Weighing the World – John Michell 1724-1793

Among Britain’s most eminent scientists of the 18th century was a very unlikely candidate in the guise of the Rector of Thornhill, a village near Dewsbury, in the West Riding of Yorkshire. The Rector’s name was John Michell and he was destined to associate with some of the best known scientists of the age and to greatly contribute to the world of science…but he has now been largely forgotten, except perhaps by those whose curiosity is aroused by reading the inscription commemorating his life in Thornhill’s Parish Church of St Michael and All Angels.

In the Chancel of this Church are deposited, the
Remains of The Revd. Jn. Michell B.D., F.R.S,
& 26 years Rector of this Parish.
Eminently distinguished as the Philosopher, & the
Scholar, He had a just claim to the character of the
Real Christian. In the relative and social Duties of Life:
The tender husband, the indulgent Parent,
the affectionate brother, & the sincere Friend,
were prominent Features in a character uniformly
amiable. His charities were not those of ostentation,
but of feeling. His strict discharge of his professional
duties, that of principle, not form. As he lived in possession
of the esteem of his Parishioners, so he has carried with
him to the grave their regret.
He died the 21st April 1793, in the 69th Year of his Age.

I always prefer to have some family connection in my Kirklees Cousins stories, but can claim no relationship at all to the Reverend John Michell, who wasn’t even born in Yorkshire, let alone Thornhill. However, he was Rector of Thornhill Parish Church and, in that capacity, some of my ancestors, generations of whom were born, married and buried at Thornhill, would have known him…and maybe some were even baptised, married or given a funeral service by Michell himself. Looking at my family tree data, there are many suitable candidates, especially in the 1770s and 1780s.

Not many other people seem to have have heard about John Michell outside the rarefied atmosphere of the Royal Society and those who frequent the libraries of Queens College Cambridge. Perhaps his name and works would have been totally confined to the libraries of the past, had not Sir Archibald Geikie been researching among the archives of the Royal Society in 1918. John Michell’s name kept cropping up again and again and this aroused Geikie’s curiosity. Why hadn’t he heard of this brilliant scientist before, whose contributions to natural philosophy and each of the sciences of geology, physics and astronomy, were truly remarkable? He set about writing a biography, entitled “Memoir of John Mitchell”.

It turned out that John Michell was a friend and colleague of many of the now “household name” scientists like William Hershel, Joseph Priestley, Jan Ingenhousz, and Henry Cavendish, and was to entertain some of the world’s top thinkers, including the American, Benjamin Franklin…but we go much too fast…so, let’s start again, at the very beginning (a very good place to start).

John Michell was born in Eakring, Nottinghamshire on Christmas day 1724, the son of Gilbert Michell, who was rector there, and his wife Obedience. The family originated in Cornwall. No portrait of John is known to exist, but contemporary descriptions say that he was a short fat man of “black complexion”. But what he didn’t possess in looks, he certainly made up for in brains. Michell turned out to be a talented student and he entered Queens College, Cambridge, as a pensioner (a paying student) and was enrolled as an undergraduate in 1742. He may have taken some time off his studies, because he didn’t take his Mathematical Tripos examination until January 1749 when he was ranked 4th Wrangler, and he graduated with a BA a few months later.

He immediately took holy orders and was appointed curate at his father’s parish at Eakring, following the tradition of his family and the expectation of his father. But, only a few weeks later Michell was elected a Fellow of Queens College.

1750 to 1767

In 1750, at 26 years old, Michell published an 80 page long “Treatise of Artificial Magnets: In which is Shewn an Easy and Expeditious Method of Making Them, Superior to the Best Natural Ones.”

Queens College, Cambridge

In this treatise, he was the first person to introduce the inverse-square law of magnetism. He also identified the point from which to measure distances as being the magnetic pole (correcting Isaac Newton’s alternative but erroneous theory). No-one seems to have taken any notice of his work and the person credited with the inverse square law in magnetism was Charles-Augustin de Coulomb, more than 30 years later! Meanwhile, Michell’s fellow students must have been bemused by his way of working, as he built all his own equipment and his rooms at Queens were full of his various implements and machinery. Perhaps he was seen as a bit of an eccentric and was not “one of the crowd”.

From now on he was unstoppable in his achievements. Michell graduated as Master of Arts in 1752 and became a Tutor of Queens College from 1751 to 1763; Praelector [a reader or lecturer] in Arithmetic in 1751; Censor in Theology in 1752; Praelector in Geometry in 1753; Praelector in Greek in 1755 and 1759; Senior Bursar in 1756; Praelector in Hebrew in 1759 and 1762; Censor in Philosophy and Examiner in 1760. Clever chap – he could have spent a lifetime in academia – but he didn’t!

Certainly, Michell’s pastoral and teaching duties would have taken up much of his time at Cambridge, but he also managed to fit in many geology trips, especially to the south of England and along the Jurassic Coast, allowed him to gain an accurate understanding of the structure of the earth’s crust. He took a keen interest in all aspects of geology and in 1760 he published his Earthquake paper, which was read during the course of a week, in five instalments, at the Royal Society. Its catchy title was:

“Conjectures concerning the Cause, and Observations upon the Phaenomena of Earthquakes; particularly of that great Earthquake of the first of November 1755, which proved so fatal to the City of Lisbon, and whose effects were felt as far as Africa, and more or less throughout almost all Europe.” (Whew!)

The Great Wave off Kanagawa by Hokusai

Michell was the first to propose that a tsunami results from the movement of rocks miles below the earth’s surface in a sub-marine earthquake and that this causes the water to travel huge distances as waves…he was also able to estimate the location of the earthquake’s epicentre.

Immediately after reading his paper, some of the Fellows of the Royal Society drew up and signed a document, recommending him for membership and he was duly elected to the Royal Society on 12th June 1760.  One of the signatories was Sir George Savile, who was Lord of the Manor of Thornhill and became member of Parliament for Yorkshire. They knew each other since being undergraduates at Queens and had become close friends.

Another new member of the Royal Society whose appointment immediately preceded Michell was Henry Cavendish, now famous for his discovery of hydrogen, with whom Michell would collaborate in the future on matters of astronomy and physics.

At this time, Michell also struck up an acquaintance with physicist, astronomer, mathematician and philosopher, Roger Joseph Bošković and they had frequent discussions on the subject of magnetism.

St Botolph’s Church Cambridge

Michell must have settled into a very comfortable existence at Cambridge, since he stayed there for 21 years. As senior eligible Fellow of Queens College, he was nominated as Rector of St Botolph’s, Cambridge on 28th March 1760, and held this Living until June 1763, graduating as Bachelor of Divinity (BD) during 1761.

From 1762 to 1764, he also held the Woodwardian Chair of Geology (Fossils), continuing to live at the College until he was forced to relinquish the chair prior to his marriage, because of the celibacy rule historically associated with the position. So he gave up being a Professor in 1764 to became Rector of the sleepy village of Compton in the valley of Itchin, 3 miles from Winchester. To a modern observer, that looks like he took a big step backwards. The village of Compton consisted simply of a long street on the side of a chalk valley, but perhaps it was the geology of the region that interested Michell when he took the post.

That year, he also married Sarah (née Williamson) of Newark, who was in possession of a large fortune…an advantageous marriage for him (which would be appreciated by all readers of Jane Austen) and providing him with enough funds that he needn’t depend on his stipend.

A Few days ago the Rev. Mr Michell, Rector of Compton, near Winchester, late Fellow of Queen’s College, and Woodwardian Professor of Fossils in this University, was married to Miss Williamson, a young Lady of considerable fortune, near Newark in Nottinghamshire. 

[Cambridge Chronicle, Vol. 2, No. 98, 1764 September 8, p. 3]

Their only child, Mary, was born on the 1st August 1765. Sadly, Michell’s wife Sarah died on September 18th 1765, aged only 38, possibly resulting from a complication of Mary’s birth or an infection and subsequent sepsis, which was not uncommon at the time. Soon afterwards, Michell became Rector of Havant Hampshire but he allowed a colleague, Dr Shipman, to carry on the work of the parish and seems to have never actually lived there…no explanation is given but it would be reasonable to suppose that he was in mourning due to the loss of his wife and probably finding it difficult to suddenly be in charge of the needs of a baby daughter, for whom he must find a nurse and make arrangements for her care…he left Havant a year later.

Board of Longitude Committee

During the 1760s, Michell furthered a strong interest in astronomy and horology (the study of time). In 1763, 1765, and 1770, he was called upon by the Board of Longitude to serve on committees evaluating chronometers, including the now famous Harrison chronometer. Harrison didn’t seem to have much faith in some of the members of the longitude committee, especially two that he referred to derisively as “parsons”, being John Michell and William Ludlum.

Unfortunately for Harrison, the Board of Longitude, on which Michell was still sitting, chose Larcum Kendall’s first marine timekeeper, known as the K-1, in preference to Harrison’s H-4 chronometer, to accompany Captain Cook when he sailed the Pacific…so no doubt Michell never redeemed himself in Harrison’s eyes.

Michell at Thornhill

Thornhill Parish Church of St Michael and All Angels

At 43 years old Michell had left Havant and travelled to Yorkshire in 1767, where he was appointed Rector of the Church of St Michael and All Angels at Thornhill. He was invited there and sponsored by his good friend and local Lord of the Manor, Sir George Saville, who held many thousands of acres in the area and held much influence. Michell would have moved into the Rectory, known as “The Parson’s House”. On the 17th Century map by Christopher Saxton, the Rectory is shown standing in its own grounds, in what is now Thornhill’s Rectory Park. Here it is on the 19th Century map

Thornhill Parish Church, Rectory and remains of Thornhill Hall and Moat – 19th Century map, published with the permission of the National Library of Scotland.

1767 was also the year that Michell was to give a reading of his newest scientific paper…with another catchy title:

An Inquiry into the probable Parallax and Magnitude of the fixed stars, from the Quantity of Light which they afford us, and the particular Circumference of their Situation.

In this paper, Michell suggested that double or multiple stars that are close together are bound by their gravitation and could not arise by chance. He predicted that many more incidences of such binary stars would be discovered and speculated on whether our sun is part of a star system, which wasn’t known at the time. He even pointed out that a knowledge of the period of orbital revolution, combined with their distance from the solar system, would provide a means of determining the mass of such a stellar pair, in comparison with the mass of the Sun. He also described how the aperture of the mirror in a telescope determines whether weaker stars can be seen. In his own words:

Binary star system (NASA Public Domain Image)

We may from hence, therefore, with the highest probability conclude (the odds against the contrary opinion being many millions to one) that the stars are really collected together in clusters in some places, where they form a kind of system, whilst in others there are either few or none of them, to whatever cause this may be owing, whether to their mutual gravitation, or to some other law or appointment of the Creator. And the natural conclusion from hence is, that it is highly probable in particular, and next to a certainty in general, that such double stars, &c. as appear to consist of two or more stars placed very near together, do really consist of stars placed near together, and under the influence of some general law, whenever the probability is very great, that there would not have been any such stars so near together, if all those, that are not less bright than themselves, had been scattered at random through the whole heavens.

Michell’s work on astronomy led the way for William Herschel to publish his own binary star observations in 1781. Hershel, known for the discovery of the Planet Uranus among other things, was another scientist whose patron was Sir George Saville of Thornhill and he had briefly been Organist at Leeds and at Halifax Parish Church, ten miles from Thornhill, before moving to Bath, where he gave his introductory organ concert on 1st January 1767. It is tantalising to wonder if Hershel and Michell met each other at Thornhill at that time. The date that Michell travelled north is unknown, though it is recorded that he took up his post as Rector at Thornhill in 1767. Could they have met, as Michell’s daughter insisted they had (passing on to her descendants an opinion that Herschel learned about astronomy from Michell), or did they miss each other by a matter of weeks or months, as is now widely believed?

The same year that John Michell had moved to Thornhill, Joseph Priestley became minister of Mill Hill Chapel, Leeds and they certainly met and became great friends. Priestley had also been elected to the Royal Society and the two men came to know each other well, living only about 10 miles apart. They got on well too, though Michell was High Church and Priestley was a Unitarian Dissenter. They were to engage in a very friendly correspondence which lasted for many years and met often. Priestley consulted Michell many times while writing his “History and Present State of Discoveries relating to Vision, Light and Colour”, and said that he had been “much assisted by Mr Michell, whom he frequently visited at Thornhill…and was very happy in his society”.

In one of his publications, Priestly wrote:

My objections to Newton’s manner of accounting for the colours of thin plates are of long standing, but the hint of accounting for them in the manner that I have attempted to do [by the doctrine of attractions and repulsions] was first suggested to me by Mr Michell, agreeably to whose conjectures relating to this subject, I have given the preceding account of the probable cause of these appearances.
Joseph Priestley

Top Scientists Meet at Thornhill

Michell had settled down at last and remained Rector at Thornhill for 26 years until his death, but during this time he was not content to be just a parish priest. In fact, something quite remarkable happened at Thornhill Rectory on May 23rd 1771, which has only recently come to light. Aged 46, still in his prime, and four years after his appointment as Rector, John Michell put on a very special afternoon meal and entertained some incredibly distinguished guests.

Michell’s best friend Joseph Priestley was present. Another guest was Jan Ingenhousz who had become wealthy due to having inoculated a grateful Austrian Royal Family against smallpox. Ingenhousz was now working on some of Priestley’s ideas about oxygen, carbon dioxide and plant respiration…and he was to discover that green plants, in sunlight, convert carbon dioxide into oxygen.

Michell’s third guest was another fellow scientist and long established friend, the American scientist Benjamin Franklin, one of the Founding Fathers of the United States who also founded the American Philosophical Society. Franklin was a prodigious inventor. Among his many creations were the lightning rod, the Franklin stovebifocal glasses and the flexible urinary catheter. Ben Franklin had already become famous because of his work on electricity and flying a kite in a storm to catch sparks. He was strongly into politics and became George Washington’s right hand man in the American Revolution. Now he was on a tour of the industrialised cities of Birmingham, Manchester and Leeds…with a small detour to John Michell’s place at Thornhill, of course.

Earlier that day, Priestley had demonstrated some new experiments on electricity and gases at his own house in Leeds. Perhaps the reason that they all travelled the 10 miles across to Thornhill afterwards was so that Michell could also show off his own apparatus and experiments. It has been suggested that they would have talked both science and politics that day…the American Revolution was not too far off and Franklin, of course, was in favour of America becoming an independent country. Priestley was to later have his house burned down for his own republican views and he eventually decided to emigrate to America himself.

Sir George Savile, Lord of the Manor of Thornhill, was also present. Who’d have thought it – all of those eminent people in Thornhill at one time and absolutely nobody knew!

It’s been said to have been a tea party, but afternoon tea wasn’t invented until 1840, when Anna, the seventh Duchess of Bedford became hungry around four o’clock and, since the evening meal wasn’t until 8pm, asked for sandwiches and cakes to be brought up She then started inviting her friends to share them. But, in 1771, the afternoon meal would be a full dinner, which was eaten between 3pm and 5pm and I have no doubt that it would have been a splendid one.

Dinner would be taken up by the soup, fish and meat courses and a dessert…and of course wine and port…not too much fruit and veg, which wasn’t popular at that time. As Michell was said to be a fat man, he must have greatly enjoyed his food and it’s likely that his table would have been plentifully supplied, even groaning, with the best that local butchers could provide…he’d want to impress the American and the European, after all!

Ruins of Thornhill Hall

The party stayed overnight and they all went for a walk the next morning, past Thornhill Hall Farm and the ruins of the Savile’s ancestral home, Thornhill Hall. The Hall was a Royalist stronghold that was destroyed by gunpowder explosions while being bombarded by Cromwell’s canon fire in the English Civil War.

They visited the newly built Calder and Hebble Navigation along with its designer, John Smeaton and then the rest of the party travelled on to Savile’s cousin’s home, Wentworth Castle, near Barnsley…how impressed must Ben Franklin have been to see the newly remodelled Castle, but would he have tactfully kept his thoughts about noble privilege to himself? He probably would.

With all this scientific research in his head, John Michell still made time to marry for a second time, to Anne Brecknock, on 13th Feb 1773, when his daughter Mary was 7 years old. There were no children of the marriage but hopefully Anne made a kind stepmother for the girl and companion for him during his later years.

Soon John Michell and William Herschel were definitely to meet. In 1781, Michell was able to enter into a friendly correspondence with Herschel, dealing with the subjects of telescope mirrors and the relative merits of different aperture sizes for reflecting telescopes. They were both constructing telescopes at this time and grinding their own mirrors, though they had started quite independently of each other. The two astronomers were able to meet occasionally at the Royal Society’s rooms, or other places in London such as the “Crown and Anchor” tavern, which was the meeting place of the Royal Society’s Club from 1780-1848, or the curiously named “Cat and Bagpipes”, a famous Chop House. On Michell’s death, Hershel bought Michell’s 10 feet long telescope for the sum of £30.  Herschel, in reading his own papers on astronomy at the Royal Society, also gave much credit to Michell for his work done at Thornhill, which he described as an elegant proof of the gathering of stars into groups.

Black Holes

Artist’s impression of a black hole (NASA public domain image)

In a paper for the Philosophical Transactions of the Royal Society of London, read on 27th November 1783, Michell first proposed the idea that there were such things as “dark stars”, that were sufficiently massive that they could generate such a strong gravitational pull that light would not be able to escape from them…he reasoned that such particles, when emanated by a star, would be slowed down by its gravitational pull, and thought that it might therefore be possible to determine the star’s mass based on the reduction in speed. This insight led in turn to the recognition that a star’s gravitational pull might be so strong that light could not escape at all. Michell calculated that this would be the case with a star more than 500 times the size of the Sun. Since light would not be able to escape such a star, it would be invisible…in other words what we now call a “black hole”.

These ideas on dark stars were outlined within a letter to Cavendish in 1784. They were only rediscovered in the 1970s and Michell is now recognised as having ideas, two hundred years earlier, that were thought to be quite new to astronomy in the 20th century.

Michell is now credited with being the first to study the case of a heavenly object massive enough to prevent light from escaping (the concept of escape velocity was well known at the time). Such an object, which he called a dark star, would not be directly visible, but could be identified by the motions of a companion star if it was part of a binary system. The classical minimum radius for escape assuming light behaved like particles of matter is numerically equal to the Schwarzschild Radius in general relativity.

Michell also suggested using a prism to measure what is now known as gravitational redshift, the gravitational weakening of starlight due to the surface gravity of the source. Michell acknowledged that some of these ideas were not technically practical at the time, but wrote that he hoped they would be useful to future generations.

By the time that Michell’s paper was rediscovered nearly two centuries later, these ideas had been reinvented by others.

Michell’s Torsion Balance

During the 1780s Michell was to visit London on many occasions as the dinner guest of various members of the Royal Society along with his friend Henry Cavendish. One year he stayed a full two months in London and was a guest of one scientist or another every week. He continued to conduct experiments at the Rectory at Thornhill.

One of Michell’s last and most important achievements was to build a torsion balance with which he intended to measure the mass of the earth. However, his health was now failing badly and he was unable to finish his experiments.

After his death the apparatus passed on, via Francis John Hyde Wollaston, to Cavendish, who rebuilt the apparatus, but kept very close to Michell’s original plan. Its creation by Michell and later use by Cavendish is now considered to be the most important advance in experiments on gravitation and has formed the basis of all the most significant experiments on gravitation ever since. However, it wasn’t known as the Michell experiment, but as the Cavendish experiment.

The torsion balance that Cavendish used to “weigh the world”


John Michell BD FRS died in 1793 at Thornhill, leaving a widow, Anne, and one daughter from his first marriage. Anne, died aged 69 in 1805.  His only child, Mary, was to marry Sir Thomas Turton of Leeds, a brilliant barrister. She died aged 71 on the 28th of January 1837 at Lower Grosvenor Place, Mayfair, London, England and was buried in St Peter and St Paul’s Church Cemetery, Lingfield, Surrey, England.

Mary always maintained that Herschel learned about astronomy from her father. This is recognised as being an exaggeration, but it is true that Herschel benefited from Michell’s work and built on it, taking it to an even greater height.

In 1910, Edmund Whittaker, a British mathematician, who contributed widely to applied mathematics and physics, wrote:

…the only natural philosopher of distinction who lived and taught at Cambridge was Michell, although his researches seem to have attracted little or no attention among his collegiate contemporaries and successors, who silently acquiesced when his discoveries were attributed to others, and allowed his name to perish entirely from Cambridge tradition.

Sir Edmund Taylor Whittaker FRS FRSE LL.D. Sc.D

To many scientists, John Michell BD FRS is now considered to be “one of the greatest unsung scientists of all time”…a great thinker and modest man whose ideas were taken up and published by other scientists but who should not be forgotten for his contribution to the world of physics and astronomy.

To me, he was simply my ancestors’ parish priest!

© Christine Widdall 2020