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PETER MEYER January 6, 1920-March 7, 2002 BY EUGENE N. PARKER PETER MEYER WAS AN experimental physicist who clevotecl his career to the mysterious origins en c! behavior of the cosmic rays, contributing substantially to present knowlecige of the diverse components of the cosmic rays. He was a frienc! en c! colleague whose presence macle the clay more interesting en cl the clifficulties less onerous. He was a clevotecl family man. He and his first wife, Luise Meyer-Schutzmeister, a prominent nuclear physicist, were enthusiastic skiers, campers, en cl mountain hikers. Music was a continuing passion. He was an excellent cellist en cl Luise a pianist. They participates! in regular chamber music evenings at their home, for their own pleasure en cl for the pleasure of those privilegecl to join in or merely to listen. Luise cliecl in 1981, en c! Peter marries! Patricia Spear, a microbiologist, in 1983. Peter and Pat actively pursued their common interest in music en cl the outdoors en cl travelecl wiclely, in aciclition to working intensely on their respective research interests. These many intense activities seemed only to refresh him for his continuing scientific assault on the elusive cosmic rays. Peter hac! to give up many of his activities cluring the last few years of his life clue to illness, but he clicl so with grace en cl style en cl continual to engage his friends en cl family with his wit en c! humor. 141

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142 B I O G RA P H I C A L EMOIRS Peter Meyer was born in 1920 in Berlin. He stucliec! at the Technische Hochschule Berlin with the famous physicist Hans Geiger as one of his teachers. His Diplom Ingenieur thesis in 1942 clealt with proportional counters. As the son of a Jewish physician en cl German mother he was cleniecl the "honor" of fighting for the fatherIancI, with the result that he survives! the war as a factory worker. His father also survived, thanks to the efforts of some of his patients. After the war Meyer continual his studies in physics at the University of Gottingen. He obtainer! his Ph.D. in 1948 uncler the direction of Wolfgang Paul (Nobel Prize in physics in ~ 989) en cl Hans Kopfermann with a precise measurement of the bincling energy of the cleuteron ~ ~ 949) . He continued working in experimental nuclear physics at Gottingen, with a year at the Cavenclish Laboratory at Cambridge University ~ ~ 950) . Then from ~ 950 to ~ 953 he was a staff scientist at the Max Planck Institute for Physics in Gottingen. In 1953 Meyer came to the Unitecl States en cl accepted an invitation from John Simpson to work in the pursuit of cosmic rays as a research associate in the Institute for Nuclear Studies at the University of Chicago. His scientific prowess as an experimentaTist was soon appreciates! at Chicago, en c! he was appointed assistant professor in the Institute for Nuclear Studies (now the Enrico Fermi Institute) en cl the Department of Physics in 1956. He was promoter! to associate professor (tenure) in 1962 en cl professor in 1966. Meyer remained at the University of Chicago for the rest of his scientific career, becoming emeritus in 1990. It was my goocl fortune to make Meyer's acquaintance when I arrive cl in Chicago in 1955 to work with John Simpson on the theoretical implications of the cosmic-ray variations that Simpson en cl Meyer were observing. Meyer's two sons, Stephan and Andreas, were born in about the same years as my daughter en c! son, en c! the chiTciren were soon acquainted!

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PETER MEYER 143 through our socializing. It was Peter's performing with his cello that encouraged my daughter to take up the violin en cl my son the cello. Peter was supportive of their musical activities, even to the extent of locating an excellent oic! cello in Germany en cl traveling by plane back to Chicago accompanied by the cello in a monster carrying case. This was but a small sample of his relationships with the younger generation. He was a sympathetic mentor en cl supportive friend of his many Ph.D. students over the years. Meyer worker! with John Simpson in pursuit of the mysterious time variations of the cosmic-ray intensity. It must be unclerstoocl that the term "cosmic rays" is a generic term for the ionizing racliation coming clown through the atmo- sphere of Earth. When Meyer began his professional career in 194S, it hacl just been establishecl that the top of the atmosphere is continually bombarded from space by energetic protons, accompanied by a smaller number of heavier nuclei with speecis up to that of light. The impact of these energetic protons on the nuclei of the air atoms near the top of the atmosphere produces all mesons (quickly decaying to ,u mesons) and gamma rays and leading to electrons, positrons, anti- protons, neutrons, en c! more secondary protons, which all come showering down through the atmosphere. These particles ionize ambient air atoms along the way. IncleecI, it was the discovery of the slight but ubiquitous ionization of the air in the laboratory a century ago that lecl to the recog- nition of the cosmic rays. In 1912 the Austrian physicist Victor Hess ascenclec! in a balloon to a height of several thousand feet to fincl that the ionization increases ciramati- cally with altitude, thereby demonstrating that the ioniza- tion is causer! by something from outsicle the atmosphere. The alternative explanation hacl been the recently cliscoverecl natural radioactivity of the rocks and soil, whose effects wouic! diminish rapidity upward! from ground! level. With

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44 B I O G RA P H I C A L EMOIRS the external origin of the ionization the term cosmic rays was coined to refer to whatever was responsible. An cl after many years of speculation as to the precise nature of cosmic rays, they turner! out to be mostly energetic protons. Over the last half century it has been establishecl that the protons are accompanied by small numbers of heavier nuclei en cl by a few electrons, positrons, en c! antiprotons. Protons are not rays, of course, but the terminology "cosmic rays" survives nonetheless. We are, after all, creatures of habit. The studies of cosmic rays mover! forward! rapidity after WorIcl War II with the advance of technology (e.g., high resolution nuclear emulsions en cl sophisticated electronic cletectors). Over the course of his career Meyer clesignec! many innovative instruments to explore the energy clistri- butions of both the major en cl minor components among the cosmic-ray particles. Simpson recognized that time variations of the cosmic- ray intensity, often correlating with solar activity, were somehow a consequence of conditions in space. Lacking spacecraft in those days to carry instruments into space for a direct look, he sought to use the cosmic-ray variations as a probe of those conditions. The iclea was to obtain quantita- tive measurements of the clepenclence of the time variations on the energy of the protons, so that various speculations on electric fielcis in space or mollifications of the geomagnetic fielcl or, whatever, couIcl be tested en cl confirmed or rulecl out. Thus, besides the five neutron monitor stations set up by Simpson at geomagnetic latitucles from 0 to 60, Simpson and Meyer exploited the magnetic field of Earth as a spectrometer with extensive north-south flights with neu- tron monitors, etc., in aircraft supplier! by the U.S. Air Force. They also launchecl many balloon-borne instruments to the upper atmosphere (~100,000 ft) to connect the ground mea- surements of the cosmic-ray intensity to the intensity at the

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PETER MEYER 145 top of the atmosphere. The gigantic cosmic-ray flare on the Sun on February 23, 1956, was a lucky event in this respect, showing the direct arrival of energetic protons from the Sun, follower! by a slow clecTine, indicating that the inner Solar System is open out to about the orbit of Mars en cl enclosecl by magnetic fielcis beyond (1956~. Together with the energy clepenclence of the ciay-by-ciay time variations inferred from the neutron monitor stations, it became clear that the variations of the cosmic rays couIcl be a conse- quence only of time-varying magnetic fielcis in interplan- etary space, implying that space was Flee with plasma (ion- ized gas) strongly influenced by solar activity (1959~. They shower! that the occasional abrupt Forbush decrease in the cosmic-ray intensity, cliscoverecl by Forbush with ioniza- tion chambers some years earlier, extenclecl to energies of 20-30 GeV en c! conic! be unclerstooc! only in terms of broac! domains of magnetic fielcl in interplanetary space. These revelations set the intellectual stage for the construction of the theoretical solar wine! concept in ~ 958. The space age was beginning at about this time, en cl Meyer colIaboratecl with Simpson in studies of the outer Van Allen racliation belt. The outer belt is fee! by fast par- ticles from the Sun en cl by the clecay of neutrons proclucecl by the cosmic-ray proton bombardment of the terrestrial atmosphere. The distribution of the trapped particles is con- tinually moclifiecl by diffusive losses en cl by azimuthal drift of the particles in the active geomagnetic fielcI. The structure en c! behavior of the outer racliation belt was a challenge to experimentalists en cl theoreticians alike. The studies carried out by Simpson en cl Meyer (1961) showocl that electrons were sometimes accelerates! in place, and, cluring times of large variations in the outer magnetosphere, the particles were carried with the clisplacecl magnetic fielcI.

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46 B I O G RA P H I C A L EMOIRS While this work was going on, Meyer was thinking about the still uncletectecl electron component of the cosmic rays, estimated to make up perhaps one in a huncirecl of the cosmic-ray particles at any given particle energy. The cletec- tion of these rare relativistic electrons among the numerous protons was quite a challenge to the ingenuity of the experimentaTist for two reasons. First, an occasional proton produces a signal in the detector that mimics the signature of an electron, en cl second, it must be ascertained that a cletectec! electron comes from somewhere out in space en c! is not proclucecl as a secondary particle in the upper atmo- sphere. Thus, a sophisticated detector system is required en c! must be flown at high altitucle on stratospheric balloons. The successful electron detection was reported by two teams just a couple of weeks apart. First, lames Earl of the University of Minnesota succeeded by visualizing the char- acteristic showers generated by electrons in a multiplate cloucl chamber flown on balloons. Peter Meyer with his graduate student Rochus Vogt clevelopec! a purely electronic detector system. The range of the electron shower, en cl hence the electron energy, was measured in a sandwich of alternating layers of leac! en c! plastic scintillators, backwarcI- moving particles, or interacting protons that couIcl simu- late shower signals, were excluded by analyzing the signals in two Nat scintillators above and below the sandwich. The contribution of secondary electrons generated in the atmo- sphere couIcl be cleterminecl as the instrument ascenclecl toward! the top of the atmosphere. One wouic! expect that the intensity of downward-moving secondary electrons would clecline in proportion to the cleclining air mass overhead. However, the measurer! electron intensity reacher! a con- stant value before the balloon approached its maximum altitucle, with only 3-5 g/cm2 of air left overhead. This clearly indicated a flux of cosmic-ray electrons arriving from space.

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PETER MEYER 147 Meyer en c! Vogt measurer! 4 x ~o-3 incoming electrons/ cm2sec sr in the energy range ~ 00-] 000 MeV ~ ~ 961 ), to be compared with about 300 x 10-3 protons/cm sec sr in the same energy range. So there was incleec! an electron com- ponent of the cosmic rays, of the same general magnitude as estimated from the observed non thermal syn chro tron radio emission from the Galaxy. Meyer en cl Vogt were able to show how the electrons variecl through a Forbush decrease (1961), receiving the same moclulation as the cosmic-ray protons, thereby show- ing that the electrons originated outside the Solar System. They were soon able to identify the temporary increases of energetic electrons proclucec! by solar flares (1962~. The next step after the measurements of the cosmic-ray electrons was the question of the cosmic-ray positrons (the anti-electrons) among the cosmic rays. Cosmic-ray electrons en cl positrons must be proclucecl throughout the Galaxy in about equal numbers by the occasional collision of high- energy protons with the nuclei of atoms in interstellar space. In fact, for positrons this secondary process must be the predominant procluction mechanism, while electrons might also be accelerates! from a sample of "ordinary matter," just like the protons en cl other nuclei. Thus it wouIcl be inter- esting to measure the abundance of positrons relative to electrons. Again the experimental clifficulties are that the positron intensity is much smaller than the protons, en cl positrons are proclucecl in great numbers by the proton collisions with the nuclei of the atmosphere en c! collisions with the instrument itself. After the electron studies were well in hand Roger Hilclebrancl relatecl how Meyer askocl him one day what he thought it might take to distinguish the positrons. Hilclebrancl repliecl that it wouIcl require a whole physics laboratory to go up with a balloon to the top

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48 B I O G RA P H I C A L EMOIRS of the atmosphere. Meyer smiler! en c! saicI, "Why clon't we give it a try?" Positrons differ from electrons in their opposite electric charge, of course, so the electron-positron separation conic! be accomplishecl with a suitable magnetic fielcI. Meyer en cl Hilclebrancl clevelope cl a sophisticate cl in strumen t much along the lines of the electron detector but with a strong mag- netic fielcl between the poles of a permanent magnet, through which the particles hacl to pass if they were to be recorclecI. The electrons were cleflectec! one way by the magnetic field! en cl the positrons the other. They usecl spark chambers insteacl of Nat scintilIators, en cl the system was again enclosecl in guarc! counters so as to be sensitive only to particles from above. The Meyer-Hilclebrancl collaboration lecl to a clean separation en cl measurement of the positrons en cl electrons as a function of energy (1965~. Very roughly, they founcl that there were far fewer positrons (~10-~) than elec- trons over the energy range 40-3000 MeV. As the positrons are produced by collisions of cosmic-ray protons with the nuclei of the ambient interstellar gas, their relative number provides a measure of the amount of matter through which the cosmic-ray protons have passed while being accelerated in their sources en cl subsequently in their passage through interstellar space before arriving at the Solar System. The surplus of electrons over positrons shows that there must be cosmic accelerators that produce the electrons clirectly, perhaps together with the protons en cl nuclei that consti- tute the majority of the cosmic rays. The next few years were devoted to improving the systems detecting the electrons en cl positrons, with an eye to obtaining the combiner! energy spectrum of electrons en c! positrons up to several hundred GeV. Gas Cerenkov counters and time-of-flight measurement techniques were introclucecl to reject background! protons en c! were combiner! with mas-

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PETER MEYER 149 sive shower counters to analyze the electron cascade in cle- tail. The instruments were calibratecl at laboratory accelera- tors (e.g., at the Stanford Linear Accelerator Center) ~ ~ 968, 1972, 1973, 1974, 1976~. Meyer acivancecl the particle detection technology to clo a number of other measurements. One interesting episode was the detection of the electrons from the Jupiter electron beacon. Simpson et al. en cl Teegarten et al. hacl found, from particle detectors carried on spacecraft out to the gen- eral vicinity of Jupiter, that Jupiter emits a powerful burst of relativistic electrons once each Manhour rotation period. These electrons can be cletectecl at distances up to ~ AU or more en c! can be iclentifiec! by their precise period! of re- currence. Jupiter orbits the Sun at a distance of 5 AU, en cl the electrons clash from Jupiter along the spiral magnetic field! in interplanetary space. Working with Jacques L'Heureux en cl using the electron detector on the OGO-5 spacecraft, they founcl that when Earth was passing through the spiral magnetic lines of force connecting out to Jupiter, Earth was bathed in the electrons from the Jupiter beacon, no longer clearly pulsing but occurring only when the fielcl connects Earth to Jupiter. At the same time Meyer and Dietrich Muller became interested in the composition of cosmic-ray nuclei at high energies. With graduate student E. JuTiusson they clesignec! a new detector system to measure the abundances of heavy nuclei at energies above ~ 0 GeV/nucleon ~ ~ 972, ~ 974, ~ 975, 1978~. The essential point is that cosmic rays presumably consist of ordinary matter in an ionized state when the matter is caught up in the acceleration process en cl the incliviclual particles are huriec! away at nearly the speec! of light. Thus, determining the precise relative abundances of the different elements among the cosmic rays tells us some- thing about where the cosmic rays were accelerated. As had

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50 B I O G RA P H I C A L EMOIRS aireacly been observer! at Tower energy, they fount! the rela- tive abundances of the nuclei to be more or less along the lines of the stanciarcl cosmic abundances cleterminecl from meteorites, etc. except for such nuclei as Li, Be, en c! B. These nuclei are rare in the general cosmos because they are burned up quickly in stellar interiors. Most of the matter in the Galaxy (inclucling ourselves) has been processed through one or more massive stars, as inclicatecl by the general presence of the heavier nuclei C, N. O et al. synthesizer! in the late stages of evolution of the incliviclual massive star. Thus when the matter is clispersecl by the supernova explosion at the end of the short life of the massive star, the matter is sent on its way with C, N. O. etc., but very little if any 2H, 3He, Li, Be, en cl B. On the other hand it was founcl that cosmic rays contain substan- tial amounts of these otherwise rare nuclei. The explana- tion is that these nuclei are spalIation products (i.e., chunks of heavier nuclei C, N. etc., among the cosmic rays knockocl off by a collision with the nucleus of an atom or ion of the interstellar gas). On this basis one couIcl determine that the cosmic rays have passed through about 7 gm/cm2 of interstellar matter. The discovery by Meyer en c! colleagues was that the Li, Be, en cl B became less abundant with in- creasing energy above about 10 GeV/nucleon. This incli- cates a shorter path length and consequently shorter life in the Galaxy with increasing energy of the heavy cosmic-ray nuclei. It shows that the cosmic rays are not graclually accel- eratec! by reflections from the magnetic fielcis of moving interstellar gas cloucis. The graclual acceleration was origi- nally suggested by Fermi as a possible origin of the cosmic rays. The gradual acceleration predicts that the particle en- ergy increases with the time spent in the Galaxy. Insteacl the measurements require that the cosmic rays be acceler- ated to their final energies in some initial short-lived event

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PETER MEYER 151 (e.g., a supernova explosion or supernova remnant). The more energetic cosmic-ray particles seem to be able to es- cape sooner from the magnetic fielcis of the Galaxy, so they generate fewer spallation nuclei. Meyer en cl {uliusson subsequently extenclecl the measure- ments beyond Fe, covering atomic numbers up to 36, the very heavy nuclei (1975~. They fount! the relative abundances among the very heavy cosmic-ray nuclei to parallel the normal cosmic abundances, further supporting the iclea that the cosmic rays originates! from ordinary cosmic matter that just happened to be hit by an explocling supernova or other catastrophe. One of the more exciting results in the next few years was the direct observation of the particles acceleratecl by shocks in interplanetary space created by an outburst asso- ciatec! with a solar flare. (We wouic! recognize the shock tociay as the result of a coronal mass ejection at about the same time as the flare.) A flare often produces a burst of fast particles, sometimes called solar cosmic rays, although their numbers diminish more rapidly with increasing energy than the true galactic cosmic-ray particles, en cl the relative abundances of the nuclei show a strong enhancement of elements with low first ionization potential. Meyer, assisted by Paul Evenson en cl S. Yanagita, founcl a population of nuclei accelerates! in interplanetary space within the shock wave from an explosive event on the Sun (1982~. A little later acceleratecl electrons were founcl as well (1985~. The measurements clemonstratec! again the remarkable efficiency of nature to accelerate nuclei to high energy. Nothing more than the common shock front is neeclecI. Incleecl it is now believer! that the shock front is probably the universal particle acceleration mechanism, because little else shows promise for converting so large a fraction of the bulk kinetic energy into fast particles.

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152 B I O G RA P H I C A L EMOIRS Another result was the detection of the energetic protons proclucecl by the clecay of neutrons created by flares on the Sun. The vigorous acceleration of nuclei (mostly protons) to high energy in flares bombards the Sun en c! provides many nuclear reactions in the solar atmosphere below the flare, emitting gamma rays en cl neutrons, etc. The gamma rays can be observer! clirectly, of course. The neutrons, equally free to escape from the magnetic fielcis of the flare, clo not get as far as Earth (S light minutes from the Sun) because their speecis are only about a tenth of the speec! of light en cl they enjoy only a 15-minute half-life. They clecay into protons of the same kinetic energy, which then channel along the spiral interplanetary magnetic field and can be cletectecl whenever a suitable particle detector meets that spiral. Detection at Earth requires only that the neutron have a direct spiral line of communication to Earth at the time it decays, perhaps having come from a flare on the back sicle of the Sun ~ ~ 983, ~ 984, ~ 990) . Inasmuch as cosmic rays are observer! to extent! up to energies above lode eV/nucleon (from unknown sources) it was clearly clesirable to extend the work on the relative abundances of the cosmic-ray nuclei to above the 100 GeV/ nucleon region achieved in the work aIreacly citecI. How- ever that extension required new technology. The number of cosmic-ray particles in a given energy interval declines with increasing particle energy E approximately as E-n with n lying somewhere in the interval 2.7 to about 3, clepencI- ing upon E. It is obvious then that to go to higher energies means far fewer particles among the general background of cosmic rays. That is to say, the background "noise" becomes deafening. Meyer with Muller en c! others came up with the iclea of looking for very energetic nuclei using the transi- tion racliation proclucecl as the nuclei pass from air into a transparent solic! en c! from the solic! into air. The transition

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PETER MEYER 153 racliation is very weak but increases rapidity as the speec! of the particle approaches the speed of light. Thus an instru- ment detecting the passage of energetic nuclei by their tran- sition racliation facles out for particles below about 100 GeV/ nucleon (traveling at a speecl of 0.99995c, where c is the speecl of light). That is to say, a transition racliation cletec- tor wouic! be clear to most of the background! noise, but it wouIcl begin to respond to nuclei of 100 GeV/nucleon or more. Even so, the instrument wouIcl have to be large, to intercept enough of the very-high-energy particles en c! then to pass the particles through enough air-plastic interfaces to get a detectable signal. The result was the "Chicago Egg," which was flown on Spacelab 2 on the space shuttle. Designed and built by Meyer en cl Muller, the Egg was 9 feet in diameter en cl 12 feet high. The instrument was encloses! in a welclec! aluminum tank: the shell of the egg. Insicle the shell the instrument consisted of scintillation counters, to define en cl clelimit the paths of the cosmic rays that it recorclecI. The heart of the instrument was the large volume of commercial polyolefin fiber forming the transition radiation generator. The essential aspect of the generator was that the individual high-energy cosmic-ray particle shouIcl pass through many air-plastic inter- faces, producing transition racliation at each interface, en cl that the transition racliation not be absorber! by the plastic fibers. The transition racliation was soft X rays en cl was detected in xenon-fi~led proportional chambers interspersed between layers of fiber material. The whole thing weighed 2.5 tons en cl cost about $10 million. The size was limitecl by the cargo bay of the shuttle, and the Chicago Egg flew on the Challenger in 1985 for several clays' exposure to the cosmic rays. During that time it acquired the most cletailecl ciata ever obtained on the composition of cosmic rays at extreme energies ~ ~ 98S, ~ 99 ~ ~ .

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54 B I O G RA P H I C A L EMOIRS Briefly, the Chicago Egg recorclec! the atomic number en cl energy of nuclei above 150 GeV/nucleon basecl on their transition racliation. The measurements faclecl out at high energies of several thousand! GeV because of the cleclining number of cosmic rays at increasing energies. Nuclei in the lower energy range 40-400 GeV/nucleon were cletectecl en c! sizer! with gas Cerenkov counters. The results of this investigation showocl that the relative abundances of the secondary nuclei (e.g., the abundance ratio B/C) continu- ally decreases up to very high energies. This can be uncler- stood with the assumption of an energy spectrum E-2 ~ pro- clucecl in the unknown cosmic-ray source, as is preclictecl for shock acceleration processes, follower! by more rapic! escape from the Galaxy with increasing E. As was aIreacly known at lower energies, the ciata indicate the enhanced abundance of nuclei with Tow first ionization potential, much as one fincis for energetic nuclei from solar flares, etc. De- tailecl comparisons with the relative abundances of cosmic- ray nuclei at Tower energies begins to give a picture of the conditions uncler which cosmic rays are created in their various sources. There are numerous other investigations that Meyer accomplishecl along with the major achievements summa- rizecl here. In aciclition to the ambitious scientific program that market! his career he took on many responsibilities at the University of Chicago en cl in national en cl international scientific organizations. For instance, he was chair of the Cosmic Ray Physics Division of the American Physical Society, 1972-73. He was a member of the Space Science Board of the National Academy of Sciences, 1975-78 en cl served as chair of the Committee on Astronomy and Astrophysics of the Space Science Board, 1975-77. He served as director of the Enrico Fermi Institute at the University of Chicago, 1978-82. He was then chair of the Department of Physics,

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PETER MEYER 155 1986-89. These responsibilities all involve consiclerable time en cl energy, but he hancIlecl them in some of his scientifi- cally most productive years. His commitment to uncler- gracluate teaching was recognizes! in 1971 by the Llewellyn John en cl Harriet Manchester Quantrell Awarcl for Excel- lence in Unclergracluate Teaching. Meyer's scientific productivity was also recognizes! in the lancl of his birth, where he became a foreign member of Germany's Max Planck Society en cl the Max Planck Insti- tute for Physics en c! Astrophysics in Munchen in 1973. In 1984 he was a recipient of the Alexancler Von HumboIcit Awarcl for Senior Unitecl States Scientists. He was electec! a member of the National Academy of Sciences in 1989 in recognition of his many funciamental contributions to present unclerstancling of the fast particles (cosmic rays) that come from everywhere, near en c! far, in the active universe. He leaves behind a scientific legacy en cl the foncl memories of his many colleagues. He is survivecl by his seconc! wife, the renowned! microbiologist Patricia Spear, who is chair of microbiology-microimmunology at the Northwestern University Meclical School, by his two sons, Stephan Meyer, professor of astronomy en c! astrophysics at the University of Chicago, and Andreas Meyer of Portsmouth, New Hampshire, en cl by two grancichilciren, Samantha Meyer en c! Niels Meyer of Chicago. THE AUTHOR RECEIVED important comments and suggestions in the construction of this biographical memoir from Rochus Vogt, Dietrich Muller, and Patricia Spear.

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156 B I O G RA P H I C A L EMOIRS SELECTED BIBLIOGRAPHY 1949 The (y,n)-reaction on deuterium and the binding energy of the deuteron. Z. Phys. 126:336. 1950 With A. P. French and P. B. Treacy. oc-particles from Fi9 bombarded by deuterons. Proc. R. Soc. A 63:666. 1956 With E. N. Parker and J. A. Simpson. Solar cosmic rays of February 1956 and their propagation through interplanetary space. Phys. Rev. 104:768. 1959 Primary cosmic-ray proton and alpha-particle intensities and their variation with time. Phys. Rev. 115:6. 1961 With C. Y. Fan and J. A. Simpson. Dynamics and structure of the outer radiation belt. 7. Geophys. Res. 66:2607. With R. Vogt. Electrons in the primary cosmic radiation. Phys. Rev. Lett. 6:193. With R. Vogt. The primary cosmic electron flux during a Forbush- type decrease. 7. Geophys. Res. 66:3950. 1962 With R. Vogt. High energy electrons of solar origin. Phys. Rev. Lett. 8:387. 1965 With R. C. Hartmann and R. H. Hildebrand. Observation of the cosmic ray electron-positron ratio from 100 MeV to 3 BeV in 1964. 7. Geophys. Res. 70:2713.

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PETER MEYER 1968 157 With J. L'Heureux. The primary cosmic ray electron spectrum in the energy range 300 MeV to 4 BeV from 1964 to 1966. Canad. f. Phys. 46:S892. 1972 With J. L'Heureux and C. Y. Fan. The quiet time spectra of cosmic ray electrons of energies between 10 and 200 MeV observed on OGO-5. Astrophys. f. 171:363. With E. Juliusson and D. Muller. Composition of cosmic ray nuclei at high energies. Phys. Rev. Lett. 29:445. 1973 With D. Muller. The spectrum of galactic electrons with energies between 10 and 900 GeV. Astrophys. f. 186:841. 1974 Composition and spectra of primary cosmic ray electrons and nuclei above 101 eV. Photos. Trans. R. So c. Lond. A 277:349. 1975 With E. Juliusson. A measurement of abundances of WH-nuclei above 0.6 GeV/nucleon. Astrophys. f. 201: 76. 1976 With J. L'Heureux. Quiet time increases of low energy electrons: The Jovian origin. Astrophys. J. 209:955. 1978 The cosmic ray isotopes. Nature 272:675. 1982 With P. Evenson and S. Yanagita. Solar flare shocks in interplanetary space and solar particle events. 7. Geophys. Res. 87:625. 1983 With P. Evenson and K. R. Kyle. Protons from the decay of solar flare neutrons. Astrophys. f. 274:875.

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158 B I O G RA P H I C A L 1984 EMOIRS With P. Evenson, D. J. Forrest, and S. Yanagita. Electron-rich par- ticle events and the production of gamma rays by solar flares. Astrophys. J. 283:439. 1985 With S. R. Kane and P. Evenson. Acceleration of interplanetary solar electrons in the 1982 August 14 flare. Astrophys. f. Lett. 299:L107. With G. E. Morfill and R. Lust. Cosmic ray nuclei and the structure of the Galaxy. Astrophys. f. 296:670. 1988 With J. M. Grunsfeld, J. L'Heureux, D. Muller, and S. P. Swordy. Energy spectra of cosmic ray nuclei from 50 to 2000 GeV per emu. Astrophys. f. Lett. 327:L31. 1990 With P. Evenson, R. Krooger, and D. Reames. Solar neutron decay proton observations in cycle 21. Astrophys. f. 73~Suppl.~:273. 1991 With D. Muller, S. P. Swordy, J. L'Heureux, and J. M. Grunsfeld. Energy spectra and composition of primary cosmic rays. Astrophys. J. 374:356.

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