Sir John Herschel
William Herschel Society 35th Annual Lecture
Saturday 14th March 2015 at Bath Royal Literary and Scientific Institute
Notes taken by William Gaskell
Lecture given by Allan Chapman MA DPhil DSc DUniv FRAS
Dr Allan Chapman became William Herschel Society 2nd President after Sir Patrick Moore
Introduction by Dr Peter Ford
William Herschel, astronomer and musician, discovered the planet Uranus in Bath on 13th March 1781. The discovery was made at William Herschel’s house in Bath at 19 New King Street. This house was saved from demolition and was instead converted to the William Herschel Museum in Bath in 1981 and this lecture was inaugurated at that time to honour this discovery.
Who was John Herschel?
John Herschel was The Leading Natural Philosopher of his day in Europe and the world. He was fluent in French and German as well as English and well-travelled in Europe. He is a philosopher as the term “scientist” was only coined in 1840. He was exceedingly cultured for example he translated Homer into German in his 60s for fun.
Although he is not notable for any particular achievement he furthered his father, William Herschel’s work, as part of his inheritance. He was the only son of William Herschel who was already wealthy when his son was born from telescope sales, selling instruments for upto £4,000 to Spain in the 1790s.
William Herschel was an esteemed member of British society but was born of humble origins to an Army drummer in Hannover. He was a friend of the leading financier Sir Joseph Banks by his 40s. He married Mary Baldwin and Sir John Herschel was born in 1791 in Slough.
Sir John Herschel’s real passions in life were optics and mathematics. He only took up astronomy to honour his father’s work. He was a genius born of a genius, mostly educated at home due to poor health caused by a weak chest but still lived to 79. He grew up in an environment with many notable houseguests including the Archbishop of Canterbury. He started off at Eton College – his local comprehensive of the day – but dropped out due to harsh regime of floggings by then headmaster, Dr Keates. He was up at Cambridge University at 18 where he notably formed the Analytic Society to bring modern French mathematics from leading mathematicians such as Laplace to the curriculum at Cambridge (this furthered Isaac Newton’s work, Principia).
He started off training as a barrister to have a serious career to support himself but gave up to become an astronomer to further his father’s work.
He learnt from William Herschel:
· How to manage telescopes
· How to best use the 18 ¼ inch reflector mirror
· No need to use the 40 foot telescope as it was too unwieldy
· Stuck to the 20 foot telescopes
· Use of the “Sweeping the Heavens” technique (which William Herschel called Gauging), allowing star drift over the course of a night to study 2 degrees of the sky per night.
He duplicated his father William Herschel’s work before his father passed away and his father’s assistant, his Auntie Carolyn, moved back to Hannover in Germany.
He contemplated of what the objects known as nebulas could be composed and some other questions of the day:
· Are nebulas stars or gaseous?
· Why are there inconsistencies in the Milky Way?
· There appear to be many nebulas in Virgo cluster but none elsewhere
Answering these questions by furthering his father’s work by studying the sky from more angles helped him to further understanding of natural phenomena:
· Postulated Steady State Theory of Universe
Family and South Africa
John Herschel married Margaret Brodie Stewart, he had three children with her before deciding to embark for South Africa to study the heavens from the southern hemisphere - work his father never managed to complete.
· Sets of for South Africa in November 1834
· Passage costs £500, a large amount, for whole household and equipment, he chartered a 600 ton vessel used to carry Imperial Viceroys to India.
· Arrives in South Africa January 1835
On arrival in South Africa he rents a large estate from the Boer’s called Veldhausen which he then buys in a shrewd move that ultimately nets him a tidy profit on top of his return passage to England 4 years later when he sells the property.
In South Africa he encounters new phenomena such as the Magellenic Clouds. At this time he invented Photometry to measure the brightness of starlight to help him determine the distance of the objects he is studying.
· He uses a device called the Astrometer
o Using a shielded gaslight with a tiny prick of light allowed to shine through along a variable distance to a prism
o He could vary the brightness he saw in eyepiece by varying the distance of the gaslight of known brightness to the star or object he observed through a telescope with the neighbouring eyepiece.
o When the two eye-pieces showed the same brightness he could then accurately record the brightness of the object he was observing
His family enjoyed a great social life in South Africa at the tie there was already established a Royal Observatory at the Cape in 1835. There are accounts that he befriends a surgeon who on one occasion was able to remove his wife’s painful tooth in their living room.
In South Africa he used guns for protection to keep wild animals at bay whilst picnicking, also at night he had to escape from wild feral dogs after observing the sky and would use a double barrelled pistol loaded with buckshot to scare away the barking dogs and make it home from his work safely.
Return to England
He was recognised by the newly coronated Queen Victoria as a celebrity with a Baronet’s title. He decided to quite Slough and move to the country and rents out Herschel House in Slough.
One of his great friends of the time was Lord Ross from the middle of Ireland who has a 6 foot telescope and they had great fun together through their shared interest of astronomy.
He used a spectroscope to discover the relative distances of objects and realises that we are not located at the centre of the Milky Way Galaxy as his time in South Africa raised the following questions:
· Is the Universe asymmetric?
· Why are more Planetary Nebulae in the Southern Hemisphere rather than the Northern Hemisphere?
· Stars seem to be denser at the centre of the galaxy
The product of his career in astronomy is a rigorous study of the Sky at Night in the Southern Hemisphere.
Later in life he used a spectroscope to discover space contains gas later discovered to be ionized Nitrogen gas.
Work on Gravity
William Herschel had published a list of binary stars in 1800. In 1820 Sir John Herschel discovers that these stars had changed orientation.
· Postulates that gravity is responsible for the observed changes in 1830s
He had a well-documented friendship with the great mathematician and astronomy Mary Somerville, who was 12 years his senior and married to a surgeon.
· They discuss using the Spectroscope – Huggins was doing work on this
He was friends with Fox Talbot of Lacock Abbey who was a photographic pioneer of the calotype method of photographic recording.
· One of Sir John Herschel’s discoveries was photographic fixation
Sir John Herschel died in 1871 after a short illness. His wife had written to Mary Somerville a few months earlier saying “their philosopher was in decline”.
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