... HARTLEY UNIVERSITY COLLEGE, NORTHERN POLYTECHNIC SOUTHAMPTON. INSTITUTE, HOLLOWAY, LONDON, N. (Close to Holloway Stn., G.N.R., and Highbury Stn., N.L.R; SESSION 1905-6. LONDON UNIVERSITY SCIENCE AND ENGINEERING Next SESSION commences on OCTOBER 2, 1905. DEGREES. Courses of Instruction are arranged to meet the requirements of Students Day and Evening Courses in the above under recognised teachers inpreparing for the DEGREES of the LONDON UNIVERSITY, for the MATHEMATICS, UNIVERSITIES of OXFORD and CAMBRIDGE, for the MEDICAL, PHYSICS, CHEMISTRY, ENGINEERING. Subjects. Professors. Separate Laboratories for Elementary, Advanced and Honours students, (Prof. W. F. Masom, M.A. (Camb. exceptionally large and well equipped. Classics and English Literature... and Lond.), Fellow of University RESEARCH. Special arrangements for students undertaking research during vacations Full particulars at the Institute or sent on receipt of postcard. late Historical Scholar of Peter REG. S. CLAY, D.Sc., Principal house, Cambridge. French and German Prof. L. J. LHUISSIER, M.A.(Camb. BEDFORD COLLEGE FOR WOMEN. (Prof. E. L. WATKIN, M.A. (Camb.), Mathematics late Scholar of St. John's College, (UNIVERSITY OF LONDON.) | Cambridge. Physics and Electrical Engineer The Principal. YORK PLACE, BAKER STREET, LONDON, W. ing The SESSION 1905-6 will open on THURSDAY, OCTOBER (Prof. D. R. Boyd, D.Sc. (Glasgow), Students are requested to enter their names on Wednesday, Octobe: 4 Chemistry Ph.D., F.I.C., late Examiner in Lectures are given in all branches of General and Higher Educatir. Chemistry for Glasgow Univer- Taken systematically, they form a connected and progressive Course : tu sity. a single Course in any subject may be attended. Biology and Geology sProf. F. CAVERS, D.Sc. (Lond.), Courses are held in preparation for all Examinations of the University 1 A.R.C.S., F.L.S. of London in Arts and Science, for the Teachers' Diploma (London) ar Civil and Mechanical Engineer- (Prof. J. EustiCE, B.Sc. (Lond.), for the Teachers' Certificate (Cambridge), and also a special Course ing ... A.R.S.M., A.M.I.C.E. Scientific Instruction in Hygiene. Education, Professor and Master /F. FLETCHER, B.A., late Classical Six Laboratories are open to Students for Practical Work. Exhibitioner, Balliol of Method... College, ... Oxford. Two Entrance Scholarships will be offered for competition in June, 190 The Early English Text Society's Prize will be awarded in June, Igor Particulars of the Scholarships and Exhibitions open for competition, and Prospectuses of all Departments, may be obtained on application at the Students can reside in the College. College. TRAINING DEPARTMENT FOR SECONDARY TEACHERS. D. KIDDLE, Registrar. A Scholarship of the value of £20 for one year is offered for the CvarsAugust 21, 1905. of Secondary Training, beginning in October, 1905. The Scholarship will be awarded to the best candidate holding a degree ENGINEERING. or equivalent in Arts or Science. Applications should reach the Head OF THE TRAINING DEPARTMENT NORTHAMPTON INSTITUTE, not later than September 18. CLERKENWELL, LONDON, E.C. BOROUGH POLYTECHNIC ENGINEERING DAY COURSES IN MECHANICAL, INSTITUTE ELECTRICAL, AND HOROLOGICAL ENGINEERING. (Five minutes from Blackfriars, Waterloo, and Westminster Bridgest FULL DAY COURSES in the THEORY and PRACTICE of the 103 BOROUGH ROAD, S.E. above subjects will commence on MONDAY, OCTOBER 2, 1905. ENTRANCE EXAMINATION on WEDNESDAY and THURSDAY, TECHNICAL CHEMISTRY AND ELECTROCHEMISTRY DAY COURSE. A complete Day Course extending over two years has been arranged im Technical Chemistry. With the object of providing as complete a cours spent in Commercial Workshops, and extend over four years. They also of training as possible, instruction will be given in MATHEMATICS prepare for the degree of B.Sc. in Engineering at the University of London. Fees for either of these Courses, £15 or Eu per annum. PHYSICS, ENGINEERING DRAWING, PRACTICAL MECHAN ICS. FRENCH, GERMAN, METAL and WOOD WORKING, au Three Entrance Scholarships of the value of £52 each, giving free in GENERAL 'CHEMISTRY, and throughout the Course parte 2 tuition for the full course in Mechanical or Electrical Engineering, will be attention will be paid to ELECTROCHEMISTRY, for which a Spel offered for competition at the Entrance Examination in September next. Laboratory has been fitted. Conditions can be obtained from the PRINCIPAL. FEE FOR THE COURSE, OCTOBER TO JULY, IN Full particulars as to fees, dates, &c., and all information respecting the work of the Institute, can be obtained at the Institute or on appli- Intending students must give evidence that they are capable of following cation to the Course with advantage, or they may be required to attend a Fre R. MULLINEUX WALMSLEY, D.Sc., Principal. liminary Course. Full particulars can be obtained on application to C. T. MILLIS, Principa' MERCHANT VENTURERS' WIGAN TECHNICAL COLLEGE, BRISTOL. MINING & TECHNICAL COLLEGE. PRINCIPAL-Prof. J. WerTueIMER, B.Sc., B.A., F.I.C., F.C.S. ENGINEERING-Prof. J. MUNRO, A.R.C.S., M.I. Mech. E. ; Prof. Principal - THOMAS T. RANKIN, C.E., B.Sc., M. Inst. M.M., M.I.M.E. SANDWICH SYSTEM OF MINING TRAINING. DAY MINING COURSES. In addition to the above the College Staff includes seventy-nine Assistant Opening date, MONDAY, OCTOBER 2, at 9 a.m. Lecturers, Demonstrators, and Skilled Artisans. There are eleven Labora Complete Diploma Course extends over a period of three or four years tories, eight Workshops, Experimental Engines and Electric Light and Two Prizes of £10 108. each awarded annually Power Station. Candidates for Colliery Managers' Certificates of Competeary boldere COURSES for CIVIL, MECHANICAL, MINING and ELECTRI | the above Diploma will be exempt from two out of the five years' practica CAL ENGINEERS, CHEMISTS, ARCHITECTS, and BUILDERS. experience required by the Coal Mines Regulation Act. UNIVERSITY of LONDON-COURSES for MATRICULATION The Home Secretary has approved for the purposes of the Coal Mine and INT. and FINAL B.Sc. (including the Engineering Degree). Regulation Act (1887) Amendment Act, 1903, the Diplomas of this Colege Prospectus post free on application to the PRINCIPAL, or FEE: TEN GUINEAS A YEAR. T. RATCLIFFE ELLIS, Hon. Sec Calendar (64.) or short Prospectus (free) on application to the BIRKBECK COLLEGE ... i New Session begins Monday, October 2, 1905. EAST LONDON COLLEGE (LATE EAST LONDON TECHNICAL COLLEGE), BREAMS BUILDINGS, CHANCERY LANE, E.C. MILE END ROAD, E. New SESSION commences SEPTEMBER 18. SCIENCE AND TECHNICAL SIDE. the University of London. Mathematics {"J. L. S. HATTON, M.A., and Chemistry SJ. E. MACKENZIE, Ph.D., D.Sc. ***W. F. S. CHURCHILL, M.A. 1 H. WREN, Ph.D., B.A., B.Sc. Physics J*R. A. LEHFELDT, B.A., D.Sc., and ** *W. H. WHITE, B.A., B.Sc. Physics ... D. OWEN, B.A., B.Sc. Chemistry /*J. T. HEWITT, M.A., D.Sc., Ph.D., and *C. SMITH, D.Sc. Mathematics E. H. SMART, M.A. Botany *V. H. BLACKMAN, M.A. Botany {: , . /*D. A. Low, M.I.M.E., and Engineering *** *J. A. DAVENPORT, M.Sc. Zoology ... H. W. UNTHANK, B.A., B.Sc. Electrical Engineering *J. T. MORRIS, M.I.E.E. Geology & Mineralogy Geo. F. HARRIS, F.G.S. ARTS SIDE. /*J. L. S. HATTON, M.A., and French, German, Spanish, Russian, and Italian Classos. *W. F. S. CHURCHILL, M.A. Latin and Greek *F. R. EARP, M.A. EVENING CLASSES in Biology, Physiology, Practical Geometry, English Language and Literature * KATE M. WARREN. Building and Machine Construction, Steam, Theoretical and Applied History *T. SECCOMBE, M.A. Mechanics. French * W. G. HARTOG, B.A. Calendar 6d. (post free 8d.), on application to the SecretARY. German CONSTANCE B. Low, M.A. * Recognised Teacher of the University of London. THE UNIVERSITY OF LIVERPOOL. Fee for the full Day Course, 10 Guineas per Session. Numerous Scholarships of the value of £40 per annum, and tenable at SESSION 1905-6 COMMENCES OCTOBER 2. the College for three years, are awarded by the Drapers' Company. Evening Courses for the Science and Engineering degrees are also held, FACULTY OF ENGINEERING. the fees for which are from Two Guineas to Five Guineas per Session. THE VICE-CHANCELLOR. CALENDAR, post free 4fd., on application. JOHN L. S. HATTON, M.A., Director of Studies. WESTMINSTER HOSPITAL MEDICAL ENGINEERING SHarrison Professor-W. H. WATKINSON, SCHOOL, (David Jardine Professor-E.' W. MAR. CAXTON STREET, S.W. Professor F. S. CAREY, M.A. A SCHOOL OF THE UNIVERSITY OF LONDON. The WINTER SESSION will commence on MONDAY, OCTOBER 2, CHEMISTRY | Grant Professor-J. CAMPBELL BROWN, 1905. Scholarships of the aggregate value of £320 are offered to students " D.Sc., F.C.S., É.I.C. entering in October. Examination on September 26 and 27. Fees 110 Gns. RAILWAY ENGINEERING JAssociate Professor-J. A. F. ASPINALL, if paid in one sum on entrance. For University Students and those who i M. Inst.C.E. MUNICIPAL have completed their anatomical and physiological studies 70 Gns. Special JAssociate Professor-J. A. BRODIE, opportunities for Clinical work and for holding the various hospital appointENGINEERING M. Inst.C.E. ments. Dental students are specially provided for. MUNICIPAL ELECTRICAL Associate Professor A. BROMLEY ENGINEERING... Prospectus and further particulars may be obtained from the Dean. ...! HOLMES, M. Inst.C.E., M.I.E.E. ENGINEERING DESIGN Lecturer J. WEMYSS ANDERSON, Telegrams: "Clinic," London. Telephone : Victoria 765. AND DRAWING... ... Assoc. M.Inst.C.E., M.I. Mech. E. APPLIED MECHANICS Lecturer-J. H. GRINDLEY, D.Sc. UNDER THE AUSPICES OF His MAJESTY'S GOVERNMENT, The courses of study in the Faculty leading to the ordinary degree of Bachelor of Engineering or the certificate in Engineering are so arranged THE LONDON SCHOOL OF TROPICAL as to afford a general scientific training for those intending to become MEDICINE. engineers or to enter any allied profession. The Honours course enables students to specialise in some branch of the profession, and opportunities (UNIVERSITY OF LONDON.) are afforded for post.graduate work and research. The special prospectus of the Faculty may be obtained on application to CONNAUGHT ROAD, ALBERT DOCK, E. the REGISTRAR. (IN CONNECTION WITH THE HOSPITALS OF THE SEAMEN'S Hospital SOCIETY.) BATTERSEA POLYTECHNIC, S.W. The next SESSION commences on MONDAY, OCTOBER 2, 1905. For Prospectus, Syllabus, and other particulars, apply to the Secretary, P. MICHELLI, Esq., Seamen's Hospital, Greenwich, S.E. THE UNIVERSITY OF LEEDS. The next SESSION will begin on OCTOBER 2. lated Students attending these Courses are registered as Internal Students University Degrees are conferred in Arts, Law, Science, and Medicine, of the University. The Classes also prepare for the following professions : -Chemistry, Mechanical Engineering The PRINCIPAL and J. W. Buttov, Civil, Mechanical, and Electrical Engineering, Mining, Textile Industries, A.R.C.S., A.M.I.M.E. Dyeing, Leather Manufacture, Agriculture, School Teaching, Commerce, Law, Medicine and Surgery. Electrical Engineering and / W. THOMSON, M.A., B.Sc. Lyddon Hall has been licensed for the residence of students. Physics |(One Vacancy.) Prospectus of any of the above may be had post free from the REGISTRAR. Chemistry (J. Wilson, M.Sc., and J. L. WEITE, D.Sc. Mathematics THE UNIVERSITY OF SHEFFIELD. G. E. St. L. CARSON, B.A., B.Sc. The Laboratories are also open for Research Work. SESSION 1905-6. Technical Day College Courses in Mechanical, Electrical, and Motor The SESSION OPENS as follows :Engineering, in Architectural and Constructional Work, and in Chemistry. FACULTY OF APPLIED SCIENCE September 11 Abridged Prospectus gratis on application. FACULTY OF ARTS ... October 4 Detailed Prospectus id., post free 3d., on application to the SECRETARY. FACULTY OF PURE SCIENCE October October 4 W. M. GIBBONS, Registrar. INSTITUTE. ASSISTANT MASTER (Science Graduate) required, Physics and Chemistry. Commencing salary, £150. Application Forms and statement Moderate Terms-Individual Assistance-Full Notes. of duties to be obtained from the REGISTRAR. Address---Mr. H. J. SMITH, B.Sc. (Lond.), Rosebery House, Breams Buildings, Chancery Lane, London, E.C. For other Scholastic Advertisements, see pages cc and ccii. 4 MATRIC., INTER., FINAL B.A. & B.Sc. .. SOUTH-WESTERN POLYTECHNIC, THE SIR JOHN CASS TECHNICAL INSTITUTE, JEWRY STREET, ALDGATE, E.C. The Day College Courses consist of 30 hours per week, and are in pre- Principal Charles A. KEANS, M.Sc., Ph.D., F.I.C paration for London University degrees of B.Sc. in Mechanical and Elec- EVENING CLASSES in CHEMISTRY, METALLI'RGY, irical Engineering, in Chemistry, Physics and Natural Science. PHYSICS and MATHEMATICS designed to meet the requirements of The composition fee for the Session of 3 terms is £15. those engaged in CHEMICAL, METALLURGICAL and ELECTRICAL The Evening Classes consist of similar courses at much reduced rates. INDUSTRIES and in trades associated therewith. The Technical Day Courses are arranged to extend over 3 years and prepare for Engineering, Electrical, Chemical and Metallurgical professions. Chemistry CHARLES A. KEANE, M.Sc., Ph.D., F. 1.C., anat H. Burrows, A.R.C.S., Ph.D., EIC.. Mathematics ** W. H. ECCLES, D.Sc. Physics ... R. S. Willows, D.Sc., M.A. 1 * J. LISTER, A.R.C.S. Metallurgy C. O. BANNISTER, A«soc. R.S.M. Mathematics G. M. K. LEGGETT, B.A. Every facility for special and advanced practical work in well-equippe laboratories both in the afternoon and evening. J. B. COLEMAN, A.R.C.S. Also preparation for the B.Sc. Examination of London Uni. * J. C. CROCKER, M.A. versity under recognised teachers of the University. Chemistry F. H. Lowe, B.Sc. Courses of Instruction in Glass Blowing will be given during the Session by Mr. A. C. Cossor. NEW SESSION begins MONDAY, SEPTEMBER 25. Botany * T. G. HILL, A.R.C.S. For details of the Classes apply at the Office of the Institute, or Geology * A. J. Maslen, F.L.S. letter to the PRINCIPAL. W. H. DAVISON, M.A., Clerk to the Governing Body. Engineering A. MACKLOW SMITH. To SCIENCE and MATHL. MASTERS.- REQUIRED immediately, (1) Science Master for important Endowed B. H. MORPHY, B.Sc. School and Technical Institute. Chemistry and Physics Only 2• Recognised Teacher of the University of London. hours' work weekly. Salary, 6200, non-resident. (2) Matbematica The Laboratories and Workshops are open for Research under the Master for School in W. London. University man preferred LIS, non-resident. - For particulars of the above and many other vacances direction of the Principal and the Heads of Departments. address GRIFFITHS, SMITH, POWELL AND SMITH, Tutorial Agerts Further particula's may be obtained on application to the SECRETARY, (Estd. 1833), 34 Bedford Street, Strand, London, who will send a full prospectus, post free, 4d. Prospectuses may be obtained at the office, price id. SIDNEY SKINNER, M.A., Principal. OUNDLE SCHOOL, NORTHANTS. A DEMONSTRATOR in the ENGINEERING LABORATORY. and TEACHER of MECHANICAL and MACHINE DRAWINI, PRACTICE) wanted. Experience in Workshop and Drawing Office. Commencing In BIOLOGY, BOTANY, CHEMISTRY and PHYSIOLOGY for salary, 6150 to £200 a year. Applications, with copies of testim nials and MEDICAL EXAMS. references, to be sent to the HEADMASTER. INSTITUTE. Wanted immediately, TEACHER OF ART for Day and Evening (Registered in Column B (Advanced Education), Teachers Registration Classes, and also for the Pupil Teachers' Centre. Time occupied abwat Council, Board of Education, S.W.), 20 hours per week Annual salary, 4110. Applications must be recave 49 and 51 IMPERIAL BUILDINGS, LUDGATE CIRCUS, E.C. by September 28. A. S. CAMPBELL, Secretary. 10 Vivian Road, Wellingborough. HARRIS INSTITUTE, PRESTON. For other Scholastic Advertisements, see pages cc and cci. ASSISTANT MASTER required for School of Art. Specially qualified to teach Perspective and Geometry, and to assist in giving instruction to the students attending the Pupil Teacher Centre. The duties amount to Chemist and Assistant Works Manager about twenty hours a week, and opportunities will be afforded for private required for a responsible position in a works near London where study. Salary, 670. Applications, stating age, qualifications and previous secret and patented processes are in operation. Commencing salary, experience, with three testimonials, to be forwarded to the undersigned £200. Investment of 62000 necessary.-Address Box 1873, NATURE before October 4. Office. CHEMICAL BALANCE for Sale; short NORTHAMPTON INSTITUTE, beam; by Bunge, Hamburg. In perfect condition ; very little to Accept 411. Can be seen by arrangement with H. S. Jxrons, LONDON, E.C. 19 Chesterford Gardens, Hampstead, N.W. The Governing Body invite applications for the appointment of INSTRUCTOR in MATHEMATICS in the Engineering Day Courses, Attendance required for 2 hours on four mornings per week. Salary, Forms of application (which should be returned at once) and further By E. L. N. ARMBRECHT. Soure, Melting Point, Properties, Salts of, Price, &c. ARMBRECHT, NELSON & CO., 71 & 73 Duke Street, Grosvenor Square, W. The Governing Body invite applications for the post of DEMON. N.B. - Sent Free on application. STRATOR in PHYSICS. The work of the Demonstrator will consist partly in conducting Physics Classes of the Secondary Day School and partly in assisting in the adult Physics Classes in the Institute. A graduate in Physics would receive preference. SEND FOR DETAILS OF OUR Commencing salary. 6120 per annum. MICRO-SLIDE LENDING For form of application, to be returned by September 28, apply to the SECRETARY. DEPARTMENT. Covering every Branch of Natural Science. SUBSCRIPTION €1:1:0 FOR 240 SLIDES. Over 58,000 Slides have already been circulated. WANTED immediately, an ASSISTANT HEAD MASTER Salary, 1 The Boxes are accompanied by descriptions of thet contents, £200. One holding the Electrical Engineering Diploma of a Technical concisely written by well-known authorities in the different College with experience in Works and Teaching preferred. departments. Applications to E. A. O'KEEFFE, B.E., M.I.E.E., d., C. BAKER, 244 HIGH HOLBORN, LONDON, W.C. TABLE OF RARE ELEMENTS. HEELE'S FAMOUS SPECTROMETER. Price £10 10 0 Including dense flint glass prism, with micrometer movement, reading to 1 minute. Universally acknowledged to be the most efficient instrument on the market. Also, smaller size, Price £6 nett, including two prisms, one being a hollow prism. As supplied to the Royal College of Science, Dublin, University College, Gower St., London County Council, St. Munchin's College, Limerick, and many other leading Institutes. DELIVERY FROM STOCK. PETER HEELE, 115 High Holborn, W.C. MAKER OF PHYSICAL, ASTRONOMICAL, AND OTHER INSTRUMENTS. IMPORTANT REDUCTION IN PRICE. SPINTHARISCOPE. HOPKIN & WILLIAMS, Ltd. Works-ILFORD, E. Revised Price List. NEW DOUBLE SURFACE CONDENSER. AS DEVISED BY The scintillations seen in this instrument are Dr See letter from PROF. Gotch on " The Spinthariscope and Retinal Excitability" (NATURE, June 22, 1905, page 174), setting forth a valuable scientific application of the A.C.COSSOR LONDON instrument. A. C. COSSOR, Telephone, 10547 Central. MINERALS purposes. Price List on Application. HARRINGTON BROS., Chemical Manufacturers and Dealers, 4 OLIVER'S YARD, CITY ROAD, LONDON, E.C. THE “IDEAL.” This is the best and cheapest Condenser on the market; all delicate parts are protected by outer jacket, and the water cannot overflow into the distillate. Made in two sizes, 6" and 8", 4/6 and 5/6 each. Ir Nature says :-“This is one of the most com. pact and efficient condensers which has come before our notice. We have tested it for condensing such volatile substances as ether, carbon disulphide, and acetone, and have found that even with rapid distillation the condensation is very complete. Generally speaking, in order to condense these substances satisfactorily, it is necessary to employ a very long condenser; of course, this means using a great amount of bench space. As the new condensers are used in a perpendicular posi. tion, the saving in space is very great." SOLE MAKERSBREWSTER, SMITH & Co., 6 CROSS STREET, FINSBURY PAVEMENT, LONDON, E.C. All kinds of Apparatus for Science Teaching. WITH ENHANCED STEREOSCOPIC EFFECT. x6, £6 0 0. : FOR TOURISTS. 0 SPECIAL TYPES FOR NATURALISTS, MARINE WORK, HUNTING, &c. Illustrated Catalogue,"In," Post Free on Application. NATURE says:--" The firm of Leybold Nachfolger in Cologne has recently issued a very complete and interesting catalogue of physical apparatus and fittings sold by them. The book starts with a history of the instruments made in Cologne during the last century. In its second section we find an account of the construction and fittings of various chemical and physical institutions. After this follows the catalogue proper, filling some 800 large pages, profusely illustrated and admirably arranged. The book will be most useful to the teacher." (No. 1846, Vol. 71.) CARL ZEISS, JENA. Branches : LONDON: 29 Margaret St., Regent Street, W. Berlin, Frankfort o/M, Hamburg, Vienna, St. Petersburg. THE CATALOGUE WILL BE FORWARDED TO SCHOOLS AND INSTITUTES ON APPLICATION. LIQUID AIR AND LIQUID HYDROGEN. Dr. HAMPSON'S AIR-LIQUEFIER is now made to a standard pattera, and numbers are in use in University Laboratories and elsewhere in various countries. The whole apparatus is neat and compact and its parts very easily moved ; the Liquefier, without stand, being a cylinder 17 inches high and 8 inches in diameter. It begins to liquefy air in from 6 to 10 minutes after the admission of air at from 150 to 200 atmospheres pressure, making over a litre of liquid per hour. It requires no auxiliary refrigerant and produces a perfectly clear liquid which requires no filtering The operator has only one gauge to watch and one valve to control. HYDROGEN LIQUEFIER to the designs of Dr. MORRIS W TRAVERS for use in conjunction with Air Liquefier. BEWARE OF DO YOU WISH PEEBLE DITATION the Kersbaw. Patent Lantern (Stroud and Rendall's and Kershaw Patents), made of best seasoned mahogany, French polished, lined with asbestos and Russian iron. Fitted with two double achromatic objectives, go silvered_prism, complete with B.T. or mixed jer, in travelling case, measuring 23" X 16" x 9". STANDS, &c CONTRACTOR TO H.M's GOVERNMENT. For Prices and Particulars apply to the Sole Makers :BRIN'S OXYGEN COMPANY, LIMITED, ELVERTON STREET, WESTMINSTER, S.W. LAW OF HELICAL SPRINGS The apparatus figured is substantially as described in Pro.. Perry's “ Applied Mechanics," and demonstrates the approximate truth of the following proposition :- If a given force be applied to deform a given length of wire, the point of application of the force suffers the same linear displacement, whether the wire is straight and the force applied to produce torsion in it from one end, or whether the wire is coiled into a clo e helix and the force applied axially to produce extension from one end ; provided that the arm of the effective moment in ihe first case is equal to the mean radius of the helix in the second case. Price £4 0 0 THE CAMBRIDGE SCIENTIFIC INSTRUMENT COMPANY, LTD., |