Tag Archives: zoonomia

Humphry Davy – Finding Love in the Colourful Age of Romantic Science

You’re a young 33, with an already impressive scientific career under your belt, and – although you only suspect it – a spectacular future ahead of you. Within 10 years, you’ll be elected President of the Royal Society.

But in November 1811, you’ve got something else on your mind.

How exactly would Humphry Davy (he of Davy Lamp fame among many other achievements) impress the first true love of his life – the beautiful widow and heiress Jane Apreece ?

Well, as it turned out……with more science of course.  And unlikely as it might seem, with quotes from the book whose spine forms the header of this very blog: Erasmus Darwin’s Zoonomia. (Erasmus was Charles Darwin’s grandfather….how many times)

Over to you, Humph….

‘There is a law of sensation which may be called the law of continuity & contrast of which you may read in Darwin’s Zoonomia [sic].  An example is – look long on a spot of pink, & close your eyes, the impression will continue for some time & will then be succeeded by a green light.  For some days after I quitted you I had the pink light in my eyes & the rosy feelings in my heart, but now the green hue & feelings – not of jealousy – but of regret are come.’

Smooth, or what?

I’m not the first to spot Davy’s creative application of ground-breaking ideas in colour perception; the above passage is from Richard Holmes’s award-winning Age of Wonder.  But what’s it all about?   Let’s start with Zoonomia.

Erasmus describes his experiments on colour and the eye in Volume I, Section III: Motions of the Retina; and Section XI: Ocular Spectra.

In his letter to Jane Apreece, Davy is referring to this experiment (Warning for the unfamiliar: f = s):

Zoonomia Vol1 Section III, p.20

Later, Erasmus restates the experiment and proposes a mechanism for the observed effect:

Zoonomia Vol1 Section III
Red Spot (Zoonomia V1 S.III p.14)

Darwin’s experiments covered a range of colour and contrast effects.  Here in his ‘tadpole’ experiment he interprets the bright after-image  we see after staring at a dark object, explained again in terms of conditioning and sensitivity of the retina.


Erasmus’s ‘tadpole’ (a little smudged after 200 years)

The drawings in Zoonomia are individually hand drawn and hand coloured.  In this passage, Erasmus encourages his readers to partake of some drawing-room diversion using silks of many colours:

Erasmus encourages his readers to lay down silks
Readers are encourgaged to lay down coloured silks

All exciting stuff, not least for Erasmus, who betrays his giddiness in this chuckling wind up to his analysis, where he curries favour with the incumbent president of the Royal Society, Sir Joseph Banks.

Joseph BanksI was surprised, and agreeably amused, with the following experiment.  I covered a paper about four inches square with yellow, and with a pen filled with a blue colour wrote upon the middle of it the word BANKS in capitals, and sitting with my back to the sun, fixed my eyes for a minute exactly on the centre of the letter N in the middle of the word;after closing my eyes, and shading them somewhat with my hand, the word was dinstinctly seen in the spectrum in yellow letters on a blue field; and then, on opening my eyes on a yellowish wall at twenty feet distance, the magnified name of BANKS appeared written on the wall in golden characters.” [Banks was elected President of the Royal Society in 1778].

Erasmus saw Banks’s name in large golden letters on his garden wall

Did Erasmus get it right with all that stuff about flexing of the antagonist fibres and analogy to the muscles? Well, he wasn’t a million miles away from the truth.   Indeed, it looks like yet another case of Erasmus Darwin not getting the credit he deserves for being ahead of the game.

Here’s a modern popular version of the tadpole ‘trick’ (Credit: from here)

The idea is you stare at the bulb for 20 or 30 seconds then look at the white space to the right of it.  The popular description of the effect is in terms of  the retina cells stimulated by the light portions of the image being desensitized more than those which respond to the dark part of the image – so that the least depleted cells react more strongly when the eye switches to the more uniform all-white image next to the bulb.

Davy Lamp (Wiki Commons)

The modern authors note also that the size of the afterimage varies directly with the distance of the surface on which it is viewed: a manifestation of Emmert’s Law.  This is consistent with Erasmus’s report of the name BANKS writ large on his garden wall.

Likewise, the modern interpretation of colour afterimages is popularly framed in terms of how ‘fatigued’ cells respond to light (See how fatigued’ aligns with Erasmus’s muscular references).  Erasmus didn’t know we have two types of light-sensitive cells in the eye: cones (that broadly speaking detect colour) and rods (that are more sensitive to absolute brightness), and that the cones themselves are sub-divided to be maximally sensitive to red , blue and green (RGB).

But he did understand the concept of complementary colours, and recognised that whatever part of the retina detects the colour red becomes fatigued through over-exposure; he’d got the principle that green appears againt white as a kind of negative red ).

If we dig a little deeper we find the brain-proper conspires with the retina to consider what we see in terms of black-white, red-green, and blue-yellow opponencies.  And the corresponding three sets of retinal cells operate in a pretty arithmetical fashion: the electrical impulse sent to the brain by the red-green cells is proportional to the net red-green exposure to light that the cell has experienced in recent time; likewise the blue-yellow sensitive cells.

That’s all clear then.

What bugs me a wee bit is that in my research for this post I never once saw a reference to Erasmus Darwin.  Rather, the standard historical reference seems to be the German psychologist Ewald Hering (1834-1919), who is credited with the first observations of the phenomenon.

Hold the horses – it’s Valentines Day

Ok, we got a bit lost in the science there.  And I got a bit hot under the collar; eh-hem.   So, the real question is: did Davy’s colourful overtures hit the mark?  Well, sort of.  Humphry Davy and Jane Apreece married the following year in 1812.  The bad news is it didn’t really work out longterm.

All the same, Davy shone ever bright in his science.  Already famous for discovering a whole range of new chemical elements, including via separation by electrolysis potassium and sodium, and chlorine gas; he went on to discover elemental iodine and, for good measure, invented the Davy Lamp – thereby saving who knows how many thousands of lives in the mining indistry.   In 1820, when Banks’s death ended his 40+ year run at the head of the Royal Society, Davy was elected President.

All of which doubtless kept a bit of colour in his cheeks.

Shop-front in Penzance where Davy served his early apprenticeship (Tks S.Klinge)

Sources

Darwin, Erasmus. Zoonomia Vol 1 Pub. J.Johnson 1796 (photos are from author’s copy)

Holmes, Richard. Age of Wonder. Pub. Harper Press (the softback is out for about £7 now – buy it!)

And Resources

The Guttenburg version of Zoonomia Vol 1 is here.

 


The Other Darwin Genius

You’ll hardly need reminding that next year is the 200th anniversary of the birth of Charles Darwin, and the 150th anniversary of his best known work – On The Origin of Species. It’s already a big deal: special events, new book editions, talks, tee-shirts, diaries, calendars, and commemorative mugs – the lot.  And rightly so – however we might nuance the term, there would be no Darwinism without Darwin. But as the celebrations bubble up to a crescendo of reverence on February 12th, I wonder if the world will spare a thought for Darwin’s own origins, and particularly his illustrious grandfather – Erasmus (1731-1802). He’ll certainly be struggling for attention, so consider this a pre-emptive strike on behalf of The Other Darwin Genius.

Charles (1809-1882)
Charles (1809-1882)

We automatically associate ‘Darwin’ with the name ‘Charles’. A mention of Erasmus in conversation brings blank looks, even from devotees of the definitive Charles. Genius twice in the same family – impossible! And if the old fellow had some notoriety in his day, surely it must pale beside that of his grandson.Yet Erasmus is not to be compared to Charles in any competitive sense. Their skills, inclinations, personality, temperament, and achievements were very different. It was their shared inquisitiveness and intellectual energy that destined each to leave a lasting imprint on the world. We all know about Charles’s lasting imprint, but few are aware that Erasmus was:

Erasmus (1809-1882)
Erasmus (1809-1882)
  • The greatest physician of his time
  • An original and popular poet
  • A respected scientist and inventor
  • A key player and catalyst in the industrial revolution

His life has been richly documented by physicist Desmond King-Hele, whose analysis reveals a breathtaking range of interests, involvements and achievements. Not associated with one single big theory or event, Erasmus confuses our conception of the traditional achiever. Charles by contrast is easy – well and truly Mr Evolution. So what makes Erasmus so appealing?

His lifelong profession was medicine. Widely recognised in England as the top doctor of his day, he famously declined to be King George III’s personal physician. (Had he accepted of course, George’s porphyria would have quickly cleared up, the King’s eye would have stayed on the political ball, and America would still be ours – yippee! Well, O.K. – maybe not; Erasmus’s sympathies actually tended towards the pro-revolutionary.) He chose rather to spread his benefaction widely, making house calls to ordinary folk in all weathers and treating the poor for free.

Erasmus’s medical knowledge is captured in the 1796 ZOONOMIA. At 5kg, the big and heavy first edition makes fascinating reading. Some of the 18th century cures sound worse than the diseases, but while Erasmus’s use of the blood-letting lancet for physical conditions may have been typical, his approach to mental disease was ahead of its time. Lunatics in his care could expect compassion instead of the more familiar beating.

Zoonomia Vol II was a catalogue of disease (Tim Jones private collection)

Charles inherited his knack for ruffling religious feathers from his grandfather, who in Zoonomia classified religion as a mental disease – a ‘Desease of Volition’. Here he dismisses it along with other fantasies in a discussion on Credulitas, or Credulity. To get a flavour of the language and its appearance, the reader is invited to struggle through this photocopy of the original text:

[text continues]………

In regard to religious matters, there is an intellectual cowardice instilled in the minds of the people from their infancy; which prevents their inquiry: credulity is made an indispensible virtue; to inquire or exert their reason in religious matters is denounced as sinful; and in the catholic church is punished with more severe penances than moral crimes…

For each desease, Darwin offers a cure. Headed ‘M.M.’ for Materia Medica, his wise council on credulity reads:

M.M. The method of cure is to increase our knowledge of the laws of nature, and our habit of comparing whatever ideas are presented to us with those known laws, and thus to counteract the fallacies or our senses, to emancipate ourselves from the false impressions which we have imbibed in our infancy, and to set the faculty of reason above that of imagination.

Rational thinking and appeal to scientific method shine through – not surprising given the very interesting people Erasmus was mixing with: James Watt and Matthew Boulton of steam engine fame, Josiah Wedgwood of pottery fame, the Scottish chemist James Kier, and the politically animated chemist and co-discoverer of oxygen Joseph Priestley.

Statue of Boulton, Watt, and Murdoch in Birmingham, UK
Statue of Boulton, Watt, and Murdoch in Birmingham, UK (Photo: Tim Jones)

With Erasmus’s support, Wedgwood got England’s first canal built, while his friendship and technical exchanges with Watt and Boulton catalysed the steam age. Together known as the Lunar Men, (so called because they travelled to monthly meetings assisted by moonlight) this group drove the industrial revolution and gave us the roots of our technological world.

A pioneering scientist and engineer in his own right, Erasmus is unsung in many fields. He discovered ‘Charles Gas Law’ before Charles -who claimed it 24 years later, glimpsed partial pressures ahead of Dalton, and explained how clouds form. His musings appear almost casually in a letter to Boulton, where we first learn that his plans for weather forecasting will be enhanced by the accuracy of John Harrison’s new clock – that is Harrison of longitude fame (this single letter is astonishing in the icons it embraces), then:

Erasmus explained cloud formation

I am extremely impatient for this Play-Thing! [Harrison’s clock] as I intend to fortell every Shower by it, and make great medical discovery as far as relates to the specific Gravity of Air: and from the Quantity of Vapor. Thus the Specific Gravity of the Air, should be as the Absolute Gravity (shew’d by the Barometer) and as the Heat (shew’d by Boulton’s Thermometer). Now if it is not always found as these two (that is as one and inversely as the other) then the deviations at different Times must be as the Quantity of dissolved Vapour in the Air.

Elsewhere in the same letter, having playfully struck Boulton off as a “plodding man of Business” he proceeds to bribe him with wine on the condition he glass-blows one of the empties into a specific form required for his (Darwin’s) researches.

The first reference to the mechanism for cloud formation comes in a 1784 letter to Josiah Wedgwood; with what amounts to a description of the universal law of adiabatic expansion of gases, which he later published in a formal journal.

Evolution is also discussed in Zoonomia and The Temple of Nature, also by by Erasmus. His coat of arms comprised three scallop shells with the telling motto E conchis omnia – ‘everything from shells’, reflecting his belief that all life started from sea creatures. Unfortunately, the device was not subtle enough to evade the local clergy, leaving Erasmus force-put to paint it out and thereby keep the peace (it remained on his bookplate). Erasmus’s gift for marrying art with science matured in his narrative poem The Botanic Garden, which brought him literary fame and the respect of influential friends like the poets Wordsworth and Coleridge, both of whom record him as an important influence on their work.

Erasmus was clever but not boring. A true man of the Enlightenment, he took all his pleasures seriously. Shunning alcohol, he preferred to act on his conviction that sugar and cream were the healthiest of foods, consuming both in quantity. He had a semi-circular profile carved in his dining table to accommodate the girth of his indulgence. Always amorously inclined, his successful bid for the hand of the young socialite Elizabeth Pole, whilst in the disrepair of his fifties, is intriguing – not to say impressive, as are his liberal reproductive powers, evidenced by 14 children including two illegitimacies.

And so it goes on: from speaking machines to steam turbines, from educational reform to carriage design, from the moon’s origin to the formation of coal; in all these areas and many more, Erasmus made a valuable and original contribution to knowledge. For me though, it is the combination of The Other Darwin Genius’s bon-viveur attitude, innovatory energy, rationality, compassion, and his measured disrespect for authority, convention and the status quo, that makes him (and I know this is blasphemy) the more interesting Darwin. Spare him a thought on February 12th.

Other Links Erasmusdarwin.org – custodians of his memory and former home in Litchfield.