MacTutor
"With the untimely death of WILLIAM MICHAEL HERBERT GREAVES, British astronomy has suffered a severe loss. Whilst he will be remembered chiefly for his pioneer work on stellar spectro-photometry, his contributions to dynamical astronomy and to geomagnetism were substantial.
He was always glad to serve the Society he was a member of Council for an aggregate of 14 years being Secretary for 7 years and holding the office of President from 1947 to 1949. Always an active member of the national and international committees on which he served, his considered advice will be greatly missed."
The above resolution by the President, Council and Fellows of the Society conveyed to Mrs Greaves the feeling of loss that we had suffered by the death of the Astronomer Royal for Scotland on 1955 December 24.
He was born in Barbados, British West Indies, on 1897 September 10, the only son of the late Dr E. C. Greaves who had graduated in medicine from Edinburgh University. Educated first in a local school and at Codrington College in the West Indies, he proceeded to Cambridge in the middle of the First World War and became a scholar of St. John's College. There he gained many distinctions. He was a wrangler at the Mathematical Tripos of 1919, gaining special distinction and the Tyson Gold Medal for Astronomy.
He was awarded a Smith's Prize in 1921, became Isaac Newton Student the same year and was duly elected a Fellow of his College.
At St. John's Greaves came under the influence of H. F. Baker who, after a distinguished career as a pure mathematician, had been elected Lowndean Professor of Astronomy and Geometry, and took up investigations of the expansions which occur in celestial mechanics, from the mathematical point of view. The earliest publications of Greaves in our Monthly Notices were in this field, and in fact Volume 82 contains no less than four papers by him. The first dealt with the existence theorem for two families of periodic orbits near Lagrange's equilateral triangular points in the restricted problem of three bodies and the second with long period irregularities in the movement of asteroids with a mean motion nearly equal to half that of Mars. For four asteroids he determined the amplitude and period of inequalities due to the action of Mars and also of Jupiter. The other two papers were prompted by G. R. Goldsbrough's work on the influence of satellites on the form of Saturn's ring and pointed out the weakness of arguments indicating instability when only first order terms were considered.
At this period Greaves became associated with E. V. (now Sir Edward) Appleton on the solution of differential equations which arose in the theory of electrical oscillations of triode valves then becoming very important for the generation of radio waves. His knowledge of the solution of similar equations arising in astronomical problems was put to good use as indicated by several papers in the Proceedings of the Royal Society, in the Phil. Mag. and in Proc. of the Cambridge Phil. Society.
In 1923 on the suggestion of Sir Joseph Larmor arrangements were made for Isaac Newton Students to spend some time at the Royal Observatory, Greenwich, to get first hand knowledge of practical astronomy. For several months Greaves worked with C. R. Davidson and this led to two short papers in Monthly Notices concerning systematic errors which might arise in parallax determinations, the more important dealing with the effect of difference in colour of the parallax and comparison stars if the hour angles were more than specified amounts.
The appointment of Dr H. (now Sir Harold) Spencer Jones as H.M. Astronomer at the Cape produced a vacancy at Greenwich to which Greaves was appointed early in 1924. He continued to work principally in the department with Mr. Davidson, but he also entered into the work of other departments. His principal contributions were in the field of spectrophotometry. In 1926, an extensive programme was started to determine the " colour temperatures of stars. The quantity actually observed in the comparison of two stars, known as the relative gradient is
The accurate determination of , involved many subsidiary investigations resulting from the peculiarities of the photographic plate in its response to light of different intensities, of different wavelength and for different lengths of exposure. But all the difficulties were overcome and finally a catalogue giving the gradients for 250 stars was published -- mostly the brightest early type stars but also including some later ones. An interesting result was the discovery that some early B type stars were as yellow as normal stars of type F0-F5. For the variable star δ Cephei the gradient followed closely the same curve as that of total light variation.
This work was carried out first with the old 30-inch reflector at Greenwich and later with the Yapp 36 inch. A large prism was used to produce the spectrum and this could be crossed by a grating to determine a scale for Am. Throughout the work Greaves was assisted by C. R. Davidson in planning the observations and by E. G. Martin in work at the telescope and in measuring the plates in the microphotometer. A number of papers have been published in Monthly Notices and The Observatory; the main body of the work is given in two publications from Greenwich.
It had long been known from Greenwich records that magnetic disturbances and sunspot activity showed the same periodicity waxing and waning in an eleven year period. Greaves with H. W. Newton, who was in charge of the solar department, investigated the connection between large individual magnetic disturbances and large sunspots. Three papers by the joint authors appeared in 1928-29. First, they confirmed the statistical relationship which Maunder (1904) had established between the occurrence, of great magnetic storms and the central meridian passages of large sunspots. The central meridian passage of the spot preceded the magnetic storm by days on the average; and this interval was attributed to the travel time of the storm-producing agency (a particle stream) which was assumed to issue nearly vertically from a disturbed chromospheric region. Secondly, they divided magnetic storms into two types, related to their geomagnetic effects: (a) great storms, mostly beginning with a "sudden commencement", which were associated with large sunspots but which showed no recurrence tendency; (b) lesser storms, apparently unassociated with sunspots, which showed a marked tendency to recur at 27-day intervals.
Later work has confirmed this distinction type (a) is now attributed to the isolated blast of particles from a flare within the sunspot region, and type (b) to the long-lived stream of particles from solar M-region. Greaves continued to take an interest in geomagnetism, was responsible for drawing a number of magnetic charts for the Admiralty and gave a most interesting address when, as President of the Society, he presented the Gold Medal to Professor Chapman for his contributions to geophysics and solar physics, and particularly to the theory of geomagnetic phenomena.
In a paper written soon after he went to Greenwich, Greaves discussed the differences which had been found for the declination of the solar apex. For this purpose he employed radial velocities and transverse velocities (from proper motions) of the same stars of types F to M. His interest in the fundamental work of the Observatory was shown by a paper in which he carried through a comparison between the right ascensions of the Second Greenwich Catalogue of Stars for 1925.0 and of the FK. A change from an earlier Greenwich catalogue was attributed to a change in the stars used for determining azimuth and the method of observing them.
In 1938 Greaves succeeded Professor R. A. Sampson as Astronomer Royal for Scotland and Professor of Astronomy in the University of Edinburgh. He found at his disposal a 36-inch reflector, similar to the Yapp at Greenwich, and provided with a Hilger prism slit spectrograph. He at once formulated plans for measurement of the total intensities of the principal hydrogen and other lines in the spectra of stars of types O and B. With the assistance of E. A. Baker a microphotometer of suitable design was constructed, largely in the Observatory workshop. The microphotometer was deliberately designed as a non-recording one.
This programme had scarcely got under way when war broke out and it soon had to be temporarily abandoned not only by restrictions on night work but because the whole activity of the Observatory had to be directed to establishing a national time service. It had previously been possible to send the six-pip time signals from Edinburgh, but in the autumn of 1940 it was decided to arrange for the sending of all the rhythmic signals usually sent from Greenwich or Abinger. The apparatus was fortunately completed so that Edinburgh could take over in the difficult days of January 1941. From then till the end of the emergency Edinburgh played an important part in the transmission of signals as it was not necessary for the lines to pass through London. To enable the time to be accurately known at Edinburgh, the necessary transit observations were made there whenever possible and the results were compared with those made at Abinger. This expansion of the time service with the introduction of Quartz Clocks left no time for the small staff at Edinburgh to engage in their normal research programmes.
With the return of peace the spectrophotometric work was resumed and pressed on with vigour. The first paper giving the results obtained by the "Greaves-Baker" method was published by E. A. Baker in the new series of "Publications of the Royal Observatory, Edinburgh" with the title, Spectrophotometric measurements of Early Type Stars-Methods of observation and results for Oe stars. The second paper of the same series appeared in 1955 -- Results for stars of type B by Greaves, Baker and Wilson.
The important novel principle used in the reduction of the microphotometer measurements was the numerical averaging of the measures of several spectra of a star, and indeed of those of several stars of the same type. It is (or should be) well known that important results may be lost, or even erroneous ones introduced, by the graphical smoothing of data. The numerical method used at Edinburgh increased the accuracy by averaging results for a number of plates, while accidental irregularities due to the grain of the plate or other causes were minimised. Lines which were too feeble to show up on a single plate because their influence did not exceed that of the accidental irregularities could be detected in this way. R. Wilson discovered a hitherto undetected series of shallow helium lines, originating in the fifth quantum level in the spectra of Oe5 stars. One of the difficulties in determining the equivalent width of lines is due to uncertainty in the intensity of the continuum and the numerical method fixes this in a manner not subject to personal error. It is agreed that measures of equivalent widths obtained by this method are more reliable than those secured from single spectra taken with more powerful instruments, and in disclosing features common to groups of stars of similar type the method is unsurpassed. The method, however, is extremely laborious, each spectrum having been measured at about 1500 different wavelengths, and, had the computing effort not been skilfully organised and pursued by Greaves with mechanical aids, it would have been almost impracticable with the small staff available. The original programme covered about 100 stars down to magnitude 5.0, of types O and B. At the time of Greaves's death the observational part of the programme was virtually complete and the reduction of the data about half complete.
Although Greaves's own researches at Edinburgh were mostly in the fields already mentioned he was able, with an increased staff, to expand the work of the Observatory. Since quite early days observations for the determination of the solar rotation spectroscopically had been carried on. Some of the techniques of accurate spectrophotometry were now applied to the solar chromosphere and have yielded valuable results in the study of the flares and of prominences. A combined spectrohelioscope and spectrograph was designed and built for this type of work by M. A. Ellison who joined the staff in 1947. The examination of the solar spectra was greatly facilitated through the construction for Edinburgh in 1948 of a recording microphotometer of unusual design by Messrs Kipp en Zonen of Delft. This could also be employed as an actinometer for stellar photometry. Greaves's interest in solar-terrestrial relations led him to welcome Ellison's proposals for the study of the ionospheric effects of solar flares at Edinburgh and support the plans for the provision of radio equipment for this purpose.
Further plans had been laid for improving the equipment of the Observatory. A 24/16-inch Schmidt telescope, designed for stellar photometry, was erected in 1951. Treasury approval has been obtained for the construction of a new grating spectrograph for the 36-inch reflector and the installation of aluminising plant capable of coating all the mirrors of the Observatory.
As Professor of Astronomy at Edinburgh University, Greaves always took his teaching duties seriously, realising their importance for the future of Astronomy. Even although the majority of the students were in their first year he derived a great deal of satisfaction and enjoyment from this work. In 1950 he got a full time lecturer appointed. At the same time a class in astrophysics was organized, suitable for honours students in physics. This led to a closer link between the Observatory and the University.
Most of Greaves's research papers dealing with the result of observations at Greenwich and Edinburgh were written in collaboration with colleagues of whom he was the senior. In addition he prepared a considerable number of addresses and reports dealing with photometry and spectrophotometry. He acted as recorder of Section A of the British Association and prepared for the B.A. in 1939 an address on Surface Temperatures of Stars, printed in The Observatory of which he had been an Editor. To our Society he delivered as President not only the address already mentioned but others on the occasions when he presented the Gold Medal to Professors Minnaert and Lindblad. He gave a presidential address on the photometry of the continuous spectrum (1948) and earlier (1941) had prepared a Council Note on The escape of continuous radiation from stellar atmospheres. In 1945 he gave the Halley Lecture at Oxford on Photometry as a weapon of astronomical research. More recently as President of Commission 25 of the I.A.U. he prepared valuable reports on Stellar Photometry for the meetings at Rome in 1952 and Dublin in 1955. All these are valuable to anyone interested in astrophysics. As he himself wrote, they "illustrate the way in which natural knowledge is advanced by an interplay between observation and theoretical investigations."
Greaves was a tall man, rather heavily built, and for a number of years had been advised by his doctor to keep down his weight. Many of his movements seemed to entail an unnecessary expenditure of energy -- he even wrote clumsily and seemed to spell out every letter slowly. When discussing anything or just telling a story he had an unusual and disconcerting way of peering into your face and on account of his height had to distort his body to do so. He was a tremendous enthusiast in everything he undertook. The labour, both mental and physical, which he put into every problem seemed to increase as time went on, and even on simple matters he would often exert himself needlessly. A nervous agitation in his actions could lead to tension with elder colleagues who preferred to go about their work quietly to them he belaboured his points. He was critical of all papers submitted to him. The criticism usually took the form of a personal check on every equation, calculation or reference and involved him in what many would have considered unnecessary work. But there is no doubt that his energy and enthusiasm gave great encouragement to those in whose work he was interested and many will remember his help with gratitude. This was specially the case with the younger and subordinate members of his staff whom he encouraged to undertake research problems of their own as distinct from more routine duties.
I worked side by side with Greaves from 1924 till I went to South Africa in 1933. We had been on the friendliest terms for more than 9 years and I remember our parting well. He spoke as if we had worked together for a lifetime and seemed to feel the break more than I did. I was looking forward to new opportunities while he was staying behind and feeling the first gap in his working life. Those who only knew Greaves as an enthusiastic and determined astronomer may be surprised that he should speak feelingly on our separation. As it turned out there were a number of changes in the staff at Greenwich during his remaining 5 years there. Then at Edinburgh he had at first a staff nearing the retiring age, then the war. After that he recruited an entirely new staff and looked forward to another ten years of activity, but this was not to be.
We are greatly indebted to Greaves for the work he did on committees-local, national and international. At Edinburgh he served on the Council of the Royal Society, holding office as Secretary and Vice-President. For many years he was Chairman of the Robert Cormack Bequest Committee for promoting astronomical knowledge and research in Scotland. He acted as chairman of a small subcommittee of our National Committee responsible for the final draft of a resolution regarding the present needs of astronomy in this country. He took on the thankless job of chairman of the committee for nominating British members of Commissions of the I.A.U. and at the General Assembly of the I.A.U. was appointed chairman of the committee dealing with this problem. He had the impossible task of trying to please everyone. When he took up this appointment the committee spent long hours in sorting out the claims of representatives of many countries-hours which most of the members would have preferred spending otherwise. To him must be given some of the credit for the system which now allows much of the work to be done leisurely by post before the meetings of the General Assembly. Greaves did nothing by halves. I remember once telling him that I proposed passing on some information to an astronomer working in a rather isolated observatory. He agreed that I should do so and then added that it would be a mistake not to do so. He travelled many times (by air) from Edinburgh to London to attend meetings of committees and frequently intervened effectively at the meetings. He was a valued member of the Board of Visitors for the Royal Greenwich Observatory and for the Jodrell Bank Experimental Station on both of which he represented our Society. Earlier he had been one of those who had strongly advocated the importance of Radio-Astronomy and the need for the construction of a large Radio-Telescope in this country.
In 1926 he married Caroline Grace, daughter of H. D. Kitto of Whiteshill in Gloucestershire, who survives him with an only son. A younger sister of Mrs Greaves married the late Dr L. J. Comrie.
He was elected F.R.S. in 1943 and a Fellow of our Society in 1921.
I am indebted to Dr M. A. Ellison for assistance in preparing this notice.
J. JACKSON.
He was always glad to serve the Society he was a member of Council for an aggregate of 14 years being Secretary for 7 years and holding the office of President from 1947 to 1949. Always an active member of the national and international committees on which he served, his considered advice will be greatly missed."
The above resolution by the President, Council and Fellows of the Society conveyed to Mrs Greaves the feeling of loss that we had suffered by the death of the Astronomer Royal for Scotland on 1955 December 24.
He was born in Barbados, British West Indies, on 1897 September 10, the only son of the late Dr E. C. Greaves who had graduated in medicine from Edinburgh University. Educated first in a local school and at Codrington College in the West Indies, he proceeded to Cambridge in the middle of the First World War and became a scholar of St. John's College. There he gained many distinctions. He was a wrangler at the Mathematical Tripos of 1919, gaining special distinction and the Tyson Gold Medal for Astronomy.
He was awarded a Smith's Prize in 1921, became Isaac Newton Student the same year and was duly elected a Fellow of his College.
At St. John's Greaves came under the influence of H. F. Baker who, after a distinguished career as a pure mathematician, had been elected Lowndean Professor of Astronomy and Geometry, and took up investigations of the expansions which occur in celestial mechanics, from the mathematical point of view. The earliest publications of Greaves in our Monthly Notices were in this field, and in fact Volume 82 contains no less than four papers by him. The first dealt with the existence theorem for two families of periodic orbits near Lagrange's equilateral triangular points in the restricted problem of three bodies and the second with long period irregularities in the movement of asteroids with a mean motion nearly equal to half that of Mars. For four asteroids he determined the amplitude and period of inequalities due to the action of Mars and also of Jupiter. The other two papers were prompted by G. R. Goldsbrough's work on the influence of satellites on the form of Saturn's ring and pointed out the weakness of arguments indicating instability when only first order terms were considered.
At this period Greaves became associated with E. V. (now Sir Edward) Appleton on the solution of differential equations which arose in the theory of electrical oscillations of triode valves then becoming very important for the generation of radio waves. His knowledge of the solution of similar equations arising in astronomical problems was put to good use as indicated by several papers in the Proceedings of the Royal Society, in the Phil. Mag. and in Proc. of the Cambridge Phil. Society.
In 1923 on the suggestion of Sir Joseph Larmor arrangements were made for Isaac Newton Students to spend some time at the Royal Observatory, Greenwich, to get first hand knowledge of practical astronomy. For several months Greaves worked with C. R. Davidson and this led to two short papers in Monthly Notices concerning systematic errors which might arise in parallax determinations, the more important dealing with the effect of difference in colour of the parallax and comparison stars if the hour angles were more than specified amounts.
The appointment of Dr H. (now Sir Harold) Spencer Jones as H.M. Astronomer at the Cape produced a vacancy at Greenwich to which Greaves was appointed early in 1924. He continued to work principally in the department with Mr. Davidson, but he also entered into the work of other departments. His principal contributions were in the field of spectrophotometry. In 1926, an extensive programme was started to determine the " colour temperatures of stars. The quantity actually observed in the comparison of two stars, known as the relative gradient is
where , is the difference in magnitude at wavelength between the stars compared. By Planck's law
where is a known constant and is the absolute temperature. It turns out that is nearly independent of . There were many difficulties to be faced in applying this formula, i.e., in determining . The most difficult obstacle resulted from the poor and deteriorating conditions in the smoky, artificially illuminated, sky at Greenwich. The work involved a comparison of the intensity of the light of various wave-lengths for stars which might be well separated in the sky (60° or more). It was generally arranged that comparisons should be made when the stars were near the same altitude when the relative atmospheric absorption would be the same (or nearly the same) for the stars compared. In this way the relative gradients were determined first of all for 25 standard stars chosen amongst the brightest of spectral types A and B. In order to obtain absolute gradients (and temperatures) it was necessary to compare at least one star with a terrestrial source of known temperature. This problem was tackled by setting up an acetylene flame on the roof of the Octagon room about 600 ft from the telescope and making the observations through the same optical train apart from the Earth's atmosphere. The reddening due to the Earth's atmosphere was determined by means of standard stars at different zenith distances as nearly as possible at the same time, as this factor could not be trusted to remain constant for long.
The accurate determination of , involved many subsidiary investigations resulting from the peculiarities of the photographic plate in its response to light of different intensities, of different wavelength and for different lengths of exposure. But all the difficulties were overcome and finally a catalogue giving the gradients for 250 stars was published -- mostly the brightest early type stars but also including some later ones. An interesting result was the discovery that some early B type stars were as yellow as normal stars of type F0-F5. For the variable star δ Cephei the gradient followed closely the same curve as that of total light variation.
This work was carried out first with the old 30-inch reflector at Greenwich and later with the Yapp 36 inch. A large prism was used to produce the spectrum and this could be crossed by a grating to determine a scale for Am. Throughout the work Greaves was assisted by C. R. Davidson in planning the observations and by E. G. Martin in work at the telescope and in measuring the plates in the microphotometer. A number of papers have been published in Monthly Notices and The Observatory; the main body of the work is given in two publications from Greenwich.
It had long been known from Greenwich records that magnetic disturbances and sunspot activity showed the same periodicity waxing and waning in an eleven year period. Greaves with H. W. Newton, who was in charge of the solar department, investigated the connection between large individual magnetic disturbances and large sunspots. Three papers by the joint authors appeared in 1928-29. First, they confirmed the statistical relationship which Maunder (1904) had established between the occurrence, of great magnetic storms and the central meridian passages of large sunspots. The central meridian passage of the spot preceded the magnetic storm by days on the average; and this interval was attributed to the travel time of the storm-producing agency (a particle stream) which was assumed to issue nearly vertically from a disturbed chromospheric region. Secondly, they divided magnetic storms into two types, related to their geomagnetic effects: (a) great storms, mostly beginning with a "sudden commencement", which were associated with large sunspots but which showed no recurrence tendency; (b) lesser storms, apparently unassociated with sunspots, which showed a marked tendency to recur at 27-day intervals.
Later work has confirmed this distinction type (a) is now attributed to the isolated blast of particles from a flare within the sunspot region, and type (b) to the long-lived stream of particles from solar M-region. Greaves continued to take an interest in geomagnetism, was responsible for drawing a number of magnetic charts for the Admiralty and gave a most interesting address when, as President of the Society, he presented the Gold Medal to Professor Chapman for his contributions to geophysics and solar physics, and particularly to the theory of geomagnetic phenomena.
In a paper written soon after he went to Greenwich, Greaves discussed the differences which had been found for the declination of the solar apex. For this purpose he employed radial velocities and transverse velocities (from proper motions) of the same stars of types F to M. His interest in the fundamental work of the Observatory was shown by a paper in which he carried through a comparison between the right ascensions of the Second Greenwich Catalogue of Stars for 1925.0 and of the FK. A change from an earlier Greenwich catalogue was attributed to a change in the stars used for determining azimuth and the method of observing them.
In 1938 Greaves succeeded Professor R. A. Sampson as Astronomer Royal for Scotland and Professor of Astronomy in the University of Edinburgh. He found at his disposal a 36-inch reflector, similar to the Yapp at Greenwich, and provided with a Hilger prism slit spectrograph. He at once formulated plans for measurement of the total intensities of the principal hydrogen and other lines in the spectra of stars of types O and B. With the assistance of E. A. Baker a microphotometer of suitable design was constructed, largely in the Observatory workshop. The microphotometer was deliberately designed as a non-recording one.
This programme had scarcely got under way when war broke out and it soon had to be temporarily abandoned not only by restrictions on night work but because the whole activity of the Observatory had to be directed to establishing a national time service. It had previously been possible to send the six-pip time signals from Edinburgh, but in the autumn of 1940 it was decided to arrange for the sending of all the rhythmic signals usually sent from Greenwich or Abinger. The apparatus was fortunately completed so that Edinburgh could take over in the difficult days of January 1941. From then till the end of the emergency Edinburgh played an important part in the transmission of signals as it was not necessary for the lines to pass through London. To enable the time to be accurately known at Edinburgh, the necessary transit observations were made there whenever possible and the results were compared with those made at Abinger. This expansion of the time service with the introduction of Quartz Clocks left no time for the small staff at Edinburgh to engage in their normal research programmes.
With the return of peace the spectrophotometric work was resumed and pressed on with vigour. The first paper giving the results obtained by the "Greaves-Baker" method was published by E. A. Baker in the new series of "Publications of the Royal Observatory, Edinburgh" with the title, Spectrophotometric measurements of Early Type Stars-Methods of observation and results for Oe stars. The second paper of the same series appeared in 1955 -- Results for stars of type B by Greaves, Baker and Wilson.
The important novel principle used in the reduction of the microphotometer measurements was the numerical averaging of the measures of several spectra of a star, and indeed of those of several stars of the same type. It is (or should be) well known that important results may be lost, or even erroneous ones introduced, by the graphical smoothing of data. The numerical method used at Edinburgh increased the accuracy by averaging results for a number of plates, while accidental irregularities due to the grain of the plate or other causes were minimised. Lines which were too feeble to show up on a single plate because their influence did not exceed that of the accidental irregularities could be detected in this way. R. Wilson discovered a hitherto undetected series of shallow helium lines, originating in the fifth quantum level in the spectra of Oe5 stars. One of the difficulties in determining the equivalent width of lines is due to uncertainty in the intensity of the continuum and the numerical method fixes this in a manner not subject to personal error. It is agreed that measures of equivalent widths obtained by this method are more reliable than those secured from single spectra taken with more powerful instruments, and in disclosing features common to groups of stars of similar type the method is unsurpassed. The method, however, is extremely laborious, each spectrum having been measured at about 1500 different wavelengths, and, had the computing effort not been skilfully organised and pursued by Greaves with mechanical aids, it would have been almost impracticable with the small staff available. The original programme covered about 100 stars down to magnitude 5.0, of types O and B. At the time of Greaves's death the observational part of the programme was virtually complete and the reduction of the data about half complete.
Although Greaves's own researches at Edinburgh were mostly in the fields already mentioned he was able, with an increased staff, to expand the work of the Observatory. Since quite early days observations for the determination of the solar rotation spectroscopically had been carried on. Some of the techniques of accurate spectrophotometry were now applied to the solar chromosphere and have yielded valuable results in the study of the flares and of prominences. A combined spectrohelioscope and spectrograph was designed and built for this type of work by M. A. Ellison who joined the staff in 1947. The examination of the solar spectra was greatly facilitated through the construction for Edinburgh in 1948 of a recording microphotometer of unusual design by Messrs Kipp en Zonen of Delft. This could also be employed as an actinometer for stellar photometry. Greaves's interest in solar-terrestrial relations led him to welcome Ellison's proposals for the study of the ionospheric effects of solar flares at Edinburgh and support the plans for the provision of radio equipment for this purpose.
Further plans had been laid for improving the equipment of the Observatory. A 24/16-inch Schmidt telescope, designed for stellar photometry, was erected in 1951. Treasury approval has been obtained for the construction of a new grating spectrograph for the 36-inch reflector and the installation of aluminising plant capable of coating all the mirrors of the Observatory.
As Professor of Astronomy at Edinburgh University, Greaves always took his teaching duties seriously, realising their importance for the future of Astronomy. Even although the majority of the students were in their first year he derived a great deal of satisfaction and enjoyment from this work. In 1950 he got a full time lecturer appointed. At the same time a class in astrophysics was organized, suitable for honours students in physics. This led to a closer link between the Observatory and the University.
Most of Greaves's research papers dealing with the result of observations at Greenwich and Edinburgh were written in collaboration with colleagues of whom he was the senior. In addition he prepared a considerable number of addresses and reports dealing with photometry and spectrophotometry. He acted as recorder of Section A of the British Association and prepared for the B.A. in 1939 an address on Surface Temperatures of Stars, printed in The Observatory of which he had been an Editor. To our Society he delivered as President not only the address already mentioned but others on the occasions when he presented the Gold Medal to Professors Minnaert and Lindblad. He gave a presidential address on the photometry of the continuous spectrum (1948) and earlier (1941) had prepared a Council Note on The escape of continuous radiation from stellar atmospheres. In 1945 he gave the Halley Lecture at Oxford on Photometry as a weapon of astronomical research. More recently as President of Commission 25 of the I.A.U. he prepared valuable reports on Stellar Photometry for the meetings at Rome in 1952 and Dublin in 1955. All these are valuable to anyone interested in astrophysics. As he himself wrote, they "illustrate the way in which natural knowledge is advanced by an interplay between observation and theoretical investigations."
Greaves was a tall man, rather heavily built, and for a number of years had been advised by his doctor to keep down his weight. Many of his movements seemed to entail an unnecessary expenditure of energy -- he even wrote clumsily and seemed to spell out every letter slowly. When discussing anything or just telling a story he had an unusual and disconcerting way of peering into your face and on account of his height had to distort his body to do so. He was a tremendous enthusiast in everything he undertook. The labour, both mental and physical, which he put into every problem seemed to increase as time went on, and even on simple matters he would often exert himself needlessly. A nervous agitation in his actions could lead to tension with elder colleagues who preferred to go about their work quietly to them he belaboured his points. He was critical of all papers submitted to him. The criticism usually took the form of a personal check on every equation, calculation or reference and involved him in what many would have considered unnecessary work. But there is no doubt that his energy and enthusiasm gave great encouragement to those in whose work he was interested and many will remember his help with gratitude. This was specially the case with the younger and subordinate members of his staff whom he encouraged to undertake research problems of their own as distinct from more routine duties.
I worked side by side with Greaves from 1924 till I went to South Africa in 1933. We had been on the friendliest terms for more than 9 years and I remember our parting well. He spoke as if we had worked together for a lifetime and seemed to feel the break more than I did. I was looking forward to new opportunities while he was staying behind and feeling the first gap in his working life. Those who only knew Greaves as an enthusiastic and determined astronomer may be surprised that he should speak feelingly on our separation. As it turned out there were a number of changes in the staff at Greenwich during his remaining 5 years there. Then at Edinburgh he had at first a staff nearing the retiring age, then the war. After that he recruited an entirely new staff and looked forward to another ten years of activity, but this was not to be.
We are greatly indebted to Greaves for the work he did on committees-local, national and international. At Edinburgh he served on the Council of the Royal Society, holding office as Secretary and Vice-President. For many years he was Chairman of the Robert Cormack Bequest Committee for promoting astronomical knowledge and research in Scotland. He acted as chairman of a small subcommittee of our National Committee responsible for the final draft of a resolution regarding the present needs of astronomy in this country. He took on the thankless job of chairman of the committee for nominating British members of Commissions of the I.A.U. and at the General Assembly of the I.A.U. was appointed chairman of the committee dealing with this problem. He had the impossible task of trying to please everyone. When he took up this appointment the committee spent long hours in sorting out the claims of representatives of many countries-hours which most of the members would have preferred spending otherwise. To him must be given some of the credit for the system which now allows much of the work to be done leisurely by post before the meetings of the General Assembly. Greaves did nothing by halves. I remember once telling him that I proposed passing on some information to an astronomer working in a rather isolated observatory. He agreed that I should do so and then added that it would be a mistake not to do so. He travelled many times (by air) from Edinburgh to London to attend meetings of committees and frequently intervened effectively at the meetings. He was a valued member of the Board of Visitors for the Royal Greenwich Observatory and for the Jodrell Bank Experimental Station on both of which he represented our Society. Earlier he had been one of those who had strongly advocated the importance of Radio-Astronomy and the need for the construction of a large Radio-Telescope in this country.
In 1926 he married Caroline Grace, daughter of H. D. Kitto of Whiteshill in Gloucestershire, who survives him with an only son. A younger sister of Mrs Greaves married the late Dr L. J. Comrie.
He was elected F.R.S. in 1943 and a Fellow of our Society in 1921.
I am indebted to Dr M. A. Ellison for assistance in preparing this notice.
J. JACKSON.
William Michael Herbert Greaves's obituary appeared in Journal of the Royal Astronomical Society 116:2 (1956), 145-151.