superior vertex). Their law of decrement cannot be reduced to an integer expression, but is represented by (: £,D*B') in the same notation. See Haiy, Tratte de Minerologte. 4to. Plate 45. (Tom, Il, p. 297.) Mr. Herscuen on Polarization by Rock Crystal. 47 proving the existence of such a cause as I have suggested in any ease where we suspect it to have operated in producing such un- symmetrical faces. Now, on examining with this view different. crystals of the plagiedral variety, I observed that in some specimens the pecuhar faces do actually lean always to the right, while in others, similarly placed with respect to the observer, they as regularly tend the opposite way, or towards his left. In other respects, as in hardness, lustre, transparency, specific gravity, &c. no marked difference appears to exist between those of the one kind and the other. Here then we have a phenomenon precisely analogous to the opposite rotations produced by the same body in the planes of polarization of light, and it could not but appear probable that both originated from a common cause. To conyert this probability into certainty, it only remained to ascertain whether or not the direction of rotation of a polarized ray be invariably dependent on that of the plagiedral faces in such crystals as possess them. It is true M. Biot in his Memoir above cited, has assured us that no peculiarity in the crystalline form (among other characters) can lead us to conjecture what may prove the direction of rotation in a given specimen of rock crystal previous to trial, but as crystals of this variety are comparatively rare it seemed not unlikely that they might have escaped his examination *. When this idea first occurred to me, the only plates of rock crystal in my possession fit for the purpose were nine very fine ones cut from a single crystal, of which I had fortunately preserved the summit, on which were two small but very distinct and brilliant faces of the plagiedral kind, leaning to the left when the vertex of * His words are ‘“‘ Enfin, puisqu’il existait des aiguilles a rotations contraires (j’en tirai comme consequence qu’) il fallait quelles fussent composées ou au moins uniformement mélées, de deux substances de nature différente, sans qu’aucun indice dans leur transparence ou leur forme cristalline pat faire soupconner cette diversité.” 48 Mr. Herscuet on Polarization by Rock Crystal. the pyramid was uppermost. (This for brevity I will call a left- handed crystal). The rotation in all these plates was to the left, to an observer looking in the direction of the ray’s progressive motion or to the right of one receiving the ray in his eye. I shall adhere to the former position. As to the direction of rotation, it is: easily recognized. We have only to enclose the plate between two cross tourmalines and notice the center of its rings, or place it in a polarized beam traversing its axis, and analysed by a prism of Iceland spar, attending only to the extraordinary image. Suppose the rotation to be the left of the ray’s motion, then, if we turn the tourmaline next the eye, or the prism of Iceland spar contmually to the left (of the observer), the minima of the blue, yellow and red rays will occur in the order here set down and of course the image will appear successively red, purple, and blue or green, or will appear to descend in the order of the rigs, whereas in a crystal of a contrary character the colours succeed one another in a contrary order, or which comes to the same, the motion must be made from the observer’s left to his right, to produce them in the same order. In this instance then we have, Direction of the plagiedral faces, right to left ©<—-—<@< Rotation ditto ditto ie On examining all the quartz crystals in my- possession, I could discover but one more in which a plagiedral face occurred. This was however very perfect and was directed to the right 33———— ». From this crystal I procured a plate to be cut, and was not a little gratified, on placing it in a proper apparatus to find its rotation such as I supposed it would. In this instance therefore we have Plagiedral faces SS—> Rotation 7 ——~s Encouraged by this trial, I procured, after some search, severai Mr. Herscuet on Polarization by Rock Crystal. 49 crystals of the variety in question, and selecting seven of the best put them into the hands of a lapidary. Of these crystals, three were left-handed <——<«<€ , and four right + >———— , and to avoid confounding them, besides giving particular directions to the workman to fold each crystal with the plate cut from it separate from the rest, I took the precaution to identify them by corres- pending diamond marks, and for greater security took care on their return to assure myself by the fitting together of the pieces, their lustre, flaws and striation, &c. &c. that no misarrangement had taken place. They were then subjected to the same examination, and the result in each instance was conformable to that of the two preceding trials, the direction of rotation to an observer looking in the direction of the ray’s motion, being in each of them the same with that of the plagiedral faces. Perhaps I might have rested satisfied with having pre-deter- mined eight times without a failure the direction of rotation, but as this seemed rather too small a number to found a general rule upon, I selected five more, in two of which the peculiar faces turned to the right 3y———> , and in the other three to the left, and having procured a plate to be cut from each, placed them in succession on a proper apparatus, and requesting a friend to notice the succession of colours on turning the index one way or the other, named the order of succession in the colours proper to each plate from the inspection of the crystals to which they belonged, and the pre- diction so made previous to any observation on my own part was declared to be verified in each instance, of which, for fear of a mistake, I took care to satisfy myself at leisure. The induction from so many instances without an exception seems conclusive, and we are authorized to state it as a fact, general as far as our present observations go, that the direction of rotation in quartz corresponds with that of the unsymmetrical faces in the plagiedral variety of its crystals, and that consequently these G 50 Mr. Herscuet on Polarization by Rock Crystal. faces are produced by the same cause which determines the dis- placement of the plane of polarization of a ray traversing the crystal parallel to its axis. What this cause may be, I have ventured. to hazard something like'a vague conjecture. Should the fact itself be regarded as in any way corroborating the idea of a force inherent in the molecules of bodies there still remains a great obscurity and indistinctness in our conception of such a force. If I mistake not, however, much of this arises from the difficulty we find in conceiving that part of M. Biot’s hypothesis which supposes a particle of matter to act on a ray with precisely the same force and in the same direction in what- ever way it is presented to it. Now this condition is not necessary. There may possibly exist in every molecule, a direction or axis in which the force of rotation is a maximum, and others in which it is nothing or even negative, that is, tending to produce a contrary rotation, while in other positions it may be intermediate, and follow some unknown law in its intensity. In liquids, in which the axes of the particles have every possible direction, the rotatory force resulting from their joint action will be an average or mean among all the values it is susceptible of, regard bemg had to the com- parative frequency of their occurrence while im crystallized bodies, whose molecules are all similarly arranged, and in which, owing to their polarizing action the effects of the rotatory forces can only be discerned in one or at most two directions (those of their neutral axes) its apparent intensity may have any value from the maximum to the minimum, according to the position of these axes within the molcule. It seems not impossible, therefore, that substances actually possessing the rotatory property, and capable of exhibiting it in a liquid state may appear divested of it in their solid form by the coincidence of their axes with positions in which it is really evanescent, and vice versd, that solids possessing the property of rotation in a very energetic degree on account of the Mr. Herscuet on Polarization by Rock Crystal. 51 coincidence of their axis by double refraction with that of their maximum rotation may, when held in solution, act much more feebly, or not at all. This may possibly be the reason why a solution of silica in potash (liquor silicum) possesses no rotatory power*. It may perhaps explain too, the very inferior energy of the rotatory force, as developed im all the fluids in which it has been recognized hitherto, to that exerted along the axis of rock crystal: a remarkable circumstance of which no other account has yet been given. The fact above recorded is interesting in another point of view. It may lead us to pay a minuter attention to those seemingly capricious truncations on the edges and angles of crystals which appear to be commonly regarded as the effect of accidental circum- stances prevailing during their formation. It may be so, but the much greater comparative frequency of some of them than others is an indication at least of greater facilities afforded to the decrements by which they are produced, by the constitution of their molecules, and it is not improbable that an accurate examination of them may afford us evidence of the operation of forces of which we have at present no suspicion. * By my own experiment. The silica employed was a portion of a plagiedral crystal which turned the plane of polarization to the left. Had siliceous sand been used, the result might have been foreseen as the opposite rotations of the minute crystalline fragments (some perhaps of one kind, some of another) of which it consists, would, among so many thousands, compensate one another. J.F.W. HERSCHEL. Stoucu, March 15, 1820. G2 52 Mr. Herscuex on Polarization by Rock Crystal. NOTE. Tue general fact announced in the above pages resting on mere induc- tion, it seemed desirable to extend this as far as lay in my power, and I have accordingly (since the communication of this paper) examined nine specimens in addition to those already enumerated, making in all twenty-three, without meeting with an exception to the law. One crystal has, however, fallen under my notice, of a very singular character which renders me cautious in asserting the absolute generality of the conclusion. It is in the possession of Mr. Brooke, and has on one and the same angle of the prism, plagiedral faces perfectly distinct and in contact, but tending opposite ways round the summit. I was not permitted to examine the action of this rare specimen on light, and can therefore say nothing of its internal structure. In the amethyst it is very rare to find plagiedral faces, even small and imperfect ones; but in searching over bags containing several hundreds of purple amethysts from Brazil, I met with three, in one of which the face in question had some extent, in another it was distinctly visible but of microscopic dimensions, while in the third, considerable doubt subsisted of its identity. In the first only could I succeed in tracing satisfactorily a uniform rotatory structure up to the immediate neighbourhood of the plagiedral face, and in this the rotation corresponded in direction with that of the face itself. It may be permitted me to mention, that in the course of this enquiry I was led by independent observation to a knowledge of the essential distinction between Amethyst and Quartz, while yet ignorant that the subject had engaged the attention of Dr. Brewster. Very shortly after, however, I received, by the kindness of that ardent and indefatigable observer, a copy of a Memoir communicated by him in Nov. 1819. to the Royal Society of Edinburgh, and printed in the beginning of the present year, in which I find all my observations on that point anticipated. J.F.W.H StouGu, Oct. 9. 1820. IV. On the Chemical Constituents of the Purple Precipitate of Cassius. By EDWARD DANIEL CLARKE, LL.D. LATE FELLOW AND TUTOR OF JESUS COLLEGE; PROFESSOR OF MINERALOGY IN THE UNIVERSITY OF CAMBRIDGE; LIBRARIAN OF THE UNIVERSITY ; MEMBER OF THE ROYAL ACADEMY OF SCIENCES AT BERLIN ; HONORARY MEMBER OF THE GEOLOGICAL SOCIETIES OF LONDON, EDINBURGH, CORNWALL, &e. &e. [Read May 15, 1820.] «< Ler us then honestly confess with Macquer,” says Proust, m closing the account of his elaborate experiments* upon this purple state of Gold, “that the nature of it is not yet well understood.” Indeed so little is generally known of its real nature that while some Chemists have considered it as an oxide of Gold+, others have believed it to be gold in the metallic state, and in a state of extreme division mixed with oxide of tin. That the oxide of Gold is similarly characterized, as to colour, may be proved by the phenomena attendant upon its combustion when exposed to the flame of the Gas Blowpipet. Pelletier first shewed that the precipitate which tin causes in a dilute solution of the muriate of gold is a compound, consisting of the oaides of tin and gold§. Proust has endeavoured to maintain a different opinion ; namely, that the gold in the purple * Journal de Physique, Feb. 1806. Vol. LXII. See also Nicholson's Journal, Vol. XIV. p- 340. + See Aikin’s Chemical Dict. Vol. I. p. 536. In the Appendix, p. 118, a reference is made to Proust’s later experiments. } See Gas Blowpipe, Exp. LXXIX. p. 90. Lond. 1819. § Murray’s Chemistry, Vol. III. p. 103. Edinb. 1807. 54 Dr. CLARKE on the Chemical Constituents powder of Cassius is in the metallic state ; and that a purple colour is natural to gold whenever it exists in a state of extreme division. For the latter part of the observation he confesses himself to be indebted to Macquer; and he ascribes to the French chemist the honour of the discovery*. But Macquer only adopted the opinion of others; and the opinion itself, respecting the metallic state of the gold in the purple powder, not only remains to be proved, but the experiments made with this precipitate are decidedly adverse to the fact; and more especially the refractory nature of the precipitate when exposed to the action of heat before the common blow-pipe. That chemists should still remain in doubt, not to say in ignorance, respecting the chemical con- stituents of a substance so long knownft, and so highly valued from its application in the arts, may well stimulate an enquiry into its real nature. Professor Thomson of Glasgow, in the last edition of his valuable System of Chemistryt, says, that the proofs which Proust has afforded of the metallic state of the gold in the purple of Cassius, do not appear to him to be quite convincing; though they certainly render the opinion plausible; ‘there can be no * See Journal de Physique, as before cited from Nicholson's Journal. + This precipitate is said to have been discovered in the middle of the seventeenth century by Dr. Cassius (see Aikin’s Chem. Dict. &§c.) and applied to the art of tinging glass of a transparent ruby colour, the red glasses of earlier date, such as we see in old Churches and Cathedrals being only superficially painted. Kunckel carried the art to such perfection that he made a chalice of this ruby glass for the Elector of Cologne, of an uniform tint throughout which weighed 24 pounds ; and he says that he used for the colouring constituent the precipitate of gold made with tim. But it is very uncertain when this precipitate was first applied to the purpose of colouring glass. In a curious work printed at Florence in 1612, entitled © L’arte Vetraria,” written by Antonio Neri, the process of colouring glass red, so as to imitate the ruby, is distinctly stated. “8% calcini Voro, che venga in polvere rossa, et questa calcinatione si faccia con acqua regis, pit volte, ritornaldola adossoli per cinque o sei volte, pot questa polvere d’oro, si metta in tegamino di terra a calcinare in fornello tanto che venga polvere rossa, che seguira in pix giorni, allora questa polvere rossa di oro data sopra il vetro fuso, &c. &e. fard allora il vero rosso trasparente di Rubino.” (Cap. 129. p. 108. In Firenze, 1612.) And Libavius, in his Alchymia, printed in 1606, speaks of the ruby colour which may be communicated to glass, by means of gold. } Vol. Il. p. 254. 5th Edit. Lond. 1817. of the Purple Precipitate of Cassius. sy) doubt,” he adds ‘‘that the two constituents of this powder are chemically combined.” According to Proust's experiments, the purple of Cassius is a compound of one part of gold and. three parts peroxide of tin*.. ‘“‘Aqua Regia,” observes. Professor Thomsont, ‘dissolves the gold and leaves the tin; on the other hand muriatic acid dissolves the tin and leaves the gold.” As some experiments which I have lately made myself with the purple precipitate do not altogether correspond in their results with the accounts given of it, and moreover have been attended with cir- cumstances that may throw some light upon its history, I conceive myself justified in making the examination of this substance the subject of the first chemical essay which has been read to the Society. Supposing, from what Proust and others have affirmed, that the gold were in the metallic state although in a state of extreme division, mercury when agitated with the purple powder would extract the whole of it; which is not the case. It would moreover be easy to exhibit a more perfect revival and aggregation of the metallic particles before the common blow-pipe. It was with this view that I placed some of the powder, which had been care- fully washed and dried, within a charcoal crucible, and exposed it to the blow-pipe. Finding it to be altogether refractory, I en- deavoured to accomplish its fusion by adding borax; but did not succeed. I then attempted to fuse it with nitre, but also failed. Thirdly, I mixed the nitre and borax together, when an _ easy fusion was efiected; the charcoal becoming covered with innu- merable minute dingy-looking metallic beadst which were not easily made to flow together, so as to become of sufficient size for the purpose of cupellation upon the tube of a tobacco-pipe. * Journal de Physique, Feb. 1806. Vol. VI. Nicholson's Journal, XIV. 336. + System of Chemistry, Vol. II. 5th Edit. as above cited. t They were brittle, but became partly malleable by further fusion with platinum foil, forming a triple compound of platinum, tin, and gold. 56 Dr. CLarKE on the Chemical Constituents Having placed one of these beads upon pipe-clay, and urged its further fusion, with the aid of a common blow-pipe, and a little borax, it became gradually diminished in bulk, sending forth white fumes, in consequence of the combustion of the ¢im, and leaving upon the pipe-clay a residue, without any metallic lustre, covered with a whitish oxide. Finding it to be impossible, by this process, to separate the gold from the fin, and being convinced that the gold (if any existed in the compound) must be in a very small proportion, I had recourse to another experiment, by which I was enabled to form an alloy comprehending the whole of the éim and the gold in the purple powder, and afterwards from the analysis of this alloy, to ascertain their relative proportion with regard to each other. A. Having mixed together, in a porcelain mortar, a small quantity of the purple powder with equal proportions of nitre and borax, I placed this mixture within a small capsule of porcelain, and exposed it to a red heat for about an hour. At the end of this time the capsule was taken from the fire and cooled ; when I perceived a brilliant globule of metal at the bottom of the vessel, having the colour and lustre of pure silver. It weighed = of a grain. B. The metallic globule mentioned in the preceding experiment, and which I believed to consist of ¢in and gold, was placed in muriatic acid, and boiled during one quarter of an hour, under an expectation that the acid would dissolve the ¢¢n and leave the gold. It produced however no change it its appearance: when taken from the acid, and washed, it weighed, as before, — of a grain; its lustre being unimpaired. €. The same globule was then exposed to the action of nitro- muriatic acid, mixed in the proportion of four parts of muriatic acid to one of nitric acid; which began to act upon the alloy of the Purple Precipitate of Cassius. 57 even when cold; and, being heated, speedily dissolved the whole of it ; leaving no residue. D. The solution being evaporated almost to dryness, and distilled water added, the liquor still preserved its transparency ; but as soon as it became heated, a white flocculent substance was precipitated. E. The liquor from D being filtered, a solution ef sulphate of iron was added to it; when a dark powder was separated, which, being collected, washed, and dried, weighed = of a grain. This being placed upon charcoal before the blow-pipe, a globule of pure gold was revived, weighing also exactly =, of a grain. F. The supernatant fluid filtered from E after the separation of the gold, yielded no precipitate of ¢in to the corrosive muriate of mercury; and as it was probable that the ¢in had been separated in the white flocculent precipitate mentioned in D, to this precipitate were added two or three drops of muriatic acid ; whence, a single drop being detached, precipitated platinum from its dilute solution in nttro-muriatic actd. Hence it was evidently muriate of tin. These experimentsare sufficient to prove that the binary com- peund, which had been analyzed, consisted of the oxides of tin and gold, and centamed those oxides chemically combined in the exact proportion of three parts of fin to one of gold: and that the alloy of the two metals, obtamed by the fusion of one hundred parts ef the purple powder, would yield Metallic tin 75 Metallic gold 25 100 58 Dr. CLARKE on the Chemical Constituents Because < of a grain of the alloy yielded, Metallic tin 0.6 Metallic gold 0.2 Total 0.8. In the foregoing experiments no attention had been paid to the weight of the purple powder used in the analysis; because I had supposed that this would always bear the same proportion to the weight of alloy obtained. That having the weight of the alloy the weight of oxygen requisite in the formation of the purple powder would always follow im a constant ratio; the chemical combination being always the same; but this is by no means true. The proportion of gold in the purple powder varies in every precipitation; which is in fact the cause of the disappointment experienced by artists, who complam that im the application of this purple powder to the art of colourmg glass, the colour is rarely in two instances the same. Much depends upon the age and the degree of concentration of the murtate of tin used in the ex- periment; also upon its temperature when added to the dilute solution of gold. In one instance, having used a recently prepared muriate of tin, almost at a boiling temperature, the precipitate had a black colour, which, however, afterwards became of a deep purple. Having washed and dried 7-, grains of this dark precipitate, and exposed it in a porcelam capsule to a strong red heat during a quarter of an hour, with a view to drive off any remaining water or acid, I mixed it in a mortar with three times its weight of nitre and borax im equal portions, and kept it exposed, in a porcelain capsule, to a uniform red heat for an hour. During this experiment the minute globules of alloy might be seen forming upon the surface of the flux, and running about in small brilliant particles, like sparks of ignited matter, which afterwards fell to the bottom of the vessel. From the whole of the 7;, grains of powder, a globule _ . ° = & . P of alloy weighing 5; grains was obtained. It had a more golden of the Purple Precipitate of Cassius. 59 colour than the alloy which I had before obtamed from the purple precipitate; and, being dissolved in nitro-muriatic acid, the solution yielded a much more considerable proportion of gold to the sulphate ef iron. The gold in this instance weighed 2° grains, and a quantity of peroxide ef tin was separated in diluting the murvate of gold, after expelling the excess of acid, which, when washed and dried, weighed 3=, grains, a little water probably remaining, as this peroxide had been dried on a filter in the open air. When ex- posed to a powerful heat it weighed only 33, grains. Hence it is therefore evident that the two metals which are chemically combined in the purple powder of Cassius, do not exist in a constant relative proportion with regard to each other. That the ¢ix sometimes exceeds the gold in the pro- portion of three to one, and in other instances that the two metals exist in nearly equal portions. Perhaps in other examples the quantity of gold thrown down may exceed that of the fin: but in whatsoever proportion the gold may -exist with regard to the fin, in the purple precipitate ef Cassius, there is not evidence to warrant the opinion of its being in the metallic state. There are, it is true, some experiments, so problematical in their results, that the chemist, in making them, is liable to be misled by appearances. A brief statement, therefore, shewing what these appearances are, and endeavourmg te account for them, may now terminate this enquiry; by which it will perhaps be satis- factorily proved that the gold in the purple powder of Cassius, is at a minimum of oxidation; and perhaps also that it is liable, after precipitation, to that spontaneous decomposition, and to those changes, when exposed to the action either of light or heat, or even of simple moisture, which the protowide of gold has been said to undergo ; namely, that of dividing itself into two parts, one portion parting with its oxygen to the other, and becoming revived in the H 2 60 Dr. CLARKE on the Chemical Constituents metallic state*. An illustration of this may be afforded by an amusing and very striking experiment. If the purple precipitate. after being washed and while it isin a moist state, be agitated m a glass vessel, so as to be made to adhere to: the interior surface of the vessel, and be then left to become dry, a portion of the gold will become revived and will appear in the metallic state. This will take place the more readily if the vessel be exposed to light in a window, or to the full action of the Sun’s rays. But a portion of the precipitate will still retain its original colour; and will be found to contain gold which has not been thus revived ; thereby apparently confirming the observation of Berzelius, referred to by 3) the author of the “System of Chemistry” as before cited. Such an appearance, resulting from the change which the protoaide of gold has sustained after its precipitation might give rise to an opinion that the metal had been origimally thrown down in the metallie state. There is another appearance yet more delusive; it results from the following pleasing experiment. The purple precipitate, after being washed, and bemg yet in a moist state, is to be agitated in a phial with mercury. Some of this mercury is to be placed in a watch-glass over an argand lamp, and volatilized, when a film of metallic gold, will remain upon the glass. Four grains =, of mercury which had been thus agitated with the purple powder teft a residue of + of a grain of metallic gold. This appearance might lead to the conclusion that the whole of the gold in the purple powder existed in the metallic state, which is not true ; for upon examining the powder whence the ; of a grain of metallic * “Ina shoré time this protozide divides itself into twe. parts. One-third deprives the other two-thirds of the whole of this oxygen and becomes perowide, while the two-thirds are reduced to the metallic state.” (See Berzelius, Ann. de Chim. 83. 166.) ‘ Berzelius thinks that there exists an intermediate oxide, (between the protoxide and the peroxide of gold) which constitutes 2 component part of the purple of Cassius. But he has not established its existence by decisive experiments.” Thomson's System of Chemistry, Vol. 1. pp. 486, 487. London, 1817. of the Purple Precipitate of Cassius. 61 vold had been thus separated, by exposing it to the action of nitro- muriatic acid, and afterwards evaporating the excess of acid and adding distilled water, it was found to contain gold, which was thrown down, from the muriate thus formed, by the usual tests of sulphate of iron and muriate of tin. The most curious thing to be attended to in separating the portion of metallic gold by means of mercury, in the foregoing experiment, is this; that the success of it depends upon the moist state of the precipitate after being washed with water; but whether the revival of the gold be owing to the hydrogen of the water, or to the cause assigned by Berzelius, of the spontaneous decomposition of the protovide of the metal*, others may determine. Twelve grains of the purple powder, which had been previously exposed to a red heat in a porcelain capsule, were agitated with well dried mercury ; but, after the volatilization of the mercury, no film of gold remained, as in the former instance ; nor any residue, whatsoever, to alter the weight of the watch-glass im which this trial of the dry powder had been made. The same dry powder, after the removal of the mercury, being placed in méro-murtiatic acid, and the excess of acid expelled, and distilled water added, yielded a solution, from which gold was precipitated. by the usual tests: From all the preceding observations it may be inferred that im precipitating the purple powder of Cassius from the muriate of gold, by means of the muriate of tin, the two metals tin and gold are thrown down as owides; which however do not chemically combine in a constant relative proportion to each other ; that the quantity of én always exceeds that of the gold; and that the difference observable in the hues of the precipitate made at different times, is to be ascribed to the different proportions in which the ovides of the two metals have combined together, and perhaps also to their different degrees of oxidation. EDWARD DANIEL CLARKE. * See a former Note. a ‘ Pp ; = Ss Se = Or ih te y. = ye. | 2s oe peng) Ap inabiie wing cei ol ; c a a ie ‘vena ——— pape Win Pat Digke Of an Fi 7) iellndhnegd ac aces ape a) a : ij: nih ad i siepyn mit i ee. a nme oo hs “ove hp bah evew Fe " é $4 ‘ nip ota - ‘ity soog OM ahh. cg ht ee? on ee . 2 7 jet ms wth 2 } falle x ava aie +a me ttle vel) xvi were (> “il sd 2 lira ray whe sveushy gatos mw Fie. grit Twn, sy ss may Ney ne ole PYT hen: patie ys) WEG wana Wi ibe inden ise rade! —— Lutter 4 \wivdeg higys iti wein't> Cope ahi, oye tf hong pe Dt Siompamy ae ai id pallcalla b earie, ee aes et lng hve ci ee 4“: / é ile’ +P a ar bolo we Jam ie rs oF ye aaaian tide ale) F ren Gh rarentiitin eval oa * te Hit! te rrbownamg, tole wt, Wr nt “pene ni wire, Howth, ayy ~y “ih eae oie : iB e lt ial pes re: a gan ia cna wh ndidy eettae she Node tike = - | o* eee Weis Sige ae sin ind tha th vate nent rent aw : ; i" : ot? ‘ mM, ala pi cebtarwow wale nis Qs SAMIR, | Waite. ofr, adonr oa “a voNiieg Re ihereths er ie. _* oe Asin “ip uae td sy anv ity Wet tii d file Pix) ire TY it a i it} ‘ . at wv >: aaah iu a” give re ii lag) The | Ae a 7 we adie tas Be ve ‘ y An : ey nh lf abd ee WF he iw shit hd bv vera) rye we AD evant & ta oly retorts ra ié te are Ye an YE s,s i ee TARE Sates, abe are ’ ad Pry ow ¥ e ‘» * e wien ota ° . bs ‘4 F ~~ / ; . 8 ° a , V. Observations on the Notation employed in the Calculus of Functions. By CHARLES BABBAGE, M. A. FELLOW OF THE ROYAL SOCIETIES OF LONDON AND EDINBURGH, AND OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. [Read May 1, 1820.] Amonest the various causes which combine in enabling us by the use of analytical reasoning to connect through a long succession of intermediate steps the data of a question with its solution, no one exerts a mere powerful influence than the brevity and compactness which is so peculiar to the language employed. The progress of unprovement im leading us from the simpler up te the most complex relations has gradually produced new modes of shortening the ancient paths, and the symbols which have thus been invented in many imstances from a partial view, or for very limited purposes, have themselves given rise to questions far beyond the expectations of their authors, and which have materially contributed to the progress of the science. Few indeed have been so fortunate as at once to perceive all the bearings and foresee all the consequences which result either necessarily or analogically even from some of the simplest improvements. The first analyst who employed the very natural abbreviation of a* instead of aa little contemplated the existence of fractional negative and imaginary exponents, at the moment when he 64 Mr. BasppaGce on Functional Notation. adopted this apparently insignificant mode of abridging his labov. So great however is the connection that subsists between all branches of pure analysis, that we cannot employ a new symbol or make a new definition, without at once introducing a whole train of consequences, and in defiance of ourselves, the very sign we have created, and on which we have bestowed a meaning, itself almost prescribes the path our future investigations are to follow. Such bemg the power and influence of those symbols* by which mathematical reasoning is carried on, it cannot be considered as unimportant either as regards the particular branch, or with refer- ence to the science in general, to examine some of the bearings ef the notation which has been employed in the calculus of functions, and to resolve some of the unusual questions which it presents. That the results to which such an enquiry will conduct us are of a nature purely speculative, is an objection to which every attempt to’ improve notation is lable; it can however never be considered an useless task to examine and strengthen that which essentially contributes to the power of an imstrument, which enables us so wonderfully to trace the connexion between the phenomena -of nature. When it became convenient to express without performing the repetition of an operation, whose characteristic is f, the method which first presented itself doubtless was similar to that which had been adopted with such advantage for the exponents of quantities, and f* (x) was written instead of ff (x) ; it now followed without any other convention that f°(x) and f” (7) represented fff. (x), and fff. (x times) (x) and also that Of e722) op (ca) ae ee (A), when x and m are whole numbers. * Euler, to whom analysis is so mach indebted, appears to have beén fully aware of the power and importance of notation; “Samma aralyseos inventa maximam partem algorithme ad certas quasdem quantitates accommodato innitantur.” Specimen Algorithmi singularis. Acad. Petrop. Comm. Nov. 1762. Mr. BaspaGe on Functional Notation. 65 At this point of generalization a question occurred as to the meaning of f” when 7 is a fractional, surd, or negative number, and in order to determine it, recourse was had to a new convention not in- consistent with, but comprehending in it the former one. The index n was now defined by means of the equation (4A) and was said to indicate such a modification of the function to which it is attached that that equation shall be verified. From this extended view of the equation (4) several curious results follow ; if n=0, it becomes f(t) =f" (2). This informs us that f° is such an operation that when performed on any quantity it does not change it, or putting f” («)=y, it gives IY) =% a result which is analogous to 2’=1, Let m= -—1, n=1, we have Prr=f\f-'(x), orf(fr'2) = 2; J~*(x) must therefore signify such a function of x, that if we perform upon it the operation denoted by f it shall be reduced to x. The number of functions possessing this property will depend on the nature of f; thus if f(z)=x", let r,, 7.,....r, be the roots of v'"—1=0; then f—' (x) may be either of the » quantities a r, ToD” oo e Py k™ 5 for if we perform the operation f/ upon any of them, or raise it to the nth power, the result is z. Here then we find JS (f-'2) = 2, in all cases; but if the negative index is attached to the first func- tional sign, we have So (f2) = 72, and one only of these values gives f ~'\fr=<. I 66 Mr. BAppaGE on Functional Notation. It was more necessary to make this observation, because several errors have arisen from not attending to it, and because that particular form of f—' which gives f—'fxv=2 possesses peculiar pro- perties: f —'(«) is then the inverse function of fx ; and if we have the equation f(x)=y, we may indicate its resolution thus x = f~' (y). Having established the connexion between positive and negative indices in functions of one variable, I shall now proceed to those containing two. If in the function ¥ (2, y,) we substitute at the same time v (2, y,) for x and y it becomes Viv(z, y), ¥(7 Wt, and for the sake of brevity this has been denoted thus we (ay): similarly, if in this we wrote ¥(2, y) for x and y we should have W*(a, y), and a few steps would lead us to the equation, Penn (a, Y)y VP ™ (ts YE HY MM™ (ty Yow ves (B). The same reasons which in the former instance induced us to generalize the first definition, now point out the propriety of assuming this as the definition of simultaneous functions, and of the modifi- cations implied by their indices. The first step is to discover the value of ¥° (x,y); for this purpose put n=0, then wrote (ay), Wr" (a, yb = W""(a, Y); and substituting v mstead of (2, 7), we have W°°(v, v) =v. If we had put m=0, n=1 instead of n=0, we should have found Wet fy (x,y), H" (x, y)j=v"! (a, y), which shews that °(x, y) is such a function of x and y that when simultaneously substituted in (7, y), for « and y, it shall give either cory: it may have different values like all other inverse functions. Mr. BapBpace on Functional Notation. 67 If in the function y(z, y), we put ¥ (x,y) instead of x it becomes wv {v(x y), ¥} which is written thus ¥”'(x, y), and continuing such substitutions we arrive at yer iy’ (2), Yy SYM (a, Y)e vee ee (C), or if the x function relative to z, and then the m'‘" function relative to y be substituted, it would be eee cea pes” = (O0Lt ay) m= Nee aD SY) os “oe fore (D). These two equations are now considered as the definition by which the meaning of the indices is known, and we proceed to enquire their values in particular cases: let »=0 in the first and we have WOE Tyn' (a, y) YS = "' (BY)5 put wv” (x, y) =v, and it becomes Ort (D5:4)) = O5 ONG (2, //) = Laceye «i s-)- (EZ). If n=1 and m=0 in the latter, Vet fa, WP? (a, yb = WP" (@ Y); whence it follows that Hy Coa) (F). If n=—m=1, (D) becomes Yer ia, Pe (@ yt = (ay) =y, hence \”~' (x, y) expresses such a function of x and y that when sub- stituted in y (x, y) for y it reduces it to y, or if VY (@,y) =2, then Y=" (ae) and eae (oy)... oc... (G). From (C) we may readily deduce as consequences, yo" (x,y) = 2, and W(x, y) = y. The same reasoning which has been employed in discovering the meaning of the indices of functions of two variables applies with 12 68 Mr. BABBAGE on Functional Notation. equal facility to those of many variables; without repeating it, it is sufficient to observe that apolete s(x, aye —ay |x cle ees) te epee, and that of YE i TLY, 2%, -- eR SUE then 4) al — ho: (oer rae Amongst the questions which arise from this notation there are two which are altogether different from any which have occurred in others, and although their solution is not attended with any very great difficulty they furnish an enquiry of some curiosity. If the expression W(x, y) be fully written out, we may seek, first, how many times will either of the quantities x or y be re- peated; and secondly, how many times will the symbol - occur. I shall begin with some of the more simple questions, and first Pros. I. How often does the quantity x occur in the expression y"n(a,y)? Suppose it occurs uw, times, then in Pra, y= We" (h (zy), ¥(@, YD}, it occurs twice as many times as it does in the preceding; hence th i he, Olio ifn=1, u,=2C=1, hence C=}, and u,=2"—', or x occurs 2"~' times in W"" (2, y). . Pros. IT. How many times is the symbol y repeated in y’""(z, y)? Let u, be the number of times; then it is found w,,, times im y'*""*" (x,y); but in going from the first of these to the second we augment the number of times ¥ occur by 2", because wherever Mr. BapBaGE on Functional Notation. 69 occurs, we introduce by putting y (2, y) for it, and as x occurs 2"-' times we by this means add 2”—' times ¥, and similarly, on account of y we add 2"~" times y, so that ae = 1. ea, — th, + 2” Au, = 2", whence uw, = 2" + C, if n=1 u,=2+C=1, or C=—1, therefore ~ occurs 2”- 1 times in ¥’’" (z, y). Pros. ITT. How often is z, repeated in W"** (a,, ... 2,;)? Suppose it to occur u, times, then in going from the " to the n+1 simultaneous function wherever 2,, 2,,...2; occur, we in- troduce z, once, but each of these occurred uw, times, and as there are t of them, we have Une ee Olathe ; , 1 : : but if n=1, u,=Ci=1, wherefore C=- , and zx occurs 2“~! times. Cor. As z2z;,...x, are all similarly involved, they each of them occur 2”—! times. Pros. IV. How often does ¥ occur in W’"""(x,, 2,. . 2,) 2 Let it occur u, times; then in the (x + 1)'" besides the uw, times that it occurs in the 7" we introduce an additional 4 wherever 2z,, 2,,... 2; occur, or since there are 7 of these quantities, and each occurs i"~' times, we have ya C z Un+, =U, +2, Whence u, = oa ie (4 : z —] if n=1, u,=——-+ C= ae » uy ane, 1, hence C eae yr cy ie and W occurs 77 times in y"""** (a, .. a). 70 Mr. BaBeace on Functional Notation. Pros. V. How many times do x and y occur in y’"' (2, y)? In passing from the x" function to the n+1" we change x into (a, y); this does not increase the number of times x occurs, and as the same reasoning applies to the n—1", n — 2",...down to the first it follows that x only occurs once in Ww’! (a, y). Again, in passing from the x" to the +1" we introduce y once, if therefore u, represent the number of times it occurs, we have Uns) = Uztl, or 4 —n-+ C, if m=1, u,=1+ C=1, or C=0, and y occurs x times in W”! (x, y). And similarly, 2 occurs » times, and y once in W"” (a, y). Pros. VI. How frequently does ¥ occur in y’”"' (a, y)? since ¥"*"" (a, y) = W"" {¥(a, y), yf, each step introduces v once, it will therefore be repeated x times. Pros. VII. In vy” (2, y) how often are « and y repeated? sl (x, y) = yr res a @ y) ie In the right side of this equation 2 occurs once, and in y’""~' (2, y) it is found (m-— 1) times; now in each of these last x occurs m—1 times by Prob. 5, so that on the whole it appears 1+n.(m—1)=mn—n+1 times. Again, y occurs once in y'” (x, y) and this latter is found » times inv” (2, y), so that y occurs 7 times in the same expression. Pros. VIII. How many times does ¥ occur in W’’" (x, y)? In wy" '(2, y), ~ is found » times by Prob.6; and y is found x Mr. Bappace on Functional Notation. 71 times ; if for y we put ¥’"—'(a, y) which contains ¥, m-1 times repeated, we shall have yer ta, yee" (a, YS = Vr" (@ Y), and the number of times W occurs is »+2(m—1)=nm times. Pros. IX. How often do'z,, v3, 25.2, OCCUL IM Vy *"" (4), a5... .2,)% First, let us consider W°"""::(z,, v,...2;), and let x, occur u, times then since Wetton, ayy... 0, SW a (oe Loy...) pura} the number of times x, occurs in the first side of the equation is Ua+i; In the second side it occurs ui times, therefore wa.,=Ua, or ua=C; but if a=1, u,=C=1, therefore uz=1, and 2 occurs only once. Again, let uw. now represent the number of times x, occurs, then in the second side x, occurs %q times in W°"'*: (2, 2,...2,), and also once besides, so that Ug+,;=Uatl, or ug=atC, if a=1, C=0, and the same result will be found for any other quantity z; except z,, hence in W!™>-- (z,, 7, .... 2), ce occurs 1 ics hati Sn ob tan a EMINES ste teicny sch otce) aiave, dork 56 5((8) Desire ve. «tas hecerakats a Let us next consider W*"**: (a,, v.:..x,), a Care Vo,-- &,)=pr” i {x,, y" SRE Cas Uo,» --U,), U3, ++. x,). On the right side of this equation 2, occurs in two places first by itself in which state by (1) it is only found once; and secondly, it occurs in the function '’~"""(a,, x2,...2,) where by (1) it is found 72 Mr. Baspace on Functional Notation. to recur b—1 times, but that function itself is repeated a times, therefore the whole number of times 2, is repeated is 1+ a(b—1)=ab-a+1: t, only occurs under the last mentioned function, and there it is found only once, but as that function is repeated a times x, must occur @ times: x; occurs in two places; in the first it is repeated a(b—1) times, and in the second a times, so that on the whole z, is found ab—a+az=ab times. z;1is found the same number of times. Therefore in y Ue (z,, Zo,-. a Z, occurs ab—a+1 eee eco ce eee e by considering the equation, aiden) (FB SRM oN ae Ed ok oY COSY (Fk, cate 9 a) we shall find that when there are three indices a, }, c, Z, occurs abc—a+1 ? BN tes ae abe—ab+a ce ead ee ab CHMES iS c)01. secs cones ee GSD ne. tak oes abe a similar process applied to ~%%°%':--(2,, 2,,...2,) would show that yn it 2, occurs abecd—a+1 meee abcd—ab+a Sridks ve abed—abc+ab\ . eke ie TIMES: ;.. Ss (4), Dy inde oo a abed Mr. BaspaGce on Functional Notation. 73 and in YA brerdestiee-(g,, ENS z,), 2, occurs ahede-a+1 i eA ae abcde—ab+a west Won abcde—abc+ab ney pe abcde—abcd +abc LENIES: . 5. eee (5) wemeeane 5.5. UiC C x, abcde the law which these expressions follow is easily discovered from those which have been given, and by their assistance it may be shewn that in the expression Apo ONG (CERT SER Beye. aU) v will be repeated abcd. . . times. Tf in afunction of two variables we wish after taking the a, 6, c,-"" functions relative to the variables 2,, x.,... m order, again to take the p™ relative to the first, the g' relative to the second, &c. some modification of our notation becomes necessary. I have proposed in the Philosophical Transactions to make use of two rows of indices the upper to signify the number of repetitions, and the lower to denote the quantity for which the substitution is made. thus FEaN=V iia vaoy), via vey, ¥@y)]}- when these indices become numerous it is desirable, for the sake of facility in printing, to have them on a level with the rest of the symbols, and this will become almost indispensible if another or possibly two other rows of indices should be employed: the farther ex- tension of the calculus may require such additions to indicate modi- fications of a different kind from those yet considered. There appear to be four circumstances connected with the indices of functions whose relations it may ultimately be desirable to express by means of them: the two first of them, namely, the number of repetitions and the quantities for which substitutions are made are already pointed out by the two rows. It may become necessary to substitute K 74 Mr. BapBpBace on Functional Notation. instead of one of the variables, not the original function but some modification of it such as ¥'* (2, y), and this might be only sub- stituted for one of the variables in certain particular places not universally ; such changes would require two additional rows. The alteration which I would propose in all cases where many indices are concerned is extremely simple: it consists in merely bringing the indices down to the level of the functional sign and inclosing them between two bars; the expression last-mentioned would be written thus a Far | (2, y). This would also possess some advantage in the case of a function of many variables being after the performance of given operations reduced to a function of a less number, (by means of some assigned relation between some of them) and then new functional operations being performed, or considered as a function of the reduced number of variables, thus WE eslF fl (Ys Bere AK GMI, which signifies that the second function of W (2, y, =) is taken re- lative to x; f(z, y) is then substituted for x and the second function of the result considered as a function of two variables is taken first with respect to x, then with regard to y. The method I have pointed out for the determination of the number of times the quantities under the functional sign would be repeated if they were written out at length is perhaps the most direct and unartificial which could be proposed; I cannot however terminate this paper without pointing out another method of a character completely opposite which promises in more complicated enquiries of this nature to be of considerable use. It bears a strong resemblance to a very elegant artifice employed by M. Laplace in order to determine the numerical coefficients of [u, and was in fact suggested by it. Mr. Bappsace on Functional Notation. m5 Since the number of times any variable is repeated is inde- pendent of the form* of the function, that number must be the same for all functions. If therefore we can find it for any particular function, we have it for all others. Let us then select the function v,+%,+...%, and take those functions which the index requires, we shall have the number of repetitions of each variable expressed by the coefficient attached to it. One great advantage of this plan is that we always have it in our power to take any function however complicated of x,+2,+ .. 2,3 as an example let it be required to find the number of repetitions of x and y in ¥*» (a, y); if (a, y) = vx + uy, yo? (2,y) = (u tue if w=v=1, this becomes We? (a, y)=(1+a.b—1)a+ay=(ab—a41)a4ay. Or x will be found repeated ab-—a+1 times, and y will occur a times, which coincides with what was proved in Prob. 7. 07 —1 r+u?,———y; v—!1 al Gee t= y) v—-1° u-l The surprismg condensation of meaning comprised in small space and yet exempt from even the slightest tinge of obscurity is nowhere more conspicuous than it is throughout the calculus of functions: and the solution of the problems contained in this paper enables us to give numerical results which will be viewed with surprise even by those who are best acquainted with the power of general signs. The equation, VO (a, y) = (2,9), is one whose solution presents no great difficulties and may be * In whatever manner the original function may involve the unknown quantities it must in this point of view be considered as containing each only once. K 2 76 Mr. BABBAGE on Functional Notation. accomplished in a few lines. To any person acquainted with the notation employed in the doctrine of functions the question is com- prehended at a single glance; yet if we apply to it the rules discovered in Prob. 1 and 2, we shall find that if it were written out at length, « and y would each be repeated 512 times, and would occur 1023 times; so that the whole expression would consist of 2047 letters, and it may be added, that if it were so developed it would require a much longer time merely to compre- hend the enunciation of the problem than it would to understand and solve it in its contracted form. CHARLES BABBAGE. Feb 26, 1820. VI. Onthe Reduction of certain Classes of Functional Equations to Equations of Finite Differences. By J. F. W. HERSCHEL, M. A. FELLOW OF THE ROYAL SOCIETIES OF LONDON AND EDINBURGH, AND OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY, [Read March 6, 1820.] Tue reduction of functional equations to those of finite dif- ferences was the means by which their resolution was originally attempted and though applicable only to particular classes of them, affords very ready solutions in those instances in which it can be practised, and these solutions have the advantage in general of indicating at the same time the number and nature of the arbitrary functions they involve. I propose therefore in the followmg pages to apply this method to a class of pretty considerable extent, in which the function to be determined is one of two or more variables, but where the condition expressed by the equation assigns to one of them a value or values dependent in a known manner on that of the other. Mr. Babbage, in the second part of his paper on Functional Equations (Phil. Trans. 1816.) has noticed equa- tions of this nature, and has given solutions of certain cases of the higher orders. With these I shall not at present concern myself, the method which I propose to exhibit extending only to equations of the first order, of which it affords the complete solution 78 Mr. Herscuet on Functional Equations. in all cases. To proceed regularly, it will be necessary to premise the following Problems, the object of which is to determine the nature of the arbitrary functions we shall be obliged to introduce. Pros. I. Required the most general form of a function ¥ (2, y) of two variables x, y, which remains the same whether P or Q, (two given functions of z) be substituted for y, or to resolve the equation ¥(@ P)=¥(@ @. Since the substitution of P for y renders (x, y) a certain func- tion (f x) of x, it is evident that im its general state (2, y) can only differ from fx by a quantity which vanishes when y becomes P, and of course ¥ (x, y) — f(z) must necessarily have y — P for a factor. Again, since ¥(x, y) reduces itself to the same function f(x) by the substitution of Q for y, the quantity y¥ (x, y) — f(x) must in lke manner have y— Q for a factor, and we must therefore have v(x, ¥) —F(@) =(¥— P)(y - Q@)-x@ ») or ¥ (2, y) =f (2) + (y — P) (y—Q)-x (a y). Let this be substituted in the equation w (x, P) = \ (x, Q), and the whole vanishes. This value of w(x, y) therefore satisfies the equation independent of any particular forms of the functions f and x, which therefore remain arbitrary. Pros. II. Required y (x, y) a function of x and y, which retains the ‘same value when each of the functions P, Q, R, &c. is severally substituted for y; P, Q, R, &c. bemg given functions of z. By reasoning exactly similar it will appear that F(x) + (y-P)(y-®) (y- R), &e. x (@, y), Mr. Herscuet on Functional Equations. 79 is the most general form of the function sought, f(x) and y(, y) being arbitrary functions, the former of x, and the latter of « and y; observing however that (x, y) must not be so taken as to become infinite of the first or any higher order by the substitution of any of the quantities P, Q, R, &c. for y. Pros. III. Required the most general form of a function which shall reduce itself to a given function Q@ when y becomes equal to another given function P, or to resolve the equation, Since v(x, y) becomes @ when y becomes P, it is evident that wW (a, y) — 9 must have y— P for a factor, and that Vy) = Q@+ (y-P).x(z,y), and x is shewn as before to denote an arbitrary function provided only it do not become infinite by putting P for y. These cases being premised, we shall now proceed to the solution of the equations we proposed to consider. Pros. IV. To begin with a simple case, let the equation proposed be Y (a, 2) — (a, 0) = a. Assume V(2,y) = o(2,h+2), h being a quantity independent on « or y, and therefore to be regarded as an arbitrary constant in the expression of y(2, y). This supposition being made, we have V(t, 1) =$(@, h+1); Y(x, 0) = P(a, h), so that our proposed equation becomes p(t, h +1) — p(a, h) =a. 80 Mr. HerscueEt on Functional Equations. Now / being independent on 2 and y, this may be regarded as an equation of differences in which the auxiliary letter ’ is the in- dependent variable, and its integration immediately gives g(a, h) = ah +C, in which C may be any function which does not change when 4 changes to h+1, that is, which retains the same value whether we put z or 0 for y: now we have already seen, Prob. 1, that the most general form of such a function is fe+yly — 2)-x(@,y). But we assumed, V(ey) = (2, b+") ¥ y = a(h +%) + C. Hence if we substitute for C its value, and suppose the constant ah included in the arbitrary function fx, we get finally, Y(@y)= at +f (2) + ¥(¥—*)-x (2 y). Some objection may be raised against the generality, or even the legitimacy, of the above solution, on the ground that in assuming (a; a) — (2, h+) we in fact limit the possible forms of the function y; for although it be true that by the combination of the elements x, h +% with each other and with constants it is possible to form any assigned function of x and y, yet to render this assertion general, the quantity must be admitted as one of those constants, and therefore our assumption should have taken notice of this circumstance, and have stood thus, ie ¥) WV (2, y) = (2, h,h + Ay A Now this will very materially affect the process which follows, as the equation will then become Mr. Herscuec on Functional Equations. SI (x, hy h+1) — P(a, h, h) =a, which is not an ordinary equation of differences in h, the first term not being altogether the same function of h+1 that the second is of h. To this however it may be answered that the equation in question may legitimately be resolved as an equation of partial dif- ferences in which only the last element varies. In fact it is evident that if we can any how determine a form of ¢ (a, 7, 2) regarded as a function of three variables x, 7, and h, absolutely independent of one another, which shal] satisfy the equation p(x, t,h+1) — p(a,t,h) =a, it will certainly follow that the function ¢ (2, 2, h) found by putting k for 2 will satisfy the same equation in the particular case of i = h, because the symbols 7 and h destroy each other independently in the first member. But without going into these considerations, it is evident that if we have got such a form of ¢ as shall satisfy the equation o(2,h+1) — o(a, h) = a, this will be sufficient, for y (v, x) beimg equal to ¢@(x,A+1) and W (2, 0) equal to ¢ (a, h) by the original assumption (right or wrong) of W (x, y) = o(«. h +%) this equation is in fact identical with the proposed, and the form of ¥ so found must be satisfactory. Pros. V. Let the proposed equation be 0 = F(a, y(a, P), v(x, Q)}, P and Q being any functions of x given in form. Suppose we had w (c, P) = ¢(z, A), ¥ (2, Q) =p (2, h +1), then would our equation become O= Fila, @(a,h), p(a,h41)}, L $2 Mr. HerscHext on Functional Equations. which being resolved as an ordinary equation of differences regard- img vas constant and / as the independent variable gives the form of ¢ (xh). The whole difficulty then is reduced to the discovery of the form of y (2, y) from the known form of the function ¢. To this end conceive @(r, 7) a function such that when y=P, @(2, 7) shall vanish, and when y=Q, @(2,y) shall become unity, then if we assume, V(ay) = pir, h +O (2, y)}, the values of W(x, P) and y (2, Q) will be those we have supposed. It only remains to assign @(2, y) so as to have at once 6(o IP) —.05, anole, Op) 1: Now, by Prob. 3, the former of these gives A(x, y) = (y—P) ., (x, y), 6, (%, y) bemg an arbitrary function. This being substituted in the latter gives (Q—P).0,(2, Q) =1, when the arbitrary function 6, (x, y) is determined. This is again a particular case of Prob. 3, and its solution is (0) =g—pt y-@-x(ey, so that we have finally (0,9) = t+ Py - Oxy), y(t, y) being any function of « and y which does not become mfinite when P or Q is put for y. The several steps in the solution of the proposed equation will therefore be as follows. Integrate the equation of differences, O = Way aaa); « bemg regarded as a constant, and A the independent variable, and let its integral be Mr. Herscuet on Functional Equations. $3 u, = (a, h, C), C bemg the arbitrary constant introduced by integration ; then will the value of W (a, y) be p ja, h+0(a, y), Ch, where 6 (x, y) is the function above determined, and C=f(r) + (y¥—P) (y-@)-x (ey), x («, y) being an arbitrary function of x and y and f(x) one of x; this value of C being found by Prob. 1, from the consideration that Cc must retain the same value whether P or Q be written for y- Pros. VI. In general, let O= FF} x, k(x, BP), te(a,1Q)5-6 @; 2); &eR This will be reduced to the equation of differences, =F jr, (2, h), o(e, h+1), (a, h+2), &e.},..---. (a) if we take W(t, y) = o{2,h + O(a, y)} 8 (x, y) being a function so determined as to give at once 6(x, P)=0; O(a, Q)=1; O(x, R) = 2, &e. Now first, the two first of these conditions give, as im the last problem, O(x, y) =(y — P).6, (2, y) ~— + (y— P) (y— Q).0, (a, y). Again, the condition @(#, R)=2 gives for the determination of A, (a, y) ? (R—P) (R—Q).6,(«, R)=2—- whence aeyy= 1 ¥ 1 4) —(R—P) (R=Q) (P= (P=R) and so on, so that finally we have L 2 +(y- R)6, (v, Y)s 84 Mr. Herscuer on Functional Equations. 6(x, y)=A(y—P) + BYy— P) (y—Q)+C(y-P) y- 9) (y—-B+ + &e. + (y—P) (y— Q) (y— R), &e. x x(x, y) x (2, y) being a function quite arbitrary, provided the substitution of P,Q, R, &c. for y do not render it infinite, and 4, B, C, &e. being the series of coefficients above determined. The law of these coefficients does not readily appear. and as their formation one from the other is rather complex, I shall observe that the value of 9(z, y) may be expressed at once by means of a very elegant theorem proposed by Lagrange as a formula of interpolation. It is evident from the progress of the steps above detailed that (the arbitrary term excepted) @(z, y) is a rational integral function of y of the dimension n—1, n being the number of the letters P, 9, &c. The question then reduces itself to finding such a rational integral function of y of this degree as shall become 0, |, 2,-..(n—1), when P,Q, R, &c. are put for y in succession. The theorem alluded to gives for the value of such a function *. 1, ¥=P)y— RB) (y—S), &e. .., ¥—-P)y- Q) (y—S)..- a ' (Q-P) (Q- R)(Q-S), &e. (R—P)(R—Q)(R—S)... , Yy¥—P)(y-Q) y—-R)--. +3. (Spy (§—O)(S—R).., * Let this be called Y, and we have 9 (x, y)= ¥ + (y—P) y—®) (y- 2) Y—-49), &e. x x(x, y), which it may be observed is 4 more extensive formula of interpo- lation than the preceding, and includes every other that can be devised. If we reduce the function Y to a series of powers of y, and courpare it with the series produced in like manner by expanding the terms of the expression A(y—P)+B(y- P) (y-Q) + &e. it will be found after all reductions that the two expressions are * Lacroix, Elementary Treatise, Eng. Transl. Appendix. Mr. HerscHet on Functional Equations. S perfectly identical, the values of 4, B, C. Xe. being those before found, viz. 1 1 : =(R-P)(R-@ (P-@ (P-B? Having thus determined @ (x, y) it only remains te consider the arbitrary functions which will be mtroduced under the form of constants in the integration of the equation of differences (c). These constants must be such functions as retain the same value when & changes to A+1, &+2, &e. that is, when y is either equal to P,Q, R, 8, &c. Hence by Prob. 2, their most general form will be T(2)+(¥—P) (v#-—@ @—R)...&e. x x)», and it therefore appears that the solution of the proposed equation afforded by the process here delivered will invelve »—1 arbitrary functions of z alone, and » of 2 and y subject only te the restriction of not becoming infinite when P, Q, Xe. are put for v. Pros. VIT. Let the proposed equation be o=F iz, (ar, Br), va, x, 8,2), Ke} at, 8x, ar, 8,2, &c. bemg given functions of 2. Assume as before & (2, y)= {2, 4+8@(x, y)}. and to determine @(x, ¥), we have @ (ax, Br) = 0; O(a,7, 8x) = 1, &e. For x in the first of these write «e—' (the inverse function of «2) in the second «,—*x, and se on, and putting Ba z= P; Bia, ‘z= @ &e. we have Q(x, P) =0; @(x, Q) = 1, &e. which are precisely similar te what were treated in the preceding problem. 86 Mr. Herscuet on Functional Equations. When the unknown function in the proposed equation is relative to more than two variables, the same artifices may be employed. I will give a single instance to shew the manner of proceeding, it being unnecessary to dwell at length on this case. Pros. VIII. Let the equation be o=f ix, v(x, P, p), v(x, Q, g)}, P,Q, p, q, bemg functions of x. Take as before V(«,y, 2) = o{2, h+0(z, y, 2)}, and determine 6 (2, y, 2), so that O(a Pop) 0); Vlas Gig) when the equation will be reduced to the equation of differences, o=F iz, p(a, h), (2, h+1)}. The most general forms of @ (x, y, =) and of the arbitrary constant, or function of x, y, 2 which has the same value for y= P and z=p as for y=@ and z=q, are then to be determined, and substitution being inade the function required is found. I will merely add one instance of the application of the method pointed out in the foregoing problems. Suppose the proposed equa- tion were 1 ; VG ’ v) = 2 (a, x). We first assume 6 (a, 2°) = 0, which gives 6 (a, ¥) =(y—2°) 6, (7, y), Again, . eC, v) =i. (ir (2, -) =I" This gives 1 1 -— 2*) 6 (2 = )) = 1 (- 1 > =) whence, / x (a, y)- x ry —1 sa aa l—2x - cs Mr. Herscuet on Functional Equations. 87 The x in the denominator may be included in the arbitrary func- tion. This done, we get by substitution, _ ay’) 1G, => 3 + Gy-NG-)-x@y)- Taking then V(r, y) = pia, h+0(2, y)}, we get p(t, h+1) = 29(2, h) and integrating, Dian) — CE - oe) whence (ey) = Cokes), or simply = €.29» | where 6(x, y) has the value above found, and C= f(z) + (wy—1) (y—2*).y (4, y); and the simplest function which satisfies the condition is ry—xe 1—2z3 Y(t, y) =? J. F. W. HERSCHEL. SLouGH, Feb. 5, 1820. | , ae) np Peet . P= OPVAAT 4 7m g) wh Sui " Pie vier oy at HE Las ; a » *. ie A a , _ r , - iw ; % As, Re gyal wah lee: hey ee “ wes me lattices dito ined agg Brotee albevsen sikh Iowgite, bare Brailes oldat wed bo sleepin oy ai aenle, wlasitag | pie ast 3 Fe ‘ont (write aarteoendbalje see git) ninth bvtienb ih or Alay Siniopy = horse emuth yaranee” scent: vgn daiery est - leet ofthe wit (Ae camdeeetin’ iidekmase elt (Seah. quad: sho weip-bonabob enuitedrae oats) hb enUR oil awe Pht is ra gr ca aL fre VIL hee iB a Sep (eee RL ED Ouherfl Comlubge: copef ree / AAKe Lf (2777 es Fa rf MALTRAAMEL naun on dtoneby (Fe: Canee ry rh Mr. Oxes on the Fossil Beaver. 177 part of the horns of a species of deer, measuring in length two feet, and in circumference at that end by which it is attached to the skull, ten inches. This, from its magnitude, must evidently belong to the celebrated extinct species found in Treland, and denominated by Cuvier the fossil Elk of that country, of which a minute account is given in the Philosophical Transactions by Dr. Moly- neux. In his description of this animal, the circumference of the horn at its root, was eleven inches. But these last mentioned fossils, it may be observed, have no connection whatever with those of the beayer, for they belong to a stratum of an antiquity of which we can form no idea, but by comparing it with the subjacent strata ; whereas those of the beaver belong to a stratum, which, if the conclusions to be drawn from our account be well-founded, may be referred to a period not very distant even in the history of this country. Indeed, to corroborate this opinion of the probable date of these fossils and the still more recent date of the stratum containing them, I need only recur to the authority of the distinguished geologist mentioned before, who among the several general laws which he has laboured to establish, concerning the relations of organized remains and the strata which contain them, has arrived at the following important conclusions : “that the bones of species which are apparently the same with those that still exist alive, are never found except in the very latest alluvial depositions, or those which are either formed on the sides of rivers, or on the bottoms of ancient Jakes or marshes now dried up, or in the substance of beds of peat, or in the fissures and caverns of certain rocks, or at small depths below the present surface, in places where they may have been overwhelmed by debris, or even buried by man; and although these bones are the most recent of all, they are almost always, owing to their superficial situation, the worst preserved.” TA sm Vai. 088 40, oa AA Jad ort: dtonst ne De eenetis, sb Yo 2ada swag By adit ot beulvatia 2 ti oie ae fing Jedd ty somone ak 7 gaolsd ybaohivs tagger shatiaxsas ai andi et ae hatedintodel: bes banked at bone? 2sinaqa tititxe haterdsies odd ob : otunin: 0 doidie tol Setter todh TotW lideok oft viva yd elo «i cd zeroitoezael leidqoedlifE silt ‘at covig ai taeooos aft to sonore, et dnenires aid Yo noitgitosab aid al, xem _. .asitiont deals ager toot ei te wort re pradé Bawritdeddo sda: We llelee Miedeiiind tend anhalt pitolsedd cod? sot os zeadt 3clP Yd caer iw tovated moitesater oi xd ted nahi on. cet oth Sue dade to giopBae ae to ihushinta 6 o} saveod afte seo? aeoube 5 aterile trevnsighoa oes tiv Si ait vst wteit wet 2f 0} atioiverioivary aft Ye: Aoidye nota 8 of, olad a2 g9% tow borsg. « of horiitsn ad ‘jain bobenet-tloa 9 pare a strrodens of boshuk. dunes vidt to grated sift ai tia? taete sigat Hite ad? bap ies set Yo sal seca ah Yo ign _ ab aedet alto hea T lard yaisintiuos onudetta aft Yo sinh ails sited hoaoiingurteiyoloag bodeinaaiteib of \Gcneuar oe daildates ot howodal ead od dyidvs awel, Intoasg fernvs2 adt Sons } | lois ntevts. od? bers actianis basiamgio to snoitalyr alt gairassade ‘ -agiaatonos inshoqei parwallot ad? ia having emf tree ssi dtiw often ol elaguqqe st foal sets Me es oa -teatal yrs okt at ign banat s9¥ 90 O18, gels Wes sahie oft no. bast roitis 948 sisi, seackt 10 ob Ise lnsials wore aagletasu 10 adel suvrvae Yo einottod set wa 2a arouse) bow sswecit all at 10. tea to.abad to sonated na otf ni .s9etm savage od? wolad saob lia 1° km * nova to arwlsly ed hoarfodetsxo riod, grad geek th Als to Fetes taour oat. one sono asadkt decodin Sup tt . sas ve old eo ania rte mph od ginkwo iia art ae a = * < ‘ 2a aie =) Oe b=+ qa /C ote P) 40 ; and the positive sign is to:be taken. And hence for the angle between the apsides 2S 0-> 20) og 4-29 +4 fl - 297), , Vere 13 hYP bos ETC a a all the succeeding terms involying g &c. And when q becomes indefinitely small = are-sin = @=arc @in = 1) = Aa nia 186 Mr. WueweE . on Orbits. of the velocity of projection to that in a circle being gV2 to ./n — 1,) that es gada aV@ =) e" = Fe — a) pe ee OLE ne -2V ee 1 Fela And to find the apsidal distances, we have the equation ONE! ETI eee =O meee): or, dividing by a’~' »°~”, — x 2 rl 2 an” Git _1 Saher ear yaaa We shall suppose ” greater than 1 and less than 3. Hence to approximate to the roots, we may observe that when 4, and there- fore x, is very small, the second and third terms of this equation become very small, and we must therefore have approximately, 1—*p-n =0, and x=aqgr". And hence, we may suppose the first side of equation (3) com- posed of two factors (a*-" - ga*" +8) and Q, where Q does not vanish for any positive value of « except x=a, and B is small compared with q’. Hence gadxz : 0 — TE ONG Oe ed S Wie ge +B) And, as before, neglecting 6, and supposing @ constant; es: > aqgdx : ee aaa xVj{2e"*—ga-"t 4 3—n which may be integrated. Let y = : a= af (since Q=a"—" nearly,) @—nVaaJ yV¥— 1) 2 ae + =e (sec a aoe =) + const. qa Mr. WuewE.t on Orbits. 187 3—n 2 and the integral being taken from e=qa~* to r=c, we have for the angle between the apsides which gives, when g becomes indefinitely small, vis = 0 he Sea MO ere = ec — FS ye’ >< ) This applies to all cases where x is greater than 1 and less than 3. When vis very little greater than 1, the angle is very nearly 7 37 as becomes 2, 6 becomes z, which is the proper value, the orbit beg then an ellipse ; this value is not confined to the ulti- mate form of the orbit. As x becomes nearly equal to 3, the angle becomes greater and greater, and finally infinite when x is 3. Beyond this value of 7, the orbit, as is known, has no second apse. Hence, we have the following values of the angle between the apsides in orbits which are infinitely excentric. When the force varies directly as any power of the distance, the angle is 90°. When the force varies inversely as any power whose index is less than 1, the angle is 90°. When the force varies inversely as the distance, the angle is 90*. When the force varies inversely as any power when index is between 1 and 2, the angle is between 90° and 180°. * The case when the force varies inversely as the distance gives the formula dd eee eee) Pe oy/ fe hyp log = -¢(@—- x) but without attempting to approximate to the integral of this expression, the law of continuity indicates sufficiently that the angle in this case will be 90°. AA2 188 Mr. WuHEWELL on Orbits. When the force varies inversely as any power whose. index is between 2 and 3, the angle is greater than 180°. By the ninth section of the first book of the Principia it appears, that when the excentricity is indefinitely small, the angle between : : 180° a6 : the apsides iS 7m 8) if the force vary directly as the x'® power - : WSOn ons : of the distance; and 7 if it vary inversely as the x” power. (3 — n) By comparing these with the preceding results we have the following conclusions. When the force is in any direct ratio of the distance greater than the simple power, the angle between the apsides increases as the excentricity increases; viz. from its value wher 180° V(3 +n)’ the excentricity is 0, to 90°, its value when the excentricity is infinite. When the force varies as the distance, the angle is the same for all excentricities, viz. 90°. When the force varies as the n power,” being a proper fraction, — either negative or positive, the angle diminishes as the excentricity : ; 180° : increases ; viz. from —,—— to 90°. The same is true when the (3 + n) variation is inversely as the distance. When the force varies inversely as the x" power, » being between 1 and 2, the angle diminishes as the excentricity in- caer 180° 180° reases ; - ir (aU aN alae creases V1Z m V(3 = n) ae When 2 is 2 the angle is 180° in all cases. When x is between 2 and 3, the angle increases with the ex- wet soll 180° 6 180° ce —_——— Sc entricity, viz. from V3 =n) ae Mr. WHEWELL on Orbits. 189 The dependance of the angle between the apsides upon the excentricity is, as appears from this recapitulation, somewhat anomalous. There is no very obvious reason why a diminution of the projectile velocity should in some cases carry the apse forwards, and in others draw it backwards. When the angle in the cir- cular orbit is less than 90° we may see in some measure why it becomes 90° in the excentric orbit, because if it were smaller there would be points of inflexion in the curve. But it becomes 90° also in cases where it is greater in the orbit nearly circular, as for instance when the force is constant. There will of course be cor- responding irregularities in the form of the orbit for intermediate excentricities ; but till we can obtain our information more imme- diately from the differential expression, we must be content with such indications of their nature as are supplied by the few cases which admit of solution. W. WHEWELL. Trinity College, March 18, 1820. 190 Mr. Wuewe.t on Orbits. NOTE. AS the reasoning by which the results in the preceding paper are deduced may be considered as offering some difficulties, it may be worth while to shew how the same conclusions may be more directly obtained. We shall take the case where the force varies inversely as a; a similar process is easily applicable in the other case. We shall also make a = 1. We have then to find dx T=1 § etpesh Is se a SSS — gq jx} c=) The brackets containing the limits of the integration, and 6 being a small positive root of sel a= 0 1 XxX Let $$ eee e Jie —¢F-a-pr}) Sie —-F} ; & being a series, r=4/ = a oe 2 eis say aan Pal 1—g°)@ : z , =fi- =a Se Ee a en i eae Q 4 w4 ' xa~-—1+ 1 Ka 1.3 4 2 2 2) 5 aoe sn gar § le Ae a Loe kas a —— 1 =e ee Ste rz Ul ie Fa Sales Now f° 14 ={—t¢ 7 a Sorc (cos = q ) ae C/ te a— gt 3— 2M = aoe 2 A | (between the limits) = § arc (cos = g) -— arc (cos = 4.) _ 3—n brats But P—*-g—-Q—g)h=0; - So=Yf1-a-)h—' 4 5 2 hence, when g and 6 become very small, we have > Ls el ama P| eS) ” 2 a ae e rz As a = { arc (cos =0) — arc (cos = 1) $ = 5 eS a” d Bi and it is to be shewn, that all the other terms of 0, involving ora fe = Hi will vanish. Mr. WHEWELL on Orbits. 191 ptm + u— 3 Cys tn , Let P pee and since 27=2°="— 93, dz==— LS pinto 2 z ? : a eet —tde (@m— i) CG—n) 2P"— dz ae BE 2h ON) eee ae a ee ef) ee 2 Cee amt Om=—D)S—n)* 2. 2Q2m+n— 3) Qaeda @m— ae =n) ar br + r—3 andie between thowlimits =a ee) : ’ 2m — 5 Gin) Ck =1 = (B—" — q*) a 2(2m + n— 8S) a ge” Tia (2m — (2m — 1) (3 —n) (3 — n) 2 2m + 2—— 3 no 2 Now 63—* — g? = k*b?; hence Bt eee a Car —s 7) 2 2 (n — 2) 228 3—n Gild and, since 6=g'—" nearly, = [eR Hence, the term which is freed from the sign of integration will involve n—J1 {a—q"}, which, since x» — 1 and 3 — 2 are both positive, will vanish when g - ; aie TELE : : vanishes. Similarly {________ &c. may be integrated in part, and the terms tl «& 3(m—1) 5(a—) so obtained will involve {g—g° " }, {g—q* “ }, &c. and therefore vanish when we make g =0. Thus the integrals after the first, in the series for 0, may be reduced to a series of terms, each of which becomes indefinitely small when g does. And hence, the limit of @ when the orbit approaches indefinitely near the center will be found by making g = 0, which reduces it to its first term. ‘That is, ultimately, Aion ne air 0 ig He PURE) ae ig © y dalle Avinins Vive pies, 9s ete ba eel wen ‘ witness nah fae tree ee scok ingy nach ae erp 2 aint i oak _ ud Beowpot sd yara & to singe pete gel twas. y saatkee 79 Berge sf life totes: prey ' ate Le i at ard aad deere anes pny |) eae ore . a . a ck ne j ‘ ot whem 5 dae em Os ae et = oumar : ‘feds fF a — -*. oe? wt ee ees ie ma ‘ ‘ veel ’ 6 edule oti er ‘se ale, On bd ee ia - ; : — ° s v Lig. 23. Fug 24 a * ab XI. On a remarkable deposit of Natron found in cavities in the Tower of Stoke Church, in the Parish of Hartland, in Devonshire. By EDWARD DANIEL CLARKE, LL.D. LATE FELLOW AND TUTOR OF JESUS COLLEGE; PROFESSOR OF MINERALOGY IN TIE UNIVERSITY OF CAMBRIDGE: LIBRARIAN OF THE UNIVERSITY: MEMBER OF THE ROYAL ACADEMY OF SCIENCES AT RERLIN; HONORARY MEMBER OF THE GEOLOGICAL SOCIETIES OF LONDON, EDINBURGH, CORNWALL, &e. &e. [Read November 27, 1820.] Tn the Chemistry of Nature, the mutual decomposition of bodies, by their action on each other, and the new synthetical results which follow this analysis, may be justly deemed among the most interesting phenomena offered to our view; and they are, perhaps, never more strikingly developed than in the formation of the native Salts, when they are found efflorescing and crystallizing upon the surface, and in the interstices, of minerals, which did not originally contain them. It has often happened to me to point out these changes, in my public lectures, to the University, and to call the attention of mineralogical Students to the operation whereby in a successive series of analysis and synthesis the eternal energies of the creative agency are continually manifested. To the attentive observer of Natural Chemistry, these phenomena are highly important; because, while they are calculated to illustrate Bs 194 Dr. Ciarke on a remarkable Deposit of Natron. the origin of some of the most remarkable substances in Nature, their consideration fills the mind with astonishing ideas of the activity, and renovating powers of that ceaseless Cause, which ordains new and beautiful forms, out of the decay and ruin of pre-existent bemgs. Many such phenomena might be here enu- merated ; but for the present I shall confine myself to one; namely, to the formation of native nafron; under circumstances which were communicated to me by Dr. Waveti of Devonshire; so well known to the scientific world by his former discovery of the phosphate of alumina; called, in honour of him, by the name of Wavellite. Dr. WaveLL transmitted to me a small parcel of a white salt, which he had lately found in the Tower of Stoke Church, in the Parish of Hartland, in Devonshire; desiring me to examine it. The description of the manner m which it was deposited, shall be given from the letter which accompanied this alkaline substance, in his own words.—‘‘ Many of the stones, in the interior of the tower, were hollowed out, and the cavities nearly filled with the Salt. Upon other stones there was merely an_ efflorescence. Some of the cavities were only large enough to admit my hand; others would nearly receive my head. I send you a small fragment of the stone, which I broke off with difficulty; for although the stones appear much deeayed, they are very hard.”— The stone in question, is evidently a slate-coloured sandstone ; but unlike any sandstone I had before seen. Perhaps it is nearly allied to the Graiiwacke of the Germans, but of a purer siliceous nature. The grains of sand are so minute, and withal so intimately aggregated, as to be imperceptible to the naked eye. It preserves its colour when first acted upon by the common blewpipe; but when wrapped in platinum foil, and exposed for half an hour to a white heat in a coal fire, its colour becomes reddish white. Exceedingly minute particles of silvery mica may then be discerned Dr. CLARKE on a remarkable Deposit of Natron. 195 with a lens. The action of heat produces hardly any magnetic pro- perty; the smallest particles beimg scarcely affected by the magnet afterwards. Its specific gravity equals 2.625, which alone proves it to be nearly pure silica; the specific gravity of Quartz being 2.6. It scintillates freely with steel. Placed in dilute muriatic acid it yields no effervescence ; but the acid being boiled, causes it to exhibit an almost imperceptible effervescence. The same acid being afterwards evaporated to dryness, and distilled water added, oxalate of ammonia detected a trace of lime. Carbonate of soda also threw down carbonate of lime trom the same solution, but with a beautiful reddish hue owing to the precipitation also of oxide of iron by means of the alkaline body. Hence it is manifest that some carbonate of Jime had existed in this sandstone ; probably asa cement; but the stone having been corroded and decomposed in the formation of the salt, I thought it right to see if any car- bonate of lime existed in the salt itself, which proved to be the case ; and this I ascertained in the following manner. I dissolved a portion of the salé in distilled water; decanting the supernatant solution so long as it continued to change the blue tincture of vegetables to a green colour. When all action upon the vegetable tincture had ceased, and the msoluble residue had been repeatedly washed with many volumes of distilled water, I poured upon it some muriatic acid; when a visible and somewhat violent effervescence ensued; particles of the effervescing body being carried up and down in the liquid. That these particles were carbonate of lime is evident from this circumstance; that the acid being now decanted into a filter and collected in a watch-glass, and evaporated to dryness, and distilled water added, the presence of lime was fully attested by oxalate of ammonia. My attention was now given more immediately to the salt itself ; in the examination of which I proceeded as follows: BB2 L96 Dr. Ciarke on a remarkable Deposit of Natron. Its taste is very slightly alkaline. Cast upon burning coal it exhibited neither deflagration nor phosphorescence. Placed in the flame of a candle it rapidly melted like ice; giving out water and carbonic acid, as will further appear in the sequel. To nitric and to murtatic acid it yielded a violent effervescence. The gas being collected precipitated carbonate of lime, from lime water. Having saturated distilled water with a-portion of the salé and filtered the solution, there remained at the point of the filter a regular hexagonal crystal of considerable magnitude, the termina- tion of which could not be accurately ascertained, because the crystal had been formed by an aggregation of parallel spicule, the points of which projected irregularly at its termination*. When the rest of the solution of the salt had passed the filter, a drop of it was suffered to fall into a solution of platinum, but caused no precipitation ; hence, it was evidently not a salt of potass. To prove therefore that it was a salt of soda, muriatic acid was added drop by drop until all effervescence ceased. This muriate was then placed over an Argand lamp, and with very gentle heat evaporated; cubic crystals of muriate of soda, beginning almost instantly to form upon the surface and fall to the bottom, which process was continued until the whole of the liquid became crystal- lized in highly transparent cubes, having the taste of common salt; exhibiting also indented cavities, as of inverted four-sided pyramids, where the crystallization had affected the regular octahedral form.— That this was a muriate of soda seemed clearly shewn; however to put this matter out of all doubt, nétrie acid was afterwards added, * This form in carbonate of soda has not been before noticed. The mode in which a regular hexagonal prism results from an octahedron, of which the principal section is 120° and 60°, is thus explained according to the common modes of truncation. It is shewn by cutting off the four edges of the principal section and the two acute angles at its extremities. Further, this prism would have right bases if the apex of each rhombic pyramid were truncated. Dr. Cuarke on a remarkable Deposit of Natron. 197 instead of the muriatic, to the solution of the salt as sent by Dr. Wavell, until all effervescence ceased ; and the nitrate being left to crystallize exhibited transparent crystals of a rhomboidal form. The filter through which the nitric solution had passed being placed in the fire, exhibited the same deflagration as touch- paper, which has been made with the nitrate of potass. When exposed to the air the crystals of the nitrate attracted moisture. From all the preceding observations it is therefore plain, that the salt discovered by Dr. Wavell in the very act of forming in the tower of Stoke Church is native natron; and it is also proved to be a bi-carbonate of soda from its action when exposed to a red heat, in passing from the state of a bi-carbonate to a common carbonate, by the loss of one half of its acid*. Like the natron of Egyptt and of Hungary}, it contains both sulphate and muriate of soda, besides the carbonate; which may be proved by adding a drop of solution of szdver, to the solution of this salt in a watch- glass, as a test of the presence of muriatic acid; anda drop of barytic water, as a test of the presence of the sulphuric; in both instances a white precipitate is caused, which in the latter case is insoluble in dilute. muriatic acid, and in the former, where the test for muriatic acid is used, turns brown and afterwards black by the action of light; and is, therefore, evidently, a muriate of silver. Having thus ascertained the nature of the curious discovery made by Dr. Wavell, I shall next proceed to account for the very singular circumstance of the formation of natron im the situation which he has assigned for it. * See the opinion of Dr. Wollaston as cited in Thomson’s Chemistry, fifth Edit. vol. IT. p- 440. Lond. 1817. + Klaproth’s Beitrage zur Chemiscen, &c. b. 3. s. 80. p. 123. Lond. 1816. t Reuss, Lehrbuch der Mineralogie, &c. b. 3. s. 5. Ibid. Jameson’s Mineralogy, vol. II. 198 Dr. Crarke on a remarkable Deposit of Natron. Stoke Church is situate upon the sea-coast of Devonshire, upon that promontory which goes by the name of Hartland Point, a little to the South West of Hartland, in the neighbourhood of Hartland Quay. As the distance, inland, to which the salt spray of the sea is carried by winds, is well known to those who reside in maritime districts ; bemg often deposited upon the window-glass ot houses, fifteen or twenty miles from the shore; it will not appear at all marvellous, that the muriate of soda is perpetually acting upon the stones of the tower of Stoke church, which in a direct line is not more than half a mile from the sea. The cavities in these stones, as we have shewn, are found to contain a certain portion of carbonate of lime ; whether derived from the mortar used in the buildig, or not, is uncertain; as the stones themselves contain hardly any of this substance. This is of no consequence; because itis only necessary to prove the existence of carbonate of lime, in contact with the muriate of soda; which has been done already. Whenever these two bodies lie in contact, being also subject to continual changes of moisture and desiccation, it isa fact generally admitted that their mutual decomposition ensues. The alkali parts with its acid, which forms a muriate of lime ; and the carbonic acid of the limestone entering into chemical union with the alkali, forms a carbonate of soda, or native natron ; which is the identical salt, now under consideration. Yet as this double decomposition of the two compounds is necessary to its formation it is rather a rare deposit in nature. The places where native natron has been dis- covered in any abundance are all of them foreign to our island. The best account of them, is given by Professor Jameson in his System of Mineralogy*. The crystallization of natural carbonate of soda is unknown; that of the artificial carbonate is supposed to be an * See vol. II. p. 312. Edinb. 1816. Dr. CiarkeE on a remarkable Deposit of Natron. 199 octahedron * of which the common base of the two pyramids is a rhombic plane, whose angles, as nearly as can be determined by the eye, without the aid of a Goniometer +, measure 120° and 60°. The obtuse angle of the rhombic crystals of the nitrate of soda is much less; being about 98° or 100°¢, which gave rise to the erroneous appellation of cubte nitre as applied to this kind of salt. The rarity of native natron in our island, gives to Dr. Wavell’s discovery an additional mterest. Its usual occurrence is as an efflorescence on the surface of decomposing rocks; in which state it appears among the old lavas of Vesuvius, where I myself found it nearly thirty years ago, during all which time this salt has been m my possession without exhibiting the slightest deliquescence or alter- ation in consequence of atmospheric changes. I shall therefore now present it to the Society that it may be placed with Dr. Wavell’s specimen in their collection of Natural History, and with an earnest hope that it may serve as the beginning of their Cabinet of ‘Mineralogy; to which I am well assured contributions from all quarters will be made. .Vatron is also found in certain Jakes that annually become dry, and to which salt-waters have access; as in the natron lakes, to the west of the Delta, in Eayer; which were visited a short time before I arrived in Egypt, by the celebrated Berthollet, together with other Frenchmen of the corps of Savants then in that country, accompanied by a military escort under the command of General Andreossi. I well remember the importance which the members of the French Institute attached to the result of * Dr. Thomson states this as a general conjecture with regard to the primitive form of the carbonate of soda of commerce; ‘“ but” he adds, ‘‘I am not aware that this form has ever been met with. At least, I have never seen it myself, although I have examined several hundred fine crystals of this salt.” See Thomson's Chemistry, vol. II. p. 440. Lond. 1817. + This is the apparent inclination of the spicule which form during the crystallization of the salt sent by Dr. Wavell, after it has been dissolved in distilled water and left to evaporate in a watch-glass. t Also conjectured from the ocular examination of crystals in a watch-glass. 200 Dr. Ciarke on a remarkable Deposit of Natron. that expedition; first, because it gave rise to the theory of Berthollet respecting the formation of Watron, which is now in general accep- tation among Chemists; secondly, on account of the difficulty of penetrating to those lakes, in consequence of the dangers arising from predatory tribes of Arabs, and from other accidents to which travellers in Egypt were then exposed. An account of this journey was published by Andreosst in the Decade Egyptienne printed at Cairo, of which three volumes are extant*. Berthollet also himself published a separate memoir upon the natron of those lakes. According to him they are six in number, of which they examined the smallest, near a ruined fort, called Kasr, which is built of blocks of native natron; “ of itself shewing,” says Andreossi +, ** that the fall of rain in this country cannot be considerable.” The lakes comprise a surface of about six leagues in length, by six or eight hundred metres in breadth; they are fed by springs of brackish water containing murtate of soda, falling from the tops of small creeks abundantly during three months in the year, when they begin to fail, and some of the lakes become dry. The bottom of the lake which they examined consisted of ‘ argillaceous mudt mixed with sand.” Berthollet also observes in speaking of the soil between the lakes, that if the soil be too argillaceous, no natron is found, but only sea salt. If it be too siliceous, no salt at all is yielded; it is therefore the more remarkable that in the tower of Stoke church where the stones, exclusively of the mortar, are almost * Memoire sur la vallée des Lacs de Natron, et celle du Fleuye sans Eau, d’aprés la reconnaisance faite les 4, 5, 6, 7 and 8, pluvidse,l’an 7¢ de la République Frangaise, par le Genéral Andreossi. Voy, La Décade Egyptienne, Tom. II. p. 93. Au Kaire An. Vit. + Ce qui annonce que les pluies ne sont pas considérables dans cet endroit. Ibid. p. 96. | Unaccountably rendered Chalk by an English translator of Gen. Andreossi’s Memoir. See Memoirs relative to Egypt, p. 260. Lond. 1800. There can be no doubt both from the observations of Berthollet and of Andreossi, that the stratum below the sand of the Desert, in this part of Africa, is of limestone; but the words here are: ‘le fond du luc est de boue argilleuse, mélee de sable.” Wid. p. 98. Dr. CiarkeE on a remarkable Deposit of Natron. 201 wholly of a stlceous nature, a deposit of natron should have taken place, so remarkable as this noticed by Dr. Wavell within the interior of the tower, where the decomposition of the stone has proceeded to such a length, as to have given rise to the cavities which he has described. In a second letter which he has addressed to me upon this subject, he says, ‘‘ The church is large and antient; the tower, a very fine one, is a sea-mark; and, in a direct line, is not more than half a mile from the sea. I observed no appearance of decay in the stones of the exterior of the tower; it seemed wholly confined to those of the interior. How have these stones been thus acted upon; and whence originates the salt with which their cavities are laden? Many from their honey-combed appearance seem to have resolved themselves into this salt.” The origin of the salt and its chemical constituents have been already sufficiently explained. The only doubt, as to its formation, may possibly attach to the source of the carbonic acid which has combined with the soda; i.e. whether it were derived from the small quantity of the carbonate of lime which the mortar contains, or has resulted from the action of atmospheric air. There is some- thing also paradoxical in the nature of the action which has pro- duced such a remarkable instance of decomposition in the stones of the tower; and this only upon the interior walls. Further obser- vations made upon the spot, may perhaps clear up these points. For the present, having already trespassed Jong enough upon the attention of the Society, any additional remarks upon this subject may be reserved for future consideration. EDWARD DANIEL CLARKE. Cambridge, Nov. 15, 1820. Cc i ines atu tei am fi aoniteath basay tise 968240) igizopa fig Rca ?: oi. iy aati via th “ perc aout miley @ vhs OF, 4) : “apne! “aniytes elt te aia ta * aang ae ess 2h du = gt : + lstmis , nitik whiny tiv iy ual thea! rota pigs ah site ‘hit vt p hn *) ou ws ie Ba haagamivy i ‘x fete ks. ote alj ie. 1 (ual ru. vi oa aL rsh rea S97 ats Ae o sso agin no t porbbin deed Saaad fh sek wot « ND af: ult bosch AS gla watt inl eedtiwa Mae sftp es Meiadh ine “goteadae Rive a «qa F ~ ganatesrids: t — pined nivikd etgr?h, pias 3 Znshab.are ete ‘ ‘Si red cele aberé an rfsevivndt | atleast) rssh oh chee nil at at nerhhiols Hn my Fr glape un ghtine: i ai! 2 bagre ce Serine afte ode doodles efely nt ont (epsioh bon Bye mas a nee y xektoles aebint * IB py Amandrag ‘anid idea qi ; ow este * aes a - A is e = iu ‘au cua aul; ny 4 tins Stow lt vito Miroby ao % : ~*~ feo! le sors abl aoe “ =. p ¥ a Higa qoInsag sath B 4 BBs i | 7 a Se * ) seu atp eee JOE ds amo + jawpr a2 itt elt ita Me om ] soe pm are ae 4 CRA ET F we ae ANE: A » oh eke > ” «. r ee eraah a \= pad bin coer ~ : a 2s) : f : A 4 = : ' ae ‘7 ¢ ’ 7 i, y «A - ’ « ee XII. Analysis of a native Phosphate of Copper from the Rhine. By FRANCIS LUNN, B.A. F.R:S. OF ST. JOHN’S COLLEGE, CAMBRIDGE, [Read March 5, 1821]. Among the Analyses of Klaproth* is one ot a. Phosphate of Copper from the Firneberg near Rheinbreitenbach on the Rhine: the mineral had long been mistaken for Malachite from its external resemblance. The German chemist obtained as his result Oxide of Copper... ...68.13 Phosphoric Acid......30.95. And this Analysis has been adopted by Haiiy— Brogniart — Thomson—Jameson—Phillips, and in short copied into every Mineralogical classification which has appeared. Its accuracy has been doubted +, it is true: for water to the amount of 15 per cent. is overlooked; but the rarity of the substance has prevented che- mists from subjecting it to a new examination. Having lately received some copper ores brought from a mine at Erpel near the town of Bonnt, among these were specimens * Beitrage zur Chemiscen, III. 206. + L’Analyse de M. Klaproth n’indique pas que l'eau entre dans la composition de ce phosphate, cependant il en conteient une quantité assez considérable; &c. &c. Cette cir- constance jette doute sur’ exactitude de l’'analyse de Klaproth; elle mérite bien d’ etre répetée Berzelius. Nov. Syst. p. 246. Paris 1819. } For these very fine specimens, I am indebted to George Samuel Kett, Esq. Brooke House, Norfolk. Vol. I. Part Il. Dob 204 Mr. Lunn on Native Phosphate of Copper. of the mineral in question. In mineralogical characters it agrees with the description of Klaproth. In colour it is emerald green, but shaded and streaked with black green, and to this colour the external natural surface approaches; it is opake, its powder is verdegris green, it has a diverging striated texture and a silky lustre, the specific gravity of one very pure fragment was 4.2, its hardness is rather beyond that of Malachite. It was m no instance crystallized, although on the external surface of some specimens an imperfect tendency to crystallization was perceptible. It occurs massive in a white opake quartz rock, in places slightly tinged by oxide of iron; and it is soluble in nitric acid. By exposure to a red heat in a close crucible it becomes of a dark olive green colour, and the powder increases considerably in bulk. Before the blow-pipe on charcoal it readily fuses into a reddish black slag adhering to the char- coal, and by the addition of carbonate of soda it is reduced to a bead of pure copper. In some specimens it is accompanied by crystals of phosphate of lead. Although the elements of this mineral are not numerous, yet wherever phosphoric acid enters, considerable caution is necessary to ensure correct analytical results: nothing can more fully prove this than the discordancies between the results obtained by two of the most expert analysts, Professors Thomson and Berzelius, and yet both have exerted their utmost skill on this very subject. It was necessary to make several previous trials to find out a precipitant which might be depended upon; or rather, to find out the mode of using any of the old ones which would pro- duce accordant results. These trials were made upon anhydrous phosphate of soda by barytes, lime, and the salts of lead. IT need not repeat a tedious course of experiments, but may mention the results: the objection to the earthy salts is that unless the solution Mr. Lunn on Native Phosphate of Copper. 205 be most strictly neutral, or even rather alkaline, a very small quantity of the phosphoric acid enters into insoluble combination ; these therefore would not answer the intended purpose, because at the very point when the re-agent would be useful the original salt was itself precipitated. To the salts of lead then we must have recourse: the muriate appears to have the preference with Berzelius*, and with this salt accordant results may be obtained; but both the saline solutions must be most strictly neutral, and the very low degree of solubility of muriate of lead after it has once been crystallized, is a considerable practical inconvenience. With the nitrate of lead I could obtain unvarying results; it is easily crystallized, and when carefully washed and redissolved is perfectly neutral and of high solubility. In both the above methods it is advisable, to ensure accuracy, that no more of the solution of the salt of lead be added than is necessary to separate the phosphoric acid; and the precipitate must be boiled in water, by which means the combination of acid mentioned by Berzeliust may be avoided. ANALYSIS. A portion of the mineral free from any foreign ingredient was reduced to a fine powder; this after being dried at the temperature of 212°, was of a verdegris green colour, and weighed 28.7 grains; by subjecting it to a low red heat in a platinum crucible it became olive green, more bulky, and lost 2.15 in weight, which was water driven off; it was not adviseable to let it remain long at that heat. for it is capable of being volatilized, which appeared by some con- densing on the lid of a crucible. The whole was now dissolved in dilute nitric acid, and formed a clear blue solution; from this as much water and excess of acid was driven off as possible by * Annales de Chimie, II. 159. + Ibid. DD2 206 Mr. Lunn on Native Phosphate of Copper. a long continued gentle heat. The whole was now very carefully neutralized with a weak solution of potash so as just to avoid the reprecipitation of the salt: nitrate of lead from fresh dissolved crystals was carefully added, avoiding excess, which was shewn by the clear liquor above the white precipitate undergoing no change from sulphate of soda nor hydriodic acid. The precipitate boiled, well washed and dried was after a red heat = 31.23 grains, equi- valent to 6.246 of phosphoric acid. A solution of caustic potash was added in excess and boiled upon the black precipitate formed; this when separated and dried at a heat below redness weighed 18.1 grains, and was Copper in the same state of oxidation as in the mineral*. Hence, Phosphoric acid........... 6.246 Per-oxide of copper. ......18.1 IWVAGEE e's cte crelete avetclaiclolcic emai 26.496 WO8Ges a slcieic’e vie ela ceisler sje vine 2 OL 28.8 Now this loss would appear considerable, if we do not take into account the impossibility of having driven off all the combined water, for reasons above stated. If we consider that loss to be water, the result will stand thus, Phosphoric acid.... 6.246 = 21.687 Per-oxide of copper18.1 = 62.847 >per cent. Water... ...esse0. 4.454 = 15.454 28.8 100. * The analysis was also accomplished in another manner, by adding hydrate of ammonia in such excess as to redissolve the precipitate at first formed. The phosphoric acid was then precipitated by cautiously adding nitrate of barytes, and after the liquor had been rendered acidulous by sulphuric acid, the copper was separated by a plate of iron. The method described in the text has, however, practical advantages. Mr. Lunn on Native Phosphate of Copper. 207 Now it is fair, at least, to compare all theory with experimental results; if we consider the mineral as composed of 1 atom of phosphoric acid, 1 atom of per-oxide of copper, and 2 atoms of water, the quantities per cent. will stand as below; and by the side I have placed the experimental result for comparison. Theoretical Composition. Experimental Result. Phosphorie: acid. 22.222. 2... 5. 625. 21.687 Per-oxide’ copper: 63-492; ..3. 0 7. 62.847 \NE Tea en gblendes i, VOL Weare nrGe code 15.454 It will be seen that the difference isin no case equal to unity except in the water*. If we were to represent the constitution of this mineral by the symbols of Berzelius, which being derived from the Latin are more general than the English initials of Thomson, but adopting the opinion of the latter with regard to the constitution of phosphoric acid, Its chemical sign would be CuP +2Aq. Its mineralogical ————- CuP +24 q. There can be no doubt of Chenevix’s artificial phosphate bemg a bi-phosphate, as stated by Thomson+; and it is rather singular that a neutral combination which has not hitherto been formed in the laboratory of the Chemist, should be the very substance formed by a natural process in the earth. * Throughout these calculations I have made use of the atomic weights recently laid down by Thomson, because in some trials of verification I found them to accord best with experiment. + Thomson’s System of Chemistry, Vol. II. p. 607. 5th edit. = s is : -? ; . base a $ ‘ WW i= , re Pos * E ‘ We) Mick satel ADIN, sent be hie sive Agate ” 4o fi Hor wiewt Ww tn wy doe ai Ro oF F Hh" tinea’ ae ; (j # * Bs Fabaceae it ied Pha FW! IRSA ref Zid) ee f : Bee ky - inf + ‘ s rc ~~ el > fax a as et i rte ee ee wii i Ye. yiniber 4 fenbia a age as wks ah tae i wish. tins Do ps on asia tickaticen pe hy thew vas as cs tevacret yas jo ‘toLatiteras on Some “e16 atind ‘alt ase having! pind fo bi aul? ‘yaitgoha. fad aoamedT. jo » alaitiat. tail apaeta o doliyt sip take aid ot sie 4 26.4 a eh a ; Pp heen oe. Bost ‘inal toads ae ne ers i _ phe +A * Latiigiler iio SU oe Nite talaga ney TWinhittn” p ainare ne iaths a ua t iii Vas 60 TE Hea 2 SHE eras wt ola poo cid ee hinliewit ahi) “ihe tort! aie! oid Noitiititteion. Terabe at sath ‘witkitbectit yr ol seh Sitios AeimadD wy ts = pe » Mandate eS dies coil ¢ Uaagond Lends See eee tut “ ogee» aa Sei wah bint ita wt tityre Beene’ anv bei b ser dizn, toa Pre o wets ug maple ae ee 9 ty 77S _fite Wis “toe 4 WF, ir x = yale. . pont 4 \ ; os : @\ ft ah i. Ve, ; tit ag a Bry ao BO gre Mp + Be oo oy ‘ > all hore at skactant *46) aa : - ¥ NIT. Upon the regular Crystauuization of Water, and upon the form of its primary Crystals ; as they were naturally developed in Cambridge, January 3, 1821, and were seen during the two following days. By EDWARD DANIEL CLARKE, LL.D. / LATE FELLOW AND TUTOR OF JESUS COLLEGE; PROFESSOR OF MINERALOGY IN THE UNIVERSITY OF CAMBRIDGE; LIBRARIAN OF THE UNIVERSITY; MEMBER OF THE ROYAL ACADEMY OF SCIENCES AT BERLIN; HNONORARY MEMBER OF THE GEOLOGICAL SOCIETIES OF LONDON, EDINBURGH, CORNWALL, &e. &c. {Read March 5, 1821.] Tue frost which took place towards the end of the last and beginning of the present year (1821), was particularly favourable for the exhibition of a phznomenon Naturalists have been often anxious to witness; namely, the perfect Crystallization of Water. This happened in Cambridge, under circumstances worthy of notice; because it exposed to view the primary form which Hydrogen oxide assumes in the solid state; and because it is a commonly received opimion, although erroneous, that to observe any appearance of this nature we must visit distant regions, liable to a much greater diminution of temperature than any part of the Island of Great Britain; such as might be found in Lati- tudes where Water is constantly maintained in the solid state. 210 Dr. CLarkeE on the Crystallization of Water. That the compound of which Water consists, does obey the same laws to which the particles of all other oxides, and of all other bodies, are liable, when they pass from the fluid to the solid state. is no new discovery—it is even older than the researches of those Philosophers to whom the first dawnings of the Science of Crystal- lography have been usually ascribed. It must have attracted the regard of scientific men as long as the ramified congelations at the surface of glass windows, during the time of a frost, have been offered to their view: the remarkable circumstance of the arrange- ment of the spicule, intersecting each other under constant angles of 120° and 60° would surely not have escaped their observation: indeed, we can prove that it did not; for the same disposition of particles, being exhibited with a striking character of symmetry in Snow, (which sometimes falls in star-like forms, with six radii, bisecting the angles of a regular hexagon,) was noticed, before the Age of Wewton, by Descartes who attempted to explain the pheenomenon. Mairan, atterwards in his dissertation upon Ice, compared the appearance with that of the Strie visible upon the surfaces of some of the crystallized sulphurets of Iron; and in connecting it with a result of the laws to which the structure of all Crystals is subjected by that force which disposes the par- ticles of bodies, when in the vicmity of contact, to combine together under geometrical forms, Matran was not far from the truth. The same subject early excited the attention of those cele- brated French Chemists, who, towards the conclusion of the last Century, were engaged in publishing an account of their trans- actions. Monge, afterwards President of the National Institute of Paris, in the Metéréological Mémoire, with which the fifth Volume of the ““ Annales de Chimie” commences, alludes to this beautiful effect of crystallization in Snow; and he gives the first satisfactory explanation of the phznomenon; illustrating what passes in the yast Laboratory of Nature, by reference to an easy experiment Dr. Ciarke on the Crystallization of Water. 211 in the Laboratory of the Chemist*. Similar Snow-erystals exhibit- ing an hexagonal disposition of particles, have simce been observed and carefully deiieated. I have myself seen them im Russia and in England+; they descend when the atmosphere is calm, and its temperature a little lower than the point of congelation. It is in fact only at this degree of temperature that the regular erystal- lization of Water may be expected; that is to say, at the precise temperature, when the particles of which Waéer consists, not being interrupted by the too sudden agency of the Laws of aggregation, are at liberty to arrange themselves with the most perfect order and exact geometrical precision. If the diminution of the repelling principle be very considerable, this cannot happen ; because the consequent encrease of the attractive force is such, that the par- ticles rush together, without any harmonious configurationt. But the phanomena to which allusion is now made, beautiful as they are, and bearing testimony of the homage paid by imanimate matter to the supreme cause of order in the universe, are but faint expressions compared with those which will presently be noticed: they exhibit, it is true, an incipient crystallization; but the full development of the process which ordains that even Ice shall put forth its blossom, remains for subsequent consideration. That the hexagonal disposition already observed in Snow-crystals, might mduce an expectation of finding water in regular hexahedral Crystals, would have been a reasonable inference from such * See “ Memoire sur la Cause des principaux Phénomeénes de la Méteréologie,” par Monge. Annales de Chimie, Tome Cinquieme, pp. 47, 48, 49. Paris, 1790. + See the figure given of those Crystals, Travels, Vol. 1. p. 11. Camb. 1810. See also figs. 1. 2. 3. representing Snow-Crystals which have since been observed near Cambridge ; and of which an account appeared, at the time, in the Cambridge Chronicle. t And this is, in fact, the reason why traces of regular crystallization are rarely discernible in Meteoric Stones; which have resulted from the sudden aggregation of particles of matter, in regions where the repelling principle is considerably diminished. Vol. 1. Part IL. Ee 212 Dr. CiarKeE on the Crystallization of Water. phenomena ; and accordingly it happened, that the regular crystals were soon discovered. The first notice of such Crystals occurs in the manuscript Mineralogical Journal of Monsieur Hericart De Thury, of which an extract first appeared in the Journal des Mines*. Another from the same source lately appeared in the Edinburgh Philosophical Journal+, describing a subterraneous Glaciere at Fondeurle, in the South of France, containing perfect crystals of Ice in the hexagonal form. The manner in which the regular crystallization of Water under a different form was recently exhibited in Cambridge, and of which, together with other members of the University, and inhabitants of the town, I was an eye-witness, may now be related. Upon the third of January, at one o’clock in the afternoon, the Mercury in Fahrenheit’s thermometer then standing only one degree below the freezing point, happening to pass over a bridge, which was fixed against a pair of flood-gates, I stopped to examine a beautiful appearance caused by the most brilliant Icicles I had ever seen, a number of which were hanging abundantly from the sides of the flood-gates and timbers below the bridge, surrounded by falling Water which was continually casting a spray over them. As those Icicles, owing to their dazzling lustre, did not resemble common Icicles, but seemed studded with spangling surfaces like the richest and most limpid cut glass, powerfully refracting and reflecting the rays of light; and instead of being shaped m lengthened cones, with even surfaces, were of a botryoidal form, with angular points and protuberances, I caused some of them to be broken off, when it appeared that the light reflected from them was transmitted through planes bounded by right lies, and that the several botryoidal masses were, in fact, so many bunches of Crystal, most of which were perfect rhombi; measuring in their *Vol. XXXII. p. 157. > Vol. H. p. 80. Dr. Crarke on the Crystallization of Water. 213 obtuse and acute angles 120° and 60°. As the temperature of the atmosphere was, at this time, lable to little alteration, I had fre- quent opportunities of returning to the spot, while the appearance continued, and of having a drawing made of it by an artist who accompanied me thither, and who afterwards at his leisure com- pleted the design which is now exhibited to the Society. I also removed some of those crystalline masses and brought them home with me; where I exhibited them to several members of the University, and frequently, in their presence, measured the angles of the rhombic crystals with the Goniometer of Carangeau; the crystals being of such magnitude that they admitted of the perfect application of this instrument with as much accuracy as a rhomb of Iceland Spar. Many of them were more than an inch in length*. Upon the sixth of January a thaw took place; the Mercury in Fahrenheit’s thermometer rising at twelve o’clock to 39°. Still the same inclination in the planes of the melting crystals, forming angles of 120° and 60°, was generally visible, although the forms of the rhombi were less perfect and the extreme points of the solid angles were rather rounded by the alteration the Ice was beginning to undergot. It was evident, therefore, that a similar arrangement of particles pervaded the entire mass of each crystal ; and that a power resisting the agency of the repelling principle preserved a degree of parallelism in the laminz of the rhombi; the surfaces of superposition being thereby developed almost as per- fectly as if they had been disclosed by a series of regular cleavages. Hence it was also evident that the rhomboid with angles of 120° and 60° exhibited the nucleus or primitive Crystal of Hydrogen oxide or Water; and that the hexahedral crystals observed at * See fig. 4. representing one of them of the size of the original. t See fig. 5. shewing the outline of one of the stalactites after the thaw had commenced. EE2 214 Dr. CrarKE on the Crystallization of Water. Fondeurle were secondary forms, resulting from the juxta-position of such rhombic particles ; which also is rendered further manifest by observing the disposition of the spicule which diverge from the radii of the star-like crystals of Snow *, shewing the order of arrangement in the rhombic molecule from which the hexagonal crystal results. It is presumed, therefore, that the question respecting the Crystallization of Water, may be set at rest by these phenomena ; because it is now no longer a mere inference, deducible from obser- ving the intersection and disposition of the spicule exhibited by Water when frozen upon the surfaces of other bodies, and in its approach to Crystallization, but it is a decided fact, shewn by regular crystals of Ice, that the compound we call Water, or Hy- drogen ovxide, crystallizes both in hexahedral prisms and in rhombi, having angles of 120° and 60°; and that the latter is its primary form. The manner too in which these forms have been displayed may guide to the crystalline forms of other bodies, by inducing a careful examination of the surfaces, points, and interstices of all minerals when they are found as Stalactites. The Stalactite formation is of all others the most likely formation to bear the marks of a regular crystallization; because it is the result of a process, in which the particles of bodies are not carried by a too sudden transition from the fluid to the solid state; but gradually approach, and become united, by virtue of their mutual attractions, as the molecule of the fluid which had separated them go off by evaporation, or by other causest. And in further confirmation of this, it may be urged, that when the Crystallization of the Stalactite Carbonate of Lime, and of other Stalactites, especially * See figs. 2. 3. + “On a donné a cette opération le nom de CrisTALLIsaTIoN.” Haiiy, Traite Elé- mentaie de Physique, Tome \. p. 57. Paris, 1806. oe : ; : - Lransocthons of thel anmtriadge LE. 1, Soct Vel LLVG B. Lig. 5, Lig. Pf . Peg 3. A ra slallizals Ql Of Thaler = . ‘ ! . ene | ‘ 7 - JA. a ae ae AA & Se oie ett nannies and ae : eS ee 2. ek a ‘eRe 7 ’ 14 a a » mre \ ig 2p A ae! . ut soe "3 it i j , - a ay . é ; c= : % dl ts i af AW n « ad = 1. + v4 ? % i P Lif 7 : : a 7 va on i * f ty ‘ » ‘ VW sho , ° a 7 ° sd , *@ . hee 3 > be. , < . ® ~*s . - a oy - ee i = + -_>-. ~ Dr. CLarKE on the Crystallization of Water. 215 Chalcedony, had been considered as impossible formations, con- tradictory to the laws by which Nature acts in the Stalactite process *, yet the primary form of the Carbonate of Lime is never- theless exhibited by the Stalactites of the Cavern of Antiparos, and the primary form of the Hydrates of Silica by the Stalactites of blue Chalcedony brought from the Hungarian Mines. E. D. CLARKE. Cambridge, Jan. 6, 1821. *«< PIERRES QUARTZEUSES Quit NE CRISTALLISENT Pas. Il y a diverses pierres dans lesquelles la matiére quartzeuse domine considérablement, et qui néanmoius ne cristal- lisent jamais, §c. Tels sont le silex, ’ agathe, le cachalon, la calcédoine et ses varietes, Y opale,” &c. Patria, Hist. Nat. des Minéraux. Tome \\. p. 129. Paris, An. 1X. The French author, however, seems afterwards aware that his mode of classification was liable to an exception in the instance of Chalcedony. “ La calcedoine (Ibid p. 165.) en général ne cristallise pas, non plus que le silex, cependant il y a quelques morceaux ov la cristallisation semble n’étre pas equivoque.” gc | “ane ‘iy sion iY “uy ar. agai slsitheven lilt git B ste Iwebshiteaws * . phe. . 4. ni sa aa foitet beset ot sienk Ui sSnleedan) aifito. cee “giatarrieg _ . smaren crit cf. “Wa tt voit Peailt 5 44 Joti wlgyer sdf ue "oc gg8itnnl 02 eh aa RAM to aaa? ayia’ vio, asian ai duiogtekt atin ar * mesa ‘ ee e ¥ ot ae { ; . we ; : ; in o ane a ae cc Nba» 2a oe fi i finn 22h ee " : es "i a - ~~ a Sead tet ues 7 . 7 he 3 ene salts ue it tcl thiiet ‘avatars a wie #a2 lilt abate. vt. atthe la, linge De Nin) etketeing oulwiuds irs ses ih fete Wnne? ae ia yer bale ah poled « + sb Miley bythe at ignee ‘eet duvide of) ah. Pee Ete ae cao ole ite wish wie ig , of adic), cave aumpuidiiadls he ohivat aM dat ase rnepeEs AL art be vs OHA setioctede gst levees 5) id WARY wiiaober 4 F* ead ve» wah i a Me a 4 ; * . Adijew seleatibei ys of ua se rdius anys} a t (¢ pubes opie bi ied 2 = S a t q + “ ~ + . te e ‘ & *s ‘ ‘cae , die Nop ' « te : 7 ~e. = ¥ a i “ . Se 7 a . i of ?_@ 4 . : "ieee . = ~ ; Le" “ re C 7 a ii . aa = eae y : a ae . yo = ry ar : XIV. On the Application of Hydrogen Gas to produce a moving Power in Machinery ; with a Description of an Engine which is moved by the Pressure of the Atmosphere upon a Vacuum caused by Explosions of Hydrogen Gas and Atmospheric Air. By THe Rev. W. CECIL, M. A. FELLOW OF MAGDALEN COLLEGE, AND OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. [ Read Nov. 27, 1820. ] Turre is scarcely any uniform operation in the Arts which might not be performed with advantage by machinery, if conve- nient and economical methods could be found for setting such machinery in motion. The extensive application of machinery, therefore, depends much upon the number and various capabi- lities of the engines which can be employed to produce moving force. Even the most perfect engines at present employed for this purpose, are not capable of being applied universally ; but each has a province peculiar to itself, beyond which the use of it cannot be extended with profit or convenience. ~ Two of the principal moving forces employed in the Arts are Water and Steam. Water has the singular advantage, that it can be made to act at any moment of time without pre- paration; but can be used only where it is naturally abundant. A steam-engine, on the contrary, may be constructed, at greater 218 Mr. Crcit on the Application of Hydrogen Gas or less expense, in almost any place; but the convenience of it is much diminished by the tedious and laborious preparation which is necessary to bring it into action. A small steam-engine, not exceeding the power of one man, cannot be brought into action in less than half an hour: and a four-horse steam-engine cannot be used under two hours preparation. These limitations exclude the use of water and steam, as moving forces, in all works which are much interrupted, and discontinued at considerable intervals, and subject to a change of place. The engine, in which hydrogen gas is employed to produce moving force, was intended to unite two principal advantages of water and steam; so as to be capable of acting in any place, without the delay and labour of preparation. It may be inferior, in some respects, to many engines at present employed ; yet it will not be wholly useless, if, together with its own defects, it should be found to possess advantages also peculiar to itself. The general principle of this engine is founded upon the property, which hydrogen gas mixed with atmospheric air pos- sesses, of exploding upon ignition, so as to produce a large imperfect vacuum. If two and a half measures by bulk of atmospheric air be mixed with one measure of hydrogen, and a flame be applied, the mixed gas will expand into a space rather greater than three times its original bulk. The products of the explosion are, a globule of water, formed by the union of the hydrogen with the oxygen of the atmospheric air, and a quantity of azote, which, m its natural state, (or density 1), constituted .556 of the bulk of the mixed gas. The same quantity of azote is now expanded into a space somewhat greater than three times the original bulk of the mixed gas; that is, into about six times the space which it before occupied: its density therefore is about -, that of the atmosphere being unity. e to produce a Moving Power. 219 If the external air be prevented, by a proper apparatus, from returning into this imperfect vacuum, the pressure of the atmo- sphere may be employed as a moving force, nearly im the same manner as in the common steam-engine: the difference consists chiefly in the manner of forming the vacuum. We will now estimate the power resulting from such a vacuum, by comparing the effects of equal bulks of steam and hydrogen. Let the line AB (Fig. 1.) represent any space: this may be formed into a perfect vacuum, by filling it with steam, and con- densing: in which case, the steam produces a vacuum nearly perfect, and equal to its own bulk. The same space may be formed into an imperfect vacuum, by exploding in it a mix- ture of hydrogen and atmospheric air: the bulk of the mixed gas being about one third of the vacuum required, and conse- quently the bulk of the hydrogen about one tenth. The effect of this imperfect vacuum may be represented, geometrically, by drawing a square ABCD upon AB; taking AE, CF, each equal to one sixth of the side of the square; and drawing a common hyperbola, through the points E, F, with asymptotes BA, BC. The ordinate GH varies inversely as the abscissa GB, and may therefore represent the density and elasticity of a given quantity of azote confined in the variable space GB; the elastic force of the atmosphere being represented by AD, the side of the square. Therefore HK will represent the excess of the atmospheric pres- sure above the elasticity of the azote; and the whole effect of the atmospheric pressure upon the imperfect vacuum will be repre- sented by the external hyperbolic area, EH FD. And the effect of a perfect vacuum, over the same space AB, is represented by * The bulk of the azote is .556 of the mixed gas; and the gas by the explosion expands to about 3.4 of the original space; hence the imperfect vacuum thus produced is about six times the space which the azote occupies when reduced to the elasticity of the atmosphere. That is, when the azote occupies a space B/, its elasticity is represented by IF. Vol. I. Part Il. Fr 220 Mr. Cecit on the Application of Hydrogen Gas the square ABCD. But the effects of equal bulks of steam and hydrogen, to produce moving force, are proportional to the frac- tion, whose numerator is the effect produced, and the denominator. the quantity employed in producing it. Hence the effect of a given bulk of steam, is to the effect of the same bulk of hydrogen, as the area of the square divided by unity, is to the external hy- perbolie area divided by the fraction ;,; which ratio is as 3: 5x {5—hyp. log. (6)} :: 3 : 16, nearly*. Thus it appears by calculation, that any quantity of pure hydrogen gas will produce more than five times the effect of the * Let BD be the diameter of the square, which is also the axis of the hyperbola, ML perpendicular to AB, and therefore equal to LB; Then GH x GB=LM x LB= LM. et Gli — 7, Gb 2 — a, a a and yx = Lie v © . the fluent of yx=a? hyp. log. « a constant quantity; -, area corresponding to ordinate GH = a® hyp. log. x + a constant quantity ; ELM = a byp. log. a + a constant quantity; -. area between ordinates GH and LM = a? hyp. log. « — @ hyp. log. « — Ga np. log. = -, area AEML = a? byp. log. ae but 4B x ne =Var; . area AEML = a hyp. log. aV/o a a* = > hyp. log. 6; z 2 *, whole hyperbolic area = a* + = hyp. log. 6 + < hyp. log. 6, = @. (1 + hyp. log. 6); *, external area DEMF = AB* — a* (1 + hyp. log. 6) = 6a” — a? (1-+hyp. log. 6) = a?.(5 — hyp. log. 6); -. whole square : external hyperbolic area DEMF :: 6a: a* (5 — hyp log. 6) :: 6 : 5 — hyp. log. 6; 5 — hyp. log. 6 | eee CT i0 - MEPS : “. the ratio required is = : 3: 5 (5 — hyp. log. 6) :: 3: 16, nearly. to produce a Moving Power. 221 same bulk of steam: and in practice the disproportion of their effects is still greater. It is here supposed, that steam produces by condensation a perfect vacuum equal to its own bulk ; but this is far from being the case: much of the power is lost by needless condensation, by the escape of steam through the piston, besides a considerable deduction for working an air pump, and two water pumps, which are necessary to a steam-engine.* It may be worth while to add in this place an experiment, calculated to obviate any objection arising from the apprehension of danger, as connected with the explosion. If a close cylinder, ten inches long, and two inches diameter, be made of thin tin, seamed up one side, and soft soldered, the ends being well secured, it will easily sustain, without bursting, the whole force of the exploding mixture. The mternal pressure against the sides of the vessel, in this case, is about 180 pounds on the square inch; or twelve atmospheres nearly.¢ From this experiment an idea may be formed, how little strength is necessary for such parts of a gas-engine as are exposed to the pressure of the expanding fluid ; a pressure which, as will hereafter appear, bears a very small proportion to the mitial exploding force, which is twelve atmo- spheres. | * The loss of power, from friction, &c. ina condensing steam-engine, even when working with a double stroke, is estimated by practical mechanics at about one-third of the gross power. + The greatest expansive force was ascertained by filling with mixed gas the cylinder just described, one end being entirely solid, the other being closed with a cork bung, accurately fitted, and confined by several strings, parallel to the axis of the cylinder, and so arranged that the tension might be equally distributed. It was observed how many strings the explosion was able to break, by pressing on a surface of three square inches. The same strings were then transferred to a common steelyard ; and it was observed how much weight they would sustain. The results of several trials, differing but little from each other, indicated a pressure of five hundred pounds upon three square inches. If to this be added 45 pounds for the atmospheric pressure on the same surface, the whole being divided by three, gives 180 pounds nearly, for the pressure upon every square inch. FF2 222 Mr. Cecit on the Application of Hydrogen Gas It is already stated, that if hydrogen gas and atmospheric air, mixed in the most explosive proportion, be ignited by an electric spark in a close vessel, the internal pressure upon the sides of the vessel is about twelve atmospheres. But if the mixture be allowed to expand into a space rather more than three times its original bulk, (suppose 3.4,) the initial force is reduced to one atmosphere, or fifteen pounds on the square inch: for the expansion is here at an end; that is, it just balances the elastic force of the atmosphere. This experiment agrees with the hypothesis, that the exploding force varies, during the expansion, inversely as the square of the space occupied by the expanding fluid, and not in the simple inverse ratio of that space; for a/ 12): w/ P24: 1 early: If this law be general, the mitial force of any exploding mixture may be known, by observing its greatest expansion. In large vessels containing hydrogen gas, there is little or no danger to be apprehended, from the unavoidable admixture of atmospheric air in small quantities. In mixtures of hydrogen gas and atmospheric air, if the hydrogen be in excess, the exploding force is very small; but if the atmospheric air be in excess, the exploding force is considerable. If the atmospheric air be only one fifth part of the whole, the explosion, if any, is not sensible; but if the hydrogen be one fifth of the mixture, it will explode with considerable force. The gas-engine about to be described, was found to work very freely when the hydrogen did not exceed one fifth of the mixed gas: but the greatest power was obtained, when the hydrogen was = of the mixture. Yet, for the purpose of economy, or that a given quantity of hydrogen may produce a maximum ef moving force, it is conjectured that a less proportion of hydrogen would be preferable. A gas-engine admits of various constructions, but we shall ex- plain at length that model only which is represented in Fig. Oeue to produce a Moving Power. 223 first describing the several parts of it, and then shewing how the motion is continued. The drawings are adapted to a_ peculiar kind of orthographic projection, digested by Professor Farish into an easy and convenient system of perspective, called the Isometrical Perspective, which is already before the Society. The representation of the central cube ABF’, formed by joming the angular points of an equilateral and equiangular hexagon with the centre of the inscribed circle, will serve as a key to the proportion and direction of the other lmes in the picture. The dotted lines represent such parts as are not visible, except on the supposition that all other parts are transparent. ABF' (Fig. 2.) isa cube, having three cylinders, of equal capa- city, attached to its sides at right angles. The vertical cylinder is separated from the narrow horizontal ones, by a moveable key or plug abcd in the cube. This plug is hollow, and open at the bottem: it has also two large apertures opposite to each other, one inch wide, and an inch and a half deep; by which, upon turning the handle ef, it causes a free communication from the vertical cylinder ABCD, to each of the narrow horizontal cylinders FG, F'G'. Inthe lower part of this plug, and below the level of the large apertures just mentioned, are two small apertures, in the same horizontal plane, and situated eighty degrees apart from each other. One of these ec, which is about one tenth of an inch diameter, corresponds with a similar hole ¢ in the face of the cube ABF’, upon turning the handle ef to the left; and by continuing this motion to the left, the aperture ¢ is again closed. If the position of the plug be reversed, by turning the handle ef to the right, as represented in the picture, the other aperture d, which is about half ap inch diameter, will be brought to coincide with d’, the mouth of the pipe ne, which enters nearly at the bottom of the cube, on the side opposite to that which has the small hole ¢. Near F is a small hole, one quarter of an inch diameter, which, 294 Mr. Crecit on the Application of Hydrogen Gas by means of a trench excavated in the solid side of the plug. admits the atmospheric air freely into the narrow cylinder FG, and restores it to an equilibrium with the atmosphere, after the vacuum has performed its office. There is another hole F’ on the opposite side of the cube, corresponding to F, by which the equili- brium is at the same time restored in the cylmder F’G'. Hence the plug abed commands six apertures, three of which, namely, the mouth of the pipe no, and the two holes F, F’, all bemg small apertures, are opened at the instant when the lever ef is com- pleting its motion to the right. The other three, namely, the two large apertures and the touch-hole c, are opened by turning the lever ef to the left; and of these the small touch-hole ¢ is opened just at the end of this motion, and immediately shut again. Fig. 3. is a vertical section, at full size, of the cube AAAA, the plug OOOO in it, and a cap BB, which screws into the top of the cube. Through the cap BB is a cylindrical hole DD, to admit the axis which turns the plug; and in the small cube CCCC is a stuffing box and collar of leathers, by which the hole DD may be made air tight if required. The vertical cylinder ABCD (Fig. 2.) is closed at the bottom by a cap CD, but not so as to exclude the external air: it has also a piston ghk connected with a parallel motion LAK, L’' Kk’, causing the piston rod to move in a vertical straight line, nearly.* * As this parallel motion is not exactly similar to any of those in common use, and produces a very near approximation to a rectilineal motion, a further explanation of it is here added. Fig. 4. A and € are fixed centres, about which the levers 4B, CD are moveable. B and : Se? 1B DE Dare moveable joints; also —— = ——. 4 CD ~ BE When AB is parallel to CD, DBE is at right angles to each of them; and is therefore a common tangent to the circles described by the points Band D. That the point E may continue in the same straight line FG, for every position of the point B, the deflection of the point Then the locus of £& is nearly rectilineal. to produce a Moving Power. 224 On the top of the pisten is a solid conical frustrum, te occupy the hollow of the plug, when the piston is at the top of the cylinder. The horizontal frame ZN is connected with a crank on the axle PQ, by an upright rod NO, jointed at its extremities. A fly- wheel, three feet in diameter, and weighing half an hundred weight, is placed upon one extremity, P, of the axle PQ, and at the other extremity Q, is a crank or handle, situated about ten degrees in advance of the crank O, causing the red wa, which slides through a fixed hole at 2, to oscillate in a vertical plane, parallel to the axis of the cylinder FG. When the red we is vertical, it touches the point s of the horizontal lever gs; and its angular velocity is then the greatest; and the horizontal levers qs, ef are moved by it, through a considerable angle, with a motion nearly mstantaneous, so as to reach their furthest point to the right, at the mstant when the piston becomes stationary at the top of the cylinder. The rod wa having passed the shoulder z, slides along the bar zv, which is at that time parallel to the plane of the red’s motion; and upon its return strikes against the shoulder y, causmg a rapid motion of the levers qs, ef, to the left; the motion, which is nearly instantaneous, being completed at the imstant when the piston point D from the common tangent, must be greater than the deflection of the point B, in the proportion of DE : BE; but the deflections, for small arcs of the same length, in different circles, are inversely as the radii ; -. rad. AB: rad. CD :: deflection at D : deflection at B:: DE: BE, or 48 = DE. CD BE The ares described by the points D and B have the same lineal magnitude ipso motus initio: but if D describe a finite arc, it will be greater than the corresponding are described by the point B; owing to the increasing obliquity of the line DBE. This will oceasion the point E to continue in the straight line FG for a much longer space than might be expected from the preceding theory: and hence itappears, that the correctness of the parallel depends in some measure upon the ratio of 4B to DE. The best proportion of AB to DE is that which makes the chords of the ares BB’, DD’, to maintain most nearly a ratio of equality. The straight line AC produced passes through the point G, and the curve is symmetrical on each side of the line ACG. The point E may in practice be made to trace out the whole double curve, by inverting the angle D. 226 Mr. Cecit on the Application of Hydrogen Gas becomes stationary at the bottom of the cylinder. After this the rod wa slides along the bar yt, which is now parallel to the plane of its motion. The angular motion of the plug abed is about 90°.* The apparatus situated upon the pipe no, for mixing the pure hydrogen with any required proportion of atmospheric air, comes next to be described. UV, WV, are two small cylinders, closed at both ends, and separated from each other by a plate of metal between the flanges by which the cylinders are connected at V. In this partition is an air-tight metallic valve opening upwards, and moveable by a wire passing through a stuffing box at U, and connected with the lever XY, whose centre of motion is X. At W there is another valve, similar to the former, and opening upwards spontaneously, as often as there is any rarefaction of the air in the cylinder VW. That this valve may open more easily, its weight 1s partly taken off by a lever parallel to XY. This lever also prevents, by its mertia, a rapid saltatory motion of the valve, arising from its conical form, and which retards in some measure the descent of the piston. Into the upper cylinder enters a pipe 7m, from a gazometer or reservoir containing pure hydrogen gas: and from the lower cylinder, a pipe no goes to the engine, and enters at the back of the cube ABF’ exactly opposite to the small touch-hole c’. The lever XY, and with * If the crank at Q were placed exactly parallel to the crank at O, or exactly opposite, that is, 180° in advance of it, the motion of the plug abcd would take place while the piston continued nearly stationary at the top and bottom of the cylinder, but it is here required that the motion of the plug may be completed at the instant when the piston arrives at its stationary points; for which reason, the crank at Q is placed a little further (about 10°) in advance. The crank at Q may also be placed about 170° before the crank at O. In this case the engine will move in the contrary direction; and _ this latter construction is to be preferred. to produce a Moving Power. 227 it the hydrogen valve at V, is elevated by the rod wa coming in contact with an obstacle on a fixed axle RZ, with which the lever XY is connected. This small apparatus, is represented on twice as large a scale as the rest of the engine. At the end of each of the narrow cylinders FG, F'G’, is a valve opening outwards, which, for the sake of lightness, is a thin circular plate of brass or sheet copper, upon which is cemented a covering of soft leather, so as to be moderately air-tight when pressed against the end of the cylinder by a spiral spring at the back of the valve: The parts of this valve are seen detached in Fig. 5. sv (Fig. 5.) is an immoveable brass cylinder, having upon it a spiral spring; rsé is the valve, having a hollow cylinder s‘v’ attached to it, whose axis is at right angles to the plane of the circle, and passes through its centre.—This pipe s‘v’ is closed at the end s’ and open at 2, so as to slide upon the fixed solid cylinder sv. Thus the centre of the valve is confined to move through a small space, (} inch,) m a horizontal line, coinciding with the axis of the cylinder FG: and the valve may upon this construction be made extremely light, which is a matter of prime importance. The valve may be made still lighter by attaching the leather packing to the end of the cylinder instead of cement- ing it upon the valve. There is also at the back of the valve an annular cushion of Indian rubber, or some other soft and elastic material, to break the impetus, which otherwise would injure its form, which is a segment of a sphere, a little flattened at the edge. At G’ is represented a flap valve, such as is used in a common pair of bellows. This kind of valve is more simple; and may be as effective, if made light, and pressed close by an elastic cushion. The engine is represented with the piston descending, and about the middle of its stroke. Let the fly wheel be turned Vol. 1. Paré Il. Ge 228 Mr. Cecit on the Application of Hydrogen Gas round : of a revolution, so as to bring the piston to the top of the cylinder. At this instant, the rod wa will sweep across with a rapid angular motion carrying the lever rqgs, and the plug abed to the right, as im the picture. By this motion of the plug, the vertical cylinder ABCD will be separated from the horizontal cylinders FG, F’ G’;—the small apertures F, F’, will be opened, admitting the atmospheric air freely into the horizontal cylinders; and the mouth of the pipe no will be opened to the inside of the cube, i.e. to the cylinder ABCD. The piston beginning to descend, by the continued motion of the fly wheel, the atmospheric air will rush in at the lower valve W, which opens spontaneously, and will occupy whatever portion of the cylinder ABCD is relinquished by the descent of the piston. When the piston has descended about =" of its stroke, the hydrogen valve at V is opened, by the rod wa touching an obstacle Z on the fixed axis RZ. The lower valve W is closed by its own weight, and also by the supermcumbent pressure of the hydrogen, which now flows freely into the cylmder ABCD; and the quantity admitted is determined by the space through which the piston descends, while the hydrogen valve contimues open. The hydrogen valve will be closed by its own weight when it ceases to be supported by the rod wa; i.e. when the piston has descended 2" more of its stroke; the obstacle on the fixed axle RZ being properly adjusted. The atmospheric air will now again rush in at the lower valve W, till the piston comes within a quarter of an inch of its lowest point, at which time the rod wa strikes against the shoulder y of the lever grs, causing a rapid motion of the plug abcd to the left: by which, first, the pipe no, and the two apertures F, F’, all being small, are closed at the beginning of the motion; then the piston finishes its stroke by descending a quarter of an inch during the motion of the lever ef; and lastly, the touch-hole ¢ is opened and shut again at the end of to produce a Moving Power. 9299 the motion; and there will be a gentle absorption at this touch-hole, the valves G, G’, being closed, and the piston having descended a quarter of an inch, between the closing of the pipe no and the opening of the touch-hole c’. By this absorption the flame of a lamp or gas light constantly burning before the touch-hole c’, and supplied with pure hydrogen by a separate pipe from the gazometer, is drawn into the cylinder, and the mixed gas is ignited, and expands so as to occupy the whole content of the three cylin- ders, as far as G and G’, the common air in the cylinders FG, F'G’, being expelled at the valves. Hence an imperfect vacuum, (density of the air 5,) will be formed in all the three cylinders, and the piston will ascend from C to A by the pressure of the atmosphere. The plug is now moved to the right by the transition of the rod w.2, and the piston descends by the momentum of the fly wheel acquired during the ascent, and is followed by a fresh portion of mixed gas drawn in from the pipe no as before.* The principal supports of this engme are two horizontal boards, 8 inches wide, 2 inches thick, 30 mches long, and 15 inches asun- der: The plane of the upper board coincides with the base of the cube ABF’, which rests upon its upper surface. The same plane supports the uprights belonging to the lever grs; on the under side of the same board, are two cast-iron bearings for the * The pressure upon the piston, at the beginning of its ascent, is <**s of an atmosphere ; or 12,5 pounds on the square inch: when the piston reaches the top of the cylinder, the pressure upon it is 3 of an atmosphere; or 11,25 pounds on the square inch: supposing the common air to be completely expelled from the cylinders FG, F’G’, and that the machine is perfectly air-tight. It is evident that a large portion of the vacuum produced by the explosion is turned to no account in working the engine; the residual vacuum, density of the air 4, being destroyed by the admission of atmospheric air at the apertures F, F’. It is probable, however, that no advantage would arise from employing the residual vacuum, which in practice is very imperfect, unless it could be accomplished without increasing the range and friction of the piston; especially in an engine which works only by a single stroke. GG 2 230 Mr. Ceci on the Application of Hydrogen Gas axle PQ. The lower board supports the bearings of the fixed axles LM and L’: also the ring at the fixed point a: the two parallel boards are connected at the ends by two uprights of the same width and thickness. An engine upon this principle is found in practice to work with considerable power, and with perfect regularity. The advan- tages of it are; that it may be kept, without expense, for any length of time in readiness for immediate action: that the engine, together with the means of working it, may easily be transferred from one place to another: that it may be worked in many places where a steam engine is inadmissible, from the smoke and other nuisances connected with it: a gas engine may be used in any place where a gas light may be burnt: in places which are already supplied with hydregen for the purpose of illumination, the con- venience of such an engine is sufficiently obvious: it may be added, that it requires no attention so long as it is freely supplied with hydrogen. The supply of hydrogen is obtained, either from a large gazometer, which may be at any distance from the engine, or from a number of long copper cylinders filled with condensed hydrogen. In the latter case, the engine, with the apparatus for working it, will be transferable from one place to another. For pure hydrogen may perhaps be substituted carburetted hy- drogen, coal gas, vapour of oil, turpentine, or any ardent spirit: but none of these have been tried; nor is it expected that any of them will be found so effective as pure hydrogen. Before the hydrogen enters the engine it is received into a small gazometer, containing about two gallons, and placed at a distance of about twenty inches from the engine. The gazometer has three pipes, each furnished with a stop-cock. Through one of them, the hydrogen passes from the reservoir into the small gazometer, and is regulated by the stop-cock, which is connected éo produce a Moving Power. 231 with the moveable part of the gazometer, after the manner of a ball and stop-cock. ‘The other two pipes are placed on the opposite side of the gazometer, parallel to each other, and about three inches asunder. One of them supplies the gas light, which burns before the touch-hole ¢; the other is a continuation of the hydrogen pipe 2m, which enters the small cylinder UV. The two pipes must not communicate with each other, but each must enter the small gazometer by a separate aperture; otherwise the gas light will be extinguished by the absorption from the other pipe when open to the engine. The use of the small gazometer, is to supply these two pipes separately with pure hydrogen, under a moderate but uniform pressure.—A column of water three inches in altitude will occasion sufficient pressure for the supply of the gas light. The consumption of hydrogen gas may be thus estimated. In the model exhibited to the Society, the capacity of the working cylinder is about thirty cubic inches; which, at the rate of sixty revolutions in a minute, requires 1800 cubic inches of mixed gas, or 450 cubic inches of pure hydrogen; the hydrogen being taken at one fourth part of the mixed gas. This multiplied by 60, gives 15,6 cubic feet of hydrogen for the consumption in one hour: and to this must be added two more cubic feet, of pure or carburetted hydrogen, for the supply of the gas light during the same time, making altogether about 17,6 cubic feet in an hour. —— * In order to ascertain with accuracy the proportion of hydrogen and common air in the mixed gas, for a given arrangement of the valves V and W, this small gazometer was filled with air: then, the valve WV being kept closed, and the hydrogen valve V being continually open, it was found that twelve revolutions of the fly wheel were sufficient to empty the gazometer. Next, the valves being restored to their natural order, the gazometer "was emptied by forty-eight revolutions of the fly wheel. From this it appeared that the quantity of air drawn in from the atmosphere was three-fourths of the mixture, which therefore consisted of three parts of common air, and one of hydrogen. By repeating the experiment with a new arrangement of the valves, i.e. by a fresh adjustment of the obstacle on the axle RZ, the gases may be mixed in any required proportion; depending however in some measure upon the velocity of the engine. 239 Mr. Crciu on the Application of Hydrogen Gas The quantity of gas required for the supply of this gas light will not be increased by enlarging the scale of the engine: also the touch-hole will be of the same magnitude, (one tenth of an inch diameter,) whatever be the form or diameter of the engine. The thickness of the metal, through which the touch-hole is bored, should not exceed one quarter of an inch; and if more than this, the hole should be countersunk on the outside, till the metal is reduced to that thickness. The touch-hole is opened only for a single instant, while the piston is stationary at the bottom of the cylinder: therefore the time, during which it continues open, may be diminished indefinitely by increasing the velocity of the engine. In this case the ignition cannot take place: the velocity of the engine will therefore be limited by a cause not connected with the friction of it: and if the velocity exceed a certain limit, the explosions will take place interruptedly; yet recurring im a certain order. But if the engine be retarded, so as not to exceed 60 revolu- tions in a minute, the explosions will take place with perfect regularity. This circumstance supplies a ready method for ascertaining how much of the power of the engine is employed in overcoming the friction. If the explosions should be found to take place alternately, when the engine has acquired its greatest velocity, it will follow that the power, for that velocity, is double the friction: if every third explosion takes place, the power is three times the friction: if every third and every second alternately, the power is to the friction as 5 : 2. The engine regulates itself by this method, but very imper- fectly ; for it occasions a waste of hydrogen, and implies too great a velocity. It regulates itself much more completely by another method, connected with the magnitude of the hydrogen pipe dm. When the bore of this pipe is diminished, which may be done to produce a Moving Power. 233 at pleasure by a stop-cock, the hydrogen is retarded in it’s progress from the gazometer; which will occasion a larger admission of common air at the lower valve W, which opens spontaneously. If the velocity be increased, the proportion of common air in the mixed gas will also be increased ; and a less perfect vacuum will be formed, attended with a decrease of power. The momentary regulation of the engine is not produced by an alteration in the stop-cock, but by an increased absorption of common air at the valve W, which increases with the velocity of the engine, the stop-cock bemg unaltered. If the scale of the engine be considerably enlarged, the admixture of the hydrogen and common air may be less perfect. though the proportion of them may be determined with even greater accuracy than before. Let then the hydrogen valve be elevated twice, instead of once, during the descent of the piston: the gases will be admitted in the following order; common air, hydregen, common air, hydrogen, common air: this will secure a perfect mixture; but in all cases the common air should be let in first; so that the equilibrium may be restored in the hori- zontal cylinders FG, F’G’, before any hydrogen is admitted. That the upright axle, by which the plug abcd is moved, may be able to adapt itself to the collar through which it passes at e, it must be connected with the plug loosely; yet so as not to admit of any relative angular motion in an horizontal plane. To this end the upright axle terminates in a solid cube at its lower extremity, which is imbedded in the under side of the solid metal, (three quarters of an inch thick,) which forms the top of the plug; and the whole is covered and made air-tight by a brass plate screwed, with two small screws, pointing upwards, against the under side of the same solid. See Fig. 3. The wear and friction of the plug abcd, which is nearly cylindrical, are entirely removed, by elevating it about one-fortieth 234 Mr. Ceci on the Application of Hydrogen Gas of an inch above its natural position; its whole weight being supported upon the small cube at e. It is nevertheless sufficiently air-tight, having its upper surface covered with water, which is supplied through an aperture in the top of the cube ABF’. As far as respects the communication of the three large cylinders, it is not at all necessary that the plug abed should be air-tight: it serves only as a momentary partition between two portions of air, each of which is in equilibrio with the atmosphere: but to prevent the influx of common air into the vacuum through the smaller apertures, the plug should be moderately air-tight. A part of the water which covers the plug, thus elevated, is pressed through it by the weight of the atmosphere, and falls upon the piston, which carries it up agai, and leaves it in the horizontal cylinders FG, F’G’, from whence it is expelled at the valves G, G’, with great velocity by the next explosion, and is received into a cistern placed below. Thus the packing of the piston and of the valves is secured from injury, and the engine is kept cool and clean in the inside. The piston may be packed with soft leather; nor will the packing be affected in the smallest degree by the explosion; for it is completely pro- tected by a lamina of cold water, a quarter of an inch deep, which constantly covers the upper surface of the piston. In every engine where there are packed pistons required to be air-tight, the friction arismg from the motion of these pistons will cause a considerable diminution of the power: and where the pressure on the piston takes place only in one direction, as in the gas engine, the loss of power by friction is twice as great as where the engine works with a double stroke. In every such engine it becomes an object of importance to reduce the friction of the piston as much as possible: and this may be done very effectually by immersing the cylinder ABCD, which is partly open at bottom, in a cistern of water. In this case the piston to produce a Moving Power. 235 will need scarcely any packing, and the friction will be incon- siderable. A small quantity of water will be forced through the piston by the pressure of the atmosphere upon the vacuum, and will be afterwards expelled at the valves G, G’, by the explosion. Where this improvement is adopted, it will be found conve- nient to invert the whole machine; making it to rest upon the four upper corners of the cube ABF’. A small cistern is also to be attached to the cap CD, and to be kept continually full of cold water—The water is gradually forced into the engine by the pressure of the atmosphere, and is afterwards expelled at the valves G, G’. By this arrangement the friction is so much diminished, that the engine will continue in motion, though the hydrogen be so far diluted with common air as to be scarcely explosive. Among the different constructions which may be adopted for a gas engine, there is one which, on account of its simplicity, should not be altogether omitted. It is represented in Fig. 6. ABCD isa long narrow vertical cylinder, divided into two parts at abd, so that the upper part ABab may be one third part of the whole cylinder. In the partition add is a large circular hole, covered by a choke valve turning upon an axis a6 which passes through a small stufting-box at a on the side of the cylinder. At the point e in the axle ba produced, is an upright handle ef connected by a cross bar fr with the lever grs, moveable about qg-* In the upper division ABab of the cylinder is a piston ghk, connected by two upright reds FH, GK, jointed at their extremities, with the horizontal frame NIH, moveable about the fixed axle L.VW. The frame is connected, at the point N, with a crank on the axle PQ, which carries a fly wheel at P. Imme- diately above the partition abd, a pipe no enters the cylinder, * This choke valve performs nearly the same office as the plug abcd, Fig. 2; and does not require to be air-tight, for the reason already stated. Vol. I. Part II. Hu % 236 Mr. Cecit on the Application of Hydrogen Gas from a vessel containing hydrogen gas, which is mixed with common air by an apparatus already described. Upon the pipe no is a stop-cock, which is opened upon the appulse of the piston to the partition abd, and shut again upon its appulse to the top of the cylinder. At CD is a light valve RST’ described above, moderately air-tight, and opening downwards. The piston, during its ascent, draws in from the pipe no a charge of mixed gas, which is exploded, on the appulse of the piston to the top of the cylinder, by the flame of a gas light, absorbed at the touch-hole ec, which is opened for a single instant by the motion of a small sliding plate. The common air is ex- pelled from the lower division abCD of the cylinder at the valve RS7'; leaving an imperfect vacuum, density 7, in the whole cylinder ABCD. The piston descends from A to a by the pressure of the atmosphere, and is raised again by the momentum of the fly wheel, being followed in its ascent by a fresh portion of mixed gas, drawn in from the pipe no. The upper division ABab, is a cylinder of brass, accurately bored: the lower division abCD, requires no accuracy of bore, and very little strength: it may therefore be made of sheet copper with a strong flange at the bottom, presenting a flat face to the valve RST. The smaller contrivances necessary for perfecting this construction, may be learnt by comparing it with the former, which has been described at large: the principle is the same in both. To remedy the noise which is occasioned by the explosion, the lower end of the cylinder ABCD may be buried in a well: or it may be inclosed in a large air-tight vessel. This vessel will be filled with condensed air, expelled together with a quantity of water from the cylinder a/CD. This condensed air may be made to co-operate with the vacuum in working the engine; and will occasion a considerable increase of power, without adding to the friction. to produce a Moving Power. 937 In the description of a gas engine, the power is shewn to arise from the pressure of the atmosphere upon an imperfect vacuum ; and is therefore quite independent of the exploding force of the mixed gas. But an engine might be constructed to work by the exploding force only; or by the exploding force and the pressure of the atmosphere jomtly. A small model of this kind was exhi- bited, about three years ago, at the Philosophical Lectures of Professor Farish. Not to enter into the construction of such engines, which would exceed these limits, it will be sufficient to add, in conclusion, a few remarks upon exploding forces in general, and the manner of applying them, with the least danger, to produce moving force. It may be laid down as a principle, that any explosion may be safely opposed by an elastic force, (the force of condensed air for example,) if the elastic force opposed has little or no inertia connected with it. On the contrary, the smallest quantity of inertia, opposed to an exploding mixture fully ignited, is nearly equivalent to an immoveable obstacle. Thus a small quantity of gunpowder, or a mixture of oxygen and hydrogen may be safely ignited in a large close vessel filled with air; for the pressure of the exploding substance, against the sides of the vessel, can never be much greater than the elasticity of the air which it condenses.* Again, if a small quantity of earth, or a piece of paper, be inserted in the muzzle of a gun, charged with powder only, the gun will commonly burst upon being fired; for in this case the powder, after being fully ignited, comes to act upon a body at rest, having inertia; and such a body cannot be moved * By a large vessel, is meant one whose capacity is not less than the greatest expan- sion of the exploding mixture. The case here supposed is exactly what would take place in a gas engine, if the mixed gas were exploded, the apertures at G@ and G’ being perma- nently closed. HH 2 238 Mr. Ceci on the Application of Hydrogen Gas out of the way, in an indefinitely small time, without a force indefinitely great; or it is equivalent to an immoveable obstacle. Of all exploding mixtures, therefore, having the same field of expansion, those are the most dangerous, and the least adapted to produce moving force, which are ignited with the greatest rapidity. Thus a mixture of oxygen and hydrogen, of which the ignition is extremely rapid, is far less adapted for such purposes than a mixture of common air and hydrogen, which is ignited more slowly. There is scarcely any exploding mixture which is ignited so slowly as gunpowder. This therefore, notwithstanding its great force and large field of expansion, is peculiarly adapted to produce either momentum or moving force; and, when opposed by a moderate quantity of inertia, is attended with less danger than some other mixtures, which explode with less force, but which are ignited with greater rapidity. But great care must be taken that the mass opposed be placed in close contact with the powder; so that the exploding force may begin to act upon it the instant the ignition commences, and that the action may cease before the ignition is completed. Thus in a common musket, if the ball be placed at a small interval, so that the powder may be fully ignited before it begins to move it, the ball in this case becomes an immoveable obstacle, and the gun will burst. It is here supposed, that the exploding mixture has itself no inertia; or that it is capable of following up the body upon which it acts, with a velocity incomparably greater than that body can acquire. Upon these principles an engine was constructed which was moved by the exploding force of gunpowder. The gunpowder was employed to contract a very strong but light spring, by a regular series of explosions: and the elastic force of the spring in recovering its former position, formed the moving power of the engine. The danger to be apprehended from an explosion, thus W Lowry, s to produce a Moving Power. 239 resisted, depends not upon the strength of the spring so much as upon the weight of it. An engine of this kind may be made to work with regularity for a short time; and the power of it, compared with its whole weight, is extremely great. It is not however proposed with any view to practical utility, being hable to great and obvious objections: particularly from the corrosion of the metals by the sulphur contained in the gunpowder, and by the sulphuric acid which is produced during combustion. It is here noticed merely to illustrate the foregoing principle. W. CECIL. Papworth Everard, Oct. 25, 1820. et, ee. peers ar vite x9 dogm: oo yiir en sav Ter Paco: delt- aogn Saas aft om bai oi To: hee ake oo, =4i to wang oi Ini. pomit Heede WE, rath tou a i Jey ‘Usuiy » 24 tale, sloitie af. del #1 “ah 2 raldsi! snot yhilifae BiG mons 4s Dew isan = ne rat 5 nolzorio> ald att, or ban obwoqmeg, 51 ¥ af) Ip ik _.aoisaidinos wannb howborg a taints bin airndipls ont y aaa ill anise add avast ar wees a ha a a mi." ; ' ae om ye a XV. On a remarkable Pecuharity in the Law of the extraordinary Refraction of differently-coloured Rays exhibited by certain Varieties of Apophyllite. By J. F. W. HERSCHEL, Esq. F. R. S. OF LONDON, EDINBURGH, AND GOTTINGEN; FELLOW OF ST. JOHN’S COLLEGE, AND FELLOW OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. [Read May 7, 1821.] Dovsty refracting crystals have hitherto been divided inte two classes; the first comprising those in which the deviation of the extraordinary ray may be regarded as arising from a repulsive force emanating from one or more axes, as in carbonate of lime; and the other, from an attractive, asin zircon. Intermediate between these, and forming, as it were, the limit between both, are bodies devoid of the property of double refraction, as fluor, glass, &c. All these substances, however, act with different degrees of energy on the differently-coleured rays, according to a law which appears subject to great variations in different bodies, and which is directly deduci- ble in any given body, from the series of tints developed by exposure to polarized light. In a former paper* I have instanced some remarkable deviations from the ordinary law of tints exhibited by certain varieties of the apophyllite, but from the mode of experi- menting there followed, the most remarkable of the peculiarities * Transactions of the Philosophical Society of Cambridge, Vol. I. Part 1. 1820. 942 Mr. Herscuet on the Double Refraction of Apophyllite. presented by the specimens employed escaped my notice. It is this, that out of the three varieties examined, two appear to belong at once to all the three classes of Media above enumerated; pos- sessing the property of attractive crystals when exposed to the rays forming one extreme of the spectrum, and of repulsive in their action on the other extreme, while for certam intermediate rays, they are altogether void of the property of double refraction, and allow such rays to pass freely through them in all directions with- out dividing them into two pencils. IT was led to a knowledge of this remarkable smgularity, by the consideration of the forms of the curves traced in Figs. 14 and 17. (See Plate in Part I. of this Vol.) whese ordinates represent the polarizing energies of the two varieties m question, on the rays whose place in the spectrum is denoted by their abscissa. It is assumed, without any particular grounds, in my former paper, that these curves lie, throughout their whole extent, on one side of their abscissee. This was natural enough, being accustomed to regard crystals as necessarily included in one or the other of the great divisions above referred to, and in the mode of experimenting there resorted to, the contrary could not be discerned, the change from attractive to repulsive being marked by no phenomenon. In con- sidering the subject more carefully, however, it struck me that, as the curves in question had been traced to the immediate vicinity of the axis, and when lost sight of were then approaching it more rapidly than in any other part of their course; it was highly puo- bable that they would meet it in that part of the spectrum out of the reach of observation, and if so, must cut it, and the portions corresponding to the two extremities of the spectrum, would thus lie on opposite sides, the absolute lengths of the ordinates given by experiment remaining unaltered. To put this idea to the test was a matter of considerable deli- cacy, as well from the imperfections of the specimen, as from its” Mr. Herscuer on the Double Refraction of Apophyllite. 248 feeble polarizing energy, and the great difference of its action on the different colours. In ordinary cases to determine whether a crystal be attractive or repulsive, nothing more is required than to place a plate of it between crossed tourmalines, so as to view the polarized rings, and then, crossing it with a plate of mica or sul- phate of lime, having its principal section 45° inclined to the plane of primitive polarization, to notice im which quadrants of the rings the tints are raised, and in which depressed. If the plate of the substance examined be then removed (without altering the position of the mica plate), and replaced by a plate of carbonate of lime, tourmaline, or any other known substance (which it is convenient to keep as a standard of comparison) it is immediately seen whether the crystal in question be of the same, or an opposite character with the standard ; the corresponding quadrants of the rings seen in the two substances, being similarly affected in the one case, and the alternate ones in the other. So coarse a method proved, as might be expected, unavailing in the present instance, the order of the tints being so completely altered by. a plate of mica of moderate thickness, as to be no longer recognized, and I was obliged to have recourse to measures taken in homogeneous light, and on a divided apparatus. The method I pursued was as follows:—Having enclosed the crystallized plate of the second variety described in my fermer paper, in castor oil, in a proper apparatus for varying its inclination to the polarized beam, and adjusted it so as to revolve in a plane 45° inclined to that of primitive polarization, I noticed the inclinations at which the first minimum of the ordinary pencil on one side of the axis took place. These were as follows: Vol. 1. Part I. er 244 Mr. Herscuen on the Double Refraction of Apophyllite. Extreme Red. Violet. 192 36: 252.) 5 br 19 48 250 a7 19 5 25 39 19 48 25 34 19 5 26) Sik 20 10 25 46 19 5 25 55 19 5 250) 27 19 5 26 54... near the Indigo. ———_— 25 16 .. extreme Violet. Mean 19° 28’ ——— 25° 51’ The variations in the observations of the violet rays arise not so much from the imperfections of the specimen, and the difficulty of taking measures in violet light, as from the rapid change of the polarizing energy, as the ray approaches the extremity of the spec- trum, and the mean result above set down is, in consequence, that corresponding nearly to the mean violet rays. I now interposed between the crystal and the reflector on which the incident hght received its polarization, a plate of mica, so thin as to polarize (alone) a blueish white of the first order; its plane being perpendi- cular to the ray. My object in using so thin a plate was to dilate or contract the system of rings, by a quantity decidedly smaller than half the interval between two contiguous ones, so as to avoid all possibility of a mistake, in the order of the ring brought under examination, by the interposition of the mica plate; the point in question, being not to obtain any precise numerical results, but merely to ascertain whether the change of the inclination corres- ponding to the minimum or maximum of any given ring, produced by a mica plate of infinitesimal thickness, would have the same or opposite signs for the two ends of the spectrum. The mica being fixed so as to have its principal section 45° inclined to the plane of primitive polarization (or in azimuth 45°), Mr. Herscuer on the Double Refraction of Apophyllite. 245 the minima of the ordinary pencil were now observed to take place at the following inclinations: Extreme Red. Violet. TSO" PLS ale y 18 1/22 29 10 17. 38 30 58 Wr y¢ See 16 55 30 14 -_—_ 29 53.. Extreme Violet. Mean 17° 17’ Se Al 33 29.. Violet bordering on Indigo. The inclination was therefore diminished for the red rays, and increased for the violet—in other words, the interposition of the mica had contracted the red rings in a direction parallel or perpen- dicular to its principal section, but dilated the violet. I now (to confirm this indication) turned round the mica plate one quadrant in its own plane, so as to reverse its action on the polarized beam, and then, repeating the measures, found as follows : Extreme Red. Violet. 20° 53 2000 Al 20 10 24 29 Te sant 4 21 36 ON Ne 20 31 Ol. Ne! 21 58 20° 57’ Op Gy The effect on the measures, as we see, corresponds to the change of circumstances, the red rings being now expanded and the violet contracted, by the action of the mica in the direction in which they were observed. To assure myself still more completely of the iden- tity of the ring examined, I detached the mica, and observed the Ir2 246 Mr. Herscuet on the Double Refraction of Apophyllite. first evanescence of the extraordinary pencil in the extreme red rays, which took place at an inclination of 27° 11’. The whole interval then from the maximum to the mimimum of the first red ring em- braces an extent of 27° 11'—19° 28'=7° 43’, while the displacement of the minimum by the mica did not exceed 2° 11’ in one direction, and 1° 29’ in the other. On the other hand, computing the first evanescence of the extraordinary pencil in violet light, from the formula* nl=t.sin@. tan @ which gives sind =(V 2p /1 +P = P)s where p= ™, we find that it will take place at 38° 12’ of inclination, and the variations produced by the mica in the place of the ordinary mini- mum being + 5° 4’ and — 3° 36’, are decidedly less than the inter- val between the maximum and minimum of the first ring which is 38° 12’ — 26° 19’= 11° 53’. However to leave no doubt on this head, I interposed an extremely thin plate of mica; which polarized but a feeble blue of the first order, and placing its principal section successively at azimuths 45° and 45° + 90° =135°, repeated the measures of the incli- nation at which the first minimum took place, taking in each case, the mean of ten observations to compensate the various irregulari- ties it was found impossible to avoid. I thus obtained the following results : | Azimuth = 45° | Azimuth = 135° Inclination at Minimum of extreme Red . 18? 539) 19° 55’ Ditto, Vaoletees ccs Ato perce Oca ree 26 15 24 35 * n= the number of periods and parts of a period performed by the polarized ray within the plate. 1 = the length of each period. t = the thickness of the plate. 8 = the inclination of the ray to the axis. Mr. Herscuer on the Double Refraction of Apophyllite. 247 The feeble double refraction, joined to the imperfection of the specimen, and the impracticability of cutting it into a prism, with its refracting edge parallel to the axis, (owing to the facility with which the lamine separate from each other,) have prevented my verifying these results by actual observations on the double refraction. There can be no doubt, however, what would be the result. The spectra formed by the two refractions would appear supernnposed on each other, but of different lengths, the indigo spaces of each coinciding. They would consequently appear as one spectrum of diluted colours, and unless examined in homogeneous light, the double refraction would not be noticed at all. There can be little doubt too that the third variety of apophyl- lite described i my paper, would exhibit similar phenomena, but I have not thought it necessary to make any experiments on it, the fact which it is the object of this paper to point out, being, I hope, sufficiently proved without it. J. F.W. HERSCHEL. Slough, March 31, 1821. The reader of Part I. of this Volume of Transactions is requested to correct the following Errata in my Communications on Polarization. Page 23, line 5, for their read thin. — 25, — 1, for their read thin. — ib, — 5 from bottom, for any read my. — 26, — 4 from bottom, for their read the. — 51, — 1 for by read of. XVI. Notice of the Astronomical Tables of Mohammed Abibeker Al Farsi, two copies of which are pre- served in the Public Library of the University of Cambridge. By SAMUEL LEE, M.A. OF QUEEN’S COLLEGE; PROFESSOR OF ARABIC IN THE UNIVERSITY; AND SECRETARY TO THE CAMBRIDGE PHILOSOPHICAL SOCIETY. [Read Nov. 13, 1820.] In making the following communication to the Cambridge Philosophical Society, I have not so much hope of contributing any thing to the stock of science which is already possessed on the subject in question, as of adding something to the history of its progress, and of bringing before the public the names of some men, who appear to have laboured with success in its furtherance: and, until Mr. Sedillot, as announced by Delambre* * Astronomie du Moyen Age, p. 166. “M. Sedillot se propose de donner des notices plus completes de lAlmageste d’Aboul Wefa, du Manuscrit d’Ebn Schathir, de celui de Leyde, et de tous ceux qu’il pourra se procurer.” It may be proper here to point out a very enormous mistake, which it is probable M. Delambre has copied either from Weidler or Montucla. In recounting the Arabic MSS. found in the Library of Merton College, Oxford, he says, ‘Mais, pour prouver avec quelle ardour les Arabes s’adonnaient a l’Astronomie, il ajoute, que dans le seul Bibliotheque Mertonienne 250 Professor Lee on the Tables of Al Farsi. shall favor the public with his more complete work ne the Astronomy of the Arabians, notices, like the present, of such works as are to be found in our Public Libraries, may not be unacceptable. In presenting therefore to the Society a notice of a very scarce and valuable work on Arabian Astronomy, I trust I shall do no more than what some of the most eminent writers on Astronomy have often called for: and, in so doing, it is my intention to avoid prolixity, and to give such details from the Preface of the work in question, and such extracts from the work itself, as may be interesting and useful. The only notice of the work, here alluded to, is, as far as my researches have gone, to be found in the Bibliotheque Ori- entale of D’Herbelot, which, from the manner in which it is given, is sufficient to shew that the writer had never seen the work in question. The notice is this, “Zig? Mohammed Ben Abibekr Al-Farsi. Tables Astronomiques composées par Mo- hammed, &c. pour le Sultan Al-Malik Al-Modhaffer Abou Mansour Joussouf Ben Omar, Seigneur de ’Jemen ou Arabie heureuse. Cet Auteur dit qwil a suivi dans son Ouvrage les observa- tions du grand Astronome Ferideddin Aboul Hassan Ali Ben Mertonienne d’Oxford, on conservait plus de guatre cents Manuscrits Arabes, tout remplies des doctrines et d’Observations Astronomiques.’ Montucla, in his Histoire des Mathemat. Liv. I. Part ii, says, Il nous apprend (i. e. Edovard Bernard) que la seule Bibliotheque de Oxford posséde plus de 400 manuscrits Arabes sur l’Astronomie. And, for proof of this, he refers the reader to the Philosophical Transactions for 1694, where not so much as one word is found on this subject. The only work there mentioned, as being connected with Edward Bernard, is a notice of the Catalogus Codd. Manuscriptorum Anglie et Hibernie. I suppose, however, the passage referred to is, Tom. I. Philosophical Transactions, p. 334, which has been cited by Asseman, p. 47, in his account of the Globus Ceelestis Cufico-Arabicus, where, writing to Huntington, Bernard says, “ Inter Codices tuos Arabicos in Museo Mertonensi (numeras autem plus quadraginta doctrine, et observationis sideralis refertos.” The quadraginta here mentioned has perhaps been mistaken for guadringenti, a mistake certainly of no-eommon magnitude. Professor Ler on the Tables of Al Farsi. 251 Abdalkerim Al-Schirvani,* dit Al-Rassed: VObservateur. II cite encore plusieurs autres Tables Astronomiques, dont voici les titres. Zig’? Al-Mosthi, Zig’? Al-Moddel, Zig? Almohakkem, Zig? Al-Zahir, Zig’? Al-Mostanfi, et Zig? Al-Olar Al-Rassadi, quwil dit étre le dernier de ceux qui ont observé par eux-mémes, ce qwil faut entendre jusqw en Vannée 541. de VHég. auquel temps cet Auteur a écrit.” This account by D’Herbelot is erroneous in several particulars : for first, instead of the Zig’ Al Mosthi, as given by him, the MS. has Zig’ Al Moghni. And again, instead of the Zig’ Almos- tanfi, the MS. has Zig’ Almostawfi. And, in the third place, instead of An. 541 of the Hegira, according to D’Herbelot, the MS. has An. 541 of the Aira of Yezdigird: from all of which, it is, perhaps, but fair to conclude, that D’Herbelot had never seen the work of Al Farsi. It is curious enough that excepting this very imperfect notice by D’Herbelot, the work of Al Farsi seems to have been totally unknown in Europe; and, although Astronomical Tables have been composed in Eurepe upon the Arabian models, yet it is ‘nost likely that these were taken from originals, which Al Farsi has shewn to be imecorrect; and on which account, he had been compelled to have recourse to observations made long after those of Albategnius, upon which these tables had mostly been con- structed. * Soyuti in his Dictionary of Patronymics, which is preserved in the Public Library in the collection of Mr. Burkhardt, says, +1 WU Creer eils | ig so BU ol sy ee &c. That is, Sharwani, with the vowel a before 7, which itself has no vowel, refers to the city Sharwan. In the MS. above alluded to, the vowel x is placed before r, And D’Herbelot, as well as the Editor of the Kamoos, places 7 before r, so that the word is written, Sharwani, Shurwani, and Shirwani. I prefer the first on the authority of Soyuti, and the Author of the Geographical Dictionary entitled | bs » Who writes it in the same way. Tol. 1. Part II. Kk 252 Professor Len on the Tables of Al Farsi. Montucla, again, in his History of the Mathematics, not- withstanding his having cited several of the Tables, or Ziges, as given by D’Herbelot, has omitted to mention those of Al Farsi, although he might have seen in D’Herbelot, that they were con- structed upon an entirely new set of observations. | It is not, however, my intention here to enter into the merits of the Tables in question:—to attempt to shew in what way they are preferable to those that went before them :—or to institute any thing like a comparison with the Tables of modern times. I shall leave these questions to be decided by those who have more leisure and skill for these pursuits, contenting myself with merely bringing to light the work in question. It is a remarkable fact that two editions of this very scarce work have lain in the Public Library of this University upwards of 160 years: one of which is the work of Al Farsi, the other an abridged edition by some unknown hand ; and undertaken, as the epitomator observes in his preface, for the purpose of facili- tating the use of the Tables, by reducing them to the era of the Hegira, the original work having been calculated according to the Persian era of Yezdigird.* I shall have no necessity to appeal to the abridged edition of the work in question, as the other MS. is in very good * The title of Al Farsi's work is, CC ALL, Cs gall cysvtel! Beploir SS! Crowle Gay It alee GL! Solu! esis Ow) Sap Oval I Coil il eS One We Ae Yas Co! yd! et es! Celis dbs Ul aay Skul Goll Ose Ce Joy LY CO GILL acl chs WU) agey Cs” ylaJl. The book of the approved Tables, known by the Professor Lee on the Tables of Al Farsi. 253 preservation, and very accurately written; with this exception, that the diacritical points are very generally omitted, which makes the work of decyphering considerable, and the ortho- graphy of some of the proper names irrecoverable. As men- tion however is made of the original compiler of the tables in the preface to this second edition, I shall take the liberty to transcribe it.* ‘‘ The most elegant work,” says this editor, ‘‘ that has been published on this subject, (namely, Astronomy) according to the longitude of Yemen, is that of the learned and excellent Mohammed Abibeker Al Farsi, which he published for the Treasury of the Sultan Al Malik Al Modhaffer, and entitled ‘Al Zig Al Mumtahan Al Khazayini.” i.e. The approved Treasury Tables. And again, speaking of the mean motion of Mercury, and con- demning the practice of some who had gone before him, he mentions another work of Al Farsi in the following terms.+ ‘‘ He the title Al Modafferi, from the observations of the learned and excellent, &c. Abi Al Hassan Ali Ibn Abd Al Karim Al Shurwani, the observer, (better) known by Al Fahhad, &e. Published by the eloquent and enlightened Doctor, for the Sultan Al Malik Al Modaffer, Badar Al Din Mohammed Abibeker Al Farsi. ‘The MS. is in large quarto containing about 250 pages, and has the class marks Ge. 3.27. It is said, in a note, to have been bought in Mocha, A. D. 1639, for 200 Ryalls of Eight; and, that it was placed in the Library a. p. 1658, by the Executors of Wm. Bretton, B. D. formerly Fellow of Emmanuel College, and afterwards Rector of Clapton in Northamptonshire. atts US En! Spb CUS C3 Ctie be QU! oly * Bild tio CMI oul! xe Cot! nsw desley aalatt ANI sind! dl olewy sll GUM! Gaba! GUS! lads GUS dinia Ce Vogl ob! Grey t qe cool Could! 5G Bal usw poo a! CN cuz! ere Ua ES cd eatyll pul 2 KK 254 Professor Lee on the Tables of Al Farsi. who wishes to know the truth of what has been said, may consult the work published by the learned Mohammed Abibeker Al Farsi, entitled, “‘ A step for the ardent mind towards solving the difficulties of the Astronomical Tables:” I cite these particulars merely for the purpose of shewing in what repute our Author was held by his learned countrymen; and to preserve the title. of one of his works. I now proceed to the preface of the work itself, which I shall give as faithfully as possible, from the words of the Author; and then the contents of each chapter of the book; and after that, a few extracts from the Tables. After a religious preamble in praise of God, and the Prophet, which I shall omit, the Author thus proceeds, ‘‘ The humble Mohammed Abibeker Al Farsi, relying on the favor of the Almighty, affirms, that the most elevating and ennobling pursuit that can occupy the attention of man, is that of Astronomy and the wonders which it possesses: and since, (adds he), it has been my good fortune to have held an office in the service of our Lord and King, the illustrious and excellent Al Modhaffer Al Mansiri, Al Malik Al Modhaffer,* &c.—Yusuf Ibn Omar Khalil, Com- mander of the faithful,* &c.—And since his favors have been continually and plentifully heaped upon me, it became my wish to publish a set of Astronomical Tables, for the Royal Treasury, unlike any that had gone before, and which should remain un- impaired to the end of time. I therefore took, as the most to be depended upon, the mean motions of the Sun, Moon, and Planets, as given from the observations of the learned and excellent Phi- losopher Ferid Eddin, &c. Abi Al Hassan Ali Ibn Abd Al . * The parts here omitted consist of the mere repetition of terms of respect, which are wltogether uninteresting to an European reader. Professor Ler on the Tables of Al Farsi. 255 Karim Al Sharwani, the Observer, known by the title Al *Fahhad, one of the most celebrated and correct of the learned moderns, and who published several Astronomical Tables, of which the following are the titles: viz. 1. Al Moghni, 2. Al Mohakkam, 3. Al Zahir, 4. Al Mostawfi, 5. Al Modddal, and 6. Al Olai Al Rassadi, which is the last published by him from obser- vations. I took this last, on several accounts, because, for instance, the accuracy of the calculations, and the demonstrations on which they were founded, were superior to any that had gone before; and because it was compiled at a time much nearer that in which the observations had been made, than any other. The date of these observations is that of +541 of the wra of Yezdigird. It has been related that Al Sharwani continued to make and correct his observations on the mean motions of the Planets, through a space of not less than 30 years, which he did by instruments, either made by his own hands, or procured from distant places for that purpose. The instruments alluded to are, the Armilla, which is used for the purpose of ascertaining the longitude and latitude of the Planets. {The Dhat Al Shuabatein, with which the (Zenith) distances of the Planets, and their diameters are observed :—and the quadrant, used to ascertain the Sun’s declination, which was divided into 5400 minutes, equalling the minutes contained in a * Pardum (domans B. in Av.) instituens ad venationem. Castell. Lex. Hept. + See the above mentioned notice by D’Herbelot. t There is no mention made of this word in any of the Dictionaries or Vocabularies, which are all extremely defective in terms used in the Sciences: the words are Crna wld i.e. having two branches: the etymology of the word, and the description of the uses of this instrument, which is given in the text, clearly shew that it was a species of the instrument invented by Ptolemy for the determination of the Moon’s parallax, and which was used by Albategnius in the determination of the obliquity of the ecliptic: it was known to Copernicus and the Astronomers of his age under the name of Regule Parallactice, and was first abandoned by Tycho Brahe. 256 Professor Ler on the Tables of Al Farsi. quadrant of the heavens, used for the purpose of correcting the observations. Nor did Al Sharwani depend on the observations of those who had gone before him, seeing as he did the great error and confusion that prevailed among them; and which attached itself, not more to the observations made by Hipparchus and Archimedes, before the time of Ptolemy, than it did to those made by them and Ptolemy himself. The same is true with respect to the observations of Ptolemy and those of the moderns, who followed the Tables called *Almumtahan, (approved). Now, between the times in which the observations of Hipparchus and Ptolemy were made, there intervened a space of about 260 years; and between the times of the Observations of Ptolemy, and those of the moderns made in the time of Mamoon a space of about 700 solar years. And in the same manner did those who followed the approved Tables disagree, so that one seemed to oppose the other. Of these Authors were the following: namely, Thabet Ibn Korra: Ahmed Ibn Mohammed A! Nahawéndi the Arithmetician : Isaac Ibn Honein: Hamid Ibn Ali Al Wasiti: + Abu Moasher Al Balkhi: Mohammed Ibn Jabir Ibn Senan Al Batani (Alba- tegnius): Send Ibn Ali: Khalid Ibn Abd Al Malik Al Mart- radhi: Ali Ibn Isa Al Astralabi: Abas Ibn Said Al Jauhari: Ahmed Ibn Abd Allah the Arithmetician: Ali Ibn Isaac Ibn Kishoor: Moosa Ibn Shakir, and his three Sons, Mohammed, Ahmed, and Al Hassan: Sahal Ibn Bashar Al Mahani: Al Kasim Ibn Abd Allah: Ahmed Ibn Abd Allah Habash: Abu Kasim Ali Ibn Al Hosein Ibn Isai Al Sharif Al Hoseini, known * By some termed the Tabule Probate; and by Mr. Caussin, Table vérifiée. Notices et Extr. Biblioth. du Roi. Vol. VII. p. 96. notes. + There is a work on Astrology with Astronomical tables by this Author in the University Library marked Ge. 3. 19. "Professor Lee on the Tables of Al Farsi. 257 generally by Ibn Aélam: Al Fadl Ibn Hatim Al * Nairizi: Mo- hammed Ibn Ahmed Yusuf Al Samarkandi: Abu Al Hassan Ali Ibn Amajur Al Turki: Yahya Ibn Abi Manstr: +Ali Ibn Abd Al Rahman Ibn Ahmed Ibn Younis: and Abu Al Hassan. The observations of all of whom differed from one another; and each of whom published a set of Tables from such materials as he had before him, and which he considered as sufficiently accurate.t § It is related by Ali Ibn Abd Al Rahmén Ibn Ahmed Ibn Younis, as told him by Send Ibn Ali, respecting Ibn Yahya Ibn Abi Manstr: namely, that Ibn Yahya’s observations could not be correct, nor have arrived to that degree of accuracy that could be wished, as he had seen the Armilla with which they had been made, sold, some time after his death, in the street of the Paper- makers in Bagdad ; and that it was divided into parts of 10 minutes each: This, says the Author, is a proof that his observations with this instrument were not perfect, on account of its being divided into parts which were sixths of a degree: but if its divisions had been of one minute each, they would have been perfectly correct. It is related by the learned and excellent Abu Al Hassan Ah Ibn Abd Al Karim Al Sharwani the Observer, above men- tioned, that he found the mean motions of the Sun and Moon agreeable to the observations of Yahya Ibn Abi Mansir, and those of Khahd Ibn Abd Al Malik Al Mararidhi:—of Abbas * In the orthography of this name I have followed Mr. Caussin, who says he was a native of Nairiz in Persia, and was famous for his knowledge of Geometry and Astronomy. Notices et Extr. Vol. VII. p. 118. t Of whose work an ample extract is given by Mr. Caussin in the Notices and Extr. Vol. VII. } From p. 60 et seq. of the Volume alluded to Ibn Younis makes the same remark. § The passage here cited from Ibn Younis, is found in Mr. Caussin’s edition above alluded to. 258 Professor Lee on the Tables of Al Farsi. Ibn Said Al Jauhari, and of Habash, all of which agreed with one another in this particular. But with respect to the two superior Planets: viz. Saturn and Jupiter, it was found in the Tables called Al Olai Al Rassadi (composed by Sharwani) that a conjunction would take place in Capricorn, in which the one would appear to touch the other, and which would happen on the * 14th of Safar, 562, of the Hejira, that is, on the 6th of Bahman Mah, ann. +535 of Yezdigird: and it so happened; so that the calculation agreed with the fact ; which was not the case with any other of the Tables that had been published from observation; but, on the contrary, the event universally contradicted the prediction: which may be sufficient to vouch for the accuracy of Al Sharwani.t It is further related, that Al Sharwani observed the mean motions of Mars, through a long space of time, and found them agreeable to the observations of Ibn Aalam. He likewise observed for a long time the mean motions of Venus, when she came in conjunction with the star in the heart of Leo, which he also found agreeable to the observations of Ibn Aalam. But with respect to the real motions of Venus, and the place of her apogee, he found some difference between his own obser- vations, and those of others who had gone before him: for, according to him, the apogee of Venus would differ from that of * Corresponding to Nov. 30, 1166, A.D. which also corresponds to 535 of Yezdigird as given by Gravius in the Epoche celebriores. See Tables. + This wra, aecording to Gravius, Epoche Celebriores, began A.D. 632, which is the year in which Yezdigird ascended the throne of Persia. { It is worthy of remark that the complaints of Ibn Younis were to the very same effect: viz. that in his day, none of the observations corresponded in time and quantity with the predictions, whence we may infer that the science of Astronomy, had received considerable improvement from the labours of Al Sharwani. See Mr. Caussin Not. et Extr. p. 122, et seq. Professor Ler on the Tables of Al Farsi. 259 the Sun in degrees, though it would be in the same sign; which is contrary to the general opinion of Astronomers. Again, with respect to the true motion of Mercury, after re- peated observations, he found it to differ from the observations of all but those of Ptolemy, with which it agreed. On these accounts (says Al Farsi) I relied entirely on his observations, because of their great accuracy and the clearness of their demonstrations, and because I had proved them during a considerable length of time, by the conjunctions of the planets one with another, or with one or other of the fixed stars; as, for instance, with the star in the heart of Leo, and others; as well as the quantity and time of dura- tion of the Solar and Lunar eclipses; in all of which I found the prediction to correspond with the event. I found, moreover, (continues Al Farsi) that most of those who had gone before me, and had composed Tables, had formed them upon the observations of others, as in the case of * Kushiar, author of the Tables called Al Jamia; Mohammed Ibn Aydtb, author of those styled Al Mofrid; and Ali Al Nasi, author of those called Al Fakhir ;—and Abi Rashid Al + Barabshi, author of those called Al Kamil, all of whom implicitly relied on the mean motions of the Planets, as given by Al Batani (Albategnius) taking all the errors and mistakes just as they found them. + When therefore I knew the character of the different Tables that had come down to my times, and found none comparable, to * There is a work on Astrology by this Author, bound up in the same volume with the work of Al Farsi. + It is impossible to be certain of the orthography of this word from the Manuscript, which here omits some of the diacritic points: thus ( aN | t We have here a further account of Tables of which D’Herbelot has taken no notice when speaking of Al Farsi, which it is most likely he would have done had he ever seen this work: and it is doubtful whether a notice of any one of them is to be found in D’Herbelot. Vol. 1. Part II. Lu 260 Professor Les on the Tables of Al Farsi. those called Al Olai Al Rassadi, either as respects their accuracy, or the nearness of the time of their compilation to that of the ob- servations on which they were founded, I took this, with some degree of confidence, as the basis of my own, which I published as conformably as may be to his models, facilitating, at the same time, the work of calculation as much as possible; and which had formerly been attended with considerable difficulty. I then gave my work the title of Al Zig Al Mumtahan Al Modhafferi, i.e. The approved Tables of Modhaffer, according to the name of our Sovereign Al Malik Al Modhaffer, (may his reign be per- petual.) The epoch of all the elements of the mean motions of the Planets, and of the equations of their apogees in these Tables, I laid down for the beginning of the year 631 of Yezdigird, on the third day of the week at twelve o’clock, which answers to the 17th day of Safar An. Hej. 661.* And the extent of time for which they are formed is An. 1321 of Yezdigird. The place, moreover, according to the longitude and latitude of which these Tables are computed, is the poimt of the great circle determining the climate of Yemen, the longitude of which eastward from the Canary Isles, is 63° 30’, and the latitude, from the Equator northward 14° 30’, which determines the boundaries of Yemen, upon which these Tables have been formed.+ I further affirm, (contmues Al Farsi) that no one has, in our times, published Tables at all to be compared with these, nor will * Which answers to Dec. 13, A. p. 1262. + In a note written between the lines in this place of the MS. it is said DADs . 4 . ; y ~ eee oe owe Lgareg gab pda! 1D wd ep! lrino MU cs drrat| This place is the city of Sena in Arabia felix, as this is the longitude and latitude given of that place.” This, upon referring to the Tables I find to be the case, which is sufficient to determine the place where Al Farsi wrote. Professor Ler on the Tables of Al Farsi. 261 any come hereafter who will equal them, whether as regards their truth, or the accuracy of their construction, excepting only, where some error might have escaped the compiler from absence of mind, either in laying down the numbers in the letters of the alphabet, or nm making the computations. My apology is therefore made, and my intention known. No one, it should be remembered, is free from error, especially when beset with difficulties, except the Almighty, whose favor and furtherance I have supplicated in the prosecution of this work, and I am not without confidence that he has answered my requests. I have divided these Tables into 40 chapters, which are as follows. The number of Chapters in these Tables. Chap. 1. On Chronology. 2. To find an unknown from a known date, by the Tables. 3. To find the beginning of the Roman, Coptic, Arabian, and Persian year. Also to find the beginning of the year and months of the Jews by the Tables. 4. To find the embolisms of the Arabian and Roman years by the Tables. 5. Explanation of the Elements, to which the mean motions of the Planets, (the Sun and Moon, with their true motions,) are reduced in these Tables; and to find any one for any given time. 6. To rectify the difference of time at any place differmg in longitude from that wherein these Tables have been composed, which is in the climate of Yemen. 7. To find the length of Day and Night, for any given time by computa- tion and the Tables. 8. Explanation of the requisites for a calculator in using the mean motions of the Sun, Moon, and Planets, and their equations, as laid down in these Tables: also their true motions. 9. To find the Sun’s place. 10. To find the Moon’s place. 11. To find the place of the Nedes. 12. To find the places of the five Planets. 13. On the retro- Ea? 262 Professor Lee on the Tables of Al Farsi. erade motions of the Planets :—and their being stationary. 14. To find the latitude of the three superior Planets. 15. To find the latitude of the two inferior Planets. 16. *To find the Sun’s declination: also to find the first and second declination by calculation. 17. To find the Moon’s latitude. 18. To find the times of the Conjunctions and Oppositions. 19. To find the places of the Conjunctions and Oppositions. 20. To find the Phases of the Moon. 21. To find the sine, the are being given; and vice versa. 22. To find the versed sine, the are bemg given; and vice versa: also to find the chord, the are being given, and vice versa. 23. On the ascension in a right sphere. 24. On the ascen- dant, and how to find the parts of the hours of day. 25. To find the Sun’s altitude from the tangent and cotangent of observation ; and vice versa: also to find the reversed shadow (i.e. the cotangent) commonly in use. 26. To find the Equation of the time of day (at any given place): also the places of the Sun and Planets by computation and the Tables. 27. To find the latitude of any place by an observation of the Sun’s altitude, and by the Tables. Also to find the longitude of any place and its meridian. 28. To find the ascendant; also the circle of the Heavens corresponding to the latitude of Yemen, from the observed altitude of the Sun. 29. To find the ascendant; also an are of the Heavens from the observed altitude of the Planets. 30. To find the parts of the ascendant : also the point of the Ecliptic that is upon the Meridian, the common and sidereal time being given. 31. To find the time when any point of the Ecliptic comes to the Meridian, either at a place having latitude, or in one that has none. 32. To find the Equation for the centre points of the twelve signs of the Zodiac. 33. To determine the cases wherein the solar Eclipses take place, * For an explanation of what is meant by first and second declination, see Delambre Ast. du Moyen Age, p. 158. Professor Leg on the Tables of Al Farsi. 263 by computation and the Tables. 34. To calculate a solar Eclipse. 35. To calculate a lunar Eclipse. 36. On the *Comet; and to find its place with respect to the Ecliptic. 37. To find the hours of the day as equated for the latitude of Yemen, by the Tables. 38. To find the greatest Meridian altitude for the latitude of Yemen, by the Tables. 39. To find the conjunctions of the Planets one with another: also the times of the conjunctions of the Moon with the Planets. 40. To find the places of the fixed Stars for the epoch of these Tables, i. e. for the beginning of the year 631 of Yezdigird : also to find the places of the 28 stars of the Ecliptic from their original places: which ends the Tables. The following are two Tables giving the mean places of the Planets, and their Apegees, which may have been influenced by the observations of Sharwani. * The word used in the text is wT, of which the Author himself says, wy! { SI CS > Gudy GUS hyd CIT Eo Ont pl DUE Kyyd be WI CU! (3 ander, WIT Observe that On| is one of the stars having a tail, nen situated in the firmament of the stars: but having its place in the etherial heaven, below that of the moon. I have therefore supposed it must mean a Comet, no assistance whatever, in this, as well as innumerable other instances, being to be obtained from the Dictionaries; but the Author speaks of this comet as if it were a solitary phenomenon, and subject to the same laws of motion as any of the planets; he has given tables of its mean place in the ecliptic for intervals of 1 year,- of 10 years, and of 100 years; a proof, if any were wanted, of the very little attention which was paid to observation in the construction of their tables. 264 Professor Lux on the Tables of Al Farsi. Table of the Mzan Praces of the Pianets, for the beginning of the Year 631 of Yezdigird, for the Longitude of 60° 30’ from the Canary Isles, Eastward. Planets. Signs. Deg. Min. Sec. The Sun’s mean place ........ 6° 28° 38’ 22” The Moon’s ditto ........+6.. 5 2 OM BA 1999 Its true place....... SEE, Se eo The? Nodes) .2i5. S228 CH GSe SDE HSS 7 Saturn’s mean place ....... othe 4h RSTOMP BO 8 Its true place’...J2..04..0.02 9 5 280) %44 Jupiter’s mean place ........ ee 24 Se Seo) 3 fis true place! S.... ie yeseel te 296 ao 9 Mars’ mean place ....eeseee-- 2 25 23 57 Its true place......seeesee. 2 16 5° ae Venus’s mean place.........+6. 7 10 14 22 its virde place’. c's re eee « 13S) 45) a2 Mercury’s mean place ......... 2 26 49 22 Its true place ......... kets ee ea eo Table of the Apocrrs of the Praners, for the year above mentioned. Planets. Signs. Deg. Min. Sec. Thirds. Fourths. The Sun/24 / Pisces eo" 2 vag) OP 1S" Go" ws Saturn...... Sagittarius. . 9. 23 30 ) 8 Jupiter ..... Virgo...... 5 29 Pst) Maras. 0c). Seis 2! atic etait 1G 6 30 Venus o1.cce Geminis ao S28 PUPP beso 7 ORzT 30 So OO. en Mercury .... Scorpio.... * This is evidently a mistake in the manuscript, as the right sign Cancer is always mentioned in other parts of the Tables. Professor Lee on the Tables of Al Farsi. 265 The positions of the Apogees given in this Table do not accord with those given by Ibn Younis in the year 220 of Yezdigird, and much less with their true places for that time, as determined by modern tables: and, the case of the Sun excepted, their plane- tary theory would necessarily give results essentially different from the true ones. The obliquity of the ecliptic is always made 23° 35’, the de- termination of it given by Albategnius, and adopted by all sub- sequent Arabian Astronomers. The Sun is said to be vertical at Sena when he is in the 9th degree of Taurus, and its latitude is stated to be 14° 30’: this would give a value of the obliquity much less than the preceding: but no inference can properly be drawn from hence, as we know not whether these results were connected with each other. It may perhaps be unnecessary to give any further extracts from the Tables, I shall therefore only remark, that in the original work they occupy 96 pages; in the abridgement 70. The chapters moreover in the abridgement are confined to 30. It was my ori- ginal intention to give a list of the principal places in the East with their longitudes and latitudes from the Tables above men- tioned: but, as I intend to present to the Society some extracts from the Geography of Abulfeda, of which a very valuable copy, written by Erpenius, is deposited in the Public Library, and which has never yet been laid wholly before the public, I now defer that part of my design to some future day, when the list of Al Farsi, and the extracts from Abulfeda may appear together. SAMUEL LEE. Cambridge, Nov. 5, 1820. rrr tr rrerrerrre rere re rrr P.S. I must not omit to mention, that I am indebted to the Rev. Mr. Peacocks, the present Secretary of the Society, for several valuable hints, during the preparation of this Paper for the Press. ae. maaan hon ofr alin actt.ac asa gers . W ose vag shy Paige ea” a sahcateal’ sit Va Seaghoult fetes nn mr dann HAs disaee alwat ayia eae iy (a fo-eancss walt Hagllicwaall Seok waists epee iow tah anette il bane f=: se gy 8 00 Se a ss OB ae | ei wht ee. ie SR ea Spe tease a unr Ws mire a ool ae so Sieh ry ae XVII. On Sounds excited in Hydrogen Gas. By JOHN LESLIE, Esq. F.R.S. E. CORRESPONDING MEMBER OF THE FRENCH INSTITUTE, PROFESSOR OF MATHEMATICS IN THE UNIVERSITY OF EDINBURGH, AND HONORARY MEMBER OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. [Read April 2, 1821.] Ip is well known that the intensity of Sound is diminished by the rarefaction of the medium in which it is produced. We might therefore expect the sound excited in hydrogen gas to be feebler than what is, in like circumstances produced in atmospheric air. But the difference is actually much greater. A small piece of clock-work, by which a bell is struck every half minute, being placed within the receiver of an air-pump, a successive rarefaction was produced, and after the air had been rarefied 100 times, hydrogen gas was introduced. But the sound, so far from being augmented, was at least as feeble as in atmo- spheric air of that extreme rarity,—and decidedly much feebler than when formed in air of its own density, or rarefied ten times. The most remarkable fact is, that the admixture of hydrogen gas with atmospheric air has a predominant influence in blunting or stifling sound. If one half of the volume of atmospheric air be extracted, and hydrogen gas be admitted to fill the vacant space, the sound will now become scarcely audible. Vol. I. Part II. Mm 268 Professor Lesiir on Sounds excited in Hydrogen Gas. These facts, I think, depend partly on the tenuity of hydrogen gas, and partly on the rapidity with which the pulsations of sound are conveyed through this very elastic medium. The celerity of the transmission of sound through common air is the same in every degree of rarefaction; but in hydrogen gas it is more than three times swifter. The bell therefore strikes a medium which is at once thin and fugacious; fewer particles are struck, and these sooner escape from the action of the stroke. To produce undulations similar to what are excited in atmospheric air, or to cause equal reciprocations in the tide of sound, it would require the impulse to be as the square of the celerity, or ten times greater than in common air. If this view of the matter be just, I should expect the intensity of sound to be diminished 100 times, or in the com- pound ratio of its tenuity and of the square of the velocity with which it conveys the vibratory impressions. When hydrogen gas is mixed with common air, it probably does not intimately combine, but dissipates the pulsatory impres- sions before the sound is vigorously formed. It would be desirable to prosecute such observations with different gases, and at various degrees of rarefaction. But I have not yet found time, and merely throw out these hints for subse- quent examination and research. JOHN LESLIE. Edinburgh, March 13, 1821. XVIII. On the Connexion of Galvanism and Magnetism. By THE Rev. J. CUMMING, M.A. F.R.S. M.G.S. PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF CAMBRIDGE. [ Read April 2, 1821. | Iv has been remarked of the Pile of Volta that it stands unrivalled in the history of Philosophy, as its discovery was not the result of accident, but the fruit of preconceived theory, without which it might have for ever remained unknown. But this, though the first, was not the only instance of the kind in the history of Galvanism.—The decomposition of the alkalis and the discovery of the close connexion, if not the identity of Galvanism and Electricity, were the results of experiments, which were not under- taken fortuitously, but successfully deduced from theoretical views. —Another instance has recently been added of the verification of hypothesis by experiment, in Professor CErsted’s discovery of the action of the Voltaic Pile on the Magnetic Needle. In repeating his experiments, I have been led to some results, which may not perhaps be unworthy of the notice of this Society. Some years before the identity of Lightning and Electricity were suspected, it had been observed that the Magnetism of the Compass Needle was not only destroyed, which might be attributed to heat, but MM 2 270 Professor CUMMING on the that it was reversed by Lightning; the same effects were afterwards produced by artificial Electricity: this seems to have been the first step in this discovery. It was noticed by Halley, and afterwards more accurately by Dalton, that the beams of the Aurora Borealis were always parallel to the Magnetic Meridian, and that the direc- tion of the Magnetic Needle deviated considerably during their continuance. These two facts seemed to prove an intimate connexion between Magnetism and Electricity, and when afterwards a similar con- nexion was observed between Electricity and Galvanism, it was an obvious inference that these three powers might possibly be identical.—Several fruitless attempts were in consequence made to communicate Magnetism to Steel Bars by placing them in the Galvanic circuit, and, excepting by the experiments of Ritter, there appeared no confirmation of this supposition. His experiments. and the conclusions he deduced from them, were too singular to be passed over unnoticed. By placing a Louis d’or in contact with the extremities of a Voltaic circuit, he caused its opposite sides to exhibit, the one the positive, the other the negative electricities, and this even after having been in contact with other metals; in this respect having acquired polarity similar to that of a magnet. Pursuing the analogy, he galvanised a gold needle, which shewed the dip and variation, and was attracted and repelled by a magnet. The conclusion he deduced from these experiments, was, that a magnet was similar to a pair of Galvanic plates, and that the affinity of Galvanism with Magnetism was still greater than that with Electricity. From some unaccountable circumstances his experiments either were not attempted, or did not succeed with others. In a work published by QErsted in the year 1807, the subject is again resumed, and the hypothesis brought forward which conducted him to a successful result. After describing some analogies between Magnetism and Electricity, he arrives at this Connexion of Galvanism and Magnetism. 271 conclusion: m Galvanism the force is more latent than in Elec- tricity, and still more so in Magnetism than in Galvanism ; it is necessary to try whether Electricity in its latent state will not affect the needle.—It seems to have been upon this principle that he founded his process. A magnetic needle was placed within the influence of a wire connecting the extremities of a Voltaic battery, and was found to deviate in different directions, varying according to its position with respect to this connecting wire.— Subsequent experiments have proved, that this wire, of whatever metal it may be composed, becomes during this process magnetical ; that two such wires possess the power of attracting or repelling each other, and that permanent magnetism may be communicated to steel by placing it within the Galvanic influence.—As your Council have done me the honor of desiring me to repeat these experiments before you, I have thought it proper to give this short account of their origin, which otherwise, as they are detailed at length in the different Scientific Journals, might have been thought unnecessary. In many of the results which I obtaimed in exa- mining these phenomena, I found, as might have been expected, that I had been anticipated by others; I shall therefore mention only those which I believe to be new, or which, though previously discovered by others, yet in consequence of my using an apparatus more suitable for the purpose, I obtained by more simple methods. The apparatus employed was a single pair of zinc and copper plates, having a surface of 24 feet, and conducting copper wires of = inch diameter, with two light magnetic needles, the one moving horizontally, and the other vertically. For examming the direction in which the magnetic force of the connecting wire acted on the needle, a thick brass wire was used, bent into a circular form, leaving an interruption in its circumference of about an inch; the ends of this wire being connected severally with the zinc and copper wires of the Galvanic plates. The ring being 272 Professor CUMMING on the placed horizontally with the needle beneath it, the deviation was, in every azimuth of the compass, such that the needle made an angle of nearly 90° with the direction of that portion of the ring which was immediately over it. This deviation is mentioned by CErsted as being about 45°; but it was shewn that its ultimate direction was at right-angles to the wire; in some cases by using a very light needle, in others by fixing it at nearly 90° by a small magnet; when, on making the connexion, it was impelled towards the right-angle, on which ever side of it the needle had been placed previously. The consequence of this was, that the needle made right-angles with the meridian, when under that part of the ring which was due North and South; and that where it was East and West the needle continued in the Meridian; but in one instance its magnetic intensity appeared to be increased, the North end still pointing towards the North, in the other its poles were re- versed.—It was obvious from (Ersted’s experiments that when the needle was placed over the ring the effects would be similar, but in opposite directions, and that when in the plane of the ring there would be apparently no effect produced. In this case a horizontal needle was used having a vertical motion. This was first placed without the ring, the direction of the needle making right-angles with that part of the ring to which it was opposed.—It was found, that, that end of this needle which was impelled upward in one position, was similarly impelled in every azimuth whilst without the ring, but on being placed within it was in every position im- pelled downwards.—On reversing these needles the effects were in all cases exactly opposite. When instead of using a common compass as in the first case, a needle was applied to the wire, sus- pended vertically below its axis, that end which moved to the right of the wire in any one point of its circumference, moved to the right in all; but on being suspended in a similar manner over it, moved to the left of the wire in all positions—From these experiments Connexion of Galvanism and Magnetism. 973 it is evident that the force exerted by the connecting wire on the magnetic needle, is in every case in the direction of a tangent to the circumference of the wire, drawn from that point of it towards which the pole of the needle is directed; and that the direction of these tangents, with reference to the wire, is always the same This may readily be conceived, by imagining the Galvanic fluid, (if it be a fluid) to revolve in a close spiral line from one extremity of the connecting wire to the other. From the opposite effects of this current on the opposite ends of the magnetic needle, it is obvious either that its particles attract one pole and repel the other, or that two electricities proceed, at the same time, from the extremities of the connecting wire, in opposite directions; the one acting upon one pole of the needle solely, the other on the other.— To separate these effects from each other, I used a needle, one end of which was steel, the other brass. The effect of the connecting wire on this double needle was, as I had imagined, considerably less than that on the common needle, but similar..... To ascertain the direction of the supposed Galvanic current with reference to the magnetic needle, we must have recourse to the case where the connecting wire is at right-angles to the Meridian. When that end of it which was connected with the zinc plate was East, the needle beneath it remained immoveable, its magnetic inten- sity being increased; when the same extremity was connected with the copper plate, the poles of the needle were reversed; in the first case then the Galvanic force coimcided with, in the second it was opposed to, that which gives magnetism to the needle.—And therefore the effects of the connecting wire upon the compass needle are precisely similar to what would have been produced by placing over it a magnetic bar at right-angles to the connecting wire, that is, parallel to the needle; having in the first case, its poles in the opposite, and in the second case, in the same direction as those of the compass needle.—In both these cases the 274 Professor CuMMING on the direction of the magnetic current in the needle, being at right-angles to the connecting wire, was either from North to South, or from South to North. I concluded therefore that if the Galvanic circuit were completed through a magnet, its force would be increased or diminished, as the Galvanic force comcided with or opposed the magnetic. On connecting the two poles of a small horse-shoe magnet,* to which a weight of 12 grains was suspended, with a pair of Galvanic plates, the weight fell when the zine plate was connected with the South end of the magnet, and on reversing the poles it was drawn upward with a strong vibrating motion, indicating increased attraction.—As when that end of the connecting wire which pro- ceeded from the zinc plate was placed in the magnetic Meridian over the North end of the compass, in the former experiments, the needle went to the right, and when under the compass to the left; it follows, from comparing this with the above-mentioned experiment, that the current which issuing from the zine plate proceeds along the wire from right to left, answering to what would be called a left-handed screw, corresponds with the magnetism which influences the needle of the compass. Similar experiments to those with the brass rmg placed horizon- tally, were made with it suspended vertically, in different azimuths. As they chiefly served to verify the direction of the supposed Galva- nic current as deduced from the former experiments, it is unnecessary to repeat them.—One result however was obtamed, which, as I have found it practically useful in magnifying the Galvanic force on the needle, I shall mention. When the ring is placed in the magnetic Meridian, the upper and lower parts of its cireumference may be considered as horizontal lines passing over and under the needle, * Since this was read to the Society I have discovered the cause of this phenomenon to be different from what I then suspected, I have therefore assigned the true cause in @ subsequent paper. Connexion of Galvanism and Magnetism. 275 and the East and Western sides as vertical lines drawn in its plane, and at right-angles to its poles. From what has been said as to the direction of the Galvanic current, it is evident that the effect of that part of the ring which passes over the needle is doubled by that beneath it, in the same manner the effect of the East side of the ring is doubled by the Western; in addition to this the effects of the horizontal and vertical portions conspire together. If therefore the ring become an ellipse, or what is more convenient in practice, the connecting wire be made in the form of a parallelogram inclosing the needle, the effect will be nearly quadruple that of a single wire passing over it. By means of this arrangement I have produced a deviation of 20° on a common pocket compass, by a battery so small as to be excited by a single drop of fluid—By diminishing the size and increas- ing the delicacy of suspension of the needle there seems every probability that this may become a more delicate Galvanometer than any we as yet possess.—After mentioning the effect pro- duced by so small an apparatus, it may seem singular that in Professor CErsted’s earlier experiments the effects were barely ap- parent, owing, as he imagined, to the feeble power of his battery. The reason of this he afterwards discovered to be, that the mag- netic effect was dependant not on the intensity but the quantity of Galvanism evolved; but he does not seem to be aware of the extent to which this observation may be applied.—My first ex- periments were made with a battery of 220 double 6-inch plates possessing very powerful effects both electrical and chemical; yet its influence on the needle was scarcely perceptible. One of these plates taken separately caused a deviation of nearly 80°. It is evident then, that, though the circuit be complete, much of the magnetic influence is destroyed by the same circumstance which generates the electrical effect. This can be no other than the tension produced, in consequence of the obstruction presented to fol. 1. Part II. Nw 276 Professor CUMMING on the the free passage of Galvanism, by the fluid interposed between each pair of plates—Magnetism cannot therefore be properly considered as the effect of Voltaic Electricity, but of Galvanism in its original form. In examining the difference between Electricity and the Mag- netic effects produced by Galvanism, I was induced to try the powers of wires of different lengths and diameters in conducting it. Electricity, it is known, is conducted almost entirely by a wire however small, provided it be not fused; and if the circnit be completed at the same time through two wires of different lengths and diameters, a very small portion of Electricity is transmitted through the larger wire, provided the smaller be considerably shorter—The law by which the Magnetic influence of Galvanism is conducted is precisely the reverse—A needle which deviated between 80° and 90° when placed under a connecting wire of = inch diameter, deviated less than 20° when placed at the same distance from a wire of x inch ; when wires of different diameters were used, the deviation increased with the diameters, although their lengths increased at the same time; and this law continued, even with a single pair of plates, until the wire was larger than 5 inch.—As it might have been supposed that this effect was owing solely to the smaller wire presenting a less surface to the needle beneath it, I placed a large connecting wire over the compass, and interposed the smaller wire in another part of the circuit, but the effect was still the same. I obtained however a still more decisive proof of the difference of the laws by which Electricity and Galvanic Magnetism are conducted. The connexion was made at the same time by means of two wires, one of which was sq inch diameter, and 3 inches long, the other 5 inch, and 5 feet in length; the needle ef a compass placed under the former devi- ated only 10°, that of a similar compass under the latter had a deviation of nearly 80°.—That the smaller wire was capable of Connexion of Galvanism and Magnetism. 277 conducting more of the Magnetic force, was shewn by removing the larger wire when the deviation under the smaller increased to nearly 20°. This influence had therefore, contrary to that of Electricity, chosen the longer passage through the larger wire, even though the smaller had not transmitted all it was capable of conducting. As in some of these experiments I had inclosed the small wires in tubes filled with water and different acids, without finding there was any increased effect produced, I concluded that these fluids would not conduct the Galvanic Magnetism; nor where a single pair of plates was used, however nearly the con- necting wires were brought together, was there any effect produced either chemical or magnetical—On placing a small copper wire, in a tube filled with nitric acid, over the needle, the deviation was gradually diminished as the wire was corroded by the acid, and when a separation of continuity took place, there was no deviation. The experiment was reversed by inclosing two copper wires in a tube filled with acetate of lead; the extremities of these wires being brought very near each other, and the tube placed in the Galvanic circuit over the needle, there was at first no deviation, but when the arborescence produced by the revival of the lead formed a metallic contact between the wires, a small deviation appeared, which gradually increased as the contact be- came more extensive.—That in using large wires the surface alone does not transmit this magnetic influence, and that there- fore in this respect it differs from electricity, was shewn by filling the above-mentioned connecting tube with mercury, and after- wards removing the mercury, and coating it with metallic foil. With mercury the effect was the same as with a wire of the same diameter; but on removing the mercury and coating the tube with gold leaf the deviation was very inconsiderable, not more NN2 278 Professor CUMMING on the than from 5° to 10°;—with platina foil, which was much thicker, the deviation was greater, yet far inferior te that of a solid wire of the same diameter. Having ascertained the difference between Galvanic Mag- netism and Electricity, as to the power of being conducted, it seemed desirable to discover whether there were any thing ana- logous in common magnetism—For this purpose I placed beneath the iron pendulum of a small clock, a horse-shoe magnet, whose force, coinciding with that of gravity; would accelerate the rate of the clock, by the going of which a measure would be afforded of the magnetic force exerted upon it. When the poles of the magnet were uncovered, the rate of the clock was accelerated trom 10’ to 12’ in 24 hours, when they were connected by a piece of soft iron the gain was not more than from 1’ to 2’; on filing away the middle of the iron the rate was gradually accelerated, and when the central part was reduced to a fine thread the ac- celeration was nearly the same as when the poles were uncovered.— When the poles were connected by a piece of iron bent down beneath the legs of the magnet, so that the length of the circuit between the poles was considerably increased, the rate of the clock was still but little affected. It appears from this, that the poles of the magnet were much more completely neutralized when the connexion between them was made through the longer but more capacious circuit, than when through the shorter and less capacious; and that in this respect commmon magnetism is analogous to that excited by the Galvanic apparatus. I have already trespassed so long on the attention of the Society, that I must defer to another meeting, an aceount of some experiments, to which I was led, by observing the facility which the Magnetic influence of Galvanism affords, for detecting its pre- sence and measuring its effects. Ez FP Trans”™ of the Cambridge Li Vol. 1. 74. XL, ae Pad + ae Le a ne : We) cet , Ae eS as. i 1 cial Cla oe bo pine al eeeay Gannon . ied | aut et do) i Ber hilt tb be ta oe here Hay Prag ln Lhe en ae ' i -' sina ; o® wet, ais ‘ a of clogs clay a a ae: ie: os % AWS / . Pee, ee eaaey ws ‘ Bete, Migr ba Win Jt Cid. fev aan : * =~ ries in sa ' : en) oy en ee rt : th a ro A ae | 3 poral i tyesenyhe pared Sie whee - + fUdeel einen Hee Kabel, tee gine CLA er Co tpl ae kas Ge ee eae ame Ft rah fi ‘s tbs Ay Sith AV on yh ide sha fenneiarte Oe The Ma devs Ree epee r ° -. Connexion of Galvanism and Magnetism. 279 PA IPA I LO LILI LOD LD OL O TD OL OLE There are perhaps few instances, in the history of Science, of nearer approximations to discovery, than some of those connected with this subject. In the 7th Vol. of Nicholson’s Journal an account is given of an experiment for ascertaining the effects of Galvanism upon a magnetic needle; which failed, as we now know, because the compass was placed fortuitously upon the pile instead of being under or over the wires connecting its extremities. When it was attempted to magnetise steel bars, by placing them in the circuit of the large electrical machine at Harlaem, it was observed that they became most strongly magnetic when the discharge was passed through them transversely. DESCRIPTION OF THE PLATE. Fie. 1. The GAaLVANoMETER. AB, the connecting wire placed over the compass needle SW. AC, BD, tubes filled with mercury for forming the connexion with the positive and negative ends of the battery, and attached to the slide EF GH. Fig. 2. The GatLvanoscope. A, K, tubes filled with mercury, to be connected with the Galvanic plates. ABCDEFGHK, a wire passing in a spiral round the compass needle NS. A small magnetised needle is placed beneath NS to neutralise the terrestrial magnetism. Fies. 3 and 4. Two forms of spirals for increasing the Electro-magnetic intensity. . a 5 o 7 x - 9 - « ing ~~ = = a = 5 _ 2 ‘ 2S -4 “7 —_ = = ._ m . ¥ > hr * as = “* yi * _ ha nm “* 7» #) a - 4 a ae .) Seer ol Gy aOR as Anh Seiten ss | aa i re ig vrtnd wily of seraliot ela qaehinny “ie pra) ita ably Jil WEE Stiefel Lali . fone ee to 8 cary eT ate ibe aden, ree Die it oe lw oe? mt wilt oe: ‘tmatg tq Gg: tilt elle qilbaen wii is—5 Re Rey eesti WE doa» oll yen is gated De Wie | ui rd i RR Lay vant oe lB Ll Aa \ : : all the Pe Se ee ee Oe col? pe ee nah) OP era am Sr At Trabgnaehia cniea eee ~\ » Pol gan Aw Rie ee | 18 ul oor en diggtng Manabe fe se ity orgie wall fq Pott Naatuy © oa a » Bena uf ae Gee Site mit ; Five : an sel we Vib) eleraii’ satire a eee ee Sublapw ig, res lb fers saeie sacenb eto vthila ae uci Pa ear: iilee fant ae With, Vala ie. eh ii at} wiVST aio Rae iv oi om Pid ae wh r Tee obits nlf ae *- i apionnahga tus wit aleve Wappreit nd a ‘ern ia “eadigy Bald Pry dh bese ae ~ 5 asta. oath. #4 sonal ayy Bin i Juice aur wit ely ca rae Aon vied ba! eve blest ae ) sere argr al ee, Mire borates ib amh crs fost om UC ae a “ aren 9 ait atel - ™ wit sunset ee ‘it eheviita bis ‘ene eae met ih se lean. XIX. On the Application of Magnetism as a Measure of Electricity. By THe Rev. J. CUMMING, M.A. F.R.S. M.G.S. PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF CAMBRIDGE. [ Read May 21, 1821. ] Tue methods hitherto in use for ascertaining the Quantity and Intensity of the Electricity produced either by Friction or by Galvanic action, are (independently of the shock on the animal frame, which obviously affords no definite measure,) derived from its power in decomposing water, or fusing metallic wires——When the Electricity is either small in quantity, or of low intensity, there are considerable difficulties in the practical application of either of these methods. The fusion of platina wire by the elementary battery of Dr. Wollaston, proves that the quantity of Electricity developed by very minute metallic surfaces is considerable; yet, exclusively of the difficulty in soldering wires that are barely visible, it is almost impossible to ascertain their length with any precision.— The other mode, that of measuring the quantity of water decomposed by a pair of small Galvanic plates, is impracticable-—The recent disco- veries of Professor Cirsted have enabled me to construct two 282 Professor CummineG on the Application of Magnetism instruments, one for discovering, the other for measuring Galvanic Electricity, with a delicacy and precision that seem scarcely to admit of limitation—The construction of the former instrument I have mentioned in a communication I had the honor to make to this Society sometime since ;—I shall now describe a few of the experiments I have as yet been enabled to make with it—A wire of zinc and another of platina, each + inch diameter, were coated with sealing wax, so as to have merely their extremities exposed : on immersing them in a dilute acid, the circuit being at the same time completed through the Galvanoscope, the needle deviated so decidedly, as to leave no doubt that a visible effect would have been produced by wires of less than half the dimensions of those I employed—As the compass though small, was by no means delicate, we may, I think, conclude from this experiment, that the Electricity developed by two metallic surfaces, each = of a square inch, may be detected, and their relations to each other ascertained, by this instrument. The minute surfaces, and consequently small quantities of exciting fluid required for experiments with this instrument, offer the means of examining Galvanic effects that have hitherto been unnoticed. Of the acids whose Galvanic effects I believe have not been examined, I have found, with small disks of zine and copper, that the oxalic and hydriodic have considerable power; the phos- phoric and acetic much less—The action of strong sulphuric acid was inconsiderable, the needle being scarcely affected, but on adding a drop of water it deviated through more than half a right angle-—Were the Galvanic action owing solely to the Elec- tricity developed by the metallic contact, the fluid acting merely as a conductor, according to a generally received hypothesis, the effect should be greatest when the stronger acid is used, concen- trated sulphuric acid being a far better conductor than when as a Measure of Electricity. 283 diluted; on the other hand, since zine or iron are readily oxidated by the action of dilute acid, though with difficulty when it is concentrated, this experiment seems to prove, that the Galvanic action depends, not on the conducting, but on the oxidating power of the interposed fluid.—Hitherto [ have not had the leisure to form that complete series of the electric relations of the metals towards each other, which this instrument affords the means of doing; yet the effects I have observed in two instances, are, I think, so remarkable, that I ought now to mention them.—On using two disks, one of iron, the other of steel, there was produced a decided deviation; since then the only difference in the metals arises from an alloy of from a = to a ;, part of the whole, it appears that this is sufficient to alter their electric relations.—The powerful affinity of potassium for oxygen, made it highly probable, that, in the Galvanic circuit, it would become strongly negative with all the metals. On my first trial with disks of potassium and zinc, the Potassium took fire before I could observe the effect; this difficulty I afterwards obviated by alloying it with mercury ; on making the contact the needle deviated through nearly a right angle: The same effect was produced with copper; it was needless to try it with the other metals, for being negative with respect to zinc, and zine being negative with respect to all the other metals, there can be no doubt that in the Galvanic circuit, potassium is the most strongly negative metal with which we are acquainted.— It is perhaps scarcely necessary to remark, that, if any proof of the metallic nature of potassium were wanting, this experiment would have afforded it. In using the magnetic needle as a measure of Galvanic effects, we may either observe the deviation at a standard distance of the connecting wire from the needle, or assume a standard angle and measure the distance.—The latter method seems to have the ad- vantage, as enabling us to use a smaller and therefore a more Vol. I. Part I. Oo 284 Professor Cummine on the Application of Magnetism delicate needle, with this additional convenience, that the scale is increased in proportion as the length of the needle is dimi- nished.—I therefore constructed an instrument, having a connecting wire fixed upon a moveable slide divided into inches and tenths, to which a vernier might be added if necessary. My first object was to ascertain the divisions on the scale, corresponding to varia- tions in the angle of deviation; for this purpose, the moveable wire was placed at different distances from the needle, increasmg in arithmetical progression, and the corresponding deviations were observed. As the effects decrease very rapidly during the Galvanic actions, the experiments were made as quickly as possible, proceed- ing from a distance of + an inch to 104 inches, and again returning to the first distance. On taking the mean of several trials, made in this manner, I found that the tangent of the deviation varies inversely as the distance of the connecting wire from the magnetic needle. It is well known that in a Galvanic arrangement, intensity is given by the number, quantity by the magnitude of the plates; but I am not aware that any notice has been taken of the effects produced by varying their distances from each other.—On placing a moveable plate of zine opposite a fixed copper-plate, I found, that, on diminishing the distance, the deviation of the needle placed under their connecting wire continued to increase, until they were in actual contact. The law of that increase, ascertained by the method I have just mentioned, was such, that the tangent of deviation varied inversely as the square root of the distances of the plates. In the construction of a Voltaic series composed of many plates, the advantages to be obtained by placing them very near each other, would be counterbalanced, by the risk of their intensity becoming sufficient to penetrate through a small distance; but in using large plates, with Electricity of low mten- sity, it is obvious, that provided they are not in actual contact, as a Measure of Electricity. 285 they cannot be placed too near each other. By availing myself of this observation, I have been enabled to repeat, with a single pair of plates, the experiments of Ampére and Arago, which were origmally performed with a battery of twelve pairs.—Of these, one of the most singular, is that by which a spiral connecting wire is made to communicate permanent Magnetism to a steel wire placed within it.*—This experiment I find may be varied, by using a straight connecting wire, and twisting round it a small steel bar; the zine and copper ends of the bar receiving the Northern or Southern Magnetism respectively, according as its spiral is from right to left, or the contrary. The repetition of this expe- riment led me to discover the cause of a singular effect, which I had the honor of exhibiting to this Society. The magnet, which was deprived of its attractive power when its North pole was connected with the zinc wire of a pair of Galvanic plates, had been placed in the circuit, by twisting the wire round its poles from left to right; on making this spiral from right to left I re- versed the effect; and when the spirals round its two poles were in opposite directions, the weights suspended from them were oppositely affected at the same time, the attractive power of one pole being increased when that of the other was destroyed. The smgular effects produced by using a large conducting wire, I have mentioned in my former paper on this subject, and the analogy it forms between the Galvanic and the common form of Magnetism.—In the further examination of this diffusion of the Magnetic influence, I have found it to be far more extensive than I had at first inagined.—On making the connexion between a pair of plates contaming about 14 foot of surface, through a copper globe of more than a foot diameter, and therefore containing full 4 square * In these, as in the previous experiments, I find that if the spiral be made of large wire it is much more efficacious than if of small. 002 286 Professor CumMiNnG on the Application of Magnetism, §c. feet of surface, every part of it exhibited Magnetic effects, either upon a horizontal or a vertical needle-——The same effects were manifested whatever were the forms of the surfaces interposed between the Galvanic plates—On varying the experiment by connecting both extremities of the plates with each other, by means of small wires, so that there was a metallic circuit through- out, (in which case it is generally conceived that all Galvanic effect ceases), I found that every part of this circuit affected the Mag- netic needle. The Magnetism of the connecting wires was examined in the usual mode; that of the plates themselves by immersing in the exciting fluid a small compass im a glass case, made impervious to the water. It is perhaps premature to form any theoretical opinions upon these few facts, which seem to me adverse to the received opinion, that the Galvanic effects are produced by the decomposition of an electric fluid circulating between the positive and negative plates; yet, if ever the mysterious agency of Galva- nism is to be detected, it must be by examining it in its simplest form ; and this, the discovery of the connexion between Galvanism and Magnetism, and the delicacy of the instruments it enables us to apply, seems to promise, more readily than any modes yet tried, the means of accomplishing. FPP ILE AL IL ILI LLDPE DDO DI LIL OD Since this paper was read to the Society, I have had an opportunity with the assistance of Dr. Clarke and Mr. Lunn, of trying the Magnetic effects of Atmospherical Electricity.— A wire of about 100 yards in length, connected with a Kite, readily magnetised a steel needle inclosed in a spiral wire, but caused no deviation in a compass placed beneath it.— I have obtained the same results in repeating Sir H. Davy's experiments both with the Leyden Jar and with sparks taken from the conductor of an Electrical Machine—It seems that the Galvanic Magnetism is most readily made sensible by the deviation it causes in the compass needle; but the Electrical by its power of communicating permanent Magnetism. The experiment on Atmospherical Electricity suggests an easy method of ascertaining, from time to time, the prevalent Electricity of the air; by inclosing small steel bars in a spiral wire connected with a conducting rod, and examining the Magnetism induced in them. XX. A Case of Extensive Solution of the Stomach by the Gastic Fhads after Death. By JOHN HAVILAND, M. D. VICE-PRESIDENT OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY, AND REGIUS PROFESSOR OF PHYSIC. [ Read Dec. 11, 1820. ] Tue subject of the following observations was a young man under 20 years of age, of sedentary and studious habits, who had previously to his last fatal illness enjoyed good health. The case came under my care on the 12th of December, 1819, the patient having been taken ill on the 5th with symptoms of fever, for which he had been bled, and had undergone appro- priate treatment under the direction of Mr. Okes.—When [I first saw the patient there were still present symptoms of cerebral de- termination, though by report these had considerably abated, nevertheless I applied leeches to the temples, and a blister be- tween the shoulders, and employed small doses of purgative medicines ; under the use of these remedies the symptoms abated. On the 18th he unexpectedly became worse, the pulse was weak and small, though not more frequent than 100 beats in the minute: there was an increased tendency to low delirium, espe- cially at night: I then had the head shaved and kept moist by a cooling application—From this time till the 22d, the day of 288 Dr. Havitanp on the Case of a Corroded Stomach. his death, the strength of the patient gradually declined without the occurrence of any remarkable symptom: the skin was gene- rally moist, and latterly profusely so: the bowels were moderately open, with about two evacuations daily, which were loose, but not otherwise unhealthy. There was no tumefaction or tenderness of the abdomen. The respiration was frequent and quick, but not particularly laborious till within a few hours of death—The appetite, as is usual in fever, was throughout the whole course of the disease almost entirely lost, but the patient took occasionally light broths and vegetable decoctions, to which he had no dislike. He also took at intervals a small quantity of port wine and water. Once, about twelve hours before his death, he asked for food, and swallowed a few spoonsfull of calves-foot jelly with apparent relish. He complained of pain no where but in the head, and that especially in the early part of his illness. The body was opened about 12 hours after death by Mr. Okes in my presence, and the following appearances were noticed :— The pia mater exhibited a slight increase of vascularity. The substance of the brain was firm and healthy. The ventricles con- tained about 12 or 14 drams of a serous fluid.—On opening the cavities of the abdomen and thorax at first nothing unusual was perceived, the viscera appeared entirely free from disease: the intestines were somewhat distended with flatus, but contained no feculent matter. On raising the stomach and examining the little omentum, we were surprised by the appearance of a dark-coloured fluid, which seemed to escape from the former viscus. A most careful search was now made, and a large opening was perceived in the stomach on the upper and back part, near the cardia. The stomach was then detached, with a portion of the e2sophagus and duodenum, when a large perforation of the diaphragm came into view, in Dr. Havitann on the Case of a Corroded Stomach. 289 the muscular part, corresponding precisely to, and communicating with the hole in the stomach: so that a portion of the contents of the latter organ had escaped into the cavity of the chest. This part of the diaphragm was next removed. A careful examination of the other abdominal and thoracic viscera did not lead to the detection of the slightest diseased appearance. There was no where ' the smallest evidence of previous inflammation, no adhesions or ulcerations of any part of the viscera. The fluid which had escaped appeared to be nothing more than the contents of the stomach, of which the wine and water formed a part, and probably gave it the dark colour. The stomach on being examined after its removal from the body, afforded the following observations. The mucous membrane appeared to be more red and vascular than usual throughout its whole extent, and here and there were small spots of what seemed to be extravasated blood, lying below the mucous coat—for these spots were not to be washed off, nor to be removed by the edge of the scalpel. There were two holes in the stomach, the larger very near to the cardiac end of the small curvature, and on the posterior surface: this was more than an inch in length, and about half that breadth. The other not far from the former, also on the posterior surface, about the size of a sixpence. The edges of these holes were smooth, well defined, and slightly elevated. The coats of the stomach were thin in many other spots, and im one in particular nothing was left but the peritoneum, the mucous and muscular coats being entirely destroyed. The hole in the diaphragm was through the muscular portion, where it is ‘of con- siderable thickness, and was large enough to admit the end of the finger. There was no appearance of ulceration or of pus ad- hering to the edges of this perforation of the diaphragm. There can be little doubt, I presume, that the appearances I have now described, were the effect of the solvent powers of 290 Dr. Havitanp on the Case of a Corroded Stomach. the fluids of the stomach, acting upon the solid parts in contact with them, after the death of the patient. It appears to me that the facts are deserving of being recorded, first because they confirm the observation originally made by Mr. J. Hunter, that the secreted fluids of the stomach do sometimes possess a solvent power, sufti- cient to enable them not only to corrode the parietes of this organ itself, but even the thick muscle of the diaphragm, and that withm the space of 12 hours after death. A fact which has sometimes been controverted, and which nevertheless should be distinctly known, it being of great importance with reference to the exami- nation of the bodies of persons who may have died under the suspicion of having swallowed certain mineral poisons. But secondly, the most striking part of the case is, that such an ex- tensive dissolution of the stomach should have occurred in the body of a person who had died from fever, and that one not remarkably rapid in its course. This patient had certainly taken no solid food, and but little of any description, for many days before his death, which was preceded by all those symptoms of debility which are common to the last stage of fever. The occur- rence seems irreconcileable with the generally received notions of the pathology of fever,—which disease is usually characterised by an extreme want of energy in the performance of all the func- tions, but more especially of that of digestion. In this case it would appear that the activity of this function, at least as far as depends on the solvent powers of the gastric juices, was unusually great. XXI. On the Physical Structure of the Lizard District mm the County of Cornwall. By THE Rey. A. SEDGWICK, M.A. F.R.S. M.G.S. WOODWARDIAN PROFESSOR; FELLOW OF TRINITY COLLEGE; HONORARY MEMBER OF THE GEOLOGICAL SOCIETY OF CORNWALL; AND SECRETARY OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. [Read April 2, and May 7, 1821.] Ina paper which was read before the Society in the course of last year, I stated that the Lizard district differed so essentially from every other part of the county of Cornwall, that I intended to make it the subject of a separate communication. [ do not however even attempt to give a complete mineral history of the country I am describing. This communication, like the former one, must only be considered as a compilation from such memo- randa as were made by Mr. Gilby and myself, during our passage round the coast. The Geological collection which we formed during the same part of our tour, will, it is hoped, be sufficiently complete to convey a correct notion respecting the character of the great mineral masses which successively presented themselves to our observation. Our examination of the cliff’ commenced near the mouth of the Helford river, and terminated at Loe-Bar. To the north of Vol. 1. Part II. Pp Extent of the country described, External a ppea rance. 292 Professor Sepewick on the Structure a line drawn between the two last-mentioned places, the country is composed of those slaty rocks, which I described in the former paper under the general name of Killas. Immediately to the south of this line the soil rests on the same formation. For the demarcation between the Killas, and those rocks which more im- mediately characterize the Lizard, commences at Porthalla, and passes in an undulating line, on the whole considerably convex to the north, till it reaches the western side of the promontory in a small cove called Bolerium, not far from the village of Mullyon. It will always be a matter of interest to trace the connexion between the physical structure of any country and its external form. When seen from the high granitic ridge near Constantine, the southern part of the Lizard district appears to be composed of a table-land, elevated some hundred feet above the level of the sea, and presenting hardly any indication of rupture or con- tortion throughout the whole extent of its outline. Farther north, the whole country descends rapidly from this elevated plain, and exhibits that undulating and broken surface which so often marks the presence of schistose rocks. It is at the same time intersected by a system of small vallies which generally termi- nate in the Helford river. The view of the same region from the western shore of Mount’s-Bay, is still more striking and charac- teristic. The upper surface seems so exactly horizontal, that one might almost be led to conjecture, that every projecting ledge of rock had been planed down until the premontory resembled a great artificial terrace. The peculiar dark colour and _ precipi- tous face of the cliffs are at the same time sufticient to distinguish them from any other part of the coast of Cornwall. On entering the table-land from the north, we remarked many partial inequalities im the surface which had before been hidden from the view. We found at the same time that the country of the Lizard District. 293 declined considerably on the eastern flank of the peninsula; in consequence of which, the cliffs on that side had a much less commanding elevation than those on the other. On the whole, however, the region had an aspect of dreary and barren uni- formity. The structure of the cliffs abundantly compensates for the structure ot want of interest in the interior. In many parts of the coast they ‘l rise out of the sea in one perpendicular ascent to the level of the neighbouring country. In other places, the mineral beds are cut through by deep ravines which descend rapidly to the edge of the water. The peculiar constitution of the rocks, which has favoured the excavation of these ravines, has also enabled the sea to encreach on the mean bearing of the coast. Hence, these lateral openings in the cliffs generally terminate in small coves or creeks, each of which affords a site sheltered on almost every side from the fury of the elements. We were not therefore surprised to find in such situations as these, some of the principal villages of the district. An extended coast presenting the finest natural sections must OF the table- evidently afford ample means for studying the structure of the “"° S° country. It must, however, be always difficult to trace the sepa- ration of formations through a district which presents an unbroken surface of a tabular form. But even this difficulty was on some accounts less than we had anticipated. The greater part of the table land rests on beds of porphyritic rock, and of serpentine. The presence of the porphyry is indicated by mnumerable bowlders composed of the hard nuclei of masses which were once spread over the surface. Almost with equal certainty, the extent of the serpentine is marked out by the brown scanty vegetation with which the face of the country is still imperfectly covered. The limits of these formations are therefore traced with considerable accuracy in Mr. Majendie’s map of the district, published m the P2 North of the Helford river. 294 Professor SeEpGwick on the Structure first volume of the Transactions of the Geological Society of Cornwall. Extensive masses of green-stone are also associated with the serpentine, and often so intimately interlaced with it, that it would be next to impossible to trace their line of separation, even in the vicinity of the cliffs. The task has not yet been successfully attempted: nor would much information be gained by the com- pletion of it, unless it lead to the discovery of some general law respecting the direction of the several formations, so as to enable us to connect together the phenomena presented in the opposite coasts of the promontory. From my own observations I doubt the existence of any such connexion. They were, however, almost exclusively confined to the coast, and to the order in which the mineral beds were asso- ciated in the cliffs. My memoranda are too imperfect, especially at this distance of time, to enable me to represent this order in a suite of colours on an outline map. The following notice will indeed be sufficient to shew that even such a limited task would not be very easily performed on any chart of ordinary dimensions. I have as far as possible adopted the orthography of the Ordnance Map. Still I have in more than one instance found great difficulty in describing the locality of certain phenomena in such a way as to enable any one to observe them who may hereafter visit the coast. In descending to the country which borders on the north side of the Helford river, we found, (about two miles to the south-west of Falmouth,) several bowlders of granite, containing such an unusual quantity of mica as to exhibit a slaty texture. Such a locality as this would certainly not be worth mentioning, except in a country where a formation of gneiss is almost unknown. On the northern margin of the river, near the village of Durgans, the cliffs were much contorted; but even at that distance from the central ridge, the rocks shewed no positive indication of a mechanical of the Lizard District. 295 origin. On reaching the cliffs’ near Mawnan we soon perceived that the schistose masses were greatly changed in external cha- racter, as well as in composition. The larger beds were of a coarse granular texture, and even the finer beds were dull, glim- mering, and meagre to the touch, and possessed none of that silky lustre which so generally distinguishes the Killas. These rocks were traversed by many contemporaneous veins; some composed of quartz, and others of ferriferous carbonate of lime. Some small cavities were coated with fine spicula of arragonite; and a much rarer substance, (which on a chemical examination by Mr. Gregor proved to be a subecarburet of iron) was found in thin plates among the lamin of the schist. Through the assistance of Mr. Rogers of Mawnan, we were enabled to procure a specimen of the last- mentioned mineral. Our examination of the coast afterwards led us to Nare point, on the south side of the Helford river. Immediately on landing, not many hundred feet from that headland, we found a low cliff, chiefly composed of yellow siliceous sand, containing many frag- ments of slate, obviously derived from the detritus of the adjacent district. The base of this ruinous cliff was occupied by a conglo- merate composed of quartz pebbles mixed with rolled and angular pieces of clay slate, all held together by a coarse argillaceous cement. An appearance so very unusual in this County, might have led to some mistake respecting the date and origin of these masses; had not the denudation of the coast proved beyond all doubt, that the conglomerate passes almost imperceptibly into common greywacké, which in its turn passes into, and alternates with still finer beds of greywacké slate, differing very little from those we had before remarked in the cliffs near Mawnan. As all these beds, both in range and dip, are strictly conformable with the mineral masses in the neighbourhood, they prove that some portions of the formation are decidedly of mechanical origin. Nare point and Menac- chan. 296 Professor SepGwick on the Structure On a subsequent occasion we crossed the country between Helston and St. Kevern, afterwards descended to the village of Menacchan, and from thence returned by the south bank of the Helford river. In the whole of this route we saw no rocks so well characterised as those of Nare point. We however observed repeated instances of a fine grained and somewhat ferruginous sand-stone. Masses of this kind are the constant associates of a greywacké formation, and are to be considered as examples of that rock where the argillaceous parts have nearly disappeared. The blocks of this sand-stone which were scattered about the surface, gave no ebscure indication of the true nature of some of the finer and more decomposing schistose beds which were hidden beneath the vegetable soil.* On the south side of Nare point the cliffs continued for some way to present obvious traces of a mechanical origm. We after- wards found some hard dark-coloured varieties of clay slate, and among them some beds of hornblende slate. Before we had descend- ed to the village of Porthalla, we observed that some of the last beds of the formation were intersected by innumerable veins of carbonate of lime, apparently of contemporaneous origin. It may be proper * We found several of these blocks of fine sand-stone on the hills south of Menacchan. The small rivulet which runs near the village has become remarkable as the locality of one of the ores of Titanium, which appears to exist in considerable abundance; for we found no difficulty in procuring some specimens of it during the few minutes we employed in seeking it near Tregonwell mill. The Menacchanite may easily be separated from the fine sand of the rivulet by help of a magnet, after the coarser impurities have been carried off by a streaming process, similar to that which is so often used in preparing metallic ores for the smelting house. Mr. Majendie (Geological Transactions of Cornwall, Vol. I. p. 37,) conjectures that this mineral is derived from the decomposition of the diallage rocks which form the hills to the south from which the stream derives its source. We were never able to find a specimen of diallage rock containing any substance which we could identify with Menacchanite. The subsequent discovery of that mineral at Lanarth, appears however to confirm the conjecture. It is there found among sand and other impurities, immediately below the soil, in front of the house of Colonel Sandys, and may be separated by the usual process, of the Lizard District. 297 here to remark, that the portion of the formation we have been describing, when considered on the great scale, ranges nearly east and west; dips, at a considerable angle, towards a point within a few degrees of the south; and therefore appears to pass under the north-eastern part of the great table land of the Lizard. The small valley of Porthalla is excavated in some very soft ruinous beds, whichare placed between the Killas and the formation of serpentine and green-stone, which succeeds immediately to the south. It was the first illustration in this district of a fact of very common observation ; that those mineral masses which occur at the junction of two formations, or in parts of the same formation where the mode of aggregation undergoes any sudden change, are often in an advanced stage of decomposition. These decomposing beds extend to the cliffs south of the village; but were in such a state of degradation that we could not see their immediate junction with the serpentine. They are intersected by some veins of fibrous car- bonate of lime, and are so ferruginous, that some of the fragments have the colour of hematite. Many portions of these beds are somewhat unctuous to the touch, and contain a great abundance of mica. In consequence of these characters, they have been con- founded with talcose schist, from which they ought to be separated. Immediately beyond these crumbling masses, we met with the first rocks of the serpentine formation; which extends along the base of the cliffs nearly as far as Dranna Point. They are difficult of access from above; but a boat may at any time be precured from Porthalla, which will enable the Geologist to examine their extent, the different quarries which have been opened in them, and the manner in which they support those blocks of green-stone which form the upper part of the escarpment. This serpentine is of a more homogeneous texture, and has more the character of a simple mineral, than that of any other portion of the peninsula. Its prevailing colour is dark green; and it is throughout intersected Porthalla. Serpentine of Porthalla, &e, (Crreen-stone. 298 Professor Sepewick on the Structure by many minute veins; some of which are superficial, while others penetrate deep into the mass. Nearly all of them are filled with steatite in different states of induration ; or with asbestos, the fibres of which are at right-angles to the fissures. The blocks have a splintery fracture, and break into very irregular fragments. In the planes of fracture, we sometimes observed small green-coloured radiating spicula, of which we were not able to make out the species with certainty, as our specimens were almost microscopic. From their mode of aggregation, silky lustre, and extreme brittle- ness, we conjecture them to belong to one of the varieties of Tremolite; which is the more probable, as that mineral has been found in the rocks of Clicker-Tor. Our specimens were too minute to enable us to make any observation on their chemical properties. We found the serpentine, as we expected, very untractable in the flame of the blow-pipe. After being acted on for some time, the edges of minute splinters became white, and presented a glazed surface. Fragments, which had remained some time in dilute muriatic acid, were superficially deprived of their deep colour, and exhibited a number of minute brilliant specks of magnetic iron ore. These particles are seldom brought to light by a recent fracture of the rock ; yet we think that they must be very generally diffused through it, as every mass which we examined acted very sensibly on the magnetic needle. In the whole of this formation we thought that we observed obscure indications of stratification, and of a dip, to a point between east and south-east, which brought all the beds under the low-water-mark near Dranna Point. The green-stone in the upper part of the cliffs did not present many varieties. It consisted principally of rude shapeless blocks, which shewed no distinct cleavage. Near Porthalla we however found, immediately over the serpentine, some beds which are prin- cipally composed of compact felspar; and are marked, superficially, by a number of fine green lines, in the direction of which they of the Lizard District. 299 may be separated, though not without some difficulty, into parallel laminze. These green lines penetrate into the substance of the stone in the direction of the planes of cleavage, and seem to be formed by many minute specks of granular diallage. Beyond Dranna Point the whole formation passed into well-marked green-stone slate, dipping to a point between west and south-west; a direction very different from what we should have expected. In one place we were able to descend to the beach, where we found this slate beautifully intersected with veins of fibrous carbonate of lime. Along these beds, dipping as we have mentioned, we descended to the village of Porthowstock ; and remarked on the way, no change of composition in the prevailing rock, beyond the occasional ap- pearance of small crystals of diallage, mixed with the hornblende and the felspar. The small valley of Porthowstock does not mark out the exact separation between two distinct formations; the cliffs on both sides of the cove being composed of the same ingredients. In their modes of aggregation, they, however, exhibit a striking difference : for in following the cliffs to the south, all trace of schistose texture immediately disappears, and the rocks soon after assume a por- phyritie structure; having a base of compact felspar, in which both hornblende and diallage exist in the form of imbedded crystals. In the proportion, as well as in the magnitude, of these constituents, there was such an unusual variety, that we were almost led to conjecture, that during the deposition of the mass, many conflicting principles had been in action, not one of which was long able to gain the mastery over the others. There were many large blocks, which m one part resembled a fine green-stone, and in another a coarse porphyritic diallage rock. Within the distance of a few feet, these varieties were observed repeatedly to alternate; some- times in the form of stripes; but more frequently in amorphous concretions, separated from each other by lines which were per- Vol. I. Part IT. Qe Porphyritic rocks south of Porthow- stock. 300 Professor SpepGwick on the Structure fectly defined : so that the whole mass was like a substance derived from the consolidation of heteregeneous materials in a state of imperfect mixture. When the structure of a formation is thus varied, we may always expect to find portions in every possible state of disintegration. The aspect of the cliffs confirmed this observation: for we found among them some hard unaltered beds, mixed with others which were crumbling and ruinous. The broken reef of rocks, called the Manacles, has undoubtedly arisen from this irregular structure. Had the cliffs been uniform in their composi- tion, they would probably have opposed a longer resistance to the inroads of the sea; and when worn down by the constant attrition of the waters; beds of sand, or of mud, would have resulted from their ruins. The reef in question is at the same time a monument, marking out the extent to which the sea has been able to intrude upon the ancient boundary of the coast. On the beach, and m the low cliff nearly opposite the Ma- nacles, we met with some beautiful varieties of porphyritic rock. One of them exhibited crystals of diallage in bright rose-coloured compact felspar. Large bronze-coloured crystals of resplendent diallage also abound in many low masses of rock which extend under the high-water-mark. No part of the Lizard district shews that mineral in greater perfection. Near the varieties last described, we met with a granular rock in which the porphyritic structure had entirely disappeared. It was composed of perfectly crystallized felspar and hornblende, with some diallage; and the three con- stituents were held together without any general connecting prin- ciple. The remaining part of the coast presented a repetition of the same phenomena in a less striking form, until we descended along a gentle declivity to the beach in Coverack Cove. This declivity is capped by a thick alluvial bank of sand, containing fragments of diallage rock and of serpentine, and some rolled masses of white quartz. of the Lizard District. 301] Though we had not known that the serpentine re-appeared in the next headland, we should have concluded with perfect confi- dence, from the existence of the cove, and the general aspect of the coast, that the rocks on which we had been descending, were about to be superseded by some new formation. ‘The whole strand was covered with fragments of rocks, such as have been before described, mixed with others perhaps peculiar to this locality. Some varieties arose from the mutual penetration of the consti- tuents, which in part disguised the porphyritic structure: a still larger number were characterised by the various colours reflected from crystals of resplendent diallage. Of these crystals, some were coal black, others olive green, others brown, and many were bronze coloured, and possessed a high degree of metallic lustre. In order to examine with advantage the junction of the diallage* rocks and serpentine, which takes place on the south side of the cove, it is necessary to visit this part of the coast about the time of low water. Near this junction we found a black bed, composed of hornblende, with a very small proportion of diallage and compact felspar; and in almost immediate contact with the serpentine was a rock, in external appearance very like antique porphyry. On a minute examination, its base proved to be nearly allied to the serpentine ; and the white spots on the surface did not arise from imbedded crystals; but from small nodules of compact felspar. When view- ed through a lens, they appeared to communicate with each other by very minute veins, which ramified through the whole mass. The true serpentme which succeeded, was of a dingy red colour, * By this term I understand a rock, generally of porphyritic structure, with a base of compact felspar. The imbedded crystals may be composed of any of the varieties of diallage described in works on Mineralogy. In the former paper on Cornwall, p. 145, I inadvertently used the word hypersténe, which is appropriated to that variety of resplendent diallage com- monly called Labrador hornblende. Had I been present when the impression was struck off I should have adopted the more general term diallage. The term compact felspar is used in this paper with some latitude, and includes one or two subspecies ; among which Saussurite (feldspath tenace) is not unfrequent. Q@Q2 Coverack Cove. 302 Professor SEDGWICK on the Structure and contained many small crystals of olive green diallage. But beyond the first line of junction, very fine specimens of porphyritic diallage rock re-appeared, in the form of thin alternating beds. Before we had passed the pier, we, however, observed that the porphyritic serpentine prevailed to the exclusion of the other for- mation. I may perhaps have been thought too minute in describing these phenomena. But all observations are important, which tend to illustrate the relations between the diallage rocks and the serpentine of this district. Some of the beds near the junction appeared to have characters common to both deposits; which seemed to shew that they originated in the same system of formation. In the southern part of the cove, there were some ambiguous indications of a sepa- ration into strata which had a considerable angle of inclination, and dipped to the south-east. A farther examination of the coast con- vinced us, that no general conclusion respecting the order of super- position could be deduced from such obscure indications. The mineral beds between Porthowstock and Coverack did not in general produce any sensible effect on the magnetic needle ; but a recent fracture of the blocks very often exposed a number of irregular spots of a steel grey colour, which always acted on the needle with greater or less intensity. These metallic spots some- times passed into a dull earthy substance of a brick red colour, when they ceased to act on the magnet. In those parts of the formation which abounded in the resplendent diallage, we always remarked that the finest specimens existed near the surface of the blocks; and therefore concluded, that the pseudo-metallic lustre was not natural to the mineral, but due to a certain alteration arising out of the progress of decomposition. We twice crossed the high downs* to the north and north-west * White quartz pebbles abound in the alluvium which caps some portions of the downs. of the Lizard District. 303 of Coverack. But among the many bowlders which were strewn over the surface, no varieties differed so much from those rocks I have already enumerated, as to require a separate descrip- tion. We now entered on the great formation of serpentine, which stretches from the east to the west coast, through a distance of six or eight miles, and occupies, in superficial extent, about one- third part of the peninsula. The cliffs between Coverack and the next headland, abounded in a black, and highly magnetic variety ; which in texture as well as colour, made a near approach to basalt. Its surface was much corroded, so as to resemble a rusty scoria from an iron furnace; and it was occasionally traversed by thin steatitic veins, contaming crystals of diallage. We remarked also, that the cliffs were divided by a double system of fissures, which separated the larger masses into blocks of nearly cubical form. One set of these fissures occasionally disappeared, and the masses then became separated mto many parallel beds; the local appear- ance of which has led to mistaken and contradictory opinions respecting the stratification of the whole formation. The most prevailing serpentine, as we continued to follow the line of coast, was of a dull red colour, with many shades of green, and much mixed with brown and olive green diallage. As we had not been taught to expect any appearances of peculiar interest, we hastened to the south-west, and for some time did not pause, except to admire the magnificent black promontories which seemed to bid defiance to the heavy swell which was continually rolling against them. Our subsequent experience made us regret that haste, in consequence of which we may have overlooked several interesting and important facts. After we had descended to a deep ravine, which is cut down nearly to the level of the beach, not far from Pedn-boar point; we were informed that a copper mine had lately been opened in Commence- » ment of the great serpentine formation. Copper mine. Diallage rocks, Saus- surite, Ke. 304 Professor SepGwick on the Structure the neighbourhood. We immediately ascended to the point where the works had commenced, but were not fortunate in meeting with any one in whose information we could place much reliance. A quantity of grey copper ore, mixed occasionally with fibres of native copper, appears, from what we could learn, to be intimately mixed with the substance of the serpentine: but neither to have that regularity of direction and of thickness, nor that continuity, which indicates a true vein. We obtained some specimens of the ore, which, though of no great beauty, possess considerable interest. They are composed of noble serpentine, common serpentine, stea- tite, bronzite, vitreous sulphuret of copper, and carbonate of copper; all intimately blended together. A copper mine was opened some years since near Mullyan, but soon afterwards abandoned. The geological relations of that deposit appear to have been the same with those above mentioned. In both instances the sulphuret and native copper are probably contemporaneous with their matrix of serpentine, and not continued in regular veins which are analogous to the metalliferous lodes of the county. Having ascended from the copper mine to the high table land on the west side of the ravine, we continued our hasty passage near the coast, until we reached a point where the whole character of the cliff was so completely changed, that we again descended to the most accessible parts of the escarpment, and commenced a minute examination of its features. After passing some singularly shattered beds of serpentine, we crossed a slope formed by many earthy decomposing masses, to which it is not possible to give any definite character. They were succeeded by a rock, in which compact felspar, and hornblende mixed with diallage, were arranged m distinctly undulating layers, resembling, in their mode of aggre- gation, the coarser varieties of gneiss. Among these beds were some veins containing minute specimens of scaly tale of a pearly white colour, with various shades of green. These phenomena of the Lizard District. 305 were soon superseded by diallage rocks of a more usual form; which were continued under different modifications several hundred yards to the west. In one part of the formation, the crystals of diallage disappeared, and the cliff was occupied by large amorphous blocks ef Saussurite. The hardness and tenacity of that mineral are well known ; it was not without long continued efforts that we broke off the specimens now placed in the Woodwardian Museum. On the surfaces, exposed by recent fracture, were many light green shades, which were at first supposed to arise from the presence of granular diallage, (smaragdite.) Where these shades of colour prevailed, the mineral had an oily aspect, and a crystalline texture ; and in the blow-pipe melted with a sheght ebullition, like the other parts of the rock, into a pale glass. The limits of the sub-species of compact felspar are not well defined. When crystalline form is either wanting, or imperfectly developed, the determination of species can only be established by a frequently repeated analysis; the sepa- ration by external characters being in such cases liable to error. As we expected that the rocks last described would have been succeeded by an extensive formation of green-stone, we were surprised to find them suddenly cut off by the re-appear- ance of serpentine. This induced us to retrace our steps to the former junction; which enabled us to pronounce with some con- fidence, that the whole mass (composed of diallage rock, saussurite, green-stone, &c.) was wedged in between two nearly perpendicular faces of serpentine; and that there was no indication whatsoever, of stratification or order of superposition. Having satisfied ourselves on this poimt, we continued to ad- vance, for about half a mile, on the high terrace of serpentine, until we reached the eastern side of Kennick Cove. The high cliffs are there abruptly cut off, and succeeded by a low bank of sand, occa- sionally interrupted by some broken beds of serpentine, which mark out the old direction of the escarpment. All these rocks abound Kennick Cove. Chl between Kennick Cove and Callean Cove. 306 Professor Sepawick on the Structure in very splendid crystals of diallage of a deep blood-red colour; a variety I do not recollect to have seen m any other part of the district. We felt assured, from the experience of facts so many times repeated, that this complete degradation of the cliff must have been connected with some alternation among the masses which entered into its com- position. We were not, therefore, surprised, on reaching the western side of the cove, to find a bed of green-stone porphyry resting on serpentine; their plane of separation dipping to the south-east, at an angle of about forty degrees. This junction is seen within a few feet of the poimt where the road, leading to the village of Ruan Minor, ascends from the beach. With some difficulty we passed to the south side of the projecting ledge of rock; and found, not many feet beyond the junction, the serpentine cut through by a nearly vertical dyke of granular felspar, not more than three feet wide. This dyke is of a dull red colour, and of a somewhat porphyritic structure; and has a very minute portion of earthy hornblende irregularly mixed with the base. The state of the tide did not permit us to extend our examination any farther. But the phenomena were of such interest, that we next day revisited this part of the coast at low water; and were enabled to pass along the base of the cliff, and to observe every change of structure in its component parts as far as Callean Cove. I lament my iability to convey, by verbal description, any thing like an adequate representation of the striking phenomena which rapidly succeeded each other. I shall therefore confine myself to a notice of such facts as seem to throw light on the natural history of the whole fermation. A black magnetic decomposing serpen- tine, studded all over with small crystals of diallage, of a bright golden lustre, extended about forty feet on the western side of the dyke. The dazzling effect produced by this contrast, was greatly heightened in those parts which had been exposed to the action of the waves. The attrition of the waters had worn off the earthy of the Lizard District. 307 decomposing crust, and produced a natural polish on the surface of these splendid porphyritic blocks. A small dyke of felspar por- phyry, contracting its dimensions as it ascended in the cliff, again intersected the serpentine; which was afterwards continued for more than one hundred feet, and a third time interrupted by a dyke,, about ten feet wide, in constitution nearly resembling the other two. All these dykes inclined a little to the south-east ; but the arrangement did not seem to have had any connexion what- soever with the gravitation of the several parts at their time of deposition. Beyond the third dyke, were many amorphous and nearly vertical masses of serpentine, separated by irregular planes, which did not underlie in any fixed direction. For about two hundred feet, these masses were only interrupted by one vertical bed of green-stone ; which contained a subordinate vein, three or four feet wide; filled with decomposing materials, from which we separated asbestos, steatite, and some small spe- cimens of foliated tale. Beyond this point, an extensive series of beds, composed of granular felspar, felspar porphyry, granular diallage rock, green-stone, and green-stone porphyry, occupied the cliff for several hundred feet. I have applied the term green- stone to those blocks which take their colour from the hornblende. I have, however, comprehended under the same term, many masses which contain minute crystals of diallage. The several minerals are so intimately associated, that it would be impossible to describe all the modifications of aggregation, without long, and I think unnecessary details. The green-stone was also sometimes pene- trated by a variety of indurated steatite, which was only seen in parts exposed by a recent fracture. Some rocks of green-stone porphyry possessed a high degree of beauty, from the contrast between the uniform dark colour of the base, and the brilliant white colour of the imbedded crystals. But a continual change of structure, which is always accompanied with a certain liability Vol. 1. Part II. Rr 308 Professor SEDGWICK on the Structure to decomposition, unfits all such masses for the purposes of archi- tectural ornament.* The granular felspar rocks exhibited the same varieties of structure; but were less striking from the want of contrast in the colour of the materials. All these different mineral aggregates alternated in masses, between which there seemed to be no fixed relation. They some- times mutually penetrated each other; so that one bed might be considered as a felspar porphyry, traversed by innumerable con- temporaneous veins of green-stone; while, in the contiguous portion of the cliff, the green-stone so far predominated, that the granular telspar rock was only seen to pass through it in minute ramifications. In some instances, the varieties were divided into parallel layers, represented on the face of the cliff by alternate red and black stripes. In other mstances the veins formed a system of zig-zag lines, and re-entering curves, which gave the appearance of one rock enclosed within the substance of the other. These phenomena we considered of great importance; in as much as they seemed to imitate, on a small scale, the geological relations of the successive formations we had been examining. ye) o 0-4 ; a ; P By ro eto i ae thet “yy ss vy o , ’ - . b < = Ss a ; ok, Oe =. a re F _ 7, : = pheh. j Suge > +) Ais ee G = = ‘ies seby cai ot XXVI. Geological Description of Anglesea. By J.S. HENSLOW, M.A.; F.L.S.; M.GS. ST. JOHN’S COLLEGE, SECRETARY TO THE CAMBRIDGE PHILOSOPHICAL SOCIETY. [Read Nov. 26, 1821.] To accompany the present Memoir, I have formed a col- lection of the rocks of Anglesea, which has been placed in_ the Woodwardian Museum. This collection is numbered throughout, and the number corresponding to any particular specimen is noted between brackets, whenever any allusion is made either to its locality or to the nature of its composition. I have to acknowledge my obligations to L. P. Underwood Esq., whose previous visits to Anglesea had enabled him to collect many interesting facts connected with its Geology, and to whom I am indebted for the locality of several trap-dykes. which might otherwise have escaped my observation. I believe that no good map of Anglesea has yet appeared. The map which accompanies this paper is compiled from two maps of North Wales, one by Furnival, published im 1814, the other by Evans, in 1797. The first of these furnishes, with con- desirable correctness, the relative positions of the towns and general outline of the country, but does not pretend to trace the indentations of the coast. Evans has enabled me to give some 360 Mr. Henstow on the of the latter, where they affect the geological details; but neither in this respect, nor in the configuration of the surface, could I procure any accurate information. What is here offered must be considered as a very rough approximation. As the map is rather complicated, it has been thought advisable to adopt an artificial arrangement of the different dis- tricts in each formation. By this means a reference can more readily be made to any particular place, without the labour of searching through the several detached portions marked by the same colour. A table explainmg this arrangement is placed with the description of the plates; and the references are made on the margin whenever they seem to be required. No other places are noted in the map than those alluded to in the paper. In the accompanying sectious, continuous lines are meant to represent the portions actually exhibited. The dotted lines are either such portions as were not visited, or were too much obscured by the concealed nature of the ground. Where no actual section exists, the junctions are marked by the dotted line, even where the boundary between two formations is suffi- ciently evident at the surface, and the order of collocation has been either ascertained along the coast, or cannot be doubtful from the characters of the contiguous rocks. As the sections are parallel to each other, a reference may readily be made to cor- responding portions, and the spot seen where the order was clearly established. Anglesea possesses no very striking features. Holyhead mountain, which forms the greatest elevation, reaches only to 709 feet above the sea. With this and two or three other excep- tions, the ground is low and undulating, although the surface possesses by no means an uniform character. A further descrip- tion may perhaps, with greater propriety, be referred to the details of each particular formation. Geology of Anglesea. 361 The plan of this paper will be, first to describe the stratified and then the unstratified rocks. The greater portion of the stratified rocks has suffered con- siderable disturbance, and they frequently oceur under characters very different from what they assume in their undisturbed state. Several of the details therefore, which would otherwise be in- cluded in this division, are deferred to the description of the unstratified masses; when it is to their intrusion that such phenomena can be referred. Quartz Rock. { Nos. 1. to 11-} The term, Micaceous schist, would perhaps by some Geo- logists, be made to include the whole series of the oldest strati- fied rocks. These, however, vary considerably in composition, but do not allow of separation into distinct formations, and would scarcely admit of geographical distribution, even in a map of the largest dimensions and most accurate construction. In one instance an exception may be made in favour of a variety, marked on the map as a quartz rock, which possesses certain peculiarities of structure, though it is not very remote in composition from other varieties included under the general denomination. It occupies two distinct localities, the one in the &.1- northern division of Holyhead Island, lying to the West of a line drawn from Port-Dafreth, to a point on the shore about midway between Holyhead and the mountain. The other, in the Southern Q. 2. division of that Island, occurs in the neighbourhood of Rhoscolyn, extending along the coast, and bounded by a line drawn from Borth-Wen to Rhoscolyn church, and thence about one mile further to the N.W. Im each case this rock rises to a greater 362 Mr. Henstow on the elevation than the surrounding country, and in the first-men- tioned situation forms the highest point of all Anglesea. On the summit of Holyhead mountain, and on the highest point near Rhoscolyn, the term given to this rock is strictly appli- cable, it being composed of little else than highly crystalline and distinctly granular quartz (1.) firmly cemented. There occur in it a very few minute white specks of earthy felspar. It is much intersected by cotemporaneous veins, and occasionally tinged red (3.). In other places it intermixes with a little mica (4. 5.). The quartz is often finely granular (6.), and associated with larger and distinct crystals of silvery white mica (7.8.), and apparently also with a little chlorite, the specimens assuming a greenish tinge. Such specimens strongly resemble greywacké, but their crystalline nature is still very distinct. With regard to the structure of this rock, nothing can be more deceptive than the appearance which it assumes in places . where no extensive section exists. On crossing Holyhead moun- tain, we seem to be walking over the edges of parallel strata, which dip at a very high angle towards the N. of W., the whole surface consisting of broken rugged lines, running from S. of W. to N. of E. Opposed to the small island called the South-stack, is a perpendicular cliff of two or three hundred feet in height, exhibiting the structure of the mountain in a perspicuous man- ner. Every trace of the former apparent disposition of the strata is lost, and the whole is seen to consist of broad strata, con- torted in a most extraordinary manner, often vertical in position, then returnmg with a sudden curvature, and forming repeated arches. Strings of white quartz, which occur in and between them, partake equally of these contortions, and also of others more complicated and independent of the general position of the surrounding mass. The effect is rendered still more striking by each stratum assuming a peculiar tint; the colours varying through obscure shades of green, brown, and yellow. Geology of Anglesea. 365 They also vary in texture, which causes the more compact portions to project in relief, and these in weathering exhibit convolutions in which the softer strata do not partake. They are sometimes divided by fissures, generally placed nearly at right angles to the curves, producing the effect of an artificial stone arch. Plate XV. represents about fifty feet perpendicular height of this section. Wherever a convenient opportunity occurs of examining the cliffs along the remainder of this district, the same appearance is repeated. Near Rhoscolyn the strata are very distinct, and among Q.2. them is one of a brick red, contrasted with others of a deep yellow colour. The same deceptive appearance of stratification running from the S. of W. to the N. of E., is seen in this dis- trict as well as in the former. The real structure of this rock, then, consists of a succes- sion of contorted strata rudely conformable to each other. That these were originally deposited in their present position seems impossible, and the whole bears a striking resemblance to the flexures that might be formed in a pasty unconsolidated mass, by the application of a disturbing force. The deceptive appearance resembling stratification, arises from the parallelism preserved between the scales of mica dis- persed through the mass, which causes an imperfect kind of cleavage throughout the whole district. In some cases this may readily be exhibited, even in hand specimens (6.), where the mica has a brown ferruginous aspect, coating over the whole surface produced by cleavage, with a plate too thin to be detached. These lamme occur about one eighth of an inch asunder, and on fracture exhibit an uneven undulating surface. A few other small scales of white mica are irregularly dispersed through the specimen. In some cases (4.) the lamimar tendency is distinct, with the intervention of a very small portion of mica, Vol. I. Part Il. 3A 364 Mr. HENstow on the and on a fracture perpendicular to this direction, its existence is marked by faint lines. In other instances the cleavages, sufficiently apparent on the large scale, would net be noticed in a small fragment. Here (7.) the mica which gives rise to them is dispersed at intervals over their surface, and is scarcely to be seen upon a transverse fracture. Other cleavages exist in the mountain, at much greater in- tervals than the former, which more nearly resemble natural fissures. These present smoother surfaces, and are probably the cause of large vertical fissures which occur towards the summit of the mountain, separating the rock imto rude rhomboidal and cubical masses, where quartz is almost the sole ingredient, and both the fissile texture and divisions of the strata are scarcely to be detected, though, in convenient situations, each may occa- sionally be traced. The exposed faces of these masses (2.) present an even polished surface, the effect of weathering; an action which apparently soon ceases, the fragments retaining their angles as sharp as when first fallen. Plate XVI. Fig. 1. represents the positions of four cleavages obtained from a projecting mass of curved strata (6.). A. The curved surface of the stratum. i= 9=5, 42° Rough calculations of the angles at which the 4b 20 2—3= 90 3 — 4 = 136 several planes are inclined to each other. Plane 3. is the cleavage which produces the apparent stratification of the whole mountain. It should seem that these phenomena arise from some effort of crystallization subsequent to the original deposition of the Geology of Anglesea. 365 materials, and subsequent also to the present contorted position of the strata. These facts may be illustrated by the appearance presented upon the transverse fracture of a calcareous stalactite, where the original structure arising from successive depositions, is exhibited by concentric circles, whilst a rhomboidal fracture marks the effects of a posterior crystallization. The strict re- semblance which some of the strata bear to those of sandstone, points out a mechanical deposition as the most likely mode of formation: their present structure may suggest an idea that crystalline force assisted by moisture and pressure is an agent of sufficient power to have produced the similar, but still more perfect texture of the oldest stratified rocks, without the neces- sity of imagining any previous solution of the ingredients which compose them. i Chlorite Schist. tNos. 12 to 187. } Under this denomination are included several varieties of schist, of which quartz and chlorite form the principal ingre- dients. Mica slate and clay slate also occur in the same forma- tion, but each of these passes into chlorite schist by insensible gradations, and [I could no where trace a boundary between them, marked either by a rapid change in the mineral character. or by some distinct geological feature. The varieties of clay slate included in this formation appear to consist of nearly the same ingredients as the chlorite schist, and to differ from them in nothing but want of crystalline structure. They are of various shades of green and red, and of a close texture. The variety which immediately succeeds the quartz rock is crystalline chlorite schist. There are four sections on the coast 3A2 Q. in) 366 Mr. Hewnstow on the -exhibiting their union. At the spot where this takes place between Holyhead and the mountain, there is a space of eight or ten feet in width, occupied by a rock intermediate in cha- racter between the two. At‘the spot on the beach where the change has become decisive, there occurs a breccia (9. 10.) of quartz rock, and angular fragments of talcose slate; from this: a vein issues, which may be traced on the shore for a few feet as far as the cliff, up which it is seen to rise, and become forked near the top (Pl. XVI. Fig. 2.). The vein consists of finely eranular materials (11.), with occasional patches of the breccia from which it proceeds. Possibly, the origin of this vein may be ascribed to a fissure in the chlorite schist having been filled from the subjacent rock, previous to its consolidation, by the force of the superincumbent pressure. At Port Dafreth, I could not ascertam whether any sudden change takes place; the strata of the quartz rock gradually be- -come thinner, and appear to pass insensibly to chlorite schist. the West of Rhoscolyn their boundary is more marked, the quartz rock rising nearly vertically, and the chlorite. schist resting unconformably against it. A small bay is there formed by the removal of the chlorite schist, so that its Eastern side is com- posed of quartz rock alone, where a broad stratum presents an undulating and nearly vertical cliff. At certam points of pro- jection; a portion of this is removed, which exposes the stratum next below; a similar exposition of the next takes place, and so on. The nature of this may perhaps be better understood by referring to Pl. XVI. Fig. 3. The last spot where this junction takes place hes to the South-east of Rhoscolyn, and West of Borth-Wen, where the confusion is greater than at either of the three other places. The quartzose strata intermix with the chloritic, and are seen on the beach like veins twisting among them. In some instances they even appear to occur in an inclined position above them. Geology of Anglesea. 367 From what has been said of the nature of these junctions, it may be a question, whether the quartz rock and chlorite schist are not members of the same formation. For, whilst the junctions at each of the Western boundaries of the former bespeak a nonconformity, those on the Eastern sides present a certain degree of intermixture. Supposing the quartz rock to have been once horizontal, and the chlorite schist reposing upon it, perhaps their present appearance may be accounted for upon the principle of an upheaving force acting obliquely from the East. Around Holyhead the chlorite schist is greenish grey, and ©. composed of nearly equal proportions of quartz and chlorite, beth highly crystalline, and finely granular. Sometimes it pos- sesses but an imperfectly fissile texture (12.), though in general this is sufficiently apparent (14.), and the quartz and chlorite predominate im alternate layers (15.). The scales of chlorite often form one continuous shining plate on the plane of cleavage (13.).. There are still finer grained varieties (16.), where the in- termixture of the quartz and chlorite is very uniform. These form an intermediate passage between the crystalline chlorite schist, and bright green silky clay slate. Quartz sometimes pre- dominates considerably (17.). Contortions of the most complicated nature are exhibited in many portions of this series. A large block will often present lamine waving in regular vandykes, or intermixing in a most confused manner (18.). The finer grained varieties appear to predominate through the remainder of the chlorite schist situate towards the Western side of the [sland. The general character of the same rock on the Eastern side is slightly different, though the composition is similar. Both the grains of quartz and the scales of chlorite are larger, and the colour of a darker green. Lenticular plates of Y 368 Mr. Henstow on the pure crystalline quartz, lie in the direction of the layers of chlo- rite, which pass regularly round them (19.). Strings of crystal- lized quartz and scales of chlorite intermix in irregular layers (21.), which appear to arise from the complicated contortions of thin lamine. Sometimes the rock is nearly homogeneous, the chlorite bemg dispersed through the quartz (23.). Some hard varieties occur in the neighbourhood of a rock 5. upon which there is erected a pillar to the Marquis of Anglesea, near Plas-Newydd. The basis is fine grained quartz, and dark grey chlorite (24.) closely united, and through the mass are disseminated small crystallme patches of light yellow epidote, and others of reddish mica. The epidote, in some cases, forms a considerable ingredient (25.), and the scales of chlorite are replaced by dark green spicule, probably hornblende. Mica slate occurs in the Eastern chloritic district, which lies to the S.E. of a line drawn from Pentraeth to Newborough. This is, however, always contaminated with some portion of chlorite, which may be detected by the earthy smell, even of the purest specimens. The hill West of Penmynydd, about the centre of this dis- trict, on the main road from Bangor to Holyhead, and the Llydiart mountain, at its N.W. termination, afford the most crystalline and genuine examples of this rock (26—29.). The quartz does not always present a distinctly granular appearance ; but rather constitutes a nearly uniform mass, through which the scales of mica or chlorite are dispersed. It is not always easy to determine whether mica or chlorite forms the second ingre- dient. Sometimes both are present, and sometimes the quartz is tinged green by an intimate mixture with the chlorite, and scales of white, or light green, mica are superadded. On the shore, between the Menai bridge and Plas-Newydd, Geology of Anglesea. 369 mica enters in a conspicuous manner as an ingredient of the schist, and forms large thin plates which are irregularly inter- mixed with an impure chlorite schist (30—32.). i Near Cadnant the scales appear to be intermediate between mica and chlorite, and coat over the whole surface of cleavage (33.). Other varieties afford an impure mixture intermediate between clay slate and mica slate, where the scales of mica are suffi- ciently distinct, but the basis no longer retains a crystalline character (35—37.). North-east of Bodwrog, on the confines of the granitic district, is a variety composed of crystalline white quartz m layers, coated with a talcose variety of mica of a light straw colour (38, 39.). Mica slate-occurs to the South of this spot, along the Eastern boundary of the granite, where it does not present a granular aggregate of quartz and mica, but forms a highly crystalline mass of quartz, to which a lamimar tendency is given by thin layers of mica, sufficiently distinct on the sur- faces of the laminz, and but faimtly marked by lines on_ the fracture perpendicular to them. Where the rock is weathered smooth, the quartz glistens in the same manner as a_ polished surface of crystalline marble (40.). A similar variety is found on the East of Tre-Sgawen (41.), situate towards the North-eastern termination of this district. The passage from the crystalline varieties of chlorite schist to the more earthy kinds (43—49.), and finally to clay slate (50—G64.), is very gradual. The yellow epidote, before-mentioned, also assumes a compact appearance, and runs in irregular strings among the schist (43, 44.). Some specimens of the clay slate present a silky lustre (50), and fibrous appearance. Patches of deep red occur inter- mixed with the green. a ~ _ ww 370 Mr. HENSLow on the These varieties of clay slate predominate to the North of a line drawn from Llaneilian to Llanfechell. On the coast, from .Llanrhyddlyd to the nearest pomt to Holyhead Island, they intermix with the crystalline varieties of chlorite schist, in the most confused manner. A boundary may once have existed between them, for the transition from one to the other is fre- quently abrupt, and resembles a series of patches of clay slate scattered over a ground of chlorite schist, sometimes presenting a distinctly laminar tendency, at others not a trace. The clay slate often assumes a hard jaspideous aspect (59-61.). Some earthy varieties, without a trace of fissile texture, appear to consist of an irregular mixture of chlorite and epidote, with patches of quartz, and carbonate of lime (65—69.), intimately ‘5. united. These prevail on the coast from Beaumaris to Cadnant, in the neighbourhoed of Llangaffo, and also between Trefdraeth ‘3. and Aberfraw. Rugged, projecting masses of schist, with lamine generally much contorted, are scattered throughout the tract on which . Holyhead is situate. The average bearing of the lamine is de- cidedly towards the N.E. and S8.W., and their dip in general to the N.W. In the Northern district round Llanfechell, the appearance is similar, but the laminze are not so much contorted, and they dip more to the North. Towards Amlwch they nearly regain their fermer position, and between this place and Llaneilian, the contortions are very complicated. Where the rock had been vertically and smoothly cut, in a recent excavation opposite to the pier at Holyhead, there was a decided appearance of broad strata, undulating in a manner similar to those of the quartz rock, and also a laminar structure parallel to the seams which marked the stratification. Geology of Anglesea. 371 A similar circumstance occurs in the high ground to the ©.2. North of Llanbabo; the surface is modified by the undulating nature of the strata, which rest upon each other conformably, and are from two to three feet thick. The schist is very flmty, and possesses but little appearance of fissile texture. In the most Easterly tract of this formation, the denuda- ©. >. tions inland often appear in small rounded eminences, with smooth surfaces dipping gradually on one side, and presenting a vertical face on the other. With a little attention these are distinctly seen to be stratified in the manner represented (Pl. XVI. Fig. 4.), which is intended for a section of the Pillar rock near Plas-Newydd, and an eminence immediately on its N.E., when viewed from the East. This character prevails on each side of a line drawn from Llandonna to Newborough: but on the coast, from Beaumaris to Cadnant, the dip is South- easterly. Where a separation into laminz does not exist, the scales of mica or chlorite still preserve a degree of parallelism in the crystalline varieties, which, combined with the curvature of a stratum, produces irregular but parallel lines upon its ex- posed surface, whose general bearing is still towards the N.E. and S.W. From these circumstances we may perhaps conclude, that wherever a laminar tendency is found in this formation, it was originally parallel! to the planes of stratification. And here there appears to exist a marked difference between this and the quartz rock, in which it should seem, that the laminar tendency has arisen from an arrangement of the particles posterior to the present contorted position of the strata. In endeavouring to account for any appearance exhibited by these rocks, it is necessary to take imto consideration the more Vol. I. Part Il. 3B 372 Mr. HEeNstow on the nearly homogeneous nature of the chlorite schist, when com- pared with the very variable strata of the quartz rock. In some places the chlorite schist is associated with rocks composed of heterogeneous materials confusedly aggregated (70— 94.). The schistose character is more or less destroyed, and the argillaceous basis intermixes with crystalline limestone, dolomite, _serpentine, and jasper. The largest tract of this description lies about one mile to the West of a line drawn from Llangefni to Trefdraeth. The ground is completely broken up by rugged pro- jectnmg rocks. Some of these are slaty, but in general they present a hard jaspideous aspect with contorted stripes, which mark the existence of former lamine. These intermix with homogeneous red jasper streaked and spotted with purple. The width of this tract may be about one mile, and it is succeeded on the West by contorted chlorite schist, and this by the mica slate already described, which, though confused, deci- dedly dips from the granite. A similar character prevails in the small detached strip of chlorite schist, which forms a ridge from Caint to Red-wharf bay, passing between Pentraeth and the Llydiart mountain. From Caint, as far North as Llanftinnan, this ridge is composed of green and red glossy talcose clay slate; but immediately North of Llanftinnan, it becomes disturbed, passes to a compact red jasper (58, 59.), and from hence to Red-wharf bay presents a series of broken elevations, composed of fragments of schist cemented by crystalline magnesian limestone, patches of which, as well as of compact limestone and jasper occur through the remainder of this district, intermixed with schistose materials. At its termination in Red-wharf bay, it forms a low but per- fectly vertical cliff, facing the N.W., intermediate between red Jasper and clay slate (60.), and possessing a fissile texture. Both Geology of Anglesea. 373 the common and magnesian limestone present different tints of grey, yellow, and flesh red (88—93.). In contact, and on the steep side of one of these projecting masses of limestone, is found a calcarious tuffa (94) enclosing fragments of slate, and recent snail shells. I mention this cir- cumstance as it may perhaps tend to shew, that some particles ot this limestone have been in a state adapted to solution at no very distant period, although its present position should seem to indicate, that this action has ceased. Fibres, resembling a coarse asbestos, penetrate the solid jasper (86.), and sometimes appear as small veins, (the fibres perpendicular to the sides) traversing a light porous mass into which the jasper passes. At the Southern point of the promontory at Llanddwyn, there is another partial formation of a similar nature. At one spot are numerous kernels, about the size of peas, dispersed through the schist (80, 81.). These appear to consist of a light green serpentine, in which lime predominates. Half way between Beaumaris and Garth-ferry, in the new road, there is a rude projecting mass of rock, composed of red crystalline limestone, and jasper (83.), embedded in, and inter- mixed with decomposing argillaceous materials. When passing close to this, it appears to form a high projecting point of the cliff, but viewed from the river, it is seen in reality to be situate in the bottom of a gap formed by the schist rising abruptly on either side. The clay slate, on the S.W. slope, and near the summit of Bodafon mountain, situate at the Northern termination of the middle district, passes to a compact mass between hornstone and jasper (95—100.). It is irregularly streaked with different shades of green, dull red, and grey. It fuses to a transparent frothy white glass, and probably contains a great proportion of 3B2 Q 5. M. 374 Mr. Henstow on the felspar. Indeed the red stripes actually pass from a compact nature to crystalline veins of felspar, which are occasionally associated with stripes of white quartz. Specks of sulphuret of copper are dispersed through the mass. Contorted patches, and strings of crystallised quartz and red felspar (121—123.), occur in several parts of the chlorite series, both among the crystalline and earthy varieties. In the -new road to Holyhead, S.E. of Llanfihangel-East*, I procured masses of crystallised felspar four inches cubed (123.). The colour varies from deep to light red; the structure is curved- laminar passing to compact. On Red-hill, to the South ef Beaumaris, is a bed of cry- stalline quartz (118, 119.), which is quarried for the Staffordshire ware. Other beds of a similar nature are met with in various parts of this schist. On the shore at Cadnant are broad veins of quartz, slightly contaminated with chlorite (120.). These veims pursue a direct course, and resemble trap dykes in external character. A broken flity ridge runs from the N.E. side of the Paris mountain to the S.W. of Llaneilian mountain. A fissile texture is sometimes visible, and the rock passes to a schist (111.). Its fracture and aspect vary from flimty to cherty, and its colours are different shades of light green (113, 114.), grey (115.), and red (116.). Sometimes there are small crystalline specks of quartz and felspar dispersed through the mass (117.), which give it a porphyritic aspect. It is semi-translucent on the edges and fuses to a white frothy enamel. This is, perhaps, more nearly allied to hornstone than that from Bodafon mountain. The transition to a compact flinty or cherty mass, is found in several other portions of this district (108—110.). * I have added “ East” to the name of this place, to distinguish it from another Llanfihangel situate on the Western side of Anglesea, on the confines of the chlorite schist (c. 1.) to the S.E. Geology of Anglesea. 375 Limestone Beds. { Nos. 124—182.} Limestone, in the form of veins and small patches, has already been noticed ; it also exists in distinct irregular beds in several places, which are marked m the map by an L. In the cliff, East of the island on which Llangwyfan church is situate, there is a bed of compact white marble mottled with black (124, 125.). Other beds of the same nature occur on the promontory South of Aberfraw. Also at Gwalchmai, immediately to the S.W. of the lake. As the limestone passes into the schist, it assumes a fissile cha- racter, and scales of chlorite are dispersed over the natural fractures (127.). A compact dark brown and grey limestone (131, 132.), not unlike some of the more crystalline varieties of mountain lime, has been quarried about Llanfacthlu to a considerable extent. There is an impure shaly substance associated with it (132.), somewhat resembling the shales of the coal measures. Small caverns occur in this spot, the surface of which are rugged, and contain hollow cavities resembling the exposed portions of a limestone district on the sea shore. No stalactites are to be found in them. Very considerable beds of a similar limestone extend from Glan-y-Don to Cemmes. In none of these beds was I able to find any trace of organic remains. Serpentine. {Nos. 133 to 187.} Two districts are laid down in the map, in which the prin- cipal masses of serpentine are found. These occur in beds sub- _ oO ~ 376 Mr. Henstow on the ordinate to the chlorite schist, and do not form one continuous line of rock. In the Southern district, they form a range of detached and nearly tabular masses, which extend from the N.W. of Rhos- colyn church to Llanfihangel, rising through swampy ground, and accompanied by projecting patches of schist which dip in yarious directions Pl. XVI. Fig.5. The compact serpentine passes into slaty; and sometimes a tabular mass exhibits this double structure, when viewed at a short distance, Pl. XVI. Fig. 6. The serpentine near Llanfechell is not sufficiently exposed to enable us to trace its connexion with the schist. The patches, in which it is found, have been quarried, and appear to be nearly envelloped by a hard compact variety of chlorite-schist. The purest specimens are dark green with a semi-translu- cent greasy lustre (133—135.), but the general appearance is that of a compound rock, in which serpentine and dolomite form an irregular mixture (141—151). Patches of light yellow also occur (145.). A considerable portion of that which is quarried at Llanfechell, consists of very compact dolomite, tinged green (146.) or red (148.); sometimes striped (150.); in which patches of serpentine are embedded. It is here associated with common compact limestone (152.). The red tinge also pervades some of the more slaty varieties (153—155.). Near Rhoscolyn the serpentine is associated with a heavy, compact and granular, black limestone, which does not resemble dolomite, although it will not effervesce in cold acids (161—163.). Patches and veins of beautifully saccharine and white dolo- mite are dispersed through each district.(159.). This occasionally exhibits a tendency to a fibrous structure (160.), which may sometimes be traced partially through several specimens of the serpentine. Geology of Anglesea. 377 Asbestos forms a thin coat over the natural fissures of the serpentine in the form of mountain leather. It also occurs in thin veins, of a hght green colour; the fibres set perpendicularly to the sides of the vein (156.), which sometimes seems to be contemporaneous (136.).. Some specimens appear to consist of broken fragments of this substance cemented in a paste of ser- pentine, in which the direction of the fibrous structure being inclined at different angles to the surface, a polished specimen (157.) has a beautiful appearance, different fragments reflecting the light at different angles of inclination. Pyrites occurs dispersed through the serpentine (136. 140.). Small crystals of jet black pyroxene form also a common ingredient (137—139.) ; but they are so intimately associated with the mass that they can not readily be detected, except upon a weathered surface, over which they are scattered in projecting points. The schistose portion of the district in which the Rhoscolyn serpentine is situate, varies considerably in composition. On approaching the serpentine, asbestos enters largely as an ingre- dient. This is intermixed with slaty and chloritic serpentine irregularly laminated, with carbonate of lime (170.). Other vari- eties approximate to chloritic slate (164—169.). A structure half fibrous half slaty is a common character (171—177.). Radiating crystals of dark green actynolite are dispersed through a more compact variety, the fibres generally lying on the surface of cleavage (180.). In the confused schist along the shore South of Lanfacthlu. are several appearances which approach the character of the Rhoscolyn district, though no considerable mass of serpentine is seen. This schist is sometimes a mixture of serpentine and chlorite, and in it are beds and veins of compact limestone (186.) and earthy chlorite (187.). a 378 Mr. Henstow on the Greywacke. {Nos. 188. to 264.} Under this denomination is included greywacké slate, and also a fine grained dark grey or black clay slate, which cannot be distinguished im composition from the green clay slate of the last series. It exists, however, above and also intermixed with the greywacké, in a manner which decidedly places it in the same formation. Whether this class of rocks originally succeeded the former in an uninterrupted order, or whether they were separated by a marked geological epoch, cannot be fully ascertained in Anglesea. Their characters are sufficiently distinct to enable us to trace their boundary on the map. In a few instances the black clay slate assumes a glossy crystallme appearance, approaching the character of a primitive clay slate (188—192.), which passes insensibly (193—196.) to the earthy varieties (197—207). It is often thin slaty, but the plates are not sufticiently regular to admit of their being wrought. The more common character is that of a shattery schist, break- ing into small irregular fragments. In several places this schist is intermixed with a greywacké conglomerate (210, 211.) con- sisting of angular fragments of slate, embedded in a fine black argillaceous basis, or it is composed of quartzose fragments with the addition of argillaceous matter (212—216.). The black clay slate intermixes also with a grey sandstone (221—229.) which cannot be separated from some of the sandstones of the old red sandstone. In the bed of the river at Dulas, the greywacké approaches a sandstone, and contains small embedded fragments of schist (209.). It cleaves into irregular laminzw about one inch in thick- ness, intermixed with others of a more shaly character. Between the laminz are hard nodules (258, 259.), of a concretionary Geology of Anglesea. 379 nature, composed of the same materials, which decompose in eoncentric crusts. The finer slaty laminz pass round them. On the Western side of Dulas harbour, the greywacké is intermixed with shaly black clay slate, which forms the greater part of the rocks to the S.W. Upen approaching its termina- tion towards the North, where the conglomerate sets on, and where it is mtersected by several trap dykes, the harder laminz (226.) increase in number until they form the body of the rock, with a very slight portion of shaly matter interposed. Con- cretionary nodules are also found here which possess a peculiar structure (260, 261.). In shape they appreach a spheroid, slightly flattened on one side. Upon examining the more con- vex surface, the nodules appear to. consist of cylinders of different sizes pressed together, so that an imperfectly columnar structure is the result; the termination of the cylinders on the surface forming rounded projections. Upon fracture these cylinders are found to be composed of a succession of cones, each about one tenth of an inch thick, placed one within the other, with their bases towards the convex side of the nodule. The surface of each cone is irregularly wrinkled longitudinally, and marked transversely with faint stria. One cone runs into another, and the whole is so blended together that it is impossible to detach a perfect cone from the rest. There exists a slight tendency to natural cleavage, inclined to the shorter axis of the nodules at an angle of about 45°, which is also about equal to the mclination of the conical surfaces to the same axis. The major axis of some of the larger nodules is two feet and a half, and the minor one foot and a half; and the conical structure ex- tends to the depth of three or four inches. The direction of the longer axis is placed parallel to the schistose laminee, which pass round the nodules. There is one hard lamina, fifteen inches thick, nearly vertical in position, which winds among the schist Vol. I. Part I. BUC, G.1. 380 Mr. Henstow on the in a most irregular manner, closely resembling a basaltic dyke in external character. It may be traced for some distance “along the beach, and alse up the face of the cliff. On one side it is completely stndded with these concretions, but in this in- stance their form is modified, the side next to the lamina being flat, and the conical structure extending through the whole of each. They are generally separated from the lamina by a thin seam of clay, but are sometimes firmly united to it. The con- eretions are confined to one side of a lamina. These lamine are frequently striated black and grey with all the regularity of a fine sandstone (226.). The broad one above-mentioned is uniform in character, and consists of finely granular and highly crystalline quartz and felspar, partially blackened by argillaceous matter (222, 223.). In the denuded patches of this series round Llanerchymedd, the greywacké character prevails, the base being a black clay slate, which encloses fragments of quartz and slate. More to the East and N.E. it generally consists of shattery fine grained black clay slate, which is also found throughout the strip ex- tending from Llanbabo to Llanrhyddlad. From the summit of Lianrhyddlad mountain towards Carnel’s point, a coarse grey- wacké occurs (219, 220.), intermixed with patches of conglome- rate contaming rolled pebbles. At the junction between this and the chlorite schist, on the shore to the West of Monachdy, there are irregular patches and stripes of greywacké breccia (210.) embedded in the fine black slate, and not conforming to the direction of the laminar tendency, which appears to indicate a complete intermixture of the materials at their first deposition, and to shew that the laminzee do not mark any order of super- position. The Western summit of Lianeilian mountain is a decided greywacké (212—214.); very similar in character to that on the Geology of Anglesea. 381 summit of Snowdon, in which the impressions of a bivalve shell occur. A fine grained black clay slate is found on the shore S.W. of Llanfaelog, and in the new road to Holyhead at the nearest point to Llanfihangel church. The small strip which runs from Bryngole towards the S.W. is of the same nature. There is a good exposition of the junction of the greywacké and chlorite schist, between Llaneilian mountain and the point. The line of junction may be traced on the horizontal section formed by the beach, and thence vertically up the face of the chff. The contact is between a fine gramed glossy black clay slate of the greywacké series, and a green slate of the chloritic. The lamine of each dip towards the N.W., and their union presents a most decided example of a fault. Proceeding East- wards along the cliff, we come to the coarse greywacké already alluded to. The termination of this is distinct, and it is suc- ceeded by fine green slate, which reposes unconformably upon a black clay slate in the manner represented PJ. XTX. Sect. A. This section is here referred to merely for the purpose of ex- hibitng the nature of the connection between the chloritic slate and greywacké, it will be again alluded to, and an explanation attempted of the phenemena which it presents. The junction of the greywacké and green slate in the middle of the mountain forms an undulating lme down the face of the cliff nearly con- formable to the direction of the laminar tendency. The transition from one to the other is gradual, the upper bed of green slate containing a few fragments of a rock resembling the hornstone found between the Paris and Llaneilian mountains, fragments of which are also found in the lower beds of the greywacké. _ The laminar tendency of this series is universally inclined at a very high angle to the horizon. In the central district, on which Llanerchymedd is situate, 6.1. 3¢2 382 Mr. Henstow on the the bearing of the greatest portion is from the E. of N. to the W. of S., and the dip towards the N. of W. The lamine are frequently vertical, often much shattered, and very thin. Where- ever the chlorite schist is exposed, along its Western boundary, it is found presenting the abrupt edges of its laminz towards the ereywacké. It is therefore most probable, that the fault ex- hibited on the coast, between Llaneilian mountain and the point, is carried directly across the Island. The principal exceptions to the general direction of the dip are about Dulas. In the harbour, the lamine, though much confused, dip nearly South, varying to points both to the East and West. In this case, therefore, they appear to dip from the high point of granite on the Llaneilian mountain. From Lianrhyddlad (on the Western coast) to the Paris mountain, the average bearing is more nearly East and West than in the former case, the dip still towards the North. The cliff formed by this schist to the North of Carnel’s point, presents the greatest degree of confusion and disrupture among the lamine, Pl. XX. Sect. N. To the South their dip is by no means regular, but inclines in different directions to the horizon, always how- ever at a very high angle. Around the point, and again on the shore to the West of Llanrhyddlad, it assumes a yellow decom- posing aspect. From Llanbabo to the South of Llanrhyddlad the appear- ances along the Northern line of junction are similar to those exhibited between Llaneilian and Llanfihangel. The actual junction on the coast near Monachdy is obscured by a mass of diluvium, but judging from the direction of the lamine on the horizontal section formed by the shore, the greywacké is unconformable to the chlorite schist, and therefore presents a repetition of the facts exhibited on the Western side of Llan- eilian mountain. A few yards to the West of this junction, Geology of Anglesea. 383 the greywacké passes to an unlaminated hard rock mottled with patches and veins of white quartz, and finally assumes a green flinty character similar to that of the chlorite schist at the. junc- tion. There is a small cavern in the cliff at this point, the roof and Eastern side of which is formed of the flinty portion, but the schist is again found on its Western side. The union of the two is very evident, the flinty mass reposing upon an inclined plane of the greywacké, Pl. XVI. Fig. 7. The cavern does not resemble a hollow excavated by the action of the sea, but appears as though the upper part had been bent from the Eastern side, when in a soft state, so as to form an arch. It may probably be referred to the nature of a fault, but this explanation admits of difficulty. ; On the Western side of the Llydiart mountain, there is a 6.4. black shattery clay slate, the lamine dip from the mountain at a high angle. In the road near Pentraeth their junction has been cut through to the depth of five or six feet, where they meet ver- tically, and each rock is broken and confused. Following their line of junction towards the North, the mica slate is seen, near Red-wharf bay, to rise from under the clay slate, and presents a smooth rounded surface without any laminar tendency. Be- tween this and the fine grained clay slate, is a thin bed com- posed of small angular fragments of slate (217.) and at the actual junction it also abounds in small fragments of quartz (218.) loosely cemented together. By one hypothesis this would be called the abraded portion of the two rocks produced by the upheaving of the mica slate. The greywacké may be traced as far South as Llanfihangel. A confused patch of shattery clay slate, intermixed with «.;. greywacké, is interposed between the chlorite schist and moun- tain lime, to the East of Llandonna. It does not attain to so great an elevation as either of the formations between which it 384 Mr. Henstow on the is situate, so that it is completely concealed at the spot where the mountain lime sets on (Pl. XX. Sect. P.) In immediate con- tact the chlorite schist consists of a confused talcose rock. Hardened veins of clay slate intermix with it (234—237.). The greywacké district placed to the West of the coal- measures, from Llangefni to the South of Bodorgon, possesses a different character from the rest (238—250.). That a portion of it consists of greywacké, is evident; but whether it belongs to the present series or to the last, or whether it be nét rather a confused intermixture of both, I did not fully ascertain. From Llangefni to Aberfraw, repeated instances of grey- wacké occur, to the East of the schist contaming jasper, and interposed between this and the coal measures. The schist near the coal-measures presents its abrupt edges to them, but no actual appearance of stratification can be traced, and the indica- tions which exist of a laminar tendency are ef a very partial nature. On the N.W. of Llangefni, there is a green talcose clay slate (242.), occasionally enclosing embedded fragments (243.) and seales of mica (244.). It possesses an imperfectly laminar ten- dency dipping to some point towards the West. Along its Eastern termination from hence towards the North, it assumes a hardened unlaminated character. At Llangefni it passes to a green crystalline quartz rock (245—247.), which possesses faint, but undoubted, traces of globular concretions cemented in a paste of quartz. An occasional fragment of uncrystallized matter is also found embedded. Through the centre of the Paris mountain, and in the di- rection of its ridge, there runs a bed of grey cherty stone (252, 253.) cutting through the schist partly hardened (254.), and the rest assuming a yellow decomposing aspect (255.), full of blebs and drusy cavities, which also occur in the chert. The simple minerals found in the extensive and well known Geology of Anglesea. 385 copper mines situate in this mountain, are sulphurets of iron, copper (256.), and lead.—Sulphate of barytes—Native copper in small quantities (257.), and still more rarely the sulphate of lead. There are two patches laid down towards the East of the Map, as included in this formation. Certain points of resem- blance to portions of the districts already described, seem to stamp them as members of the greywacké series. But they are found under such peculiar circumstances, that it is impossible to speak decidedly on this point. The small patch to the South of Beaumaris is seen near the top of Red-hill, and m Lord Bulkeley’s grounds, on the slope of the hill above the ferry-house. It appears to be an un- stratified mass sticking upon the steep side of the chlorite schist, which rises very abruptly from hence towards Llandonna. It consists of small angular fragments and nodules of clay slate, highly pellucid quartz, and crystallized felspar, either firmly cemented together (263, 264.), or embedded in a hardened argil- laceous paste (265—267.). The fracture sharp, and approaching the conchoidal. A perfectly flinty slate (268, 269.), with an irregular fracture is associated with it. The specimens bear a close resemblance to those procured between the clay slate and mica slate on the N.W. slope of the Llydiart mountain (216— 218.) ; differing from them only in a greater degree of com- pactness. The patch which extends from Garth-ferry, about one mile, towards Cadnant, scarcely reaches above high water mark. The chlorite schist rises abruptly on the West, and forms a high ridge of rugged rocks. The rock at the base is formed of small angular fragments of quartz (270—273.) running together and passmg to a compact mass, interspersed with specks of earthy felspar, and fragments of slate (274.). This is intermixed with a few irregular patches of black clay slate, and a compact mica- G. 6. 386 Mr. Henstow on the cious sandstone resembling those in the greywacké about Dulas. (275.) There is scarcely any trace resembling stratification, but the whole rises confusedly towards the chlorite: schist. The greywacké on the opposite coast, immediately South of Bangor, in contact with the coal-measures, seems at first sight to consist of large and small rolled pebbles, firmly embedded in a basis composed of fragments of felspar, quartz and clay slate (280—284.). Upon examination, the rude breccia thus formed is found to possess certain peculiarities of structure, which appear to throw some light upon the nature of a substance found in con- nection with it, and mentioned in Mr. Greenough’s Geological Map of England as ‘‘a remarkable steatitic rock, associated with the old red sandstone between Czrnarvon and Conway” (285, 286.). Many of the pebbles, or rather nodules, are found to indent the surface of a contiguous nodule, as though the latter had been in a soft state, and pressed by the former. The surface of one bed, from which a nodule has been removed, is often abruptly intersected by the surface of another. The surface of the nodules are found to be impressed by the angular projec- tions of the fragments which form its matrix. All the speci- mens exhibit these facts, and on the natural fracture of one of them (280.), where several contiguous nodules are cut through, they are particularly striking. These facts admit of explanation, by supposing that the nodules are in reality rolled pebbles, which have been softened im some degree, and pressed, since they were brought together. There are, however, other circumstances which appear to destroy such an hypothesis. The nodules themselves are found in several instances (281.) to be composed of angular, crystalline fragments, which are often sufficiently apparent towards the surface, but which form a compact and homogeneous flinty mass towards the centre, Geology of Anglesea. 387 resembling hornstone, and occasionally containing small pieces of pellucid crystalline quartz. Others are wholly formed of quartz, in different states of crystallization, or are slightly intermixed with compact felspar. The matrix also assumes the same cha- racters. The bed and surface of each nodule, upon a recent fracture, is coated with a ferrugmous or ochreous crust. This crust appears also in irregular patches dispersed through the matrix. From these facts I am inclined to think, that the appearance of a breccia arises from a concretionary structure impressed upon the same kind of fragmental quartz rock, (intermixed with. slate) as that which is found on the opposite shore, and that the steatitic rock to which allusion has been made, is a further result of a similar action. This rock consists of white quartz, partly cry- stalline and partly compact, formed into irregular nedules which run together, but leave several interstices between them filled with a light green talcose substance (285.). The irregular seams which produce the nodular structure are also talcose and ferru- ginous. Some of the nodules, especially the more crystalline, which attain to one or two inches in diameter, are distinctly composed of irregularly concentric layers (286.). The surfaces of several of these layers are also partially coated with the talcose ingredient, which on weathering becomes detached, and leaves a hollow space between the lamine. The homogeneous character which the whole rock must once have possessed, is evident from the numerous veins of quartz or chlorite, which traverse it, always passmg through the no- dules, however small, which they happen to encounter in their course (283, 284.). There are veins of crystalline quartz with patches composed of small fragments embedded in them (287.). How far this rock extends to the South, I did not examine; Vol. I. Part If. 3D 0.5. 388 Mr. HENstow on the but between this place and Czernarvon, the rocks to the East of the coal-measures rise high and abrupt. A specimen (288.) from them, at Moel-y-don ferry, consists of a flinty mass filled with embedded fragments of crystallized felspar and quartz, resembling the imternal structure of some of the concretions just described. It is traversed by numerous fissures, which separate it into small fragments, and these also are coated with the same ferruginous crust as the nodules. As a concretionary structure was not suspected during the investigation of these rocks, it is most probable that specimens might be selected which would better illustrate the facts of the case, than those which were procured under a different impression. From Garth ferry (on the Bangor side) as far as Aber, the dark clay slate is sufficiently regular. Immediately to the South of the ferry, it reposes upon a confused mixture of hardened clay slate of various shades (276—279.), which terminates in the nodular rock, just described. It should seem then, that this is the lowest portion of the greywacké series; but the junction with the dark clay slate is on too small a scale to enable us to speak decidedly, though, as far as it is visible, the faet of Sh position is sufficiently evident. Old Red Sandstone. {Nos. 289 to 372.} This formation varies considerably in mineral character. It occurs as a fine red sandstone, (315—321.), along a narrow strip about half a mile in width, stretching S.W. from Dulas harbour as far as Bryngole. Even here it is intermixed with shades of green (313, 314), and beds of a coarser description (290, 291.), (295—298.). A few other small patches of a similar sandstone are met with in other parts of Anglesea, but the more common Geology of Anglesea. 389 form is that of a coarse breccia. Between Llanfihangel and 0.1. Llanfaelog it is generally composed of angular fragments of slate, intermixed with quartz (289.); a character which prevails as far North as Gwindu. From hence to Lianerchymedd a coarser variety is found with pebbles (366.), which on the beach S.W. of Dulas harbour, form a breccia of the rudest description 0.5. (293.). The upper beds extend from Bodafon to the mountain- lime on its East, and consist of a coarse grit, not to be dis- tinguished from some grits of the coal-measures (299, 300.). About one mile and a half to the South of Bodafon, and a little 0.6. to the East of an extensive marsh in that neighbourhood, this grit reappears for a short space, rising through the limestone which dips from it in opposite directions. The fine red sandstone round Bodafon mountain, contains o.;. small nodular concretions of carbonate of lime (320, 321.). The strata generally bear in the same direction as the la- minar tendency of the last formation, but their average dip is not so considerable. In the largest district, there is no section 0-1- sufficiently extensive, which might enable us to ascertain their nature. In several small quarries about Llechynfarwy, we meet with a laminar tendency, often thin slaty (308.), inclined at an angle of 65° towards a point 30° to the W. of N. This direction of the dip prevails throughout the remainder of the district. Numerous edges of broad strata, nearly vertical, project between Llanfaelog lake and Ceirchiog, and generally possess a slight degree of curvature towards the S.E., which gives them the appearance of having been the bases of arches gone to decay. In the greater portion of this district, the subsoil is completely choaked with large fragments of the strata, and as the black clay slate is found on the shore to the South of Llanfaelog lake, it is not improbable that the whole consists of a rapid succession of faults, which haye completely dislocated the old red sand- 3D2 0. 5. 9 390 Mr. HENstow on the stone, and left but few patches which may truly be said to remain in sitt. In the portion between Dulas harbour and Bryngole, the dip is more gradual and reversed, being about 10° towards a point 20° to the N. of E. The strata consist of broad, ill defined beds. In descending the hill to the North of Bodafon towards Dulas, the succession is—a thick bed of green and red sandstone —thin shaly red sandstone—thin beds of green sandstone, with coarse fragments of quartz and slate, and intermixed with partial beds of finer materials—and at the bottom of the valley, the stream to the South of the bridge runs over a shattery black clay slate, the amine much confused, but dippimg upon the whole at a high angle, in a direction opposite to those of the sandstone strata: an additional reason for supposing these laminze to be wholly independent of the original order of deposition, and perhaps also for suspecting that the thin slaty beds, mentioned -In the quarries about Llechynfarway, may be of a_ similar description. In the small isolated patch to the N.E. of Llanerchymedd, the strata dip to a point 30° to the W. of N., and are inter- stratified with thin seams of black clay slate: which appears to indicate a gradual transition from the greywacké to the sand- stone. The termination of the strata to the East is remarkably abrupt, and forms the summit of a low ridge running to the N.E. They repose upon a rotten greywacké, confused and of a yellowish brown aspect (251.). In the patch to the S.E. of the Paris mountain, the strata dip 50°, and run from the N. of W. to the S. of E., intersectng the former direction at a considerable angle. It seems highly probable, that no marked separation exists between the greywacké and the old red sandstone, but that the latter merely presents an extreme case of one common formation. Geology of Anglesea. 391 The greater part of this series appears to have undergone considerable alteration since its deposition. This is particularly the case about Llanfaelog-lake, Llanfihangel, and in the out- lying masses round Llanerchymedd (322—350.). By this change both the coarse (322—330.) and fine grained (331—335.), (341, 342.) varieties assume a more compact texture, arising from an intimate union, and greater degree of crystallization, of the several ingredients. In the coarser specimens, there are traces of large pebbles and fragments (322—326.), some of which may still be detached (327.); but others have become a crystalline mass (328, 329.) passing into the body of the rock, which assumes a more uniform aspect. Towards Llanerchymedd, where the quartzose fragments predominate, the rock in some places passes to a nearly homogeneous mass of quartz (341.). Bodafon mountain affords a remarkable instance of this nature. Without minute investigation, it might be mistaken for an unstratified mass of quartz rock, rising abruptly through the old red sandstone. It is cleft by vertical fissures, breaks into rude shapeless blocks, and presents a barren shattered aspect, not unlike the quartz rock of Holyhead mountain. The sum- mit is subdivided into small elevations, some of which are per- fectly rounded and smooth, whilst others are as much _ the reverse, jagged and splintery. The sides of the fissures which traverse the quartz, are coated with red oxide of iron (345.). The quartz has a flinty semi-crystalline aspect, and is of different shades of red; or mottled with white, grey and green (343—346.). These pass to less homegeneous varieties (347.), in which may be seen distinct traces of a finely granular structure. Others exhibit a coarser texture (349, 350.), and contain quartzose frag- ments, but so intimately associated with a basis of the same nature, that they cannot always be detected upon a_ recent fracture. On a weathered surface, however, they are left oO. 392 Mr. HENSLow on the projecting, owing to the removal of a portion of the matrix in which they are embedded. Small patches of fine white pulve- rulent matter, probably silica, (for it is neither fusible nor soluble in acid) are dispersed through the solid rock (348.). This is the oldest formation in Anglesea, in which I found traces of organized bodies, and these were in three separate localities. At one spot, there are three projecting masses of rock, which rise at a few hundred yards to the South of the -tenth milestone from Holyhead to Bangor. It is in the mass furthest from the road, and at its Eastern end, that the fossils are to be seen (351—364.). Another locality is where a small rock protrudes in the centre of a field immediately N.E. of Liechynfarwy church, forming the angle between the roads to Llanerchymedd and Llantrisant (365—371.). The third spot is in a quarry on the Eastern side of the road from Llechynfarwy to Llanerchymedd, and about one mile from the latter (372.). The appearances alluded to, consist principally of the im- pressions of bivalve shells. In the two Jast-mentioned locali- ties, the bed is coarse, and partly composed of nothing but rolled quartz pebbles in a gravelly sand (366.). The only species found here appears to be an anomia. It somewhat resembles the common pecten varius (on a small scale), except that the indentations which cause the winged hinge, are in the present instance wanting. The general size is about half an inch wide, but some reach to a full inch. In the first-mentioned locality, the basis of the rock is a finer grained and more com- pact green sandstone, with partial traces of a slaty structure. Besides the shell already mentioned, it contains the impressions of some other species, which are not in general so well preserved as the former specimens. Among them is one somewhat similar to the last, but the striz are finer and much more numerous. Another is a smooth elliptical shell (352, 353.). A little of the Geology of Anglesea. 393 shelly matter still incrusts some of the casts (354.), which are in general coated over with small scales of mica. Mountain-Limestone and Coal-Measures. {Nos. 373 to 421.} A distinction is made, in the colouring of the map, between the mountain-limestone and the coal-measures, although each is supposed to be a member of the same formation. The term coal-measures is meant to include the upper portion, which con- sists of grit, sandstone, shale and limestone, interstratified with each other, and occasionally containing subordinate beds of coal. In the most Westerly and principal district of this forma- M. 1. tion, no attempt was made to investigate the exact boundary between the two subdivisions, which would have required more time than a subject of such comparative unimportance seemed to merit. All that is intended in the map, is to note their general limits, and by this means mark their relative position to each other. The lowest portion of this series consists of a thick bed of stratified limestone, generally of a compact texture, and dark grey colour (373, 374.). It varies also through different shades of brown (376—379.). Sometimes it is composed of a mass of broken fossils firmly cemented together (380, 381.), each of which being formed of calcareous spar, the specimen often assumes a crystalline appearance (382.). Magnesian beds occur subordinate to these. In Priestholme island they are composed of pearl 3 spar intermixing with the common limestone (384, 385.). Chert and chalcedony are also embedded in the limestone, even in the lower strata, before the grit sets on. Some large madrepores (419, 420.) from Priestholme Island, are partly composed of dark limestone, and partly of translucent bluish M. 394 Mr. Henstow on the chalcedony, passing to chert. In some places the cellular coat- ing is chalcedony, and the imterior, which was limestone, has disappeared. Black and white chert, intermixed with the limestone (386.), is more abundant after the grit has made its appearance, and quartzose pebbles are occasionally intermixed with the strata (387.). The limestone becomes more argillaceous (388, 389.) and slaty, and finally interstratifies with clay shale (390, 391.), coarse erit (393—396.) and sandstone (398, 399.). Specks of coal are dispersed through the grit and sandstone, .in Red-wharf bay, North of Llanfiinnan, and at the Menai bridge (400—403.). To the West of Llanfihangel East, and also to the East of Trefdraeth, coal is worked. At the former place I was informed by the overseer of the works, that it is fonnd in three strata, the thickest of which is two yards, the next one yard and three quarters, and the last four feet. It is peculiarly glistening, and does not contain organic remains. In some clay shale from the pit I observed an impression resembling a flag- leaf. . In the limestone, on the Western side of Red-wharf bay, there are large cylindrical holes filled with grit which formed a por- tion of the superincumbent stratum, and which is probably the lowest bed of the coal-measures. The partial removal of this stratum has exposed the top of these eylinders, in several of which the action of the sea has worn away the outer crust of the grit, and the hollow in the limestone presents a smooth surface. This circumstance appears analogous to what occurs so frequently in chalk countries, where holes of this description are filled with gravel and sand. Upon this grit is imposed a bed of shale four feet thick, from which the sulphates of iron and alumina effloresce. This is succeeded by a thick bed of grey limestone, traversed by Geology of Anglesea. 395 nodules of jet black and white chert, and filled with the im- pressions of shells—then a brown sandstone 15 inches—clay shale 4 inches—erit three feet and a quarter—clay shale three Inmches— brown sandstone 14 inches—dark impure argillaceous limestone to the top of the cliff. This enumeration will serve to shew the nature of the alternations which take place among the strata of this formation. In the grit, immediately South of the Menai bridge on the Cernarvonshire side, there is a peculiar rock, which appears to form a vertical vein, but the ground is too much covered up to ascertain the poimt. The basis consists of a coarse heavy red sandstone, containing fragments of quartz, which are also coloured deep red, and through the mass are dispersed numerous small round and oval nodules, from the size of a linseed to that of a small pea (404.). These nodules are composed of concentric crusts of a yellow and brown earthy matter, and exhibit a smooth surface coated with the red oxide of iron. They pro- bably result from some action similar to that which produced the steatitic rock before-mentioned, and which is found at no great distance from this spot. To the North of Bodorgan, at the Southern extremity of the largest district, the grit is composed of small angular fragments of quartz studded with white earthy specks of carbonate of lime (398.). These specks are frequently arranged in parallel lines, inclined to the direction of the strata: an effort, if so it may be called, to produce a fissile texture in a coarse substance where it could scarcely have been expected. The particles of the quartzose fragments appear likewise to have undergone a partial re-arrangement; for several contiguous fragments possess a common cleavage. Some of the strata are traversed by fissures, which separate them into blocks, and these decompose in concentric crusts marked by different shades of brown. This compound structure is represented Pl. XVI. Fig. 8. Vol. I. Part I. 3 E M. 2. M. 1. +o. alte 396 Mr. Henstow on the The only exposed portion of this formation which succeeds the old red sandstone conformably, lies to the E. and N.E. of Bodafon mountain. From the Eastern side of Dulas harbour, the mountain limestone stretches towards the S.W. forming a low precipitous cliff, which bounds a marshy ground on its West, as far as Llangefni. From Llangefni to Bodorgan the junction takes place along the side and near the top of an elevated ridge of schist. On the Eastern side of the river, there is another ridge of schist which extends from Caint to Llanddwyn. Between these two ridges there lies a flat swampy ground, beneath which is the only explored coal district of Anglesea. About midway between Pentraeth and Bodafon, the lime- stone and grit attain to a considerable elevation. The strata are either nearly horizontal, or dip from 5° to 10° to various points between 5° and 40° to the E. of 8S. Their direction is there- fore N. of E., and S. of W. Hence the line of junction from Dulas harbour to Bodorgan must intersect the strata, obliquely to their course, from the lowest upwards in a regular succession. Between Llangefni and Bodorgan, several opportunities occur of examining the nature of their union with the adjacent rocks. In every case the limestone and grit are confused and broken. The schist also rises in a shattered and abrupt manner, dipping from the limestone wherever there happens to exist any ten- dency to a laminar structure. In some places it projects in peaks surrounded by the limestone or grit, at others it encloses small patches of the latter. Immediately S.W. of Llangefni there is a quarry of limestone, on the brow of the hill rising from a marshy ground, which presents a section exhibiting the confused nature of this junction, Pl. XVII. Fig.1. The strata are nearly horizontal, but sensibly bent upwards next the schist on either side. In a small elevation lately cut through in forming the new road from Bangor to Holyhead, on quitting the marshy ground, the limestone and shale dip towards the S. E. Geology of Anglesea. 397 at an angle of 45°, and exhibit a fault by which they are up- heaved towards the schist. Similar appearances to these may be seen in different quarries between this spot and Trefdraeth. At Bodorgan, an isolated patch of schist rises through the confused and dismembered grit. Between the grit and schist there is a loose breccia chiefly composed of angular fragments of the latter (392.), which may be accounted for in the same manner as the breccia interposed between the clay slate and mica slate on the N.W. side of the Llydiart mountain. On the W. of the Pentraeth river, near Red-wharf bay, the limestone dips 45° to the W. of N. In Pentraeth their in- clination reaches as high as 80°. At Caint they are confused, broken, and sometimes contorted without fracture, Pl. XVII. Fig. 2. But on proceeding to the West of these several places, we find the strata nearly horizontal. They present several low cliffs, which are not so abrupt as those on the Western boun- dary of the series. These facts seem to indicate, that the grit and limestone terminate abruptly against the schist to the East, with the intervention of a few hundred yards of disruptured and broken strata. East of Llandonna, the limestone presents an abrupt chiff ™- to the sea, the strata are nearly horizontal, their edges re- posing on an inclined plane, the summit of which is chlorite schist; but at a lower elevation we find the shattery schist before-mentioned, so that the limestone overlaps this in the manner represented Pl. XX. Sect. P. Large fragments of the limestone strata are scattered over the steep sides of the chlo- rite ridge between this spot and the sands of Red-wharf bay. This district extends to the East as far as Priestholme island. Near the pomt to the North of Penmon, some coarse grit sets on. The dip is towards the E. of N. at no great angle or in- chination. 3E2 M. 2. 398 Mr. HENSLow on the The appearance presented by Great-Ormes-Head* P]. XVII. Fig. 3. on the opposite coast of Czrnarvonshire is such as might lead us to expect a continuation of the same strata at that place. I did not visit the spot, but it is evident from the opposite coast, that a considerable indentation Northwards takes place towards the Eastern extremity of the Head. This must expose each stratum at some point further to the North than its Southern boundary, where (owing to the former dip towards the E. of N.) it will be seen at a less degree of elevation, which would give rise to the deceptive appearance of bason shaped strata exhibited towards the East of the figure. In the tract lying to the S.W. of Bangor, the strata belong to the coal-measures. A little to the South of the spot where they first appear, there is a large limestone quarry, which lies beneath some beds of grit and shale, and is possibly a portien of the series belonging to the mountain-lime. The strata here also dip towards the E. of S., and are in contact on the East with greywacké, and the older rocks dipping also, when lami- nated, in nearly the same direction. The line of junction is obscured by a cultivated valley. They are bounded by mica and chlorite slate on the West. The fossils found in this formation are anomie, madrepores, trilobites, and others identical with those from the mountain- lime of England (405—421.). ~ Magnesian Limestone. { Nos. 422 to 474.} To the South of Plas-Newydd park, there commences a series of limestone and sandstone strata, which overlie the coal-measures, * This place lies to the East of Priestholme island, but is without the limits of the Map. Geology of Anglesea. 399 and appear to belong to a separate formation. They are better exposed, and may be examined with greater convenience on the opposite coast. The lowest portion consists of rolled fragments of limestone, cemented together by argillaceous and calcareous matter (422.). To this sueceed beds of limestone, grit, and sandstone, varie- gated with deep yellow and brick red colours. Their order from the bottom is, feet 1. Yellowish brown sandstone (424.) ......csecceccseeccesess 5 2. Compact and crystalline grey limestone, with saad | Sac : ao dD and cavities filled with yellow ochre (423.) ........6.- Sompbluishistiales. (tHia Wed) je ioxe syeie ote Var j0_0.cielersvel alejorefaieresaloveroia)ojejete 4. Compact flinty dark grey sandstone, nearly a pure quartz rock, which separates into rude distinct masses coated by a deep yellow ochre (444). This inter-\ | 49 mixes with, 5. Fine red, striped sandstone, (442.), containing frag- ments: of broken tossils ((436.) ¢ -.jaisjccejsae ops oe oaiee The two last beds contain variable portions of lime. 6. Thick bed of compact red limestone (427, 428.), which has been quarried to a considerable extent. Upon this are imposed other strata of a similar nature to those described, whose order of superposition it is not so easy to ascertain. They are all more or less characterised by con- taining beds of bitter spar (437—440.). The fossils are generally in an imperfect and shattered state, intermixed with pebbles (434, 435.). The more perfect madrepores are frequently traced in deep red upon a light ground (432—434.). These fossils appear to have belonged to the mountain lime, and may be considered as embedded fragments in the present formation. Although I found no good section, by which any positive 400 Mr. Henstow on the information might be obtained of the nature of collocation be- tween this series and the last, still it seems probable, that they lie unconformably to each other. Immediately South of Plas- Coch, the black limestone and shale of the coal-measures dip towards the E. of S., and a few yards to the East of this spot, the red beds of grit are found dipping in a contrary direction. On the opposite coast, to the East, of Plas-Newydd, the lowest strata of the red grit and limestone dip gently to the E. of S., apparently conforming to those of the coal-measures; but sud- denly their dip is considerably increased, as if they were repos- ing upon the brow of a steep hill. As the red beds appear to be entirely wanting over the marshy tract in which the coal of Anglesea is situate, it is not unlikely that in the present place they overlie a considerable body of that formation. New Red Sandstone. { Nos. 475 to 482.} Over the strata of the last series, there occurs a rude mass of argillaceous and sandy materials (475.) intermixed with large fragments derived from the older rocks. The basis is occasion- ally consolidated into thin lamine, giving rise to a_ slight appearance of stratification. The whole is of a deep red colour. Tt commences a little South of Moel-y-don ferry, on the East- ern side of the Menai, and extends as far as Czernarvon, but in Anglesea it forms only a small hummock on the North of Tan-y-voel ferry. Both this and the preceding formation ter- minate to the E. and W. in the same abrupt manner as the coal-measures. Many of the fragments dispersed through it, are of a large size, and generally consist of quartzose materials. Some are of grit in which the fragments run together and pass to a homo- Geology of Anglesea. 401 geneous quartz rock (476, 477.), others approach chert (478.) or hornstone (479—481.), and nearly all are tinged red. A fault in the coal-pit near Llanfihangel East, contains fragments of quartz intermixed with red sand (482.), and may probably have arisen from a portion of this formation having filled up a fissure. Trap Dykes. Although these form but inferior members among the un- stratified rocks, still it seems advisable to commence this part of the account with their description ; since the facts which they present tend materially to confirm the conclusions drawn from phenomena observed in more extensive districts, apparently of similar origin. As their number is very considerable, and as a detailed description of each would only occasion repetition, a selection has been made of those which are accompanied by appearances of the greatest interest. Where their course is sufficiently exposed, it is represented on the Map in the usual way, by a particular colour placed between parallel lines. But there are many slight indications of trap, where it is either impossible to trace the course of the dyke, from the concealed nature of the ground, or it only presents an isolated mass rising through the schist. In these cases, the locality is marked by placing a (7) as near the spot as pos- sible. References of this description will seldom guide a second person to the dyke, but may serve a different purpose, and shew the number and relative situation of the places where trap was actually met with. Mr. Underwood has submitted specimens of several of these dykes to the examination of Professor Cordier, whose method of analysing the basalts, and accurate knowledge of their mine- M. 2. 402 Mr. Henstow on the ralogical composition, is too well known to need a comment. I have enriched this account with his description of several specimens, and it will be seen that, judging merely from their composition and texture, and unacquainted with the geological phenomena by which they are accompanied, he supposes them to be of volcanic origin. The dyke with which I shall first commence, is seen on the shore, immediately South of Plas-Newydd, between two and three hundred paces from the landing place. The phenomena with which it is accompanied are exhibited on a scale sufhi- ciently large, and are besides so unequivocal in their nature, that the results deducible from their examimation may be con- sidered as of the greatest importance towards the elucidation of this class of rocks. The width of the dyke is 134 feet, and it cuts perpendi- cularly through strata of shale and limestone. The strata on each side form an abrupt cliff, about 15 feet high, but the dyke affords a gradual ascent to the top, arising from the effects of its decomposition. ‘On the beach also the same cause has con- tributed to produce a slight excavation worn by the action of tide. In fact the decomposition is generally so far advanced, as to render it capable of bemg dug with a spade, and it is applied to the same purposes as coarse sand, being mixed with mortar as a material for building. There is no absolute certainty of its further extent Westward, than about forty or fifty feet, through which it may be traced in Plas-Newydd Park, where some person, perceiving its nature to be different from that of the surrounding strata, has been at the pains of driving a level up it, in the fruitless hopes of discovering a metallic ore. The substance of this dyke is ‘‘indubitable basalt, com- posed of felspar and pyroxene.” Prof. Cordier. Geology of Anglesea. 403 The effect of decomposition probably does not extend to any great depth, for the workmen soon find the rock become too solid to be used for sand. In the more solid parts the texture is rather coarse, and the proportion between the felspar and pyroxene variable. Sometimes these are nearly equal (483.), but in general the latter predominates considerably (484—486.), and the rock is of a dark colour. Sometimes the basalt is very compact (486.), and does not exhibit any signs of decomposition. Carbonate of lime is very generally disseminated through every part. In the midst of the friable and decomposing portion, there occur irregular, concretionary nodules (487.), about the size of walnuts, which consist principally of felspar rudely crystallized in one mass, through which are dispersed small crystals of black pyroxene. These nodules are remarkably tough. The dyke is found on the opposite shore of the Menai, but there is no section by which an opportunity might be afforded of obtaining any satisfactory conclusions. Similar varie- ties of basalt occur in five other places, which bear so nearly in a straight line with the two already mentioned, that it is highly probable they are all portions of this dyke, but the concealed nature of the ground renders it impossible to obtain certain information of the fact. The nearest spot is in a quarry, on the North side of the road which runs South of Plas-Gwyn to Llanddaniel, and at 170 paces East of the bridge over the Braint river. Two other places, within fifty yards of each other, were lately exposed upon digging the foundation for the new road from Bangor to Holyhead. They lie to the South of Llanfi- hangel-East, on the brow of the hill to the East of the marshy ground over the coal-measures, and the basalt is continued along the steep Northern bank of a small stream which here crosses Vol. 1. Part IU. 3 F & 404 Jr. HENSLOow on the the road, and then runs parallel to it on the South. The last spot is on the opposite side of this marsh, about a quarter of a mile to the 8.W. of Llanchristiolis, at a spot called Tin-rath. The cliff which bounds the dyke, at Plas-Newydd, is com- posed of clay-shale and argillaceous limestone. On the Northern side it may conveniently be divided into four parts. The lowest consists of thin, dark, shaly beds, containing a considerable quantity of lime. In it are found the impressions of small anomiz common in this formation (490.). Upon approaching the dyke, the shale undergoes various degrees of alteration. At fifteen feet from the contact, it forms a compact bluish grey mass (492.) with spots of a fainter colour. The substance of some fossils, which coat a natural cleavage, puts on a crys- tallme appearance. In contact, it is of a very compact nature ; bluish-green (493.), with irregular streaks of a lighter tinge, fracture conchoidal; not easily scratched. Several small crystal- line plates of carbonate of lime are dispersed through the mass. The shaly structure disappears, in a great measure, upon ap- proaching the dyke, but a partial separation into parallel beds is still evident. Owing to the variable nature of this shale, we cannot expect a gradual passage from its original aspect to the indurated part. Together with the hardened variety just mentioned are patches (at five feet from the dyke) of yellow clay, slightly indurated (494.), and intermixed with fossil shells composed of crystallized limestone (495.). At two feet, a light yellowish clay forms the basis, through which are dispersed patches of dark brown; and black specks are placed in the centres of small spherical ker- nels of crystallized carbonate of lime (496.). On a weathered surface these are removed, and the rock is indented with the small cavities which contained them. It is in the next portion, above this, that the more striking Geology of Anglesea. 405 phenemena, on this side of the dyke occur. At fifty feet from the dyke it consists of a soft, dark coloured plastic clay shale, which separates into thin laminz (498, 499.). On approaching the dyke this becomes, at thirty-five feet from the contact, rather indurated (500.). At ten feet, it forms a cherty mass (501.), with a splintery fracture, and of a buff colour, associated with patches and streaks resembling black flint (502). In it are patches of highly crystalline limestone. It scarcely admits of being scratched by the knife. In contact, it is a hard porcellanous jasper, which readily cuts glass, extremely splintery, and the fragments fly from the hammer in all directions, producing an appearance similar to the effect of fracture on unanealed glass (503—509.). Its colours are light and dark grey, sometimes intermixed in irregular stripes parallel to the former position of the shaly structure. Sometimes the light grey assumes a reddish tinge (505.), and the specimen somewhat resembles a piece of fine porcelain, and is translucent at the edges. The fracture is_ splintery- conchoidal. Another variety is dull greenish-brown, and more nearly resembles a piece of chert (504.). The impressions of broken shells, generally anomize both large and small, occur in the interior of the solid mass (507, 508.). It does not divide into parallel beds except in one or two instances, where the natural divisions are formed by a crust containing impressions of these anomie. This crust has a feru- ginous aspect externally, but possesses a resinous fracture and lustre within, and effervesces in acids. There is a circumstance which generally takes place on the surfaces of small natural fractures or flaws, dispersed through hardened shale in contact with this and other dykes in Angle- sea. On such surfaces there are small glittermg plates (503.) from less than 5 of an inch to full + of an inch squared. 3F2 406 Mr. HeNstow on the Different plates may be exhibited by presenting a surface at different angles of inclination to a ray of light, so that it seems to be entirely composed of them. These plates cannot consist of one uniform facet, for in that case the fracture would present an uneven surface of re-entering angles. Each plate is — therefore formed by reflection from an aggregation of several minute polished facets, inclined at a common angle to the sur- face in the same plate; but this angle in different plates must vary. The third division of this cliff consists of a dark argillaceous limestone about three feet thick, containimg impressions of shells (488.). This is also capable of a partial subdivision into thin lamine, but does net possess so decidedly a shaly structure as the two last, neither is the proportion of argil so great. In contact it forms a remarkably tough, close-grained mass of a speckled dull green and brown colour (489.). A similar argillaceous limestone in contact with the dyke, on the opposite coast, is not so much changed. It assumes a hard character without much alteration of colour, and becomes finely granular and crystalline. Through it are dispersed specks of pyrites and impressions of shells (497.). Above this we find another bed of clay-shale (510.), whose contact with the dyke is not exposed on the Northern side. It constitutes the main body of the low cliff to the South. This shale is also partially converted to a flinty mass similar to that already described. The flinty portions lie in irregular strings of various thickness, parallel to the position of the beds, and the rest of the shale assumes a confused appearance of crystalliza- tion and globular structure. The perfect crystals which occur intermixed with the mass, present two decided mineral varieties. A description of the specimens, selected for the Woodwardian Museum, will perhaps be the best method of enabling others to judge of their nature and mode of formation. Geology of Anglesea. 407 (511). Shale, of the consistence of hard clay, passing on one side to a globular structure, of a dirty white, earthy aspect. The globules, from one-tenth to three-tenths of an inch in diameter, run into each other, and are harder than the rest of the mass. It effervesces rather briskly for some time, without falling to pieces. (512). The whole possesses a concretionary structure. The concretions white, some of the same size, but harder than in the last specimen. These are interspersed with smaller globules, about the size of mustard seeds. The interstices are filled with a soft brown clay. . HEeNstow on the tion is in their smoother surface, and more angular fracture: but this will frequently escape observation where a moment’s inattention may carry us across one at a single step. It will be seen in Pl. XVIII. Fig. 4. at a and 6, that there is a deceptive appearance as though these dykes terminated abruptly downwards; but in these cases the course may be considered as tending upwards, obliquely to the plane of the paper, when placed vertically, and commg from some point behind it. The deception arises from the face of the cliff in- tersecting the inclined side which bounds the furthest extent of the dyke to the East, a fact which I verified in one instance, by removing the schist from below. There is a marked dis- tinction in this apparent mode of termination, and that which is seen in Pl. XVIII. Fig. 2. at a. In the latter case, the fissure containing the basalt, gradually becomes thinner towards the end, in the former, the entire width is preserved. The specimens examined by Professor Cordier, from this neighbourhood, were ‘dolerite. The pyroxene very evident, with fer titané.” ‘* A basaltic lava, but more felspathic than the others. The felspar has the filamentous character of volcanic products, re- sulting from the crystals being flattened. To see this, two sides of the specimen must be placed at right angles to each other.” The appearance of the flattened crystals is common to seve- ral of the very compact dykes, and may be seen in some parts of the one near Cadnant, towards its Western termination. In the small dyke Pl. XVIII. Fig. 2. a, these crystals are few, and extremely minute (642.), the basalt being more remarkably fine gramed and tough, than any other which I met with in Anglesea. An evident intermixture often takes place, between the trap and the surrounding schist, along the line of junction, which Geology of Anglesea. 423 sometimes resembles the gradual blending of two different colours in a mass of striped jasper (642.). Small portions of schist are embedded, near the sides of the dyke, which intermix with the trap, and modify its appearance and composition (641, 643.). The schist, in contact, has frequently a blistered aspect, with irregular cavities and flaws (644, 645.). Dykes immediately to the North of the Menai bridge. “« Dolerite with superbe pyroxene.” Prof. Cordier. **Felspar and pyroxene with crystals of pyrites (665.). The circumstance of having crystals of pyrites, though rare in streams of basalt, is easily accounted for in a dyke. The extended sur- face presented to the air by the stream, would enable the sulphur to evaporate, but in the dyke it is condensed. Perhaps also the dyke never came to day.” Prof. Cordier. The presence of pyrites, frequently in the form of distinct crystals, is common to most of the dykes in Anglesea. Dykes to the South of the Menai bridge. ‘* Basalt very rich in felspar.” Prof. Cordier. ‘Basalt poor in pyroxene.” Prof. Cordier. On the South-western coast near Aberfraw. “ Plus travaillée than the other dykes—blistered.” Prof. Cordier. The passage to the earthy traps is perfectly insensible, and portions of the most genuine basaltic dykes are frequently ot this nature. At Llangwytan— Waceké endurcie. It is full of green earth, and ought to become cellular m an acid.” Prof. Cordier. Most, if not all, of the varieties of trap included in the dykes of Anglesea are occasionally amygdaloidal and porphu- ritic. Some contain nodules of crystallized carbonate of lime, which do not always exhibit the usual appearance of a rhom- boidal cleavage common to the whole nodule, but possess ar C.3. 424 Mr. HENstow on the uneven fracture, although the specimen is perfectly pellucid, approaching the character of saccharine marble (658, 659.). Embedded crystals of felspar are more common in the compact and earthy traps (661.), than in the crystalline (660.). The compact portions, of several dykes, assume a confused appearance of crystallization, and break into small fragments, a few inches in diameter, bounded by perfectly smooth surfaces. Several of these form accurate rhomboids (676.), others exhibit this figure modified by a diagonal cleavage (675, 677.); but it generally happens that their figure is less regular, and that no two faces are parallel to each other (678, 679.). The effects of decomposition frequently extend to a considerable depth in the dyke, and we find each of these fragments, partially decomposed, presenting a portion of unaltered trap in the interior (680). Granitic Districts (including the Granite and Greenstone). { Nos. 789 to 844.} A rock formed of quartz felspar and mica, is found in each of the tracts laid down as including the granite; but the mineral character of the whole district is far from uniform. In the Southern portion, about the neighbourhood of Gwalch- mai and thence towards Llanerchymedd, the surface is broken by small detached rugged eminences, rising through a marshy ground, which is bounded East and West by an abrupt termination of the stratified rocks. The external character of all these protrudmg masses is so very similar, that it is impossible to calculate beforehand on what may be the real composition of any one in_ particular. On examination they are found to vary extremely ; one may be a true granite, the next a pure quartz, the third a greenstone, &c. Geology of Anglesea. 425 A better notion of this variety of composition may be obtained by referring to some of the specimens which were procured in the neighbourhood of Gwindu, within four miles North and South of the Inn. Among the granitic rocks the quartz is generally white ; the felspar is either white (724, 725.), brownish yellow (726, 727.), or flesh-red (728—737.); the mica silvery white (725.), black, or green (730—732.). In the latter case it becomes associated with chlorite, which in many places entirely supersedes it (739, 743.), tinging both the quartz and felspar of a greenish hue (740.). The chlorite also mixes with hornblende (741—744.), and these two substances frequently predominate so much as nearly to obliterate the quartz and felspar (753, 754.). Sometimes the felspar, of a flesh red colour, forms the basis of the rock, and the other ingredients are sparingly dispersed through it (728, 729.), (745, 746.). In other places, chlorite and mica supersede the rest (752.), and we then find only patches and veins of felspar and quartz, completely enveloped in the more trap-like rock (750, 751.). A beautiful variety is composed of dark green horn- blende crystallized in large plates, and intermixed with irregular patches of white felspar (755.), which however frequently assumes a greenish tinge (756.). At the same spot there are patches of crystallized carbonate of lime penetrated by yellowish green spiculz of epidote (757.), a substance pretty generally diffused through the surrounding rock, either in vems (758.), or interlaminated with the hornblende (759, 760.). It occurs also in compact masses, intermixed with quartz (761.). Patches of genuine basalt are scattered throughout the district, completely enveloped by the granite, and possessing the same character as the trap found in the dykes of various other parts of the Island (762, 763.). All these varieties are highly crystalline; but with them we find rocks of another description, whose composition is more 496 Mr. HENstow on the nearly homogeneous. They possess a flinty aspect approaching to hornstone, and are of various shades of white (766, 767.), grey (768.), or green (769.). Here and there a crystalline structure is exhibited, or a few crystallme specks lie dispersed through the compact base. This variety in the mineral composition is chiefly confined to those parts of the district which present a broken rugged outline. In the elevated ridge which stretches from Gwalchmai to Lanfaelog, the character is more uniformly granitic and the surface of the ground unbroken. The quartz and red felspar have not the distinctly granular appearance which they gene- rally assume in substances of this nature, but are imtermixed with a more pasty aspect than usual (734.), and the lustre frequently deadened by a superabundance of the oxide of iron (737). The Northern district occupied by the granite is not so variable in its character; the usual appearance being that of an regular and large grained intermixture of quartz, white felspar and silvery mica. A greasy lustre is frequently given to portions of this granite, which apparently arises from its being contami- nated by a considerable quantity of tale (790—801.). By referring to the Map it will be seen that there are two districts which consist entirely of greenstone. The general cha- racter of the rocks which compose them, is so nearly allied to some parts of the granitic district to the South of Gwindu, and their relation to the surrounding strata so very similar, that little doubt can exist of their belonging to the same formation. The district to the North of Llanerchymedd is marked by rugged, and rudely shaped masses, projecting through the surface. These extend from a spot about one mile to the North of the town, on the West of the road to Amlwch, towards the North of East, and pass a little to the North of Llandyfrydog. A pre- Geology of Anglesea. 427 vailing character is that of an hornblende rock, composed of large crystalline plates interlacing in various directions, and cemented together by a little felspar and carbonate of lime (689.). The felspathic cement gradually increases (690.), till it forms a greenish compact basis, through which the crystals of horn- blende are dispersed (691.). Other varieties present a more perfect intermixture of these two ingredients (692 — 694.), with the addition of small shining plates, apparently diallage (695.). White felspar and dark grey hornblende form also a finely granular compound, which resembles some varieties of the trap included in the dykes (696, 697.). Distinct, green crystals of hornblende are embedded in a basis of crystallized white felspar, and it is worthy of remark, that some of these crystals have been broken, and the fragments lie in different directions, surrounded by the felspar, the edges of their corresponding ex- tremities tallying with each other (699.). The greenstone to the East of Llanbabo is not well ex- hibited. Its characters are precisely the same as the former (712, 713.). Having proceeded thus far with the description of the granitic districts, before any attempt is made to establish the probable history of the rocks which they include, it may be here re- marked, that the phenomena which accompany them are so very similar to those presented by the trap dykes, that we can have little hesitation in ascribing their origin to the action of the same cause. This circumstance is premised, that the object may at once be seen for which any particular appearance, tend- ing to establish the theory of their common origin, is recorded. From what has been stated, it will readily be conjectured, that the theory alluded to is that which ascribes the formation of these rocks to the influence of volcanic action, and it must be perfectly unnecessary to recapitulate the arguments which have Vol. I. Part I. 31 428 Mr. HENstow on the been urged by others in its support, and drawn from appear- ances similar to those described under the details of the several dykes enumerated in the preceding part of this paper. They are such as will suggest themselves to every one, and some speak so strongly in its favour, that it seems scarcely possible for the most sceptical on this head not to allow the force of their evidence. In addition to those arguments which may be deduced from such phenomena, it may be stated, that the number of these dykes must be very considerable; for many of those enumerated have become exposed, by mere accident, in the different quar- ries opened for the purpose of repairing the roads, and it may reasonably be expected that there are very many others concealed beneath the cultivated surface, as well as several which have escaped observation. In no one instance does it appear, that they are in any way associated with a superincumbent mass of the same nature, and indeed the great variety of mineral cha- racter which they assume is alone a strong argument against supposing them ever to have formed members of a common body. None of the veins and fissures which contain them appear to terminate downwards, whilst on the contrary it should seem, that, in some instances, their termination upwards has been clearly ascertained. In others, there is every probability, that a considerable part of their course lies beneath the rock with which they are in contact at the surface. There is one argument brought against the igneous theory which may be supposed to derive weight from the investigation of Anglesea. This is, that the trap, if projected in an ignited state, would have produced results of a more uniform character, whereas in many cases it should even seem that it has pro- duced no alteration whatever upon the surrounding rock. Now, one decided example of alteration should speak more plainly Geology of Anglesea. 429 towards establishing the nature of these dykes than any nega- tive argument which might be drawn from those cases in which no such alteration is found to take place; for we know it has been determined by experiment that certain rocks, when fused, will afterwards return to their former state, if placed under those very circumstances which most probably must have existed at the time of their fusion. This fact may be illustrated by referring to the phenomena which accompany the dyke at Plas-Newydd. The alteration which there takes place in the surrounding rock, although of the most decided nature, is by no means uniform, even in the same stratum. On one side, we have a mass of soft clay shale assuming a hard jaspideous character, whilst, on the opposite side, this alteration is partial, and the rest puts on a crystalline structure; and intermixed with this we also find some portions in an earthy state. That the whole is not crystallized may readily be accounted for, by supposing a superabundance of calcareous and argillaceous particles, above the requisite pro- portion necessary for the formation of the crystals; still, how- ever, it shews us that in the very spot where the change is the most marked, it is yet possible for some portion to remain unaltered. If the granite of Anglesea be justly ascribed to the same class of rocks as these which compose the trap dykes, it should seem equally certain, that some portions of it must either have resulted from the fusion of the surrounding strata, or else have been considerably modified by an intermixture with them, and consequently that it is more recent than any with which it is associated. At the South-western termination of the Northern granitic district, there is a patch of old red sandstone. Although the whole of this appears to have been considerably changed from 312 O. 4, 430 Mr. HENstow on the its original character, and to have assumed a more compact and crystalline structure, yet at the furthest point West from the granite, it is evidently composed of sandstone mixed with coarse breccia containing pebbles of quartz and slate (784.). The strata run directly towards the granite, and several oppor- tunities occur of examining the alterations which they sustain. Upon approaching the granite, the crystalline character increases, the materials become more firmly cemented, and pass into each other (785—788.), till at length, without any abrupt transition (789.), the strata merge into a crystalline rock (790—796.), in which the nodular concretions of quartz have scarcely lost the aspect of pebbles (790.). Felspar, frequently of a talcose or steatitic aspect (792.), forms the principal ingredient of the re- sulting granite (798—801.), which contains large, distinct concre- tions of quartz and mica. Through it there are also dispersed irregular masses of impure adularia, which cleave with great facility (797.). At the spot where the sandstone has first assumed the decided character of a granite, there occur a few specks of galena (796.). A repetition of similar appearances may be traced. along the boundary between the old red sandstone and South granitic district. Towards its Northern termination, immediately to the West of Llanerchymedd, the granite is found in the bottom of a valley which passes between two portions of the sandstone. At the last spot where its effects are distinctly marked, there is a quarry im which the rock may truly be said to constitute the intermediate passage between the two. The remains of a coarse sandstone are evident in some parts of the quarry, and the passage (777—780.) to a perfectly crystalline mass (781.) distinctly visible. The whole shatters into small fragments, and a con- siderable portion is converted to yellow ochre, which also coats over the natural cleavages in the more solid portions. A vein Geology of Anglesea. 431 of crystalline quartz, one inch and an half thick, traverses the decomposing, porous portion of the rock (783.), and with it are intermixed irregular stripes of chlorite, which penetrate the quartz, and are so disposed, as to form rudely parallel lines inclined to the sides of the vein at an angle of 45° (782.). Where the chlorite is not present, the quartz still preserves a tendency to cleave in this direction; a circumstance which bears a striking resemblance to a fissile texture, oblique to the disposition of a bed. About one mile to the South of this spot, there is one of the localities already pointed out, for the fossils in the old red sandstone. The quarry in which they occur is on the confines of the granite, and the neighbouring mass of rock, which pro- jects a few yards to the East, is in fact completely crystallme. Some parts of the quarry also approach the same structure, and a gradual obliteration of the fossils is the consequence. The impressions are coated with oxide of iron (369.), and as the matrix loses its original character, their position becomes marked only by an irregular cavity, retaining a partial impression of some portion of the cast (370.), till at length the spot where they formerly existed is simply traced by a shapeless ferruginous patch (371.).. Having found the impressions of anomie in the midst of the altered shale at Plas-Newydd, and even where it had assumed a crystalline structure, it did not seem improbable, that some traces of these shells might also be met with in the neighbouring granite, derived from the altered sandstone. But the search proved fruitless, and indeed we can scarcely expect that any such can exist. The less compact state of the sand- stone, and the character of the resulting rock, so much more uniformly crystalline than that of the altered shale, would render it less likely that any appearance of this description could be preserved. It may seem singular that I should have searched in the granite for a fossil, as a circumstance likely to increase the oO. 432 Mr. Henstow on the number of arguments in favour of its igneous origin. But what has been stated may serve as a caution against forming any hasty conclusion to the contrary, should such a discovery be ever made. The altered appearance of the old red sandstone, which lies to the West of the Southern granitic district, was remarked in the description of that rock. The facts which have been just stated seem to point out a cause adequate to the expla- nation of this circumstance, and there are besides some other particulars connected with its history, which tend materially to -confirm this supposition. From the lake at Llanfaelog, to Lianfihangel, the surface is swampy and uncultivated, through which many masses of bare rock project. Several of these present an aspect so highly crystalline, that at first sight a question might easily arise, whether we were not still in the midst of the granite, until a second blow from the hammer clears up the doubt, by exposing a mass of hardened sandstone. In short, the state of this sandstone appears to be only a degree removed from the more crystalline structure of the granitic district which lies to the North of Gwindu. Near Llanfihangel church, on the South, and in the midst of an assemblage of rocks distinctly composed of the brecciated materials, we find a mass of trap (804, 805.). The felspar is sufficiently distinct, and forms the chief ingredient in the basis of the rock, through which a few embedded crystals of the same mineral are scattered, giving it a slightly porphyritic character. The whole assumes a greenish tinge, but the colouring substance does not appear to be of a very crystalline nature, and is pro- bably chlorite. This intermixes with a confused aggregation of hornblende and diallage (807, 808.), passing by insensible shades to the breccia which surrounds it. In the very midst of the more crystalline portion we find small patches possessing a trace of the original character not quite obliterated (809.), Geology of Anglesea. 433 The rock often passes also to a light green felspathic mass, spotted or mottled with dark green. Several such appearances occur in the form of smooth nodules, already alluded to as embedded pebbles, but I strongly suspect that they must be of a concretionary nature, similar to those in the steatitic rock near Bangor. The whole of the exposed rock to the S.E. of Lianfihangel church, has more nearly the external character of a mass of trap than of any other substance. It possesses no traces of stratifi- cation, but is rent by fissures which divide it into prismatic and rhomboidal blocks. One of these is so singular in its appearance, that I have given a sketch of it, Pl. XVIII. Fig. 5. It resembles a basaltic column lying upon its side, and is com- posed of felspathic and chloritic matter, mottled and blended together (810, 811.). On the N.W. of the lake near Llanfaelog, there are several instances of a similar passage of the breccia to a trap rock (812.). This apparent conversion of the schistose breccia, belonging to the old red sandstone formation, to a trap rock, seems more distinctly to connect the greenstone with the granite, and to point out a common origin for the two, which also receives additional confirmation from the examination of the tracts occu- pied by the former rock. The patch of greenstone to the North of Llanerchymedd is surrounded by greywacké, the basis of which is a glossy black clay-slate. In the immediate vicinity of the greenstone, this greywacké is curiously affected; the embedded fragments of schist assume a yellow decomposing tinge, whilst the quartz becomes more crystalline (701—705.). The next step presents a rock of decomposing aspect, through which are scattered traces of crystalline structure, resulting from an imperfectly formed hornblende, mixed with felspar (706— 710.). The latter is distinctly marked, but the crystals of thre 434 Mr. HENSLow on the former bear a strong resemblance to fragments of slate. They are frequently broken transversely, a circumstance which it has been stated also occurs in the genuine crystals of the same substance in the neighbouring hornblende rock, It does not appear very evident why hornblende should here result from the fusion of schist, and that pyroxene should be a constituent of the dykes which are presumed to be of similar origin. There is, however, one point of difference between them. In the dykes, the fused matter appears to have been injected into a fissure of the superincumbent rock, but in the present instance the alteration has taken place without any progressive motion. There are other rocks, in this part of Anglesea, of which hornblende is an ingredient, where the transition from the schist to the trap is not marked by a distinct line, and where a similar explanation might be given of their origin. Near the summit of Llaneilian mountain, towards the South, we find masses of this rock, protruding through the greywacke, in which the hornblende is sometimes well crystallized (715.), and at others scarcely to be detected (716.). At the bottom of the cliff, to the N.E. of the highest point of this mountain, a similar rock is found, but the hornblende is not so distinct as in the former case (717.). Upon ascending the cliff the appearance of a dyke is gradually lost, and it scarcely exhibits a structure sufficiently crystalline to separate it from the schist (719—722.). Through this dyke there run several veins of quartz, which also abound in the surrounding rock, a fact which I do not recollect witnessing in any other dyke in Angle- sea. Irregular strings of reddish compact felspar, of a cotem- poraneous character, are also found in it (718.). The schist in contact is a fine grained clay-slate (723.), and in the dyke there occur seyeral strings, or thin lamine, of clay-slate of the same nature. Geology of Anglesea. 435 Patches of glossy crystalline clay-slate are also found among the hornblende rocks to the North of Llanerchymedd. On the South side of the road from Llanerchymedd to Llechynfarwy, before quitting the former place, there is a quarry which partly consists of clay-slate, and partly of hornblende rock and greenstone, similar to that on the North of the town. Considering the extensive influence which must have been exerted to form the granitic districts, we might also expect to find the rocks in their vicinity modified by its action. Where the South granitic district joins the older rocks to the East, it is not so easy to ascertain when an alteration has taken place; since we are not always certain of the original cha- racter which these rocks themselves possessed. In some places, however, there appears to be little doubt of the fact. On the sea-shore, immediately South of Llanfaelog lake, the confusion and alteration impressed upen the schistose rocks are of a very marked description. They vary in composition and aspect at every step, and have scarcely a trace of fissile tex- ture remaining. There are slight appearances of a crystalline rock, resembling some varieties in the granite round Gwindu (824.), but the general character is that of an homogeneous flinty mass of different shades of green (825, 826), grey (827.), and brown (828, 829.). Since all these will fuse before the blow- pipe, though with difficulty, they seem to approach the cha- racter of a hornstone. One of the specimens presents a sin- gular fact, and as the experiment was several times repeated, there can remain no doubt of its accuracy (827.). It forms a dirty white mass between compact and_ finely granular, and seems to consist principally of quartz, but contains also a little lime disseminated through it. A few faint streaks of green matter, resembling chlorite, are intermixed with the substance of the stone. When the specimen is exposed to a red heat, the Vol. 1. Part Il. 3K 436 Mr. HeNnstow on the green veins immediately turn jet black, assume a laminated texture, and strongly resemble pyroxene. It then fuses, with some difficulty, to a black glass. There are some portions of a more compound nature (830.), intermixed with the homo- geneous rock, which appear to be composed of small fragments of quartz firmly embedded in a paste of the same substance (831.), and others in which the embedded fragments are so loosely set, that they might be detached (832, 833.). With these are associated patches of blistered schist, gradually blending itself with the compact mass (834.). Proceeding Eastward along the shore, we find traces of a laminated texture making its appearance. The whole rock still forms a flinty mass, but the smooth surfaces exhibit parallel contorted lines of obscure yellow upon a green ground (835—837.). This character prevails until we arrive at Llangwyfan, after which the rocks become more regularly schistose. There are numerous trap dykes scattered throughout the whole of this district (813—823.). These vary considerably in character; some form a _ perfect basalt highly charged with crystallized carbonate of lime, tinged green (813.), but the generality, are of a more earthy nature, and vary through different shades of dark grey and green. In texture and com- position, they often resemble clay-slate so closely, that a detached specimen might easily be mistaken for this rock (820—822.). They are generally porphyritic, containing embedded crystals of felspar, and alter their character completely, and suddenly, through different parts of their course. Many of them are seen to ter- minate in both directions, and some form mere bumps rising through the hardened schist, and are themselves again inter- sected by smaller dykes of a different character. There are several other appearances of a similar description impressed upon the schist near the granite, both in the neigh- Geology of Anglesea. 437 bourhood of Llanerchymedd, and of the North granitic district. In one spot, about a mile and an half to the N.E. of the Paris mountain, it is intermixed with vems of a granitic description. They consist principally of dull mica, which is associated with felspar, quartz, and a steatitic substance (802.). The surrounding schist assumes a hardened aspect (803.). Perhaps we may also ascribe the flinty beds dispersed through- out the schist, to the West and S.W. of this spot, to a change of character impressed by the granite. If so, the chert, which traverses the Paris mountain, will rank with them; and the de- composing schist, which accompanies it on either side, must be ascribed to the more partial influence of the same action. The external character of this mountain is very striking. On the N.W. it slopes gradually from the top, but to the S.E. it pre- sents a precipitous side, from which project the edges of the schistose laminz, to all appearance as sharp as though they had scarcely sustained the action of the weather since they were first placed in their present position, although the materials of which they consist are in a very decomposing state. Although the circumstances detailed above seem to indicate that the granite and greenstone have been derived from the fusion of the stratified rocks in their neighbourhood, still, the marks of violence and disturbance which accompany them, tend further to shew, that some portions of these rocks have been protruded from below. The structure of Llaneilian mountain affords an interesting and important illustration of this fact, and forms a prominent feature in the Geology of Anglesea. In PI. XIX. Sect. B, we have the greywacké dipping from the granite on the West, and succeeded in order of superposition by the chlorite schist, dipping also in the same direction. Upon referring to Sect A, which is exhibited on the coast, the greywacké is found to be terminated abruptly to the West by a vertical 3K 2 438 Mr. HENstow on the fault, which explains the apparent anomaly of the superposition of the older rock. This greywacké also reposes unconformably upon some black clay-slate of the same series. The explanation which suggests itself is, that the granite has removed the grey- wacké from its original position, and that the lowest beds of the portion removed, repose towards their termination North- wards upon the superior beds of the same series. The hollow tract which runs across the mountain, between the summit and the highest point of granite, is composed of glossy black clay- slate, intermixed with patches of quartzose rocks, which project in irregular masses. The lowest portion of the removed grey- wacké is a green clay-slate, which may have formed either the lower beds of the greywacké series, or the upper of the chlorite schist. It is much shattered; a circumstance which causes the alluvial matter to collect, and consequently the line of demarca- tion, between it and the black slate below, is distinctly marked by the vegetation which covers it. A deep ravine runs from the Northern termination of the granite to the sea-shere, from which part of the removed portion may have been derived. The most Westerly, and therefore the uppermost beds of the disturbed greywacké, are composed of the same black clay-slate as that upon which the lower beds repose unconformably. Another circumstance which seems to have resulted from the intrusion of the granite, occurs to the East of this spot. Descending from the Eastern summit of the mountain towards Dulas harbour, the ground forms a gradual declivity, broken by projecting hummocks. These, as well as the rocks on the shore, consist of a most heterogeneous mixture (857—867.). Hardened sandstone (863—865.); clay-slate, which shivers into sharp hard fragments, each tarnished with a glossy coat (866, 867.); large masses of quartz and schist, rudely intermixed and bound together by a basis of fragmental matter (859—862.). Geology of Anglesea. 439 Among this confusion there are patches of purely crystalline rock, consisting of red felspar, quartz, and chlorite (857, 858), which appear to assimilate this tract to some portions of the district round Gwindu. This conglomerate is seen, at its Northern termination, reposing upon the clay-slate, which assumes a com- pact quartzose aspect (852.), and contains concretionary nodules (851.). In one spot it consists of crystallme quartz, through which are dispersed numerous fragments of slate (853.). These fragments have, in many instances, sustained an alteration in character, and become blended with the quartz. On a weathered surface they decompose, the quartz assuming a cavern- ous appearance. By referrmg to the sections it may be seen, that the in- trusion of the granite in the two principal districts, has produced effects in opposite directions. In the Northern district, the dislocation and tilting of the schist lies on. the West, the older members having been upheaved and brought to the surface on that side of the granite, whilst on. the East we find the newer rocks comparatively in a state of repose. In the Southern dis- trict the reverse is the case,- and the upheaving of the mica and chlorite schists has taken place to the East, the old red sandstone being in contact to the West. Havmg examined the phenomena which accompany the granite and trap, the next endeavour will be to explain certain appearances where a cause seems to have been exerted, similar to that which preduced these rocks, though without the actual protrusion of any volcamic product. A reference to the localities noted on the Map will be sufficient to shew that there can scarcely be any part of Angle- sea which has entirely escaped the influence of an action so general as that which formed the numerous dykes seen bursting through so many parts of its surface, and we may naturally G.1. 440 Mr. HENsiow on the expect that some places must exhibit traces of this influence, where the results are more equivocal than those already de- scribed. At Carnel’s Point, the appearances so closely resemble those exhibited on the confines of the granitic districts, that it seems scarcely possible to ascribe their origin to the action of a dif- ferent cause. Upon approaching the Point, a little to the North, the greywacké is associated with a rock, which at the time I mistook for a conglomerate of rolled pebbles, but which is com- posed of concretions running together in the same manner as the steatitic rock near Bangor (870.). This passes to a perfectly crystalline mass formed of quartz, felspar, chlorite, and mica (871—878.), in which the traces of a concretionary structure are sometimes evident (871.). In other places the transition to the earthy rocks which are contiguous, is sufficiently marked (880.). The character of the surrounding schist is singular. In part it appears to have sustained no alteration, but the greater portion assumes a yellow decomposing aspect, and in some places it passes to a hard semi-jaspideous mass (883, 884.). Rather large crystals of quartz are found attached to compact masses of the same nature, which are dispersed through these rocks (881, 882.). Another spot, which has strongly the appearance of having been subjected to some violent disturbing cause of the same nature, occurs at Moel-y-don ferry, on the Czrnarvonshire side of the Menai. The strata of limestone and grit, belonging to the magnesian limestone, are found confused, tilted, and, for several yards, disposed in a most disorderly manner. The alteration which the substances composing the strata undergo, is also of a marked description. The sandstone, which in other places is red, becomes white (452.), hardens, and passes to a compact siliceous stone, resembling white flint (453.). In some places it approaches the common dark chalk-flint (454.). It is Geology of Anglesea. 441 intermixed with crystallized limestone and bitter spar (456—462.), and some portions of the specimens are in a pulverulent state. The red limestone either becomes very compact and crystalline (463—467.), passes to a brown bitter spar (469.), or assuimes the character of a nearly arenaceous white limestone (470.). About the centre of the disturbed portion, the materials of the several strata are mixed together (471—473.), presenting a singular scoriaceous appearance (474.). The dyke which crosses the Menai at this spot, intersects the line of the disturbed portion at right angles. A little to the North of the ferry where the disturbance ceases, the sandstone, which is fine grammed with small pebbles dispersed through it, appears to have been hardened and turned white (451.), and is here quarried as a whetstone. The present disposition of the stratified rocks, from the greywacké upwards, seems strongly to favour the hypothesis which ascribes the formation of the granite and trap to volcanic action. If we suppose the different portions of each formation to have been once continuous, their original bearing appears to have been from N.E. to S.W., and their dip towards the S.E. In every case they terminate with great abruptness against the older rock, and near the junction they frequently appear to have sustained some violent action. The singular transition from old red sandstone to quartz rock, on the summit of Bodafon mountain (p. 391.), resting upon hornstone derived from the clay-slate (p. 373.), appears to be the Northern termination of some volcanic influence which extended Southwards to Llangefni, and from thence, towards the S.W. to Aberfraw. Hand specimens cannot convey a just idea of the appearances exhibited in a quarry of this hornstone. The irregular intermixture, which takes place in the different shades of colour, strongly resembles the result afforded by ~ 442 Mr. HEeNstow on the agitating the ingredients of a semi-fluid mass, and the solid horn= stone passes to a blistered schist. Proceeding Southwards, we come upon a peculiar variety of chlorite schist, in which the quartz forms a homogeneous basis, and the chlorite or mica lies disposed in parallel lamine (p. 369.). At the spot where this occurs furthest to the North, it forms a mass of rock scarcely protruding above the surface of the swampy ground on the East of Bryngole, and is not easily accessible. From hence, some patches of schist are found which pass to jasper, and others to the same translucent, green quartz rock, with a glo- bular structure as that at Llangefni, (p.384.). In an inter- mediate state, the schist has a fragmental aspect, the fragments drawn out into strings (243.). At Bodorgan, we find a mass of basalt and greenstone protruding in the midst of the small patch of schist which rises through the grit (p. 397.). It should seem therefore, that the disturbing force, which cut off the further extent Westward of the mountain limestone and coal-measures, has acted upon the old red sandstone, clay-slate, mica-slate, and chlorite-slate, and that the respective results are quartz rock, hornstone, homogeneous quartz with scales of mica or chlorite, and jasper or translucent quartz rock. To this list may be added another substance, equally singular. To the West of the spot where the chlorite schist passes to quartz rock, North of Llangefni, the grit rises abruptly to the East of the river, and through it there protrudes a rude tabular mass of white quartz rock (868.), which may be supposed to have re- sulted from an alteration of the grit, (see Pl. XX. Sect. H). The district lying North and South of a line from Gwalch- mai to Llangefni, will, by the above supposition, be included between two distinct modifications of volcanic action, which were probably united beneath it. The result, as might be expected, is the utter confusion and complete alteration of the Geology of Anglesea. 443 intervening rocks, the appearance of which has been already described (p. 372.). Among other phenomena which tend to confirm this hypothesis, is the occurrence of several large hum- mocks of white quartz, scattered over the surface in the neigh- bourhood of Trefdraeth (869.). They consist of sandstone passing to quartz rock, and are possibly the remains of grit, from the strata belonging to the coal-measures; and if so, it is equally possible, that the hard compact limestone found with the jas- per may have been derived from the same source. A similar explanation will apply to the other districts of this nature, and particularly to the jaspideous ridge which extends from Llanftinnan to Red-wharf bay, (p. 372). There are a few circumstances connected with the history of the serpentine which render it probable that this rock is the result of an action impressed upon some of the limestone beds, dispersed through the chloritic districts. The general outline of each of the serpentine districts, pre- sents an aspect of great disturbance, want of stratification, and other appearances usual in a trap formation. At the Eastern termination ef the Southern district, the transition from the chlorite schist to the old red sandstone is abrupt, and on the Eastern side of the line of junction we meet with a trap rock, apparently derived from an alteration impressed upon a portion of the latter formation, a description of which has been given, p. 432. The connection between serpentine and greenstone Is equally remarkable at Llanfechell. The patches of serpentine run S.W. from the principal quarry, and with them are found some which seem intermediate between that rock and green- stone (589—591.). Others pass from a compact and crystalline variety of the latter; including veins of serpentine and epidote, to a more earthy rock, with a greasy chloritic aspect, contaming but few crystals of pyroxene. The chlorite schist in the neigh- Vol. I. Part I. aul; w 444 Mr. HENStow on the bourhood is much hardened, especially in the high ground to the S.E. of this spot. Veins of epidote are found where the rock approaches the character of greenstone (592—596.). To the West of the pool at Gwalchmai, the chlorite schist is intermixed with limestone, and a dyke intersects the rock close to a small bed of this mineral. The natural fissures of the dyke are coated with an unctuous substance resembling serpentine (584.), and some portions of the dyke itself have the earthy chlo- ritic aspect of the greenstone in the serpentine at Lilanfechell (585.). Veins of crystallized carbonate of lime are found in it, and when the primitive rhomb is extracted from them, two of its faces appear finely striated parallel to the longer axis (586— 588.). Conglomerates. { Nos. 885—913.} There are two tracts laid down in the Map under this deno- mination, one of which has been already alluded to, as its connection with the North granitic district appeared to afford an explanation of its origin. The other, which occurs at the most Northerly point of Anglesea, possesses a few characters m common with the former, but there is no evidence to shew that it has resulted from an action of a similar nature. It consists of a most confused intermixture of chlorite schist, grey- wacké, clay-slate, large masses of quartz, and limestone, with several traces of trap, Pl. XVIIT. Fig. 6. To the East of Cemmes, the cliff consists of yellow ochre and steatite (895.), both of which are there quarried as articles of commerce. ‘They evidently result from the decomposition of the schistose rocks, and the gradual passage from the solid to the earthy state is distinct (892—894.). The large masses of quartz, which are dispersed through the Geology of Anglesea. 445 district, have sometimes an homogeneous aspect (889.), but im general they retain the traces of a coarse breccia (885—887.), or sandstone (888.), from which they seem to have been de- rived. In the midst of the steatite there are some which possess a porous earthy aspect (896.). The limestone, which intermixes with this conglomerate, is the same as that about Llanfacthlu, and belongs apparently to the chlorite schist (906—913.). It does not appear to have sustained any alteration, except in one or two places where it is in contact with some trap (908.). In one spot to the West of Cemmes it consists of small irregular black globules firmly cemented in a basis of rather lighter colour, which at first sight resembles the traces of an organic structure (909, 910.). In another spot where it possesses the same shaly character as at Lianfacthlu (912.) there are slight appearances resembling an- thracite (913.). Although the ingredients which compose this conglomerate cannot be said to lie in distinct strata, still there are several places where a rude kind of alternation is visible, somewhat like the arrangement which often takes place m a mass of diluvial matter. These rudely formed beds indicate a considerable dip towards the North; from which it should seem, that the con- glomerate succeeded the chlorite schist in order of superposition, and that the present inclined position was impressed upon each at the same time. Diluvium. { Nos. 914—980.} Deposits of diluvial matter are scattered over each of the chlo- ritic districts which bound Anglesea to the West. They occur in the form of very obtuse conical hills, the diameters of whose bases varies from about a quarter to half of a mile, and the 3L 2 446 Mr. Henstow on the surface, in consequence, presents a succession of gentle undu- lations clothed by cultivation, the subjacent rock being exposed only in the hollows between them. The internal structure of these hills is exhibited in several places along the coast to the South of Lilanfacthlu, and also between Monachdy and Wilfa. They consist of fine grained sandy materials deposited in layers, and in several instances it happens, that the coarser ingredients form the uppermost portion. The rolled pebbles are not nume- rous, and there are a few large blocks of schist, greenstone and limestone, dispersed through them. From Penmon to Beaumaris there is a low cliff of dilu- vium, through which are dispersed numerous large blocks of limestone and grit, derived from the coal-measures. This ter- minates immediately to the South of Beaumaris, in a mass about sixty feet thick. The character of this diluvium does not re- semble that which is found to the West of the Island (where it bespeaks a succession of deposition), but forms a rude mass m which the materials appear to have been brought together by a single effort. A suite of specimens has been selected from the embedded pebbles. The smallest and most rolled con- sist of various granites, traps, and the older stratified rocks. Some of the blocks of limestone and of the more recent strata, are of very large dimensions, especially as we approach the mountain lime at Penmon. Alluvium. Wherever the coast to the S.W. is low, the neighbouring country has suffered from drifts of sand, which in some places have covered up the soil to a considerable distance inland, pre- senting a dreary outline, broken only by a few projecting points of schist. This sand is still active in making its annual encroach- ments, if we may judge from the half buried walls which have Geology of Anglesea. 447 been recently built over the low ground on each side of a road from Newborough towards the N.W. In the preceding pages it has been my endeavour to relate those facts which appeared most likely to facilitate the future investigation of the Geology of Anglesea. It cannot be expected that a first account of any complicated: country, should be accu- rate in all its details; for, in such cases, the time necessarily consumed in obtaining a clue to the examination, will seldom leave sufficient opportunity of accurately verifying all the points of relation. which may exist between contiguous formations. 448 Mr. HENstow on the EXPLANATION OF THE PLATES. ees PuateE XV Coxrortions in the strata of the quartz rock at Holyhead mountain. Sketched: from ‘the: South Stack 2. ..:95 55 cw. wean... cewek p- 363. Puate XVI. Fig. 1. Cleavages exhibited by the strata of the quartz rock... p. 364. Fig. 2. Vertical section of a mass of breccia (a), and a quartzose vein (b) connected with it, which rises through the chlorite schist, near its yunchen withthe ‘quartz-rock 2°. 07-0). . era. p. 366. Fig.3. Junction of the quartz rock (a), and chlorite schist (b) to the Woest:.c8 Rihoseolyni.. ..<.. 7 ose scors saa aa eee ee p. 366. Fig. 4. Section of the stratified chlorite schist .................. p- 371. Fig. 5. Serpentine (a) rising abruptly through the chlorite schist (0), which. dips: In, various «icectiona: 9. 600585 <2. G2 vw ees oes p. 376. Fig. 6. Massive serpentine (a) gradually assuming a_ schistose cha- racter 40). 2.5555 cs Tee a eee OE SEE p. 376. Fig. 7. Appearance presented by the greywacké slate on the shore near Monachidy, tau ate ease «ads ee ee . p- 383. (a) Hard, green, and tiolaanindied portion, passing “qrdbslly on one side to a schistose black slate (b), and terminated abruptly against a similar rock on the other. Fig. 8. Arrangement of particles in the stratified grit at Bodorgan, p. 395. Geology of Anglesea. 449 Pirate XVII. Fig.1. Junction of mountain limestone and schist to the South of Llan- (el LL) eat ALR eter Di RAN 2 OR ee ROME LF RC ES es p. 396. (a) Hard, quartzose schist, scarcely laminated, rising abruptly through the limestone on the East. (b) Fault, thirty yards wide. (ce) Rubble, consisting of fragments of the limestone. (d) Soft, shattery green and red clay slate. Fig. 2. Contorted limestone and shale, at Caint ................ p- 397. Fig. 3. Appearance of Great-Ormes Head from Beaumaris...... p- 398. N.B. In the following figures, the shaded portions represent trap. Fig. 4. Dyke in Dulas harbour containing embedded fragments of clay 1 Lee a ch ee ee ee a BR aon enna ss staan A ya asta ett p. 421. | Figs. 5 and 6. Two sections, at right angles to each other, of a mass of chlorite schist, between» Port-Dafreth and Borth-Anna, exhibiting the termination upwards of a basaltic dyke...................... p. 416. Fig. 7. Section, ninety feet in length, along the course of the dyke which runs through Holyhead Island. The trap is seen, surmounted UWI: SG Gate She oedcdsd: Iegdbeaeunooee nanaod Bir.e pie'eciee veces p. 416. Puate XVIII. Fig. 1. Section along the course of the dyke at Cadnant...... p. 413. (a) Road from Beaumaris to the post road. (4) Marshy ground to the East of Castellos. Figs. 2, 3, 4. Sections of some dykes exhibited in the cliff between Beaumaris! sand > Garthiclerty 5 wit iain seihieua Rha o's rain siete oe p. 422. Fig. 5. Portion of the old red sandstone, passing to a variety of green- SiGe, witha, Colummarl: StrUCLULG. <5. . ..ocs 25 cs sci cease caeee a p. 433. Des Gre Can momemieual @W ED...,).2). cass cssiesn-b ge ttnnes ibs eles p. 444. (a) Quartz. (6) Basaltic dyke. A456 Mr. Henstow on the Piates XIX and XX. _(A to M). A series. of parallel sections across Anglesea from N.W. to S.E., referred to on the Map by corresponding letters. (N to O). Two parallel sections from S.W. to N.E., at the North- Western corner of the Island. (P). Section at the N.E. corner. A few changes in the mineral character of some rocks included in the same formation are referred to in the following manner : (a) Green clay slate, (6) Black clay slate, (c) ‘True greywacké slate, (dq) Micaceous schist, (e) Chlorite schist, (f) Conglomerate of jasper, limestone, &c. in the chlorite schist. Puate XXI. Geological Map of Anglesea. The principal districts included in each formation are artificially divided, for the purpose of easy reference, in the following manner,— (the order of arrangement always proceeding from West to East,) see page 360. Quartz Rock. (Q). Q. 1. Most Westerly portion of Anglesea, including nearly half the Northern division of Holyhead Island. Q. 2. Also in Holyhead Island. To the S.W. of its Southern division. Chlorite Schist. (C). C.1. Includes the greater part of Holyhead Island, and is bounded to the North by a line from Llanrhyddlad to Llanbabo, and on the S.E. by continuing this line through Llanfihangel to the sea. C.2. The Northern part of Anglesea—between Carnel’s Point and Lianeilian Point. PULYEL POPPY TOL] YIAS yp ay) aisodde yoo Lon Mayflag gg MBusoy dy popursy boy 7 lop b spp mpsuagr or at y, enn ee ee eas rN Ns MSY et A Penny mR NNR Nar WN aN td 48 LR a Ne Wn EPO LANA PB WsaP eer nae ee een ey mee PERL L'2% Gawog qoorydosogryer ofpuigueng eys fo ruargousumey ayer | ae eye fn ake DY chp Te eee « SN t , t H ‘ t ‘ ' 1 1 1 H H \ Lrinted by Kowney FP oyler. ic i See peat hy cy nt nia See ~~ ee — — a et — a > ie Tete 2 1 Se ta el net i ete > oatmeal ak ens raed fhe artnet tee tla > fC ee ee ee ree | i \ a ¥ tb edeete sk Aa i as | Be sentra by Leowner ® Fefler London, Si Aenwlow dec. ©. Scharf Lithog- Lrontrah by wre © Lranted by Hiawney © borfter Loridon. | _~ CG Scha Lithog- | we! YW it iy M of Llanelan Me esa I) 795577 Wi; | Mitt Farts Me een Le Ui Llanerchymeda LS Henslow del: C-Scharf Lithog : . PET Pts / fe, ——— NTFS 2 cal OS se ~~ sl ve ‘ il oA Bodafon M? <> : Bily | ST Leg ayan ee ees eee lo eye eee neta ee Red wharf BY of — J Gross, 2c Cursitor Str® re \ 3 - “~~ e —= i Hoy - = ~ ° —— ” ~ ++ : Se =: ih + Ff r -_ of ’ re <*> - - as tw * é ‘ae &% ™ « * 1. >- * ~ * , : * ’ ~~ " = , e's - * * a = << — 2 Ce on Se . ’ e ~ ~ ~ - i e,2 s Geology of Anglesea. 451 .3. Middle district—from Dulas on the North to Aberfraw on the South. .4. Small strip to the East of the last—between Red-wharf bay and Caint. .5. Western district—from Llandonna to Llandwyn. Serpentine. (S). .1. In Holyhead Island—from Rhoscolyn to Llanfihangel. .2. Near the centre of C, 2.—to the S.W. of Llanfechell. Greywacké. (G). .1. Between C. 1. and C. 2., and to the East of each as far as C. 3. . 2. Towards the North of C.3.—a small strip running from Bryn- gole to the S.W. .3. Bounds C. 3. on the S.E.—from the North of Llangefni, to the South of Aberfraw. -4. Between C. 4. and C.5.—from Red-wharf bay to Llanfihangel East. Small patch N.E. of the last—at Llandonna. Da At the Eastern termination of C. 5.—West of Beaumaris. “I To the South of the last—At Garth-ferry, and on the opposite coast of Cernarvonshire, from Bangor to Aber. Old Red Sandstone. (QO). .1. Separates C.1. and C. 3. at their Southern termination, and runs as far North as Llanerchymedd. .2. A small patch at the N.E. termination of the last—immediately South of Llanerchymedd. .3. A similar patch to the N.E. of Llanerchymedd. .4, Another, to the N.E. of the last—in contact with the Northern granitic district. Vol. 1. Part Il. 3M 452 Mr. Henstow on the Geology of Anglesea. 0.5. On the N.E. of C.3.—From Dulas harbour to Bryngole. 0.6. A small spot, surrounded by the mountain lime, to the East of the last. Mountain limestone and Coal-measures. (M). M.1. The most extensive district of this formation—from Dulas harbour to Bodorgan. M. 2. S.E. of C. 5.—From Garth-ferry to Plas-Coch. M. 3. N.E. termination of Anglesea—including Priestholme island. -Magnesian Limestone and New Red Sandstone. These lie to the South of M. 2. Granitic Districts. (Gr). Gr. 1. Largest district—towards the centre of the Island — round Gwindu. Gr. 2. Small patch in G.1., to the South of C. 2.—EKast of Llanbabo. Gr. 3. S.E. of the last, and North of Llanerchymedd. Gr. 4. Northern distriet—from Lianeilian mountain to Dulas. Conglomerates. One of these oceurs at the most Northerly pomt of Anglesea—the other to the East of Gr. 4. Trap Dykes. These are referred to the formation in which they occur. N.B. By an error of the Engraver, the references to these in the Map are made with a (7), instead of with a (7) as mentioned in p. 401. St. John’s Colt. J.S. HENSLOW. Nov, 26, 182). XXVII. Some Observations on the Weather accom- panied by an ewtraordinary depression of the Baro- meter, during the Month of December 1821. By tHe Rev. JOHN HAILSTONE, M.A. F.R-S. FELLOW OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY, LATE FELLOW OF TRINITY COLLEGE AND WOODWARDIAN PROFESSOR, In a Letter addressed to the Rev. Grorce Pracocn, Secretary. [Read Feb. 25, 1822.] Sir, As the weather during the late winter has been of a very unusual character, I have thought a register of it for the month of December last, might be acceptable to the Society. This register, as will be seen by inspection, consists of observations made on the heights of the Barometer and Thermometer at three several times of each day, viz. at eight in the morning, two m the afternoon, and eight again in the evening. There is also a column which registers the lowest point to which the ther- mometer had sunk during the night. The quarter from wich the wind blew at the time of each observation is also noted. I have not thought it necessary to add the temperature of the 3M 2 454 Mr. HAttsTone on an extraordinary mercury in the barometer at each observation, because the instrument stood in a room which varied very little in that respect, not more than from 45° to 50° during the whole of the month. The thermometer hung in an aspect to the North, and about four feet from the ground. The barometer was made by Cary, and is of the portable kind, having been origi- nally contrived and fitted up for the purpose of measuring altitudes. The Gage is not a floating one, but a fixed linear sight to which the surface of the quicksilver in the basin is brought by means of a screw; and it is almost needless to add, that this adjustment was made previous to every observation. The most remarkable phenomenon in the register is beyond question the extraordinary depression of the barometer, which took place on the 24th and 25th of the month. On the 19th thunder was distinctly heard here proceeding from the N.W., and on the 20th the glass seems to have commenced its fall : it will be seen by the evening observation of the 24th, that it had fallen so low as 28.37, and as it was then still falling, I paid particular attention te it, till at 3a.m. on the 25th I observed it at 28 inches precisely, a degree of depression I believe [ may say almost unprecedented in this climate. The weather which accompanied this unusual state of the barometer was distinguished by violent gales from the W. and S.W. attended with incessant heayy rains. It appears from the public papers, that this remarkable depression of the barometer has been general through Europe, and at the same period of time. The accounts from Germany state, in addition to the storms of wind, that it was attended with a shock of an earthquake. This was particularly the case at Mayence, where a slight shock of an earthquake is said to have taken place on Christmas day, about half past eight in the evening. At Bamberg and at Francfort about 7 p.m. on the Depression of the Barometer. 455 24th, an igneous meteor was observed of the size and shape of a full moon, which taking a North-Easterly direction, fell to the ground, and disappeared with an explosion as loud as that of a cannon. But it was in Italy that the tempest appears to have been the most violent. In a letter from Genoa, dated the 29th, there is the following passage: ‘“‘ The inhabitants of Genoa have often witnessed ravages occasioned by tempests, but not one so dreadful and prolonged as that which we experienced during the night of the 24th instant. It will ever be memorable in the annals of our State. During several days previously, the air was charged with thick vapours, which vented them- selves in torrents of rain; the wind was S.E.; on the 24th at six in the evening it settled in the South, and blew with intense violence; at ten o’clock it had reached its utmost force. The sea rose progressively. At eleven the vehement conflicts betwixt the two elements had the full character of a hurricane, and in the language of the country was a terremoto di mare.” Doubtless we may expect farther details and observations of this most unusual state of the atmosphere, and I therefore await the arrival ef the various scientific Journals published on the Continent with some degree of impatience. From America I have met with no accounts to which I can draw the atten- tion of the Society. It is certainly an object of considerable importance, to ascertain the limits of barometrical phanomena with regard to their geographical position. Having finished my remarks on what may be considered as the great meteorological feature of the year 1821, perhaps it will not be thought uninteresting, if I add a few observations on the mean temperature of the latter months of that year, as compared with the corresponding months of the year preceding. I estimate the mean temperature of any month, by first finding the mean of each of the four thermometrical columns of daily 456 Mr. HAitstone on an extraordinary observations separately, and then taking the mean again of the four results thus found. By this method the temperature of the month of April last, according to a register which I kept, is found to be 48°53, which is also the precise temperature of our springs. And this confirms the truth of a remark which I have heard, namely, that the average heat of the menth of April affords a good estimate of the heat of the whole year. Conversely also, the coincidence may serve to confirm the accuracy of the above method of estimating the mean monthly temperature. The heat of December last, averaged in this manner from the register is 42°5; in the preceding year of 1820, it is only 39° for the same month. Of the months of September October and November last, the mean temperature was 58°45, 49°5 and 46°3, respectively. The corresponding numbers for the same months in the preceding year 1820 were 54°, 46°5, and 40°5. Thus it appears the heat of December last was three degrees and a half above the heat of the same month in the preceding year. And November also when compared with October of the prior year, is in this respect, very nearly equal. From several experiments made by sinking a thermometer in garden earth to the depth of twelve or fifteen inches, the mean heat during the month of December last was found to be 44. This portion of the earth’s surface comprises the ordinary region of vegetation, which, as appears from these experiments, was in the very depth of winter inferior only by 44 degrees of temperature to that of the whole year. Such an extraordinary mildness in the season was accordingly very perceptible in all the productions of the garden. The autumnal flowers contmued blowing late, till they were superseded by those of the spring, which appeared in the same degree, early. The Depression of the Barometer. 457 animal creation felt also its genial influence, and the blackbird ushered in the new year with a carol as loud and as articulate as is usually heard in the months of April and May. I have the honour to be, Your very obedient servant, JOHN HAILSTONE. Trumpington, Feb. 10, 1822. 458 DECEMBER 1821. Eight o’Clock Morning. Two o’Clock Afternoon. Eight o’Clock Evening. . “ > | Day of Month. Barometer, Barometer. Night Thermometer. Thermometer, Barometer. Thermometer Thermometer 8 | | cs re) EXTRACT FROM THE MINUTE BOOK OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. Nor. 26, 1821. XXVIII. Notice of a remarkable instance of Fossil organic Remains found near Streatham mm the Isle of Ely. By Dr. FREDERICK THACKERAY. Tins bone was picked up among the materials for forming the turnpike road in the neighbourhood of Ely: all the natural grooves or channels in which the blood-vessels formerly ran, may be seen, confirming the observation of Cuvier, that these reliques have not been acted upon by attrition in water; and of which many more striking examples occur among specimens lately found in the neighbourhood of Cambridge. In order to account for this, it may be observed, that the finest examples of organic remains, characteristic of beds of ‘alluvium, rather rest upon the line of junction between clay and gravel, than in the gravel itself. The present specimen consists of limestone with a slight impurity of alumina and oxide of iron: the ex- terior of it retains some portion of phosphate of lime; and (what seems very singular), a minute quantity of animal matter, which was manifested by its peculiar foetid smell on being submitted to destructive distillation. A very considerable part of the skeleton of a Mammoth was lately found in a gravel-pit near Chatteris. Vol. 1. Part II. 3N - _ 7 [in a be ; . a ey. =! as 4 Ad - ee = 7 5 a male . ‘+ + d | _ o* o> ra ivtes "ire 7 am ghia ns fang aden tenia " 7 4 74 a ote a Sat “pea? ia: f 2 “=p ye oe PPOREARS: ‘ ‘= THe" siowwgosisynri AipeTAA EAD: ta; yh i . qa a it . al ee ea brit ev is . 8 > Lad . bn 1s igs Vato QW watbaad. Son ay ee rt Ne sr hee he SL) a sages ent aT ‘ang ae ino st f od % a : “ ey a - bs . i > , - : a % Bs , i &. ej _ i { . _ a a" ESTAR R este E ae, vet , . ‘2 eet f erie yee “wie Ai mal watt idd ote iene’ faniaky wens ad ie ma fugaie thie sav ti = iq Lawat pepe gee te alf Ut “hatey dk ame ae ‘ haeyt ‘ie eh etl St “Hoadues at Ahi “e uly wal wale T) to waiin ered ai Aquila Si baute, « adn i i ae niet hy a vis wonty, ‘hat lea dont ot * pale ae) ie Hines » ea kehat vise rs, Bisset bk u? “nti. al o adbbyiow)), 19, Linas famitnp MT ott ph id J er arin abi ad | dripetagal ae: hou. ui ett wi f doud rere’ we tre het Ine. alpeistes “sidaitabrargndbe yi arduert rah aiptaittans “valy- ‘testi 7 notRan ih ovalles | perth! wi, Ney Mister mph, Taji wT, » Visite : f vf! eT Aye "ipa ot Sy Raa a inh re Pear a luetn wi) 9 pinila) Th I A | it tied Suton aie ti 4 eh at LEP Mi the Lh, J due Sedu pare ke ‘ hot paittid? i with wir Dy big ol ut roa i Feat oy Pe o* 4 apf ta] Cite by Sy il te bf uy ‘eb, ne pode aft a) ae et akties cal ian hive vasa f pee we, Oe OR a “i s obec en lal _ Ae 1820. A LIST OF DONATIONS TO THE . LIBRARY ann MUSEUM OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. — I. Donations to the Liprary. Donors. Account of Smithson Tennant ......... Dr. E. D. Clarke. TES ECT es Coe Gane Nee TPN ——_—_____—. American Journal of Science, Nos. 1,2,3,4... Mineralogical Journal, Vol. I. No. 2... Carnot Geometrie de position ........... Rey. B. Bridge. Christian’s Dissertation on the Rules of Evidence. — Prof. Christian. Deidier Calcul differential et integral... ... . Rev. B. Bridge. Edinburgh Philosophical Journal Nos. (1—5.) .. |W. Whewell, Esq. Greenough’s Geological Map of England . . . . R. Sheepshanks, Esq. Lhuilier Elemens d’analyse geometrique....°.. Rey. B. Bridge. Map of the World on Mercator’s projection. . . — J.S. Henslow, Esq. Bogland: -39i.¥™ apuacr- aise: SH. ——<—<—$—$— RODE cg. (op or chs Aci otgck ls. xs, 2 us Shae ——— Cambridgeshire. 4;, -2.joraie: asel- Bis = 2 J. Okes, Esq. Paris on the Physiology of the Egg ....... Dr. E. D. Clarke. PhysiquesdeRohanlt... paegek. ee deari ieee Rey. B. Bridge. Quarterly Review, Vols. (1—23.) ...... . Rev. Whitworth Russel. Rosetta: Inscription” <4. sitive. 240 AI. Rev. E. D. Clarke. Sayer’s Antiquarian Miscellanies.......... Stackhouse on the Balsam and Myrrh trees... £©£——— 3N2 462 1820. Mar. 6. May 15. Nov. 13. 27. 1821. Mar. 19. Nov. 12. Donations to the Library, Stackhouse de Libanote, &c. Schweigger de Plantarum Classificatione . . Vindicia Geologice oe pute ds pe we. ath « Ral at & Watsoniana. <2, pane ieee noe On the developement of exponential Functions. " On circulating Bonctions” <>... 2 On the application of the Inverse theory of PUUMeHONS 2 «26 an... ee. eee ns Consideration of various points of Analysis . On the action of crystallized bodies on homogeneous*light?) 27) ¥) OSES : Isoperimetrical Problems <2 5. : 2325 : Method of computing Astronomical refrac- LEO TESS rath cogey crlas acy Geet Al cal ee an Method of correcting the approximate ele- ments of the orbit of a Comet ..... Annals of Philosophy, Vols. (g—14.).... Nouveau Journal de Medecine, tom. (1—9.) Viaggio per la Toscana di Georgio Santi. . Discours sur Nicholas Kopernik Liebkneght clarissima testimonia Diluvil . British and French Expeditions to Teembo . Geography of North-western Africa... . Epimetrum de quibusdam monumentis cum Pollionis Histor'a conjunctis....... Elenchus plantarum Hort. Bat. ....... Transactions of the Asiatic Society, Vols. (G99 i eed et eee of the Royal Society ee Edinburgh, Vol. LX. Part. 1. On the circular polarization of the Amethist . oes: tae Connection between the primitive forms of minerals and their axes of double re- fraction Donors. Dr. E. D. Clarke. Prof. Buckland. Dr. E. D. Clarke. J. i. W. Herschel, Esq. Rev. John Brinkley. Dr. E. D. Clarke. Dr. Haviland. Prof. Santi. Dr. Slawinsky. Dr. Thackeray. T. E. Bowdich, Esq. C. J. Reuvens. Asiatic Society. Royal Society of Edinburgh. Dr. Brewster. 1820. Nov. 12. Dec. 10. 1822. Feb. 25. April 22. 1820. Mar. 6. May 1. Nov. 27. 1821. Mar. 5. and to the Musewn. Superstitions of the Egyptians, Abyssinians and: Achantees: 3.0) Wienges ee, on Introduction to Ornithology Analysis of the Natural Classification of Moarmmmialiag. 9 :.0 25-5 o2c. naewnt aah Theory of Equations Translation of Cagnoli, on the method of ascertaining the exact figure of the earth Notice of a paper on the structure of the Alps History of the Crinoidea Observations on the Lituus Reply to Samuel Lee by John Bellamy . . piel <0) 6) 40\>.0) ©) xe) Pol eketnel « Biel vem «, \¢ CO ONO nO ha ci AG On the Circular Sterns of Ships of War . Contradictions in Park’s last Journal ex- plained Technical Repository, No.l. ....... Elements of Conchology .54cdt- errShaic The Rudiments of Plane and Solid Geometry Intrcduction to Solid Geometry Transactions of the Astronomical Society Vols & Part 1. Observations on the Geology of the Isle of Man Essay on Political Economy......... Journal of the Royal Institution (Nos. 1-13.) enon me! i) 6.0 (6) ee} ef sie) i gaia) eae II. To the Museum. Fossil tooth from the coast of Scarborough Collection of British Shells and Insects Medal of Copernicus Oe > a eA Co eet oO Impressions of leaves in coal-shale . . 463 Donors. T. E. Bowdich, Esq. Rev. B. Bridge. F. Baily, Esq. Prof. Buckland. J.S. Miller. Dr. E. D. Clarke. Rey. Prof. Lee. Sir R. Seppings. T. E. Bowdich, Esq. Dr. E. D. Clarke. T. E. Bowdich, Esq. N. J. Larkin, Esq. Astronomical Society. J.S. Henslow, Esq. The Author. M. Ramsay, Esq. Rey. J. Hailstone. J.S. Henslow, Esq. Dr. Slawinsky. Rev. T. Kerrich. 464 1821. Mar. 19. Nov. 12. 26. Dec. 1822. Feb. 25. Mar. 25. April 22. Donations to the Museum. Quariz and Fluor from Beeralston . British Insects Ditto Ditio White varieties of the Goldfinch, Sparrow, and Mole » Fossil breccia. of Gibraltar =>...) - British Insects and Birds’ Eggs Collectionsof Minerals: «2-.+.-5-.-. 22 -. Three specimens of a Pinna from Guernsey Snakes and Scolopendra from Trinidad Large specimens of Fluor and Quartz from Meateniioar 5: TOs ee ee Very large Crystal of the Sulphate of Barytes Fossil Bone Specimens of the Areeka nut......... . Crystallized Carbonate of Barytes from Fallow field—Northumberland Masses of Shale, from the Coal-measures @ J/aigle) Aas in Anglesea, converted to Garnets and Analcimes, in contact with a trap dyke. FosalévertebraleBone «.*.-4.5.2.% %°si..6 Collection of Foreign Shells and Corallines. Sulphate of Barytes and Fluor from Matlock. Series of Models of Geometrical Solids Specimens of Scolopendre Lizard from Bencoolen Donors. Rey. T. Ross, Esq. Dr. Leach. F. Stephens, Esq. J.C. Dale, Esq. J.S. Henslow, Esq. C. Collins, Esq. H. Englehart, Esq. Rev. A. J. Carrighan. Rey. M. Vernon. Rey. Miles Bland. Rey. G. Peacock. G. E. Wood, Esq. Dr. F. Thackeray. Dr. Ingle. R. Lyon, Esq. J.S. Henslow, Esq. Dr. F. Thackeray. Mrs. Tyrritt. Prof. Cumming. N. J. Larkin, Esq. Rey. G. Jermyn. Dr. Ingle. 465 ——> Page Page Acrvynourre in INTR ESE Sanacpec dost 377 || Curistre, S.H. Esq. On the laws of AdulariaintAnolesea Se ASO Magnetic attraction . ..... - 147 AL Farsi. Notice of the Astronomi- CLARKE, Dr.E.D. Onihe sler pre- cal Tables of, by Prof. Lee. ...... 249 cipitate of Cassius. ....-.-....... 53 7 pow Te Analcime in the Coal-Measures of Angle- On native Natron - 193 SEAM oe SESE IE Ne oe SAO — On the crystalliza- Anglesea. Geological description of it Honjok Water soelractdeci(- clack aeires 20s) by J. S. Henslow, Esq. ...... ++. 359 || Clay slate in Anglesea .......... 369, 378 Apophyllite, on the double refraction of Clicker Tor, variety of serpentine there 144 it, by J. F. W. Herschel, Esq. . .-.- 241 Cligga Point, overlying granitic rock Apsides, angle between, in certain orbits 187 there - -. +... sess cere ee ee ee eee 131 Asbestos in the Serpentine of Anglesea.. 377 Coal converted to cinder, in contact WithsastrapmdyKelensi-ocicicitels ees 415 Astronomical Tables of Al Farsi. ...... 249 Atmospherical Electricity, produces no deviation on the Compass needle ... 286 BasBaGe, C.Esq. Onthe notation em- ployed in the Calculus of Functions. 63 Barometer, extraordinary depression of He) ot Sn becouse UdiewaLU SOog es Ate ao oe os: Basalt in Anglesea, (see Trap-dykes). Beaver, fossil remains of one, found in Cambridgeshiresmemeeers eee 75 Indigenous to Great Britain ...— Calcareus tuffa in Anglesea .......... 373 Calculus. Notice of a large Human one 347 Anexceplionto the usual com- position of large Calculi .......... 348 Cassius. On the purple precipitate of, by Dr. DAClarker srt. 53 CeciL, Rev. W. on the application of Hydrogen Gas to produce a moving [NOG Steodt oo cece abppppoccods Alp Chlorite schist in Anglesea .......... 365 Chloropha@ite in trap ................ 415 Coal-measures of Anglesea...........- 393 Compass-needle. Law of its deviation beneath a connecting wire .....- 284 Concretion. Notice of a large one from the intestines of a Horse . ........ 348 Concretionary nodules in clay slate .... 379 in Greywacké ... 387 Conglomerate in Anglesea....-....... 444 -in Somersetshire & Devon- shire: <)./s7./-" wes: OO Cornwall, On tig Geolay 0 of by ‘e Rey. Prof. Sedgwick . eae SO CUMMING, Rev. Protest On the con- nexion between Galvanism and Mag- MCTISIMFS ee eee Se cloeie os rare esse eine LOO On Magne- tism as a measure of Electricity.... 281 OS On a large Humrany Calenlus/ 1c. cs ccucisl even eo OAD —- —— Analysis of a variety of Analcime ............ 408 298, 301, 309 Diallage rocks of Cornwall .. 466 Diluvium of Anglesea ....---+++++5> Double Crystals, relative position of .. Dykes. Electricity of the Leyden Jar produces no deviation on the Compass needle Trap-dykes of Anglesea . .... Electricity and Magnetism, their con- ducting powers follow different laws Electro-magnetism, the direction of ils current ascertained ........--+++- — its influence on the compass needle increased by in- closing it in a spiral .....--.-+-- ——- its effects dependent rather on the quantity than the inten- sity of Galvanism. .....---.--++- conducted imperfect- ly by small wires and thin cylindric surfaces diffused over large SUMACES) pertee = =)rekeevasleteeht ial -ilete —___ not destroyed by com- pleting the metallic circuit through- out the Galvanic pile .. . eye te eee Elephant, fossil remains of one, found in Cambridgeshire Elk, fossil remains of one found in Cam- bridgeshire Ss chee comusteccrerats Epidote in Anglesea ........-.+-+--- Farisu, Rev. Professor, on [sometrical perspective ° Felspar, crystallized masses sak. it, in sabia Fluor. On the double crystals of it, by W. Whewell, Esq. mode of measuring the angles be- tween the double crystals Fossils in the old red sandstone of Angle- SOA cites oisre he eer JORe era 2200 Functional Equations. On the solution of, by J. F. W. Herschel, Esq. Galvanic plates, the law according to which their effects are increased by diminishing their distances .,...... INDEX. Page 445 Galvanometer described . Beni te 338 || Galvanoscope described . sh50¢ 401 — its sensibility .......... — ils application ..... atte. 286 |! Garnet in the Coal-measures of Anglesea ; in the Mountain-limestone of 276 High=Neesdale . ....-.-...4-=aeexere Granitein Anelesea .-) 2. s...4- 2 sinters 2 (Oi comme in Cormwralll <7) ),c10cteters ae — decomposition of ........ 102, 275 Granite veins in Cornwall .........-- y —— connected with the central Granilescy oe cine ieeerer Bod <5 D7 || GREEN SEONE ns olntatisl-talel atetelaleistatstatstaiettat-ie _- =pinjAngleseams/racmr acts totes - of the Lizard Point .... 315, 277 || Greywacké of Anglesea ............-- — of Somersetshire and Devon- 285 Shire ~ 0's sjocrtgiapotys Gee eee — of the Lizard Point .... 295, Hartstoneg, Rey. J. Observations on 280 the weather during December 1821. HAVILAND, Dr. On the case of a cor- 176 roded) stomach << mieielcisae eters HENstow, J.S. Esq. On the Gcoloy 177 of Anglesea ......... 425 | HerscHet, J.F.W. mn cuiniedsutile refraction of Apophyllite . ........ a -—————— On the Tints de- iA veloped by polarized light ........ = - On_ polarization 331 by Roel: enystal esr). aepeiels least _,, || Holyhead mountain. Construction Oli en Hornblende rock in Anglesea ........- 392 Hornstone in Anglesea Hydrogen gas. On its application to = produce a moving power ........ ‘G On sounds excited in it Jasper in Anglesea .\.i. 0's oases oe 284 || Integrant molecule, vague use of the term ¢ Tron and Steel, their different electric relations Ser CIS Tsometrical Perspective. On it, by the Rev. Professor Farish. . Killas of Cor seer ymlion with the Granites eee ode 5s att (Os ee iy veins Of. Granite -1.5,.6 - sae eee various rocks sub- ordinate to it. . Laws according to which masses of Tron influence Magnetic Needles. By SEs Christies Eis @icraast-rteel eta Lex, Rey. Professor. On the Astrono- mical tables of Al Farsi : LESLIE, Professor. On sounds excited rela hope eects 56 Ay Gcn8 segsogso Limestone, beds of, in chlorite schist . .. crystallized, in contact with Trap sono cHWOCant: subordinate to the Killas of Cornwallacte crestor tetas eyed +o Lizard district. On the structure of it, by the Rev. Prof. Sedgwick . se LuNN, F. Esq. Analysis of Native Phos- pliatelot Coppers -ei--ieia) i Magnesian limestone of Anglesea .... .. Magnet, how affected in the Galvanic circuit soon : Magnetic attraction. On the laws of, by S. H. Christie, Esq. ..... Magnetism and Galvanism, their ana- logy suspected by Ritter, proved by QRrsted e oss.5cceres cl sicher sue aces Magnetism. Comparison between the common and the Galvanic Its application as a mea- sure of Hlectricity -.. 2 .- ests MANDELL, Rev. W. On an improve- ment in the apparatus for procuring Potassium 3 Menacchanite in Cornwall............ Vol. 1. Part Il. INDEX. A467 Page Page Mesotype in the trap of Anglesea...... 411 283 Meteor, igneous one, observed at Bam- berger nt . 456 1 || Micaceous schist in Anglesea. ........ 361 Mica slate in Anglesea ......<....... 368 114 Mountain limestone in Anglesea ....... 398 Natron, native in Devonshire 193 LG in the old lavas of Vesuvius.... 199 A ils ATS HU meee Sses oan alee: ——— 135 2 i : New Red Sandstone in Anglesea 400 Nodules concretionary in Clay slate.... 379 147 Greywacké .. 387 Notation employed in the Calculus of 249 Functions. By C. Babbage, Esq... 63 Oxes, J. Esq. On a dilatation of the 267 Wreters: 5 =: cs cere -) Bi 375 On the fossil remains of 75 the Beaver . . ) doranae e175 ta Old Red Saenet in angina AC pie 388 Orbits. Their form when very eccentric 180 141 Organic remains, in the Killas of Corn- wall . Hohecicheierste 139 291 Phosphate of nage Renae of, ee F. Lunn, Esq. . ‘ 205 203 Polarization by Rock Crystal, i J.F.W. 398 Herschel, Esq. . See 43 Polarized light. On ie tints Geese 285 by it, by J. F. W. Herschel, Esq... 21 Porphyritic rocks South of Porthowstock 299 147 at Coverack cove.... 301 Potassium. The most strongly negative metal... wie) oe dehetcieheteee Lao 9 =e — Improved method of pro- ane CUMIN coogemeEDGacoosub alcoce ore) p Pyroxene in the serpentine of Anglesea 377 281 Quartz Rock in Anglesea ............ 361 Rock Crystal. On polarization byt it, by Jo ReaWelverschelipbisq setae se) iin oo 343 Saint Michael’s Mount Cornwall .. . ¥0S 206 Saussurite in Cornwall .. .. 304 30 468 Schorl Rock in Cornwall SepGwick, Rev. Professor. On the Geology of Cornwall Se —_—— —- On the physical structure of the Lizard dis- trict 3 Serpentine of Anglesea .............. of; Clicker Tor’ .oo.)< «1-0 of the Lizard district Shale converted to Jasper converted to Analcime .......... converted to Garnets ...... Soap Rock of the Lizard.............. Sounds excited in Hydrogen gas Qa GT IN GSGEY Cog is dscns cue oe & Steatitic rock near Bangor Stoke church Devonshire. Native Natron im the tower Ofit ch oc. averse sce! Steel bar magnetized INDEX. Page 106 || Structure of the country between Dart- more and Land’s End.............. 89 Sulphate of Lead in Anglesea ......... Tints developed by polarized light . ... Tin-work. An open one at Carglaze .. 291 Tol-Pedn-Penwith. A cavern in the 375 CHIR eRe Bice ste:} oe sisseinieisterclnietoiets 144 || Trap-dykes in Anglesea ..........-.+-- 207 Tuffa, calcareous in Anglesea .......-. 405 || Ureters. On a dilatation of them, by 406 UROL CEs IEG) She ogdanecooumeagdac 410 Water. On its crystallization, by Dr. a EDs Clarke 2 cin dee ee ee Weather. Observations on it during 267 December US2 1 yeee wire wae sleet ere 444 | WoHeweELL, W. Esq. On the double 386 crystals of Fluor spar ..... PS Oe 285 — On the positions of the apsides of orbits of great 194 CECEHEICILY, ie clsleieisl viele teiniete niviolelete a 469 DESCRIPTION OF THE PLATES. N.B. In the First Part of the Transactions, none of the Plates are numbered; the numbering of the Figures being carried on from 1 to 25, with the exception of 11 and 12, which are omitted.—These are followed by two litho- graphic drawings of the Bones of a fossil Beaver. In the Seconp Part, some of the Plates are numbered, and, to prevent confusion, the following description of the whole is given, in order that each Plate may more readily be referred to the Paper which it is meant to illustrate. In Parr I. Prates I, Il, III. include Fig*. 1 to 10.—To accompany Professor Farisu’s Paper, No. 1. on Isometrical Perspective : I. includes Fig*. 1 to 7, representing several perspective views of simple figures. 1. Fig. 9. Perspective view of a piece of machinery. i. Fig. 10. Perspective view of a furnace. Puate IV. Fig’. 13 to 20.—To accompany Mr. Herscnex’s Papers (Nos. 2 and 3.). Pirate V. Fig*. 21 to 25.—To accompany Mr. Wuewe.’s Paper No. 10.) Pirates VI, VII. Two lithographic drawings of the Bones of a fossil Beaver.—To accompany Mr. Oxes’s Paper (No. 9.). VI. contains a single figure. VII. contains three figures. A470 DESCRIPTION OF THE PLATES. In Parr II. Piate VII. B. Crystallization of Water.—'To accompany Dr. Crarke’s Pirate VIII. Pirates IX, Prate XI. Pirate XI. Puatre XIII. Fig. 1. Fig. 2. Puate XIV. Paper (No. 8). This plate is numbered, and refers to Mr. Cecix’s Paper (No. 14). X. These two plates are wanting. It was originally intended to make three plates from the figures included in Plate VIII ; but, by an error of the engraver, their sizes were dimi- nished, and the whole placed together. This Plate is numbered, and contains the Galyanometer and figures described in Professor Cummine’s Paper (No. 18). To accompany Mr. Wuewe t's Paper on the double crystals of Fluor (No. 22).— The figures in this plate represent the intersections of cubes, &c. This plate is numbered, and refers to Professor Cummine’s Paper on the Calculus (No. 24). The Calculus of the natural size. Section of the same along the line AB. Lithographic drawing of the dilated Ureters described in Mr. Oxes’s Paper (No. 25). Piare XV—XXI. To accompany Mr. Henstow’s Paper on the Geology of Anglesea (No. 26). N.B._ A description of these plates is given at the end of the Paper. o, : ial "e4q ' ae a ies 7 ta eT : e y A — Stee » Sane 165 = - ay : a an ee tine at ed a ad & . om, 4) ">a _ 7 cand ae ae - deed ol nee as - Rs is an = 7 a ot 4% 2 Foo cue fini, mp eeigs 4 ae 6 GRR Tam hang Ab Qaepes! ts ig #2 ie Ak IE AN Ree Same Coke t ane SK Tie [0 « eroetehy: ped silly as - eh et ee ee hee ty C Pow 23. T¢ee,.a: Sy Wig ees hase te Be 2° te & Ge FU Gt Oe = - - - ee eee bro B. >) wr2 Pe Ag at ae es _ on »or e* » ae ne a a > Teste WF s4aerrath a eae vin, Org 7 Gee ¢ Nae ry, wu Fo someiney SAcettainkenh Wied i ' W@etee ace = a + hpers ~ die sly & pm ial ee _ = Q Cambridge Philosophical Al Society, Cambridge, Eng. c1g Transactions vel Physical 8 Applied § Serials PLEASE DO NOT REMOVE CARDS OR SLIPS FROM THIS POCKET UNIVERSITY OF TORONTO LIBRARY iS Op Gs alee? ee Lee ae BAAS sane es Py is ~~ » ’ Cee ae L184 8 it a yi) * ft ' ae wee as > e ty Siete ‘ t . Tet eh 89 c Bt ay a0 ; : . ry oF nates ‘ PN Ceara aes ss Pais hp oee Seka . i : - oak Te wit ne ee i¢e a f abets ete = 5 raed i ~ . ~e8 . : OLgld oa alrily Pao } F dasa 4 x : : Sater 5 ‘ Fie * : “Sy wees 3 a ~s . + . 4% MANNS, . a Sees ae 7 4, ’ Sedeuisacts ‘ Leos * . Seta i se ¥ : SSE Sete . TERA % ae Eee ate ete “4 oe SEES SENS SRA REN SNS : S ence A : =o. SRSA Seen CANA ERS Pawns i‘ : SEARS eh ‘ . SOLE Wash ss riche : - ~ ns ane “" ; a +A i : : ” ty . Sy ee Fare Sone ig le ~ Seco ahi wo REE. i e: Nis ot hfe be : Oaks ti . See ah ets nate oy Sept SESE aes ‘ AT ‘ * oN Sse ok » Woes . at aaste? ‘ af: ak Rist QoS . ase RIAA AL RAL , : SSO STS nk uns . ‘ BS OREN Ee x “ Ee A 3 ’ ‘ eee ey . Oe is Ss nnn ey ee . MA Sheettergines eS Ahn ANS ROTOR aT : BOS %, : whe AN Ss ote wes SNe as Fy we r 7 ey RAS SES SEN eagia deers . : Ba SAPS NS as ; spies ey ater thts OS dap S46 i NY te nye, : Crete pen eee i : ~ aan tye “s +* ~ ‘ ‘ ‘ . et hae ae &. a her r giistss : s ’ SEE eS eA Tk SE SSS! . a hah he = i ee ee 4 ‘ SENN re NEES ‘ sath ls SS eee EEN rans Pi ‘ Lae rites ‘ * a ae Ve