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HENRY CROZIER PLUMMER, President of the Society from 1939 to 1941, died at Oxford on 1946 September 30 within a few weeks of his seventy-first birthday.
Plummer was born at Oxford on 1875 October 24, the eldest son of W. E. Plummer, then first assistant at the University Observatory (he was appointed when the Observatory was established in 1873) and subsequently Director of the Observatory of the Mersey Docks and Harbour Board and Honorary Reader in Astronomy in the University of Liverpool. He was educated at St. Edward's School, Oxford and Hertford College, where his distinctions included Firsts in Mathematical Moderations and Final Schools, and the Open Mathematical Scholarship. After studying physics for a year Plummer went to Owen's College, Manchester in 1899 as Lecturer in Mathematics, returning to Oxford after a year as Demonstrator in the Clarendon Laboratory; a year later he was appointed assistant in the University Observatory, of which H. H. Turner was then Director; there he remained until 1912, except for a year's sojourn at Mount Hamilton as Fellow of the Lick Observatory. As a young and ambitious astronomer Plummer early realized the immense potentialities of spectroscopy, and his year's stay in America gave him the much-prized opportunity of making himself conversant with the large-scale developments then proceeding rapidly in the great American Observatories. In 1912 he succeeded Sir Edmund Whittaker as Andrews Professor of Astronomy at Trinity College, Dublin and Royal Astronomer of Ireland. At Dunsink Observatory Plummer found an institution that had, on the whole, passed its meridian as regards effective practical work; the many natural advantages of Dunsink as a place of residence could not compensate a young and eager astronomer for the almost certain prospect of having to make the best of the existing equipment without any hope of acquiring instruments of such power and variety as the contemporary state of astronomy required. The political troubles in Ireland during and immediately after the first world war made things unpleasant for Plummer who, by nature, was gentle and retiring and opposed to violence in any shape or form; circumstances thus forced him into an almost monastic seclusion from which he was glad to escape when, in 1921, a vacancy occurred in the Professorship of Mathematics at the Military College of Science at Woolwich. Here Plummer found a congenial sphere of scientific activity till his retirement in 1940; he returned to Oxford where he lived until his death in 1946. In 1924 he had married Beatrice, daughter of H. H. Howard, M.R.C.S.; their kindliness and gracious hospitality during the war years are remembered with gratitude by many of Plummer's astronomical colleagues. Mrs Plummer died in the early spring of 1946, a blow which prostrated Plummer and from which he never recovered; there were no children of the marriage.
Plummer's astronomical researches covered a very wide field, and there was hardly a department which did not excite his interest and stimulate him to make some further advance. In his early days at the Oxford Observatory the current work on the Astrographic Catalogue claimed a great deal of his attention, and he made a meticulous study of the many problems, mathematical and practical, inherent in the reduction of photographic plates; at the time there was a great deal of controversy on such matters, but Plummer's mathematical ability, his knowledge of the capacity of any instrument for the job in hand and his almost uncanny skill in the theory of errors overcame all criticism. It may be added that Plummer found a peculiar satisfaction in these investigations, for his father when at Oxford had been responsible for much experimental work and preparation for the Oxford share of the enterprise in addition to representing Pritchard (the first Director) at the Paris Astrographic Conference of 1891.
In his early years at Oxford, too, he made his first investigations in planetary theory, mainly on "oscillating satellites"; as is well known there are five exact solutions of the problem of these bodies in each of which the bodies preserve a constant configuration which revolves with uniform angular velocity; if one of the bodies is of negligible mass and is slightly displaced from its position of relative equilibrium, it describes a periodic orbit with reference to the equilibrium point (the body is then called an oscillating 44 satellite"). Plummer's work in this field was stimulated by the investigations of Darwin and Charlier; it may be added that he returned to this subject in 1932 in a paper suggested by the extensive numerical investigations then being carried out at Copenhagen Observatory. In these early years Plummer wrote on such diverse subjects as occultations, the application of projective geometry to the determination of binary-star orbits, the accuracy of eye-observations of meteors and the determination of radiant points, the possible effect of radiation on the motion of comets, the theory of aberration and the principle of relativity. He was always very much interested in the geometry of instruments and his last address in 1941 as President of the Society dealt with the development of the vertical telescope, a subject to which he had made notable contributions in the first decade of the century; some of his suggestions found practical expression in the tower telescope at Mount Wilson.
In 1911 Plummer contributed a valuable paper on the problem of the distribution of stars in globular clusters, in which he devised elegant mathematical formulae giving the relation between the space-distribution of the cluster-stars and their two-dimensional distribution on photographs. About this time he began a long series of investigations on the parallaxes of stars mainly of types B and A; starting from the assumption that these stars (in or near the galactic equator) have no component perpendicular to the galactic equatorial plane – or, alternatively, that the velocity, relative to the Sun, of any :star perpendicular to the galactic plane is equal to the parallactic velocity in this direction – Plummer derived a simple formula from which the parallax of a star could easily be calculated from the known values of the proper motion and radial velocity.
At Dunsink, Plummer and his assistant, C. Martin, began an extensive programme on the photographic photometry of short-period variable stars with the 15-inch telescope of the Observatory; the light curves were subjected, in each case, to periodic analysis. Although this work has been superseded by more recent observations of superior accuracy – Plummer's estimate of the probable error of a single magnitude determination was ± 0.03 – it led him to one important conclusion, namely, that such variables cannot be spectroscopic binaries, as the variability of their radial velocity measures seemed at first to suggest, but that the periodic changes in radial velocity could plausibly be ascribed to radial pulsations in the atmospheres of the stars. This hint of a new physical class of stars was first made in 1913, and developed in subsequent papers; later, Shapley's investigations supported Plummer's suggestion. The pulsation-theory of Cepheids was now fully launched and it soon gave Eddington full scope for a searching mathematical analysis.
Plummer wrote many additional papers at Dunsink on such topics as the velocity of light and Doppler's principle, a further investigation on the distribution of stars in. globular clusters, statistics of minor planets, bright meteors, general precession, the ellipticities of the Maclaurin ellipsoids, stationary radiants, multiple solutions in the determination of orbits.
In 1932 Plummer contributed an illuminating paper on the nature of "dependences" in the reduction of astrographic plates; "dependences" had been introduced by Schlesinger some time previously, and Plummer's elegant analytical treatment was an important contribution to this new method of photographic astrometry. In 1937 there appeared a paper on the masses in single-spectrum binary systems, written by Plummer on the text – taken from Dr Aitken's book "The Binary Stars" – that "the value of the mass-function is frequently omitted by the computer of orbits, for it gives. very little definite information". Referring to this statement Plummer remarks at the beginning of his paper: "This is a hard saying, for it implies that from all the work. spent in deriving orbits of single-spectrum stars no information bearing on the masses of the systems can be deduced". Plummer's line of attack in deriving the mass-ratio of such systems was to recognize that the mass-function may be regarded as a function of and the mass-ratio , the value of the former for any class being taken from the statistics of the corresponding double-spectrum systems. The method is. applied to all single-spectrum systems in considerable detail.
During his period (1939-41) as President of the Society Plummer gave the addresses on the awards of the Society's Gold Medal to M. Lyot (1939) and Dr E. P. Hubble (1940) and a third address in 1941 on the development of the vertical telescope already alluded to.
Plummer's interest in celestial mechanics led to the publication of his most important book Dynamical Astronomy in 1918, a notable contribution to the subject; here he revealed very conspicuously a freshness of outlook and an elegance in mathematical. presentation so long familiar in his papers. His Principles of Mechanics appeared. in 1929; his great knowledge of the "theory of errors" found expression in Probability and Frequency published in 1939.
Plummer was keenly interested in the history of science and when, in 1939, the Royal Society appointed a committee to advise on the publication of Newton's works. and letters he willingly undertook the difficult task of editor. Unfortunately, it was. found impossible under war conditions to have anything published in time for the tercentenary in 1943 of Newton's birth; this great enterprise when completed will owe an enormous debt to Plummer's self-denying labours in the earlier war years when. his strength was still unabated. At the Society's triple centenary celebrations on 1942: October 9, at which Galileo, Newton and Halley were commemorated, the address on Newton was given by Plummer. He was Halley Lecturer at Oxford in 1942, the subject of his address – notable for the extent of historical research which it reveals – being "Halley's Comet and its Importance".
In disposition Plummer was modest and reserved, with an unsuspected sense of humour. To those who had gained his confidence he was a staunch friend and loyal colleague. Elected a Fellow of the Society on 1899 December 8, he served on the Council in 1915 and from 1935 to 1942; he was a Vice-President in 1936-1937 and again in the year following his Presidency during the first two of the difficult war years. He was elected to the Royal Society in 1920.
W. M. SMART.
Plummer was born at Oxford on 1875 October 24, the eldest son of W. E. Plummer, then first assistant at the University Observatory (he was appointed when the Observatory was established in 1873) and subsequently Director of the Observatory of the Mersey Docks and Harbour Board and Honorary Reader in Astronomy in the University of Liverpool. He was educated at St. Edward's School, Oxford and Hertford College, where his distinctions included Firsts in Mathematical Moderations and Final Schools, and the Open Mathematical Scholarship. After studying physics for a year Plummer went to Owen's College, Manchester in 1899 as Lecturer in Mathematics, returning to Oxford after a year as Demonstrator in the Clarendon Laboratory; a year later he was appointed assistant in the University Observatory, of which H. H. Turner was then Director; there he remained until 1912, except for a year's sojourn at Mount Hamilton as Fellow of the Lick Observatory. As a young and ambitious astronomer Plummer early realized the immense potentialities of spectroscopy, and his year's stay in America gave him the much-prized opportunity of making himself conversant with the large-scale developments then proceeding rapidly in the great American Observatories. In 1912 he succeeded Sir Edmund Whittaker as Andrews Professor of Astronomy at Trinity College, Dublin and Royal Astronomer of Ireland. At Dunsink Observatory Plummer found an institution that had, on the whole, passed its meridian as regards effective practical work; the many natural advantages of Dunsink as a place of residence could not compensate a young and eager astronomer for the almost certain prospect of having to make the best of the existing equipment without any hope of acquiring instruments of such power and variety as the contemporary state of astronomy required. The political troubles in Ireland during and immediately after the first world war made things unpleasant for Plummer who, by nature, was gentle and retiring and opposed to violence in any shape or form; circumstances thus forced him into an almost monastic seclusion from which he was glad to escape when, in 1921, a vacancy occurred in the Professorship of Mathematics at the Military College of Science at Woolwich. Here Plummer found a congenial sphere of scientific activity till his retirement in 1940; he returned to Oxford where he lived until his death in 1946. In 1924 he had married Beatrice, daughter of H. H. Howard, M.R.C.S.; their kindliness and gracious hospitality during the war years are remembered with gratitude by many of Plummer's astronomical colleagues. Mrs Plummer died in the early spring of 1946, a blow which prostrated Plummer and from which he never recovered; there were no children of the marriage.
Plummer's astronomical researches covered a very wide field, and there was hardly a department which did not excite his interest and stimulate him to make some further advance. In his early days at the Oxford Observatory the current work on the Astrographic Catalogue claimed a great deal of his attention, and he made a meticulous study of the many problems, mathematical and practical, inherent in the reduction of photographic plates; at the time there was a great deal of controversy on such matters, but Plummer's mathematical ability, his knowledge of the capacity of any instrument for the job in hand and his almost uncanny skill in the theory of errors overcame all criticism. It may be added that Plummer found a peculiar satisfaction in these investigations, for his father when at Oxford had been responsible for much experimental work and preparation for the Oxford share of the enterprise in addition to representing Pritchard (the first Director) at the Paris Astrographic Conference of 1891.
In his early years at Oxford, too, he made his first investigations in planetary theory, mainly on "oscillating satellites"; as is well known there are five exact solutions of the problem of these bodies in each of which the bodies preserve a constant configuration which revolves with uniform angular velocity; if one of the bodies is of negligible mass and is slightly displaced from its position of relative equilibrium, it describes a periodic orbit with reference to the equilibrium point (the body is then called an oscillating 44 satellite"). Plummer's work in this field was stimulated by the investigations of Darwin and Charlier; it may be added that he returned to this subject in 1932 in a paper suggested by the extensive numerical investigations then being carried out at Copenhagen Observatory. In these early years Plummer wrote on such diverse subjects as occultations, the application of projective geometry to the determination of binary-star orbits, the accuracy of eye-observations of meteors and the determination of radiant points, the possible effect of radiation on the motion of comets, the theory of aberration and the principle of relativity. He was always very much interested in the geometry of instruments and his last address in 1941 as President of the Society dealt with the development of the vertical telescope, a subject to which he had made notable contributions in the first decade of the century; some of his suggestions found practical expression in the tower telescope at Mount Wilson.
In 1911 Plummer contributed a valuable paper on the problem of the distribution of stars in globular clusters, in which he devised elegant mathematical formulae giving the relation between the space-distribution of the cluster-stars and their two-dimensional distribution on photographs. About this time he began a long series of investigations on the parallaxes of stars mainly of types B and A; starting from the assumption that these stars (in or near the galactic equator) have no component perpendicular to the galactic equatorial plane – or, alternatively, that the velocity, relative to the Sun, of any :star perpendicular to the galactic plane is equal to the parallactic velocity in this direction – Plummer derived a simple formula from which the parallax of a star could easily be calculated from the known values of the proper motion and radial velocity.
At Dunsink, Plummer and his assistant, C. Martin, began an extensive programme on the photographic photometry of short-period variable stars with the 15-inch telescope of the Observatory; the light curves were subjected, in each case, to periodic analysis. Although this work has been superseded by more recent observations of superior accuracy – Plummer's estimate of the probable error of a single magnitude determination was ± 0.03 – it led him to one important conclusion, namely, that such variables cannot be spectroscopic binaries, as the variability of their radial velocity measures seemed at first to suggest, but that the periodic changes in radial velocity could plausibly be ascribed to radial pulsations in the atmospheres of the stars. This hint of a new physical class of stars was first made in 1913, and developed in subsequent papers; later, Shapley's investigations supported Plummer's suggestion. The pulsation-theory of Cepheids was now fully launched and it soon gave Eddington full scope for a searching mathematical analysis.
Plummer wrote many additional papers at Dunsink on such topics as the velocity of light and Doppler's principle, a further investigation on the distribution of stars in. globular clusters, statistics of minor planets, bright meteors, general precession, the ellipticities of the Maclaurin ellipsoids, stationary radiants, multiple solutions in the determination of orbits.
In 1932 Plummer contributed an illuminating paper on the nature of "dependences" in the reduction of astrographic plates; "dependences" had been introduced by Schlesinger some time previously, and Plummer's elegant analytical treatment was an important contribution to this new method of photographic astrometry. In 1937 there appeared a paper on the masses in single-spectrum binary systems, written by Plummer on the text – taken from Dr Aitken's book "The Binary Stars" – that "the value of the mass-function is frequently omitted by the computer of orbits, for it gives. very little definite information". Referring to this statement Plummer remarks at the beginning of his paper: "This is a hard saying, for it implies that from all the work. spent in deriving orbits of single-spectrum stars no information bearing on the masses of the systems can be deduced". Plummer's line of attack in deriving the mass-ratio of such systems was to recognize that the mass-function may be regarded as a function of and the mass-ratio , the value of the former for any class being taken from the statistics of the corresponding double-spectrum systems. The method is. applied to all single-spectrum systems in considerable detail.
During his period (1939-41) as President of the Society Plummer gave the addresses on the awards of the Society's Gold Medal to M. Lyot (1939) and Dr E. P. Hubble (1940) and a third address in 1941 on the development of the vertical telescope already alluded to.
Plummer's interest in celestial mechanics led to the publication of his most important book Dynamical Astronomy in 1918, a notable contribution to the subject; here he revealed very conspicuously a freshness of outlook and an elegance in mathematical. presentation so long familiar in his papers. His Principles of Mechanics appeared. in 1929; his great knowledge of the "theory of errors" found expression in Probability and Frequency published in 1939.
Plummer was keenly interested in the history of science and when, in 1939, the Royal Society appointed a committee to advise on the publication of Newton's works. and letters he willingly undertook the difficult task of editor. Unfortunately, it was. found impossible under war conditions to have anything published in time for the tercentenary in 1943 of Newton's birth; this great enterprise when completed will owe an enormous debt to Plummer's self-denying labours in the earlier war years when. his strength was still unabated. At the Society's triple centenary celebrations on 1942: October 9, at which Galileo, Newton and Halley were commemorated, the address on Newton was given by Plummer. He was Halley Lecturer at Oxford in 1942, the subject of his address – notable for the extent of historical research which it reveals – being "Halley's Comet and its Importance".
In disposition Plummer was modest and reserved, with an unsuspected sense of humour. To those who had gained his confidence he was a staunch friend and loyal colleague. Elected a Fellow of the Society on 1899 December 8, he served on the Council in 1915 and from 1935 to 1942; he was a Vice-President in 1936-1937 and again in the year following his Presidency during the first two of the difficult war years. He was elected to the Royal Society in 1920.
W. M. SMART.
Henry Crozier Keating Plummer's obituary appeared in Journal of the Royal Astronomical Society 107:1 (1947), 56-59.