Remember the days of old, consider the years of many generations: ask thy father, and he will shew thee; thy elders, and they will tell thee.
Oh Spring! Dear Spring! Thou more must bring
Than birds, or bees, or flowers-
The good old times, the holy prime
Of Easter’s solemn hours:
Prayers offer’d up and anthems sung
Beneath the old church towers.
The mid to late 19th century was a period of frenetic astronomical activity in Britain. Inspired by the enthusiasm of home grown ‘clerical’ popularisers of astronomy, such as W.R Dawes and T.W Webb, a new generation of amateur astronomers, forming societies across the length and breadth of the country, would take up the gauntlet of observing the heavens in search of booty. Telescopes were becoming more popular, not just the achromatic refractor, which held a special place in the history of Victorian astronomy, but also the Newtonian reflector, which was experiencing a bit of a Renaissance owing to the introduction of silver-on glass mirrors offering decent aperture at prices that suited the budgets of many more amateurs. It was in this renewed spirit of enthusiasm that William F. Denning was to make his mark on the astronomical community.
Little is known of his early life. The eldest son of Lydia and Isaac Denning, William was born on November 25, 1848 in the picturesque village of Redpost, Somerset. Isaac was a retired army officer-turned-accountant, who provided a modest income for his family. When William was seven, the Denning family moved to the city of Bristol, presumably to realise a higher standard of living by entering an accountancy partnership – Denning, Smith & Co – where they prospered, and were further blessed by three more children – a brother Frederick and twin sisters, Margaret and Emma. Not much is known of William’s education, although judging by the standards of his many later astronomical correspondences, it is reasonable to assume that he received a good foundation at school. After leaving formal education, William followed his father into the accountancy business, remaining with the firm until Isaac’s death in 1884. William showed great promise as an athlete, cricketer and even dabbled in hockey. Indeed, according to a later account by T.E.R Philips, Denning was invited by the legendary cricketer, Dr. William G. Grace, to be a wicket keeper for the county of Gloucestershire – a considerable honour in itself – although for reasons that still remain obscure, he declined the offer. One guess is that the young man had other ambitions related to astronomy, which he had expressed an interest in as early as 1865, aged just 17.
One event that may have consolidated his decision to follow an astronomical career was the great Leonid meteor showers that occurred between 1866 and 1868, during which time many spectacular fireballs were witnessed streaming across the mid-November night sky, and having opened a correspondence with Alexander S. Herschel, the son of Sir John Herschel, who had carried out pioneering work on meteor spectroscopy. And while meteor watching was to become the enduring passion of Denning’s later life, his earliest forays into the hobby were decidedly varied. In 1865, Denning bought his first telescope, a good 4.5 inch refractor, with which he would carry out extensive work on the groupings of sunspots, observations of the transit of Mercury in the year 1868, as well as transit timings of the Galilean satellites of Jupiter, the latter of which formed the basis of his first publication, aged just 20, appearing in the Astronomical Register 6, Vol 92, 1868, and auguring his subsequent meteoric rise in the community of British amateur astronomers.
This first publication in the Astronomical Register was immediately followed up by several others in the next few years, during which time Denning was to spear-head a coordinated effort among dozens of his fellow amateurs to observe the Sun for a month-long period between March 14 and April 14 1869, in order to search for the elusive planet Vulcan, which was postulated to exist inside the orbit of Mercury. Although no such planet was ever seen, it did not in any way diminish his enthusiasm for coordinating multi-observer surveys in the future. Indeed, it was this boyish enthusiasm for his work that led to him founding a new society with the help of his more influential astronomical friends. Known as the Observational Astronomical Society (OAS), it was established on July 1 1869, with Denning himself acting as its first treasurer and secretary. Although the OAS did not ultimately have the legs to endure the sweeping changes that occurred over the coming years, ceasing altogether to exist after 1872, many would agree that it was a legitimate foreshadowing of the much more successful British Astronomical Association(BAA), which was founded in 1890, and which is still going strong today.
Intrigued by the growing interest in large aperture silver-on-glass reflectors that were the talk of the town during these years, and sensing ‘the pomp and ceremony’ of refractor culture, Denning used his brain and took a punt on a 10-inch f/7 With-Browning reflector with a simple alt-azimuth mounting, which he purchased in 1871. Being unusually enthusiastic about exploring the telescope’s potential under the starry heavens, the truth soon set him free, and he embraced the same instrument to embark on an extraordinary program of visual work on the bright planets. It was these observations, and his subsequent commentaries, that were to abruptly hurl the young man into the limelight of the international astronomical community.
Over the next 15 years or so, Denning became universally acknowledged as one of the finest planetary observers of his age, and especially of Jupiter. Having access to the best astronomical literature of the day, he became acutely aware that the drawings made by astronomers using larger telescopes were not revealing as much detail as one might have anticipated from their superior aperture. As a case in point, he argued that the Jovian whole disk drawings carried out by the Third Earl of Rosse using the 72 inch Leviathan of Parsonstown were no more detailed than backyard telescopes with very modest apertures in comparison. In addition, being intimately familiar with the work of other great observers of his era, such as the English solicitor and amateur astronomer, Stanley Williams, who had used a 6.5 inch Calver reflector on a simple equatorial mount to make all of his highly detailed drawings of the Giant Planet, Denning reached this remarkable conclusion in a publication communicated in 1885:
Many people would consider that in any crucial tests the smaller instrument would be utterly snuffed out: but such an idea is entirely erroneous. What the minor telescope lacks in point of light it gains in definition. When the seeing is good in a large aperture, it is superlative in a small one. When unusually high powers can be employed on the former, far higher ones proportionally can be used with the latter. We naturally expect that very fine telescopes, upon which so much labour and expense have been lavished, should reveal far more detail than in moderate apertures, but when we come to analyze the results it is obvious such an anticipation is far from being realized. The glare of excessive light and the endless mouldings and flaring of the image can only have one effect in obliterating delicate markings.
Denning’s comments were made in response to some criticisms of both his work and the observations made by other keen observers he enjoyed correspondences with, who seemed to confirm rapid atmospheric changes in Jupiter’s massive turbulent atmosphere. In particular, they were directed at the comments made by the professional American astronomer, G.W. Hough, who employed the 18.5 inch Dearborn refractor in his own Jovian studies, but who had failed to notice the same changes. Consequently, Hough dismissed the reports of Denning et al as being attributed to “the poor quality of the images” in the smaller telescopes. Rising to Hough’s criticism, Denning not only reaffirmed what he and others had seen but began to seriously wonder why Hough had missed seeing these changes with such a formidable telescope. In another 1885 publication, Denning writes:
Apertures of 6 to 8 inches seem able to compete with the most powerful instruments ever constructed……a very large aperture shows the rushing of vapours across the disc, and violent contortions of the image, which are the inevitable result.
In support of his conclusions, Denning pointed out that the disk drawings of Mars made by Asaph Hall and the Scots-born American astronomer, William Harkness, were noticeably ‘bland’ in comparison with those drawn by the Reverend Dawes and Giovanni Schiaparelli, who both used instruments of 8-inch aperture, as well as the fine work of the British artist, Nathaniel Green, who had conducted extensive Martian observations from the Madeira archipelago, off the coast of Morocco, using a 13-inch silver-on-glass reflector.
Reference: Sheehan, W, Planets and Perception, University of Arizona Press, (1988), pp 103.
In addition, Denning also brought Sir William Herschel’s opinions in these matters to the fore:
Sir William Herschel seems to have the non-utility of large instruments in the observation of bright planets for he wrote as follows: “On the course of these observations[on the belts of Saturn] I made ten new object specula and fourteen small plain ones for my 7 foot [6.3 inches] having found that with these instruments I had light sufficient to see the belts of Saturn well and that here [Bath, England] the maximum of distinctness might be much easier obtained than where large apertures were concerned.
After Nathaniel Green acquired his ‘ultimate’ telescope back in England – a reflector of 18 inches aperture – he found it useful to fit it with a “convenient gradation of stops.”
This was just the ammunition Denning needed to drive home his own findings:
If a large diameter telescope is useless without stops, wherein does its utility consist? Better at once to adopt a smaller speculum and obviate the more troublesome manipulation of a large instrument. True there are very rare occasions when all the aperture may be utilized; but are they worth waiting for, and when they come, do the results answer expectations?
Denning undoubtedly had a point, as the air cells coursing over the British Isles do indeed seem to favour moderate but not large apertures, but it was not true everywhere. For example, in a study conducted by the American astronomer, Charles A. Young, using the 23-inch Clark refractor at Princeton, New Jersey, he admitted that while small apertures are less sensitive to the vagaries of the Earth’s atmosphere, in his opinion, the images through the 23-inch were generally far superior to those garnered by the 9-inch glass with a frequency of about one night in three.
Notwithstanding these comments, Denning was no Luddite, acknowledging that for other avenues of astronomical observing, aperture was an indispensable commodity:
In certain departments of research large apertures are absolutely required, and have performed work utterly beyond the capacity of moderate instruments.
Denning’s keeness for observing was legendary, so much so that it is no wonder he did so well with such a modest telescope without a driven mount, and no cooling fans; a circumstance that flies in the face of the modern amateur, who often regard such devices as ‘essential.’ Denning’s reports are also entirely in keeping with the author’s own field experience with a modern 8-inch f/6 Newtonian, which has proven to be his best and most used telescope (also un-driven and with no cooling fans).
We may gain a glimpse of Denning’s extensive experience by taking a look at a few comments he made in Chapter VIII of Hutchinson’s Splendour of the Heavens:
The telescope’s definition of Jupiter varies greatly according to the altitude of the planet. From 487 nights of observation (ten inch reflector) at Bristol the following percentages were observed:-
% Nights Very Good Good Fair Bad Very Bad
Jupiter South of Equator 7.0 14.1 15.5 33.8 29.6
Jupiter North of Equator 19.8 29.1 25.6 18.6 7.0
The reader will note the great advantage of observing the planet higher in the sky as viewed north of the celestial equator, where the orb is less affected by atmospheric turbulence. Note also the percentage of useful nights and/or observing spells Denning enjoyed from Bristol; a number wholly inconsistent with the ‘perpetual bad weather myth’ promulgated by modern amateurs. Self evidently, there were more clear nights where work could be done over ‘cloudy’ England than is commonly reported today.
Reference: Philips, T.E.R (ed.), Hutchinson’s Splendour of the Heavens, Vol 1, Hutchinson & Co, (1923), pp 337.
Intriguingly, this anomalously high frequency of good observing nights/spells communicated by Denning was also independently reported by the consummate British amateur, Charles Grover, who’s biographer revealed that he observed on 146 nights (40 per cent) during the year 1886.
Denning was a keen observer of Jupiter’s Great Red Spot (GRS), watching it change in colour, shape and size over many years with his 10-inch With-Browning speculum, and about which he discusses at great length in Splendour of the Heavens. On the evening of February 13 1888, he made a sketch of the Giant Planet with his alt-azimuth reflector, which shows a considerable amount of detail.
The size of the GRS is relatively enormous though, much larger in comparison to anything seen in recent years. The reader will note a large bright cloud-like structure encapsulated within the spot. Out of curiosity, this author examined another Jupiter drawing by the young E.E. Barnard using a fine 5-inch f/15 Byrne refractor, made as close in time as possible to Denning’s sketch. As this link shows (bottom right sketch) dated April 22, 1886, Barnard’s superb eyesight recorded an equally large GRS with the same cloud like structure inside it, and with an accompanying note (seen on the previous page) which states:
A white cloud has formed over the middle of the Great Red Spot, almost obliterating it.
Could Denning and Barnard have observed the same feature, albeit a couple of years apart? I dare say, it’s very probable!
Do you have the historical evidence to dismiss this possibility out of hand? I’d be happy to weigh the evidence.
Comparing the detail of the two sketches, we see the superior resolving power and contrast transfer of Denning’s reflector coming into play, don’t you think?
Denning’s contribution to planetary astronomy extended well beyond Jupiter though. For example, in 1876, Professor Asaph Hall using the great 26-inch refractor at the U.S. Naval Observatory, recorded an equatorial spot on Saturn, which he followed and measured through 60 rotations, and from these data deduced its period to be 10 hours, 14 minutes and 24 seconds. Hall was careful to stress that this may not have been the rotation period of the planet per se, only that of the spot itself. Back in England, both Denning and Stanley Williams, using far more modest 10 inch and 6.5 inch specula, respectively, were following vague markings on the Saturnian globe and came to a rotation period just two seconds shy of Hall’s estimate, all of which are in agreement with the best modern values for the planet’s rotation.
Reference: Clerk, A., A Popular History of Astronomy During the Nineteenth Century, Cornell University Press, 2009, pp 167
An Aside: Quality Never Goes Out Of Fashion
How good were With and Calver mirrors? In a word, ‘excellent’, by all accounts. Calver deliberately left his mirrors slightly undercorrected to compensate for the natural overcorrection a mirror would exhibit as it cooled off. This is also the case with the majority of modern, mass produced mirrors. A few years back, I had the pleasure of conversing with London-based amateur astronomer, Robert Katz, who lovingly restored a magnificent 10-inch f/8 Calver reflector on a simple alt-azimuth mount. He was kind enough to share his experiences of the telescope with me.
The optics are fine and because the focal length is actually less than that of a standard SCT, views of deep sky objects are impressive with a low power eyepiece. It comes into its own with the planets, though, and the exceptional opposition night of Jupiter in September 2010 was memorable in many ways. Thanks to good seeing in South West London – the telescope is in Hampton Hill – I spent most of the night watching Jupiter turn in exquisite detail using a fine telescope made in 1882 by one of the two great telescope makers of his day; but a telescope so simple that a child can learn to operate it confidently in five minutes.
Thus, by all accounts, these fine Newtonian telescopes were first rate tools that enabled their owners to conduct detailed studies of the firmament. The fact that Denning and others used an alt-azimuth mounting to conduct his planetary studies (most of which was published in the best astronomical journals of the day) is also to be noted. Today, there is a tendency among some amateurs to dismiss the use of an undriven alt-azimuth mount because it doesn’t keep the planet in the centre of the field. Truth be told though, there will be plenty of opportunities (his was a f/7ish remember?) when the finest details of a planet’s aspect can be made out as it crosses the field of view, as this author has discovered over several years of continued work with simple, undriven mounts. So, like everything else in life, intrepid folk always find a way ’round such technical ‘obstacles’.
In parallel to his growing interest in planetary observing, Denning took up the activity of comet hunting sometime in the 1870s, and he was rewarded for his efforts in the predawn hours of October 4 1881, when, shortly after a spell observing Jupiter, he inserted a low power eyepiece and began sweeping the sky in its vicinity. Almost immediately he caught sight of a ‘suspicious’ object that turned out to be a new short period comet. Nearly another decade elapsed before discovering his next icy interloper, which he stumbled upon in 1891 and this was followed by two other comet discoveries in 1892 and 1894. For each of these discoveries, Denning was awarded the Bronze Medal by the Astronomical Society of the Pacific. Denning was also the co-discoverer of a comet with the famous Americcan astronomer, E.E. Barnard in 1891.
His publication rate rising to some 20 articles per year, Denning’s reputation as an observer of repute grew steadily, so much so that he was elected President of Liverpool Astronomical Society for the year 1887, increasing its already large membership from 440 to 641.
In addition to his published articles, Denning embarked upon writing books on amateur astronomy. While his earliest forays into this brave new world was met with unnecessarily harsh criticisms from the priggish founding editor of Nature, Sir Norman Lockyer, his later books, including, Telescopic Work for Starlight Evenings (1891), were enthusiastically endorsed by the powers that be.
Many more accolades were bestowed upon F.W. Denning in the closing decade of the 19th century, not only at home but abroad also. The Valz Price of 1895 was awarded to him by the French Academie des Science, and in 1898 Denning received the prestigious Gold Medal of the Royal Astronomical Society in recognition of his monumental work on meteors. He was even given a mention in chapter 2 of H.G. Wells’ famous novel: The War of the Worlds, which was first serialised in 1897.
While it is undoubtedly true that Denning expressed an interest in the Martian canal theory, he was not convinced of their reality stating that, ” they were far more highly suggestive of natural than artificial production.“
It is not known exactly when Denning acquired his largest telescope, a 12.5 inch Calver reflector, but what is certain is that he never acquired equatorial mounts for any of them. Nor did he bother building an observatory for his telescopes; a custom quite out of sink with the prevailing culture of his day. His voluminous drawings of all the major planets are not striking for their artistic renderings but they do reveal the workings of a true telescopic draughtsman, where accuracy and objective truth were held in higher esteem than artistic license.
By the end of the 19th century, W.F.Denning was one of the most famous astronomers in the world, commanding an extraordinary web of correspondence with the scientific giants of his age. And while the accolades kept piling up, Denning’s reaction to this new-found fame was not in keeping with a man of his standing. An admixture of declining health and bitter criticism over his ideas regarding the stationary nature of meteor radiants, conspired to alienate the consummate English amateur so much so that he eschewed the limelight and became increasingly reclusive, giving up telescopic astronomy altogether by 1906.
It is not known how Denning made a living in the last few decades of his life, but it is known that he did receive a Civil List Pension by the British Government beginning in 1904, when he was 56 years old. This amounted to an annual stipend of £150, “ in consideration of his services to the Science of Astronomy, whereby his health has become seriously impaired and of his straitened circumstances.” And while there is no evidence that he earned an income from the family accountancy business, it has been suggested that he received sporadic payments for his literary works, and some occasional prize money for his discoveries that just barely kept the wolf away from the door.
Though he lived a solitary life, Denning kept up communication with the outside world through his many letters of correspondence and scientific publications. And while his telescopic career was now far behind him, it was by no means the end of his discovery days. In a singular period between 1918 and 1920, Denning, now a septuagenarian, observed a nova in Aquila (V603 Aql), the discovery of which was later contested. However, during a routine meteor watch in August 1920, the 72 year-old Denning discovered a new star in Cygnus, shining with a magnitude of 3.5. Nova Cygni was the talk of the astronomical world for many months to come and he enjoyed a surge in correspondences from an adoring international following.
As well as his correspondences, Denning took to writing poetry, in which he often explored the themes of Nature, her cycles of decline and renewal. It has been suggested that he was a Christian.
The last decade of Denning’s life is one of great sadness. Upon visiting him at his last known address at Eggerton Road, Bristol, in 1922, Dr. W.H. Steavenson recalled meeting a wretched soul, living in abject poverty, and with only an open fire and a tobacco pipe as sources of comfort. Even when Denning left the house, he became the butt of every schoolboy’s joke, who ignorantly taunted the eccentric astronomer .
Denning remained an active observer of the heavens right up until a few weeks before his death, aged 83, caused by heart disease, on June 9th 1931. Entirely self taught, and arguably the most active and gifted observer of his generation, he will be remembered for his unbridled enthusiasm for his science, his love of nature and for his encouragement of a new generation of stargazers across the world. W.F.Denning (1848-1931); an extraordinary life lived.