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ROYAL INSTITUTION OF The UNIVERSITIES of MANCHESTER,

GREAT BRITAIN.

ALBEMARLE STREET, PICCADILLY, W. TUESDAY next, March 21, at Five o'clock, Professor W. E. DALBY, M.A., B.Sc., M. Inst.C.E. First of two lectures on Engineering Problems." Half-a-Guinea the Course.

THURSDAY, March 23, at Five o'clock, THOMAS G. JACKSON, Esq., R.A., M.A., F.S.A. First of two lectures on "The Reasonableness of Architecture." Half-a-Guinea.

Subscription to all Courses in the Season, Two Guineas.

DEPARTMENT OF TECHNOLOGY. CITY AND GUILDS OF LONDON

INSTITUTE.

EXAMINATIONS in TECHNOLOGY will be held from April 29 till June 24.

All applications from Local Secretaries for Examinations in Technology must reach the offices of the department on or before MARCH 20.

Only by payment of an additional fee can applications be received after that date.

Candidates in Technology not attending any registered class should apply

LIVERPOOL and LEEDS.

The next MATRICULATION EXAMINATION will commence on Wednesday, July 5, 1905, and will be held simultaneously at the three Universities and in Schools approved by the Joint Matriculation Board. The fee is due on or before June 3.

Information as to Scholarships awarded on the results of this examination and on other matters may be obtained from the undersigned. R. F. GWYTHER,

Secretary to the Joint Matriculation Board,
Owens College, Manchester.

the

FOR SALE-The Instruments in Observatory of the late Mr. Edward Crossley: a 9-in. and a fin (both photo-visual object glasses) Equatorial Refractor by Cooke; a 3in. Transit Circle by Cooke; a 6-in. Sextant and a 5-in. Transit Theodolite by Troughton and Simms; Siderial Clock by Cooke; Parallel-wire and Double-image Micrometers by Troughton and Simms; Microscopes by Ross and Zeiss; Apparatus for Lectures on Light, Polarisation, &c., by Harvey and Peak; Measuring Bars and Rods-12-in., 40-in., 3-ft., 10-ft.-by Troughton and Simms; Standard Barometer by Hicks; Two Spectroscopes; Two Controlled Clocks.Apply to Mr. J. GLEDHILL, Bermerside, Halifax.

AT ONCE to the Secretary of the nearest Technical School or Local Centre. Hepatica Britannica Exsiccatæ, being a

It is only in very exceptional cases, when no other arrangements can be made, that applications will be entertained for the examination of candidates at the Offices of the Department. All such applications should be addressed to the DEPARTMENT OF TECHNOLOGY, CITY AND GUILDS OF LONDON INSTITUTE, EXHIBITION ROAD, LONDON, S.W., and should be accompanied by a Postal Order for 1s. 6d. in addition to the amount of the fee, as given in the programme, the subject and grade of the Examination being clearly stated.

TO SCIENCE, MATHEMATICAL AND OTHER MASTERS.-Required (1) Second Master for important Grammar School-Mathcs. and Science. Salary, £160 to £180. (2) Head Master for Public Institution School near London. Knowledge of Commercial Education necessary. Age 35 to 45, unmarried. Salary, £200, with board and private rooms. (3) Chemistry, Botany and some Physics, £150 to £160. (4) Chemistry, Mathcs. and Botany, £140. Particulars of the above and other Science posts will be sent on application. Candidates seeking appointments either at once or for after Easter are invited to apply forthwith. Address, Griffiths, Smith, Powell and Smith, Tutorial Agents (Estab. 1833), 34 Bedford Street, Strand, London.

B.A. AND B.Sc. EXAMS.

MATRICULATION, INTERMEDIATE, FINAL. PREPARATION by CORRESPONDENCE and ORAL TUITION on a THOROUGHLY INDIVIDUAL SYSTEM. Fees based on

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80 Wigmore Street, Cavendish Square, London, W. (late 44 Old Bond Street).

MATHS. and SCIENCE.

Attractive Appt. Experienced and successful Army Tutor desires to meet with a Univ. man with above quals., able to take responsibility of Vice-Principal, with view to, later, sharing profits, and a possible partnership. Age 26-32. Salary, £150, res., or £200, non-res. Many other Science Appts. Write or call, NEEDES & SELLICKS, Clock House, Arundel Street, Strand, W.C.

MERCHANT VENTURERS'

TECHNICAL COLLEGE, BRISTOL. JUNIOR ASSISTANT for PHYSICS; £130 to 160. Particulars obtainable from the REGISTRAR by sending a stamped addressed foolscap envelope, not later than March 23, 1905.

CHEMIST, B.Sc. (1st Class Honours in

Chemistry), Ph.D., F.I.C., late 1851 Exhibition Science Scholar, with large experience in Chemical research and in quick and accurate methods of analysis, including all classes of minerals, gas analysis, foods and commercial products, desires permanent and responsible position in Works or Laboratory (as partner or chief assistant), or where experience would be useful; Great Britain or abroad, climate and distance no object. Has held several important appointments, and understands the handling of workmen. Energetic, and speaks German and Spanish. Excellent testimonials. Salary required, £100 to £150 to commence Please address "B. M.," c/o NATURE.

with.

Collection of 100 Specimens of British Hepaticæ, including many rare species, carefully prepared, named and mounted. Price 1 5s.-W. H. PEARSON, Park Crescent, Victoria Park, Manchester.

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A.

Fraunhoffer, &c.

LISTS ON APPLICATION.
CLARKSON & CO.,

28 BARTLETT'S BUILDINGS, HOLBORN CIRCUS, LONDON, E.C.

DRAWING INSTRUMENTS.

Best Make and Finish.
SET SQUARES,

T SQUARES,

DRAWING BOARDS.

Obtained through any Optician.

ROBERT NICHOLL, 153 HIGH HOLBORN, LONDON.

FOR SALE, at Reduced Prices.

MICROSCOPIC SLIDES (dispersal of Mr. Hornell's collection), ser Micro. Editor's note, June No. of Knowledge, Sections of Flower Bod &c., also Marine, suitable for Students and Exhibition, prices from 3d. each.

MICROSCOPE, Baker's D.P.H. and fittings, £7 165.; Beck's London and fittings, £6 6s.; many others, Pillisher, Ross, &c. Objectives. Bail's Eye Condensers. Abbe Condensers. Goerz PRISMATIC BINOCULARS Photographic Lenses. SURGEON'S OPERATION Outfit, very fine. new, for sale, cheap. LANTERN SLIDES, English Church Arch tecture. Many other useful articles. Lists.

Mr. HERBERT CLARKE, 104 LEADENHALL STREET, LONDON.

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46, HATTON GARDEN, LONDON, E.C.

Telephone No. 1981, Holborn. Telegrams-"Rapkin, London." ACTUAL (WHOLESALE) MAKERS OF ALL KINDS OF METEOROLOGICAL INSTRUMENTS. Quarto (11 x 8), cloth. 24s. net.

A MONOGRAPH OF

THE ANOPHELES MOSQUITOES
OF INDIA.

By Capt. S. P. JAMES, M.B. (Lond.), and
Capt. W. GLEN LISTON, I.M.S.

With 15 Full-page Coloured Plates, 64 Illustrations in Half-Tone (on 15
Plates), a Map, and 30 Diagrams and Illustrations in the Text.

Second Edition. Demy 8vo, cloth. 75. 6d. net.

MALARIAL FEVER

AND MALARIAL

PARASITES

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THURSDAY, MARCH 16, 1905.

MODERN OPTICAL THEORY.

An Introduction to the Theory of Optics. By Prof.
A. Schuster, F.R.S. Pp. xv+340.
(London :
Edward Arnold, 1904.) Price 15s. net.

PROF. SCHUSTER has done excellent service

to teachers and students alike by publishing this book, which fills a very obvious gap. It is an introduction to the theory, and purposely does not deal with details of methods of measurement or instrumental appliances; these are properly left to courses of laboratory instruction. At the same time the necessity for experiments and observations is every where present to the author's mind. The book is not a mere mathematical treatise on simple harmonic motion; indeed, the analysis is generally easy, and purely mathematical difficulties are avoided. Prof. Schuster writes as a physicist. The physical meaning of the steps and processes employed is everywhere insisted on, and the student is made to think through

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"The equations which at present represent the electromagnetic theory of light have rendered excellent service, and we must look upon them as a framework into which a more complete theory must necessarily fit, but they cannot be accepted constituting in themselves a final theory of light. "The study of physics must be based on knowledge of mechanics, and the problem of light will only be solved when we have discovered the mechanical properties of the ether. While we in ignorance on fundamental matters concerning the origin of electric and magnetic strains and stresses, it is necessary to introduce the theoretical study of light by a careful treatment of wave propagation through media the elastic properties of which are known. A study of the theory of sound and of the old elastic solid theory of light must precede therefore the introduction of the electromagnetic equations."

The book proceeds on these lines; the first part is almost entirely kinematical; the second part deals with theories of light, starting first from an analysis of the equations of motion of an elastic medium; then passing to those of the electromagnetic field, and developing the two theories side by side as .far possible.

as

To turn now to some details. In the earlier chapters, in accordance with the views expressed in

the preface, the author deals with the properties of vibrating mechanical systems, e.g., the air in a closed space, or a stretched string. After some discussion as to periodic motion in general, the equation of motion for an elastic body, propagating plane waves of distortion, is found in an elementary manner, and certain fundamental results are shown to follow from its similarity to the equation for a stretched string. Huyghens' principle of the superposition of small motions is explained, and then the reader, after a chapter on the nature of light, is introduced to the principle of interference.

The problems of diffraction are treated very fully, making use of the method of Fresnel's zones; the method is modified by the author in a manner which permits numerical results of a high order of accuracy to be obtained without the introduction of Fresnel's integrals.

After an interesting chapter on diffraction gratings we come to one on the theory of optical instruments, in which the resolving power of telescopes and spectroscopes is carefully discussed. The theory of the microscope does not find a place in Prof. Schuster's book; perhaps it belongs rather to the domain of geometrical optics.

Fresnel's theory of double refraction is given very fully, and it is based not on any unsound dynamical reasoning, but on the observed experimental fact that the velocities of wave propagation of a plane wave moving through a crystal are given by the axes of the section of a certain ellipsoid by the plane of the wave; this is clearly the right way to deal with this problem. When the laws of the propagation of light in a crystal are once determined the discussion of the rays and brushes due to the interference of polarised light follows easily, and thus we are led to Part II., which, as has been already said, deals with theories of light.

The equations of motion are found both on the elastic solid and electromagnetic theory, and the simpler phenomena are considered from both standpoints.

The weak points of the elastic solid theory, however, soon manifest themselves, and for the rest of the book the equations of the electromagnetic theory are mostly used; in dealing with dispersion Sellmeyers' hypothesis of sympathetic vibrations is applied to the electrons of a molecule, following Drude, and the usual expression connecting the refractive index and the frequency obtained; the same method is applied to explain the rotatory effects of sugar and other active substances, and in a most interesting series of sections the Zeeman and other allied effects are dealt with. In the last chapter we have a discussion on the nature of light as the resultant disturbance arising from the individual vibrations of the molecules of the source. Enough has probably been said to show the nature of the book, but one characteristic should not be omitted. Prof. Schuster has included short historical accounts of the men who have made the science of physical optics. Among them we find the names of Young, Fresnel, Cauchy, Stokes, and Maxwell; the interest

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