Balfour Stewart

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Balfour Stewart (1 November 1828 – 19 December 1887) was a Scottish physicist.

Stewart was born in Edinburgh, and was educated at the University of Edinburgh. The son of a tea merchant, he was for some time engaged in business in Leith and in Australia, but, returning to his studies of physics at Edinburgh, he became assistant to J. D. Forbes in 1856. Forbes was especially interested in questions of heat, meteorology, and terrestrial magnetism, and it was to these that Stewart also mainly devoted himself.

Radiant heat first claimed his attention, and by 1858 he had completed his first investigations into the subject. These yielded a remarkable extension of Pierre Prévost's "Law of Exchanges," and enabled him to establish the fact that radiation is not a surface phenomenon, but takes place throughout the interior of the radiating body, and that the radiative and absorptive powers of a substance must be equal, not only for the radiation as a whole, but also for every constituent of it.

In recognition of this work he received in 1868 the Rumford Medal of the Royal Society, into which he had been elected six years before. Of other papers in which he dealt with this and kindred branches of physics may be mentioned "Observations with a Rigid Spectroscope," "Heating of a Disc by Rapid Motion in Vacuo," "Thermal Equilibrium in an Enclosure Containing Matter in Visible Motion," and "Internal Radiation in Uniaxal Crystals."

In 1879 he was appointed director of Kew Observatory, and there naturally became interested in problems of meteorology and terrestrial magnetism. In 1870, the year in which he was very seriously injured in a railway accident, he was elected professor of physics at Owens College, Manchester, and retained that chair until his death, which happened near Drogheda, in Ireland, on 19 December 1887.

He was the author of several successful textbooks of science, and also of the article on "Terrestrial Magnetism" in the ninth edition of the Encyclopædia Britannica. In conjunction with Professor P. G. Tait he wrote The Unseen Universe, at first published anonymously, which was intended to combat the common notion of the incompatibility of science and religion. A devoted churchman, Stewart was prominently identified with the Society for Psychical Research.[1] It was in his 1875 review of The Unseen Universe, that William James first put forth his Will to Believe Doctrine.

Contents 1 Obituary 2 Stewart Super Flare 3 Writings 4 References

[edit] Obituary

Dr. Balfour Stewart^[1] was born in Edinburgh on November 1st, 1828, and died in Ireland on December 18th, 1887, having just entered his sixtieth year. He was educated for a mercantile profession, and in fact spent some time in Leith, and afterwards in Australia, as a man of business. But the bent of his mind towards physical science was so strong that he resumed his studies in Edinburgh University, and soon became assistant to Professor J. D. Forbes, of whose class he had been a distinguished member. This association with one of the ablest experimenters of the day seems to have had much influence on his career; for Forbes's researches (other than his Glacier work) were mainly in the department of Heat, Meteorology, and Terrestrial Magnetism, and it was to these subjects that Stewart devoted the greater part of his life. In the classes of Professor Kelland, Stewart had a brilliant career; and gave evidence that he might have become a mathematician, had he not confined himself almost exclusively to experimental science.

In 1858, while he was still with Forbes, Stewart completed the first set of his investigations on Radiant Heat, and arrived at a remarkable extension of Prevost's “Law of Exchanges." His paper (which was published in the 'Transactions of the Royal Society of Edinburgh') contained the greatest step which had been taken in the subject since the early days of Melloni and Forbes. The fact that radiation is not a mere surface phenomenon, but takes place like absorption throughout the interior of bodies, was seen to be an immediate consequence of the new mode in which Stewart viewed the subject. Stewart's reasoning is, throughout, of an extremely simple character, and is based entirely upon the assumption (taken as an experimentally ascertained fact) that in an enclosure, impervious to heat and containing no source of heat, not only will the contents acquire the same temperature, but the radiation at all points and in all directions will ultimately become the same, in character and in intensity alike. It follows that the radiation is, throughout, that of a black body at the temperature of the enclosure. From this, by the simplest reasoning, it follows that the radiating and absorbing powers of any substance must be exactly proportional to one another (equal, in fact, if measured in proper units), not merely for the radiation as a whole, but for every definitely specified constituent of it. In Stewart's paper (as in those of the majority of young authors) there was a great deal of redundant matter, intended to show that his new views were compatible with all that had been previously known, and in consequence his work has been somewhat lightly spoken of, even by some competent judges. These allow that he succeeded in showing that equality of radiation and absorption is consistent with all that was known; but they refuse to acknowledge that he had proved it to be necessarily true. To such we would recommend a perusal of Stewart's article in the 'Philosophical Magazine' (vol. 25, 1863, p. 354), where they will find his own views about the meaning of his own paper. The only well-founded objection which has been raised to Stewart's proof applies equally to all proofs which have since been given, viz., in none of them is provision made for the peculiar phenomena of fluorescence and phosphorescence.

The subject of radiation, and connected properties of the lumini-ferous medium, occupied Stewart's mind at intervals to the very end of his life, and led to a number of observations and experiments, most of which have been laid before the Royal Society. Such are the “Observations with a Rigid Spectroscope," and those on the "Heating of a Disk by rapid Rotation in vacuo" in which the present writer took part. Other allied speculations are on the connexion between “Solar Spots and Planetary Configurations," and on “Thermal Equilibrium in an Enclosure containing Matter in Visible Motion."

From 1859 to 1870 Stewart occupied, with distinguished success, the post of Director of the Kew Observatory^[2]. Thence he was transferred to Manchester as Professor of Physics in the Owens College, in which capacity he remained till his death. His main subject for many years was Terrestrial Magnetism; and on it he wrote an excellent article for the recent edition of the 'Encyclopædia Britannica.' A very complete summary of his work on this subject has been given by Schuster in the 'Manchester Memoirs' (4th series, vol. 1, 1888). In the same article will be found a complete list of Stewart's papers.

Among the separate works published by Stewart, his 'Treatise on Heat,' which has already reached its fifth edition, must be specially mentioned. It is an excellent introduction to the subject, though written much more from the experimental than from the theoretical point of view. In the discussion of radiation, however, which is given considerable length, a great deal of theoretical matter of a highly original character is introduced.

On another work, in which Stewart took a great part, 'The Unseen Universe,' the writer cannot speak at length. It has passed through many editions, and has experienced every variety of reception — from hearty welcome and approval in some quarters to the extremes of fierce denunciation, or of lofty scorn, in others. Whatever its merits or demerits it has undoubtedly been successful in one of its main objects, viz., in showing how baseless is the common statement that “Science is incompatible with Religion." It calls attention to the simple fact, ignored by too many professed instructors of the public, that human science has its limits; and that there are realities with which it is altogether incompetent to deal.

Personally, Stewart was one of the most loveable of men, modest and unassuming, but full of the most weird and grotesque ideas. His conversation could not fail to set one a-thinking, and in that respect he was singularly like Clerk-Maxwell. In 1870 he met with a frightful railway accident, from the effects of which he never fully recovered. He passed in a few months from the vigorous activity of the prime of life to grey-headed old age. But his characteristic patience was unruffled and his intellect unimpaired.

He became a Fellow of the Royal Society in 1862, and in 1868 he received the Rumford Medal.

His life was an active and highly useful one; and his work, whether it took the form of original investigation, of accurate and laborious observation, or of practical teaching, was always heartily and conscientiously carried out. When a statement such as this can be truthfully made, it needs no amplification.
P.G.T.

[edit] Stewart Super Flare

While much attention has been focused on the Carrington Super Flare, which occurred on September 1, 1859 and the associated magnetic storm for which reached the Earth on September 2, 1859, there was an earlier super flare on August 28, 1859, which was documented on the self-recording magnetographs at the Kew Observatory and described by Balfour Stewart ^[3][4] in a paper presented to the Royal Society on November 21, 1861.

It is unnecessary to enter into further particulars regarding this meteor, as the description of it given by observations at places widely apart have been collected together by Professor E. Loomis, and published in a serious of papers communicated to the American Journal of Science and Arts. I shall only add that, both from the European, the American, and the Australian accounts, there appear to have been two great displays, each commencing at nearly the same absolute time, throughout the globe, —the first on the evening of the 28th of August, and the second on the early morning of the 2nd of September, Greenwich time.

Magnetic disturbances of unusual violence and very wide extent were observed simultaneously with these displays. These were recorded more or less frequently at the various observatories; but at Kew there is the advantage of a set of self-recording magnetographs (the property of the Royal Society), which are in constant operation.

As a description of these instruments has already been published^[5] in the volume of the Reports of the British Association for 1859, it is only necessary here to mention that they afford the means of obtaining a continuous photographic register of the state of the three elements of the earth’s magnetic force—namely, the declination, and the horizontal and vertical intensity. Reduced representations of these traces furnished by these instruments during the great disturbance under discussion accompany this paper; and it will now be necessary to give a short description of these.

Stewart goes on the make the following observation.

I now proceed to notice some of the peculiarities of this magnetic storm.

It appears that we have two distinct well-marked disturbances, each commencing abruptly and ending gradually, the first of which began on the evening of August 28 and the second on the early morning of September 2. These two great disturbances correspond therefore in point of time to the two great auroral displays already alluded to.

The second disturbance is now known as the Carrington Super Flare, while the fist disturbance is unnamed. As Stewart recorded and described this disturbance, this event will be referred to as the Steward Super Flare in this discussion.

At the November 11, 1859 meeting of the Royal Astronomical Society, Richard Carrington presented a paper^[6] describing his observations of the super flare which occurred on September 1, at 11:18 GMT and later named in his honor. In what appears to be a editorial addition made after the meeting the follow observation was appended in parenthesis.

(Mr. Carrington exhibited at the November Meeting of the Society a complete diagram of the disk of the sun at the time, and copies of the photographic records of the variations of the three variations of the three magnetic elements, as obtained at Kew, and pointed out that a moderate but very marked disturbance took place at about 11^h 20^m A.M., Sept. 1st, of short duration; and that towards four hours after midnight there commenced a great magnetic storm, which subsequent accounts established to be considerable in the southern as in the northern hemisphere. While the contemporary occurrence may deserve noting, he would not have it supposed that he even leans towards hastily connecting them. “One swallow does not make a summer.”)

From this addendum, it is clear that Richard Carrington was not willing to professionally commit to connecting the magnetic disturbance with the event he had observed on the surface of the sun even though they occurred at nearly identical times and he displayed the magnetographs at the Royal Astronomical Society meeting. The time of 11:20 GMT is good agreement with other reports but the time of 4:00 GMT on September 2, 1859 for the commencement of the magnetic storm is an hour earlier than reported by Stewart.

Stewart also reported^[4] on the magnetic disturbance which occurred at the same time as the event observed by Richard Carrington.

But, beside these two remarkable disturbances into which it divided itself, this great storm comprehends a minor disturbance, not approaching these two in extent, but yet possessing an interest peculiar to itself, which entitles it to be mentioned.

On September 1, a little before noon, Mr. R.C. Carrington happened to be observing, by means of a telescope, a large spot which might then be seen on the surface of our luminary, when a remarkable appearance presented itself, which he described in a communications to the Royal Astronomical Society.

(Richard Carrington’s paper is then quoted at length.)

On calling at Kew Observatory a day or two afterwards, Mr. Carrington learned that at the very moment when he had observed this phenomena the three magnetic elements at Kew were simultaneously disturbed. If no connexion had been known to subsist between these two classes of phenomena, it would, perhaps, be wrong to consider this in any other light than a casual coincidence; but since General Sabine has proved that a relation subsists between magnetic disturbances and sun spots, it is not impossible to suppose that in this case our luminary was taken in the act.

This disturbance occurred as nearly as possible at 11^h 15^m A.M. Greenwich mean time, on September 1, 1859, affecting all the elements simultaneously, and commencing quite abruptly.

By sighting the previous research of Edward Sabine, which established a correlation between sunspots and magnetic storms, Stewart was able to correctly advance the theory that the event observed by Richard Carrington and the magnetic disturbance which was recorded at the same time were in fact connected. The magnetic phenomena which occurred at about 11:18 GMT on September 1, 1858 are now known as a Solar Flare Effect (SFE) or a Magnetic Crochet, but the connection would not be proven for another 80 years^[7]. The SEF is a sudden ionosphere disturbances caused by soft X-rays and Extreme ultraviolet (EUV) driven enhancement of the ionosphere current vortices responsible for the regular daily variation observed on magnetometer traces. SFE are mostly observed in locations close to the sub-solar point (i.e. the point on earth when the sun is overhead) and can only be observed from stations in the sunlit hemisphere at the time of the solar flare. Using Stewart’s times, the magnetic storm associated with the Carrington Super Flare took 17 hours and 45 minutes to reach the Earth.

Stewart reported that the magnetic storm from the Steward Supper Flare, began at 22:30 GMT on the evening of September 28, 1859 as recorded by self-recording magnetographs at the Kew Observatory. Assuming that the transit time for the first super flare was the same as the second or 17 hours and 45 minutes, the Steward Supper Flare occurred at about 04:45 GMT on the morning of September 28, 1859. As the Solar Flare Effect can only be observed from the sunlit hemisphere the question becomes, what time was sunrise at the Kew Observatory on the morning of September 28, 1859?

The coordinates for Kew Observatory are (51°29'N, 0°17'W). Using the US Naval Observatory “Sun or Moon Rise/Set Table for One Year” calculator,sunrise on the morning of August 28, 1859 sunrise was 05:06GMT. The Kew Observatory was still 21 minutes from sunrise and the Solar Flare Effect would not have been registered by the self-recording magnetographs at the Kew Observatory.

Steward did not publish the magnetograph records for the morning of August 28, 1859. While it is extremely unlikely, the original magnetograph records for that date should be inspected to determine if any disturbance was recorded because of the uncertainties in timings and the nearness of sunrise.

[edit] Writings

• Elementary Treatise on Heat (1866; sixth edition, revised, 1895)
• Lessons in Elementary Physics (1871)
• Physics (1872)
• The Conservation of Energy (1875; ninth edition, 1900)
• Lessons in Practical Physics with W. H. Gee, (volume i, 1885; volume ii, 1887)
• Books by Balfour Stewart available in the Internet Archive
• Books by Balfour Stewart available in Google Books
• Papers by Balfour Stewart available in Google Scholar

[edit] References

• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.