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Book Reviews

compare frequencies in intensities and amplitudes, and if we try to give it meaning byconverting the amplitudes to intensities it becomes false . The Seidel aberrations of a thin lensare calculated and "It is interesting to note that the thin lens is free from distortion"! Eitherthe authors do not know or they have forgotten that this statement is only true if the aperturestop is at the lens, not a particularly frequent configuration ; in fact such physical things asstops are nowhere mentioned . In discussing the gaussian optics of a single refracting surface,the Heaviside step function is dragged in to represent the variation of refractive index alongthe axis . Many other examples could be adduced to show the alienation from physics and loveof formalism in this book . I will mention only two more, a diagram in which the incoherentOTF for a square pupil is shown as a pyramid with straight edges, and the suggestion to use aneon lamp with a filter to isolate 6328 .E for a coherence experiment ; this wavelengthcorresponds to a forbidden transition and it could not be obtained from an ordinary neonlamp . The book is claimed to be for "advanced undergraduates and beginning graduatestudents"; I would not recommend it to those or to any other class of student . It could best bedescribed as in the mood of such fin de siecle texts as those of Herman and Heath, both goodsources of mathematical exercises but somewhat lacking in physics. Perhaps ContemporaryOptics will prove useful in the same way .

W. T. WELFORD

Adaptive Optical Components . Edited by SANDOR HOLLY and MAJOR LAWRENCE JAMES .Vol. 141 of SPIE Proceedings . (Society of Photo-Optical Instrumentation Engineers,1978 .) [Pp . 120 .]

THE idea of adaptive or `active' optical components is a fascinating one . Instead of the preciserigidities of traditional optical systems we can think in terms of surfaces that can change shapeor position, as required, to minimize image defects. The ability to do this continuously, to ironout the effects of atmospheric inhomogeneity for example, is only realizable when high-speederror detection systems are available which can provide the data for the immediate calculationand implementation of the control actions necessary to achieve the desired state of perfection .There is obviously a large variety of such systems, many possible criteria of perfection and awide range of methods for implementing the required physical changes . The SPIE seminarcovered by this `yellow jacket' sought to show the results of recent military and commercialapplications of adaptive optics . The four sessions were not filled or arranged in any systematicway, papers on relatively unrelated subjects were mixed together and there would have been aconsiderable gain in the coherence of the presentation if like had been grouped with like .There were two papers of a tutorial nature, one of these was sensibly given right at thebeginning to establish the historical context of the subject and to define the current classes ofapplication . The second was given at the beginning of the second session and covered the mostimportant aspects of wavefront assessment and control .

Only two papers covered instruments which did not make use of induced change incomponent shape . One of these dealt with an optometer embodying an adaptive system whichprovides continuously variable spherocylindrical power and linear scales (in commercialproduction for 5 or 6 years), and the other applies pneumatic focusing control of microscopes,as pioneered by Bovey of Sira years ago, to a fully adaptive automatic microdensitometerscanning system .

It is a pity that the usual errors of spelling and punctuation are still evident and thatterminology continues to be misused in places . Perhaps the greatest omission from thesepatchy proceedings is a paper which makes the limitations of adaptive optics crystal-clear . Theimage monitoring or beam position sampling systems inherently limit adaptive optics to verynarrow fields of application, however important they may turn out to be . B. S. BROWN

Coherence in Spectroscopy and Modern Physics . (NATO Advanced Study Institute Series .)Edited by F. T . ARECCHI, R . BONIFACio and M . O . SCULLY . (New York: Plenum Press,1978.) [Pp . viii+402.] Price £24 . 88 .

A SERIOUS problem in the scientific literature at the present time is that,while there is noshortage of review articles covering a wide variety of topics, most of them start at too high alevel for the reader with little or no previous background in the field of research considered .The answer for the outsider may be to attend a Summer School, or one might hope to consult a

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book, such as the present one, an end-product of such a meeting . The two-week NATO coursein 1977 entitled "Coherence in Spectroscopy and Modern Physics" was undoubtedly anexcellent one to attend, with an impressive array of international speakers and the atmospherepresumably enhanced by the Italian climate . This volume, which consists of written-upversions of the lectures, is unfortunately a little disappointing, although it will obviously serveas a nice memento for the original participants!

The operative part of the title is the ubiquitous word `coherence', which can be applied toalmost any effect concerned with the interaction of radiation (particularly laser radiation) withmatter, and is here interpreted so loosely that in some of the articles the word does not appearat all . There are contributions on numerous aspects of laser (including picosecond)spectroscopy, on superfluorescence and effects with related properties such as superconduc-tivity and surface plasmons, as well as on optical bistability, microwave resonances inbiological systems, two-photon amplification with ultrashort pulses and the free electronlaser . In all, there are 19 articles, some derived from lecture courses and others from individualseminars. The level of presentation is fairly modest, and in some cases the contributionscertainly do serve as reasonable introductions to the topics covered . To single out articles forspecial mention may perhaps be invidious (and the choice may reflect the reviewer's owninterests) ; but the articles by Dr . Richard Brewer on coherent optical transients and by Dr .Serge Haroche on Rydberg state spectroscopy did seem particularly clear and well organizedand will serve as valuable summaries of the respective fields .

The main problem with the book is that for familiar practical reasons it has been produceddirect from camera-ready manuscript with no opportunity for editorial intervention . Thelecturers have had widely differing ideas about what has been expected from them, in terms ofboth quantity and quality . Some have submitted expanded versions of their lectures, otherscontracted versions . Some have benefited from access to word-processing facilities, takingcare to check the text carefully and sending in high-quality printed copy, while others havejust submitted raw typescript, sometimes rich in errors . The result of all this is a patchwork inmany respects . While this volume is therefore perhaps only of limited value to mostindividuals, nevertheless every serious quantum optics research group must definitely order itfor their library .

G. H. C . NEW

Seeing is Deceiving : the Psychology of Visual Illusions . By S . COREN and J . S. Gixeus . (JohnWiley & Sons Ltd ., 1979 .) [Pp . ix+255 .] Price 012 . 70 .

THIS book deals with visual illusions produced-to quote the authors-" by lines scattered onpaper, e .g. the Wundt-Hering illusion in which two parallel straight lines, intersected byradials from a point midway between the lines, appeared to be curved in opposite directions ."The Mach bands, the dynamic illusions discovered by MacKay and the ambiguous figures(such as the Neckar cube) are not included .

The first three chapters describe each of the illusions and illustrate the principal details .Most of the remainder of the book deals with a large number of theories which have beenproposed, usually by psychologists, to explain illusions . The authors generally neither entirelyreject nor entirely accept any of the theories . They consider that most illusions do not have asingle cause, and that no one theory is capable of explaining all the illusions . They devote achapter to an attempt which they themselves have made to classify illusions by examining thevariation in the responses of a large group of observers to 45 illusions. I find this chapterinteresting but not completely convincing .

The authors include, among causes of visual illusions, distortions due to diffraction and toaberrations of the dioptric system of the eye . This field is not their speciality, and somestatements are mistaken . Also, at certain points in the discussion, they should allow forimperfections in the reproduction of the diagrams due to the spread of printing ink and to thetexture of the paper . Figure 12 .2A is incorrect in that the vertical line (measured under amicroscope) is at least 0 .6 mm. longer than the horizontal line to which it should be equal . Thisadds to the illusion .

The book is valuable as a reference book in which can be found details of a large number ofillusions and psychological theories of illusions . Over 400 papers are listed . The book is for thespecialist rather than for the general reader .

R. W . DITCHBURN