This article provides a summary of the life of Robert Hooke (1635-1703) up to when he published his magnum opus, ‘Micrographica’. ‘Micrographia’, meaning ‘little pictures’ in Latin, was the first substantial book about the microscopic world ever published.
Hooke was a very talented scientist who came up with an incredible variety of new ideas. Even to this day he is not fully recognized for his considerable accomplishments. His misfortune was that he incurred the wrath of that vindictive genius Isaac Newton. After Hooke died Newton was able to rewrite history all but erasing Hooke from the scientific record.
Robert Hooke was born on 18th July 1635, the son of a curate from Freshwater on the Isle of Wight. As a lowly curate John Hooke, Robert’s father, was far from wealthy.
Robert, like many children of the time, suffered from bad health and was not expected to survive to adulthood. If he had been healthy then Robert would have been expected to continue the family tradition by joining the church. With his sickly constitution Robert’s parents gave up on his education and left him much to his own devices.
Robert made the most of his free time. He was fascinated by everything that surrounded him on his island home- the rocks, farms, animals, rugged cliffs and sandy beaches.
He made many things including a model of a fully rigged ship with working guns. Robert also showed a considerable talent as an artist.
There just happened to be a portrait painter, John Hoskyns, working in Robert’s home village. Robert used to watch Hoskyns at work and soon began imitating his paintings. Robert soon demonstrated that he had the potential to develop into an outstanding artist. After the death of his father in 1648, with an inheritance of £100 in his pocket, he was sent to London to be apprenticed to Sir Peter Lely, a renowned portrait painter of the age.
Robert’s apprenticeship was short lived; the smell of the paint in Lely’s studio gave him blinding headaches. He used some of his £100 inheritance to pay for an education at the school located in the grounds of Westminster Abbey. At Westminster School Hooke studied Latin, Greek, Geometry and Mechanics. He proved to be an accomplished musician and played the organ to a high standard.
In 1653 Hooke secured a music scholarship at Christ Church College in Oxford.
Having already spent much of his inheritance Hooke found himself short of money. He secured additional income to finance his studies by working as a paid assistant to the famous chemist and physicist Robert Boyle.
In this painting Robert Hooke is setting up an experiment using the air pump Hooke designed and made specifically for Robert Boyle. Hooke can be seen fitting the glass globe while Boyle is supervising proceedings.
This original diagram shows all the component parts of Hooke’s apparatus.
Using Hooke’s air pump Boyle was able to formulate the law which now bears his name (Boyle’s law) describing how the pressure of a gas increases as volume decreases.
Hooke became friendly with the author and natural philosopher John Wilkins ( 1614- 1672). Wilkins gave Hooke a copy of his book ‘Mathematical Magic, or the Wonders that may be Performed by Mechanical Geometry’. This book provides an explanation of the principles behind the design of 17th century machines.
Hooke’s association with Wilkins encouraged him to try to invent a flying machine. A diary entry Hooke made in 1656 when studying with Wilkins reads as follows:
“I contrived and made many trials about the art of flying in the air, and moving very swift on the land and water, of which I showed several designs to Mr. Wilkins….and at the same time made a (machine), which, by the help of springs and wings, raised and sustained itself in the air; but finding by my own trials, and afterwards by calculation, that the muscles of a man’s body were not sufficient to do any thing considerable of that kind.”
Hooke was later to describe other types of flying machine in his Philosophical Collections of 1679 including Francesco Lana di Terzi’s airship….
….and Besnier’s flying apparatus.
Hooke assisted Dr Thomas Willis (1621-75) with his dissections. This image shows engravings of a human and a sheep brain from Willis’s book ‘On the Anatomy of the Brain’ published in 1664.
The range and scope of Hooke’s interests was breathtaking. He came up with the idea of improving the accuracy of pocket watches by using balance springs.
Hooke’s idea might have led to the invention of a chronometer that would have been accurate and reliable enough to provide a precise determination of a ship’s longitude at sea and preventing ships losing their bearings.
Hooke never did reveal the secret of his radical design which might have netted him a fortune. He objected to a clause in the patent which would have allowed other people to reap the financial benefits of any improvements made to his design at any future and indeterminate date.
In 1662 Hooke left Oxford to join ‘The Royal Society of London for Improving Natural Knowledge’ to became the first ever ‘Curator of Experiments’. ‘The Royal Society’ as it was more commonly known, found its first home at Gresham College in Holburn, London.
In his capacity as ‘Curator of Experiments’ Hooke was required to demonstrate at least three scientific experiments every time ‘The Society’ met, which was every week! It is unlikely that anyone other than Hooke, with his thirst for knowledge and his prodigious work ethic, could have contemplated taking on such a heavy workload.
In fact Hooke reacted to the impossible task set him by producing a wealth of original ideas over the following 15 years. It would be fair to say that it was as a result of Hooke’s prodigious output and genius that the Royal Society prospered.
The demands heaped on his shoulders meant that he rarely had time to follow through individual ideas in any great detail as one might have expected a leading scientist to do. He appeared to relish the job of ‘Curator of Experiments’ which meant he could jump from one half thought out idea to the next.
In his early days at the Royal Society Hooke found himself short of money. He was only kept afloat financially through the generosity of Robert Boyle. Hooke’s financial worries largely disappeared in June 1663 when he was elected as a ‘Fellow’ of the Royal Society. In 1664 The Society finally agreed to pay Hooke a salary of £80 per year.
In 1665, under the auspices of the Royal Society whose Coat of Arms appears on the title page, Hooke published Micrographia.
The work begins with a dedication to King Charles II of England, patron of The Society: “I do here most humbly lay this small present at Your Majesty’s royal feet. And though it comes accompanied with two disadvantages, the meanness of the author, and of the subject; yet in both I am encouraged by the greatness of your mercy and your knowledge”.
Hooke recorded observations using microscopes he designed himself which were improvements of earlier versions made by others. Hooke frequently used a two-lensed compound microscope because it offered a wider field of view that a simple, single lens microscope, albeit with a greater degree of distortion.
For investigations requiring higher magnification Hooke used a single lens instrument which produced clearer, more detailed images.
One major obstacle Hooke had to overcome was the problem of images appearing too dark. To overcome this problem Hooke designed an ingenious method of lighting up his specimens; he passed light generated from an oil lamp through a water-filled glass flask. This diffused the light and provided an even and intense illumination of his samples.
Contents of ‘Micrographica’
Micrographia is divided into sixty different scientific explanations, mostly based on the magnified structure of a range of objects and natural phenomena. Hooke lavishly produced one hundred fine engravings and illustrations and described each of the magnified objects in exquisite detail.
Below are a few excerpts taken from his magnum opus.
Observation I- Of the Point of a Sharp Small Needle
The first observation pointed out microscopic irregularities in man-made objects which, to the naked eye, appear to be perfection itself. Hooke called the tips of needles and blades of razors, “rude mis-shapen things” and noted that “…when viewed with a microscope, there is little else observable, but their deformity.”
Hooke remarked how a needle appeared “to the naked eye very smooth” but which in reality hid “a multitude of holes and scratches”.
In contrast to imperfect man-made objects, Hooke described products of nature as being perfectly formed and well suited to their purpose.
Observation XIV Of Several Kinds of Frozen Figures
Hooke observed how snow drops, “were always branched out with six principal branches, all of equal length, shape and make, from the center, being each of them inclined to either of the next branches on either side of it, by an angle of sixty degrees.”
Observation XVII- Of Petrified Wood and other Petrified Bodies
Hooke noted the very close similarities between the structures of fossilized (‘petrifed’) wood and rotting wood. Hooke was the first scientist to correctly allude to the processes by which fossils are formed.
He explanation of the process of fossilisation read as follows: “Petrified wood having lain in some place where it was well soaked with petrifying water (that is, such a water as is well impregnated with stony and earthy particles) ….by this intrusion of the petrifying particles, this substance also becomes hard….Dead wood could be turned to stone by the action of water rich in dissolved minerals, which would deposit minerals throughout the wood.
Hooke went on to state that wood is not “the only substance that may by this kind of transmutation be changed into stone… I lately made (observations ) on several kinds of petrified shells.”
Observation XVIII- Of the Texture of Cork
Perhaps the most famous of all Hooke’s observations was the discovery of the structure of cork. When Hooke viewed a thin slice of cork through a microscope he discovered empty spaces surrounded by walls. He named these empty spaces cells because they resembled the ‘cellulae’ or small rooms inhabited by monks.
What Hooke actually saw was the walls of dead plant cells as they appeared under the microscope. By the time modern cell theory was first postulated in 1839 in which each living cell was described having a central nucleus, the term ‘cell’ was in wide use.
Hooke wrote: “I could exceedingly plainly perceive it to be all perforated and porous, much like a honey-comb, but that the pores of it were not regular. . . . these pores, or cells, . . . were indeed the first microscopical pores I ever saw, and perhaps, that were ever seen, for I had not met with any writer or person, that had made any mention of them before this. . . “
Observation XX- Of Blue Mould and of the First Principles of Vegetation arising from Putrefaction
Hooke’s microscopic observation of ‘blue mould’ growing on leather….
was the first ever description of a micro organism, the micro fungus ‘Mucor’.
Observation XXVI- Of Charcoal or Burnt Vegetables
Hooke developed a theory of combustion which anticipated the discovery of oxygen by JB Priestly 100 years later.
Following his observations of burnt charcoal Hooke concluded that the nitrous part of air (or ‘aerial nitre’) was a combustion-enhancing component contained within air.
Whenever ‘sulfurous’ or inflammable substances like wood were heated to a high temperature, ‘aerial nitre’ (or nitrous air) dissolved the wood and released volatile ‘sulfurs’ contained within the wood.
Hooke concluded that the ‘aerial nitre’ which brought about the combustion of charcoal was entirely similar to the ‘nitre’ present in ‘saltpetre’ (the modern compound we call potassium nitrate), a key ingredient of gunpowder.
Observation XXXIV- Of the Sting of a Bee
Hooke noted how a bee had,“a sheath shaped almost like the holster of a pistol” and which he could “most plainly perceive to be hollow, and to contain in it, both a sword or dart, and the poisonous liquor that causes the pain….the other part of the sting was the sword…with claws which can be closed up also, or laid flat…”
Observation XXXIX- Of the Eyes and Head of a gray Drone-Fly
Hooke produced an amazingly detailed image of a fly, complete with painstakingly drawn compound eyes.
“The greatest part of the face, nay, of the head, was shaped into a multitude of small hemispheres (‘ommatidia’,) placed in a triagonal order…ranged… in very lovely rows…there were observable two degrees of bigness, the half of them that were lowermost, and looked toward the ground or their own legs, (and the other half) that looked upward, and side-ways… and backward.
Observation XXXVI- Of Peacocks, Ducks and Other Feathers of Changeable colors
Hooke noted that peacock feathers, “do not only reflect a very brisk light, but tinge that light in a most curious manner; and by means of various positions, in respect of the light, they reflect back now one color, and then another, and those most vividly. Now, that these colors are only fantastical ones, that is, such as arise immediately from the refractions of the light.”
Hooke was describing ‘structural coloration’- the production of color by microscopically structured surfaces fine enough to interfere with the passage of visible light.
For example, peacock tail feathers are pigmented brown, but their microscopic structure makes them also reflect blue, turquoise, and green light. Peacock feathers are often iridescent; iridescence occurs where luminous objects appear to change from one color to another when viewed from different angles.
It was Hooke’s observations of ‘fantastical’ colors which prompted Newton to begin investigating the separation of visible light into the spectrum of its component colors.
Observation LIII- Of a Flea
Hooke is full of praise for the tiny creature with its “strength and beauty”.
He notes the flea’s powerful jumping mechanism: “These six legs he (pulls them) up altogether, and when he leaps, springs them all out, and thereby exerts his whole strength at once…As for the beauty of it, the microscope manifests it to be all over adorned with a curiously polished suit of sable armor, neatly jointed, and beset with multitudes of sharp pins, shaped almost like porcupines’ quills… the head is on either side beautified with a quick and round black eye..”
Observation LIV- Of a Louse
Hooke observes that the louse, “has six legs..and jointed exactly like a crab’s, or lobster’s; each leg is divided into six parts by these joints…at the end of each leg it has two claws, very properly adapted for its peculiar use, being thereby enabled to walk very securely both on (people’s) skin and hair; and indeed this contrivance of the feet is very curious, and could not be made more commodiously and compendiously, for performing both these requisite motions, of walking and climbing up the hair of a mans head…”
When the great 17th century diarist Samuel Pepys walked through the City of London to visit his bookseller on the 2nd January 1665, he thumbed through a recent publication which would forever change the way people thought about the microscopic, living world.
When he eventually received his copy of the book on 20th January 1665 he pronounced it, “a most excellent piece…of which I am very proud.” Pepys was so captivated by Micrographica that he “sat up” reading “till two o’clock” in the morning. He though Micrographica “the most ingenious book” he had ever read.
An unabridged version of Micrographica at Gutenberg.org