Editing Robert Hooke (section)

== Science ==
Hooke's role at the Royal Society was to demonstrate experiments from his own methods or at the suggestion of members. Among his earliest demonstrations were discussions of the nature of air and the implosion of glass bubbles that had been sealed with enclosed hot air.{{sfnp|Inwood|2003|p=28}} He also demonstrated that a dog could be kept alive with its [[thorax]] opened, provided air was pumped in and out of its lungs.{{sfnp|Inwood|2003|p=43}}{{efn|Hooke was distressed by the experience of [[vivisection]]. In a letter to Boyle, he wrote: "I shall hardly be induced to make further trials of this kind, because of the torture of the creature".{{sfnp|'Espinasse|1956|page=[https://archive.org/details/roberthooke0000marg/page/52/mode/2up?view=theater 52]}} }} He noted the difference between [[venous]] and [[arterial]] blood, and thus demonstrated that the {{lang|la|Pabulum vitae}} ("food of life"){{efn|"Here then we observe a striking similarity between combustion and animal respiration. The ancients seem to have had a more accurate idea of respiration than most of the philosophers who followed them. They supposed that the air contained a principle proper for the support and nourishment of life, which they called ''pabulum vitae''" {{snd}}  [[Thomas Garnett (manufacturer)|Thomas Garnett]], ''Popular lectures on zoonomia, or the laws of animal life, in health and disease'' (1804).{{sfnp|Garnett|1804|page=[https://archive.org/details/McGillLibrary-104436-149/page/n61 28]}} We now know this to be [[oxygen]].}}  and {{lang|la|flammae}} [flames] were the same thing.{{sfnp|Waller|1705|p=ix}}{{sfnp|Long Hall|1976|p=156}} There were also experiments on gravity, the falling of objects, the weighing of bodies, the measurement of [[barometric pressure]] at different heights, and the movement of [[pendulum]]s up to {{convert|200|ft|m|abbr=on|adj=mid|long}}.{{sfnp|Waller|1705|p=ix}} His biographer {{notatypo|Margaret 'Espinasse}} described him as England's first [[meteorologist]], in her description of his essay ''Method for making a history of the weather''.{{sfnp|'Espinasse|1956|p=[https://archive.org/details/roberthooke0000marg/page/50/mode/2up?view=theater 50]}}  (Hooke specifies that a thermometer, a [[hygrometer]], a wind gauge and a record sheet be used for proper weather records.{{sfnp|Hooke|1734|p=173{{ndash}}179}}{{efn|Hooke described a wind speed gauge in ''Method'', but he did not invent it. See {{slink|Anemometer|Plate anemometers}}.}}) 

=== Astronomy ===
[[file:Saturn Robert Hooke 1666.jpg|thumb|Hooke noted the shadows (a and b) cast by both the globe and the rings on each other in this drawing of Saturn. |alt=Hooke's drawing of the planet Saturn]]
[[file:Moon Micrographia Hooke.png|thumb| Drawings of the Moon and the Pleiades from Hooke's ''Micrographia'']]

In May 1664, using a {{cvt|12|ft}} [[refracting telescope]], Hooke observed the [[Great Red Spot]] of [[Jupiter]] for two hours as it moved across the planet's face. In March 1665, he published his findings and from them, the Italian astronomer [[Giovanni Cassini]] calculated the [[rotation period]] of Jupiter to be nine hours and fifty-five minutes.{{sfnp|Inwood|2003|p=51}} 

One of the most-challenging problems Hooke investigated was the measurement of the distance from Earth to a star other than the Sun. Hooke selected the star [[Gamma Draconis]] and chose the method of [[parallax]] determination. In 1669, after several months of observing, Hooke believed the desired result had been achieved. It is now known his equipment was far too imprecise to obtain an accurate measurement.{{sfnp |Hirshfeld |2001 |pages=[https://archive.org/details/parallax00alan/page/144 144–149] }}

Hooke's ''Micrographia'' contains illustrations of the [[Pleiades]] star cluster and [[lunar craters]]. He conducted experiments to investigate the formation of these craters and concluded their existence meant the Moon must have its own gravity, a radical departure from the contemporaneous [[Gravity#Ancient world|Aristotelian celestial model]].{{sfnp|Gribbin|Gribbin|2017|p=57}} He also was an early observer of the [[rings of Saturn]],{{sfnp|Alexander |1962 |pages=108–109}} and discovered one of the first-observed [[double-star]] systems [[Gamma Arietis]] in 1664.{{sfnp|Aitken|1935| page = [https://archive.org/details/dli.ernet.15387/page/1/mode/1up 1]}}

To achieve these discoveries, Hooke needed better instruments than those that were available at the time. Accordingly, he invented three new mechanisms: the [[Hooke joint]], a sophisticated [[universal joint]] that allowed his instruments to smoothly follow the apparent motion of the observed body; the first [[clockwork]] drive to automate the process; and a [[micrometer screw]] that allowed him to achieve a precision of ten [[second (arc)|seconds of arc]].{{sfnp|Jardine|2003|pp=44,45}}{{sfnp|Inwood|2003|p=82}} Hooke was dissatisfied with [[refracting telescope]]s so he built the first practical [[Gregorian telescope]] that used a silvered glass mirror.{{sfnp|Atkin|n.d.}}{{sfnp|Gribbin|Gribbin|2017|p=98}}{{efn|Between Gregory's initial effort and Hooke's improvement, Isaac Newton had built a reflecting telescope{{snd}}but because its mirror was made from polished steel, it tarnished and rapidly became useless.{{sfnp|Gribbin|Gribbin|2017|page=96}}}}

=== Mechanics ===
{{further|Hooke's Law|Simple harmonic motion}}
In 1660, Hooke discovered [[Hooke's law|the law]] of [[elasticity (physics)|elasticity]] that bears his name and describes the linear variation of [[tension (mechanics)|tension]] with extension in an [[elasticity (solid mechanics)|elastic]] spring. Hooke first described this discovery in an anagram "ceiiinosssttuv", whose solution he published in 1678 as {{lang|la|Ut tensio, sic vis}} ("As the extension, so the force").{{sfnp|Hooke|1678}} His work on elasticity culminated in his development of the [[balance spring]] or hairspring, which for the first time enabled a portable timepiece{{snd}}a watch{{snd}}to keep time with reasonable accuracy. A bitter dispute between Hooke and [[Christiaan Huygens]] on the priority of this invention was to continue for centuries after the death of both but a note dated 23 June 1670 in the journals of the Royal Society,{{sfnp|Oldenburg|1670|page=  [http://www.livesandletters.ac.uk/cell/Hooke/hooke_folio.php?id=80&option=both 81]}} describing a demonstration of a balance-controlled watch before the Royal Society, may support Hooke's claim to priority for the idea. Nevertheless, it is Huygens who is credited with building the first watch to use a balance spring.{{sfnp|Hall|1978|pages=261{{ndash}}281}}{{sfnp|Gould|1923| pages=158–171}}

Hooke's announcement of his law of elasticity using an [[anagram]] was a method scientists, such as Hooke, Huygens and [[Galileo]], sometimes used to establish priority for a discovery without revealing details.{{sfnp|Nielsen|2008|page=Back}} Hooke used mechanical analogues to understand fundamental processes such as the motion of a spherical pendulum and of a ball in a hollow cone, to demonstrate central force due to gravity,{{sfnp|Rousseaux|Coullet|Gilli|2006|pages=531–540}} and a hanging chain net with point loads to provide the optimum shape for a dome with heavy cross on top.{{sfnp|Gribbin|Gribbin|2017|pp=80, 81}}

Despite continuing reports to the contrary,{{sfnp|Rosen|2012|pages=74, 331|ps=: for example}} Hooke did not influence [[Thomas Newcomen]]'s invention of the [[steam engine]]; this myth, which originated in an article in the third edition of ''[[Encyclopædia Britannica]]'', has been found to be mistaken.{{sfnp|Jenkins|1936|pages=1–11}}

=== Gravitation ===
{{more|Newton–Hooke priority controversy for the inverse square law}}

While many of Hooke's contemporaries, such as Isaac Newton, believed in [[aether theories|aether]] as a medium for transmitting attraction and repulsion between separated celestial bodies,{{sfnp|Turnbull|1959|p=404{{ndash}}406 |loc=[https://archive.org/details/correspondenceof0001hwtu/page/404/mode/2up 150 Newton to Oldenburg]}}{{sfnp|Gribbin|Gribbin|2017|pages=165{{ndash}}175}} Hooke argued for an attracting principle of gravitation in ''[[Micrographia]]'' (1665). In a communication to the Royal Society in 1666,{{sfnp|Stewart|1816|page=[https://archive.org/details/b28041604/page/434/mode/2up 434] }} he wrote:
{{blockquote|text=I will explain a system of the world very different from any yet received. It is founded on the following positions. 1. That all the heavenly bodies have not only a gravitation of their parts to their own proper centre, but that they also mutually attract each other within their spheres of action. 2. That all bodies having a simple motion, will continue to move in a straight line, unless continually deflected from it by some extraneous force, causing them to describe a circle, an ellipse, or some other curve. 3. That this attraction is so much the greater as the bodies are nearer. As to the proportion in which those forces diminish by an increase of distance, I own I have not discovered it.&nbsp;...}}

Hooke's 1674 Gresham lecture, ''An Attempt to Prove the Motion of the Earth by Observations'' (published 1679), said gravitation applies to "all celestial bodies"{{sfnp|Hooke|1679|page= [https://archive.org/details/LectionesCutler00Hook/page/n23/mode/2up page 2, 3]}} and restated these three propositions.{{sfnp|Hooke|1679|page= [https://archive.org/details/LectionesCutler00Hook/page/n49/mode/1up 27, 28]}} 

Hooke's statements up to 1674 make no mention, however, that an inverse square law applies or might apply to these attractions. His model of gravitation was also not yet universal, though it approached universality more closely than previous hypotheses.{{sfn|Wilson|1989|p=  239}} Hooke did not provide accompanying evidence or mathematical demonstration; he stated in 1674: "Now what these several degrees [of gravitational attraction] are I have not yet experimentally verified", indicating he did not yet know what law the gravitation might follow; and about his whole proposal, he said: "This I only hint at present&nbsp;... having my self many other things in hand which I would first {{notatypo|compleat}}, and therefore cannot so well attend it" (i.e. "prosecuting this Inquiry").{{sfnp|Hooke|1679|page= [https://archive.org/details/LectionesCutler00Hook/page/n49/mode/1up 27, 28]}}

In November 1679, Hooke initiated a notable exchange of letters with Newton that was published in 1960.{{sfnp|Turnbull|1960|pages=297–314, 431–448}} Hooke's ostensible purpose was to tell Newton he (Hooke) had been appointed to manage the Royal Society's correspondence;{{sfnp|Turnbull|1960|p= 297 |loc=[https://archive.org/details/correspondenceof0002hwtu/page/297/mode/1up document #235]}} Hooke therefore wanted to hear from members about their research or their views about the research of others. Hooke asked Newton's opinions about various matters. Among other items, Hooke mentioned "compounding the celestial motions of the planets of a direct motion by the tangent and an attractive motion towards the central body"; his "hypothesis of the {{notatypo|lawes}} or causes of springinesse"; a new hypothesis from Paris about planetary motions, which he described at length; efforts to carry out or improve national surveys; and the difference of latitude between London and Cambridge.{{sfnp|Turnbull|1960|p=297 |loc=[https://archive.org/details/correspondenceof0002hwtu/page/297/mode/1up  Document #235]}}

Newton's reply offered "a {{notatypo|fansy}} of my own" about a terrestrial experiment rather than a proposal about celestial motions that might detect the Earth's motion; the experiment would use a body suspended in air and then dropped. Hooke wanted to discern how Newton thought the falling body could experimentally reveal the Earth's motion by its direction of deviation from the vertical but Hooke went on hypothetically to consider how its motion could continue if the solid Earth had not been in the way, on a spiral path to the centre. Hooke disagreed with Newton's idea of the body's continuing motion. A further short correspondence developed; towards the end of it, writing on 6 January 1680 to Newton, Hooke communicated his "supposition&nbsp;... that the Attraction always is in a duplicate proportion to the Distance from the {{notatypo|Center Reciprocall}}, and Consequently that the Velocity will be in a subduplicate proportion to the Attraction and Consequently as Kepler Supposes {{notatypo|Reciprocall}} to the Distance".{{sfnp|Turnbull|1960|p=309 |loc= [https://archive.org/details/correspondenceof0002hwtu/page/309/mode/1up  document #239]}} (Hooke's inference about the velocity is incorrect.{{sfn|Wilson|1989|p= 244}})

In 1686, when the first book of Newton's ''[[Philosophiae Naturalis Principia Mathematica|Principia]]'' was presented to the Royal Society, Hooke said he had given Newton the "notion" of "the rule of the decrease of Gravity, being reciprocally as the squares of the distances from the {{notatypo|Center}}". At the same time, according to [[Edmond Halley]]'s contemporaneous report, Hooke agreed "the Demonstration of the Curves generated thereby" was wholly Newton's.{{sfnp|Turnbull|1960|p= 431 |loc= [https://archive.org/details/correspondenceof0002hwtu/page/431/mode/1up document #285]}}

According to a 2002 assessment of the early history of the inverse square law: "by the late 1660s, the assumption of an 'inverse proportion between gravity and the square of distance' was rather common and had been advanced by a number of different people for different reasons".{{sfnp|Gal|2002|page=9}} In the 1660s, Newton had shown for planetary motion under a circular assumption, force in the radial direction had an inverse-square relation with distance from the centre.{{sfnp|Whiteside|1991|pages=13–20}} Newton, who in May 1686 was presented with Hooke's claim to priority on the inverse square law, denied he was to be credited as author of the idea, giving reasons including the citation of prior work by others.{{sfnp|Turnbull|1960|pp=431{{ndash}}448}} Newton also said that, even if he had first heard of the inverse square proportion from Hooke (which Newton said he had not), he would still have some rights to it because of his mathematical developments and demonstrations. These, he said, enabled observations to be relied upon as evidence of its accuracy while according to Newton, Hooke, without mathematical demonstrations and evidence in favour of the supposition, could only guess it was approximately valid "at great distances from the centre".{{sfnp|Turnbull|1960|p= 436,437 |loc= [https://archive.org/details/correspondenceof0002hwtu/page/436/mode/2up document #288]}}

Newton did accept and acknowledge, in all editions of the ''Principia'', Hooke and others had separately appreciated the inverse square law in the solar system. Newton acknowledged Wren, Hooke and Halley in this connection in his "Scholium to Proposition 4" in Book{{nbsp}}1.{{sfnp|Newton|1729 |p=[https://archive.org/details/TheMathematicalPrinciplesOfNaturalPhilosophyVolume1/page/n114/mode/1up 66] }} In a letter to Halley, Newton also acknowledged his correspondence with Hooke in 1679–1680 had reawakened his dormant interest in astronomical matters but that did not mean, according to Newton, Hooke had told Newton anything new or original. Newton wrote:
{{blockquote|Yet am I not beholden to him for any light into that business&nbsp;... but only for the diversion he gave me from my other studies to think on these things & for his {{notatypo|dogmaticalness}} in writing as if he had found the motion in the Ellipsis, which inclined me to try it.{{sfnp|Turnbull|1960|p= 447 |loc= [https://archive.org/details/correspondenceof0002hwtu/page/447/mode/1up document #291]}}}}

Whilst Newton was primarily a pioneer in mathematical analysis and its applications, and optical experimentation, Hooke was a creative experimenter of such great range who left some of his ideas, such as those about gravitation, undeveloped. In 1759, decades after the deaths of both Newton and Hooke, [[Alexis Clairaut]], mathematical astronomer eminent in his own right in the field of gravitational studies, reviewed Hooke's published work on gravitation. According to [[Stephen Peter Rigaud]], Clairaut wrote: "The example of Hooke and that of Kepler [serves] to show what a distance there is between a truth that is glimpsed and a truth that is demonstrated".{{efn|Original French: "{{lang|fr|L'exemple de Hook & celui de Kepler [serve] à faire voir quelle distance il y a entre une vérité entrevue & une vérité démontrée.}}"}}{{sfnp|Rigaud|1838|page=[https://archive.org/details/historicalessay00newtgoog/page/n77/mode/2up p. 66] |ps=, cited in {{harvp|Ball|1893|page=[https://archive.org/details/anessayonnewton00ballgoog/page/n81/mode/1up 69]}} }}<!--Rigaud's (and thus Ball's) attribution of this aphorism to Clairaut is questionable, but until it is challenged by later research we must accept it at face value. See section "a truth that is glimpsed and a truth that is demonstrated" at the talk page for this article. --> [[I. Bernard Cohen]] said: "Hooke's claim to the inverse-square law has masked Newton's far more fundamental debt to him, the analysis of curvilinear orbital motion. In asking for too much credit, Hooke effectively denied to himself the credit due him for a seminal idea".{{sfnp|Cohen|1985|p=221}}

=== Horology ===
[[File:Fotothek df tg 0003783 Uhr ^ Uhrwerk.jpg|thumb|upright 1.0|Drawing by Christiaan Huygens of one of his first balance springs, which is attached to a balance wheel]]

Hooke made important contributions to the science of timekeeping and was intimately involved in the advances of his time; these included refinement of the pendulum as a better regulator for clocks, increased precision of clock mechanisms and the use of the [[balance spring]] to improve the timekeeping of watches. 

[[Galileo]] had observed the regularity of a pendulum and Huygens first incorporated it in a clock;{{sfnp|Inwood|2003|pp=31}} in 1668, Hooke demonstrated his new device to keep a pendulum swinging regularly in unsteady conditions.{{sfnp|Inwood|2003|pp=101}} His invention of a tooth-cutting machine enabled a substantial improvement in the accuracy and precision of timepieces.{{sfnp|Inwood|2003|pp=101}} Waller reported the invention was, by Hooke's death, in constant use among clock makers.{{sfnp|Waller|1705|p=ix}}

Hooke announced he conceived a way to build a [[marine chronometer]] to determine longitude.{{sfnp|Inwood|2003|pp=31,32}}{{efn|As [[Gemma Frisius]] had already observed, each four minutes of time difference is equivalent to one degree of longitude difference. The latitude is easily determined by [[sextant]].}} and with the help of Boyle and others, he attempted to patent it. In the process, Hooke demonstrated a pocket-watch of his own devising that was fitted with a [[coil spring]] attached to the arbour of the balance. Hooke's refusal to accept an [[escape clause]] in the proposed exclusive contract for the use of this idea resulted in its abandonment.{{sfnp|Inwood|2003|pp=31,32}}{{efn|His exclusivity would lapse as soon as another made any improvement to it which, he argued, would be easy to do.{{sfnp|Inwood|2003|pp=31,32}}}}

Hooke developed the principle of the balance spring independently of Huygens and at least five years beforehand.{{sfnp|Sample|2006}} Huygens published his own work in ''Journal de Scavans'' in February 1675 and built the first functioning watch to use a balance spring.{{sfnp|Hall|1978|pages=261–81}}

=== Microscopy ===
{{main|Micrographia}}

In 1663 and 1664, Hooke made his microscopic, and some astronomic, observations, which he collated in ''[[Micrographia]]'' in 1665.  His book, which describes observations with microscopes and telescopes, as well as original work in biology, contains the earliest-recorded observation of a microorganism, the microfungus ''[[Mucor]]''.{{sfnp|Gest|2004}}{{sfnp|Gest|2009}} Hooke coined the term "[[cell (biology)|cell]]", suggesting a resemblance between plant structures and [[honeycomb]] cells.{{sfnp|Hooke|1665|page=[https://archive.org/details/micrographiaorso00hook/page/113/mode/1up 113]}}The hand-crafted, leather-and-gold-tooled microscope he designed and used to make the observations for ''Micrographia'', which [[Christopher Cock]] made for him in London, is on display at the [[National Museum of Health and Medicine]] in [[Maryland]].{{sfnp|Gase|2019}} Hooke's work developed from that of [[Henry Power]], who published his microscopy work in  ''Experimental Philosophy'' (1663);{{sfnp|'Espinasse|1956|p=[https://archive.org/details/roberthooke0000marg/page/54/mode/2up 54]}} in turn, the Dutch scientist [[Antonie van Leeuwenhoek]] went on to develop increased magnification and so reveal [[protozoa]], [[blood cell]]s and [[spermatozoa]].{{sfnp|'Espinasse|1956|p=[https://archive.org/details/roberthooke0000marg/page/78/mode/2up 79]}}{{sfnp|Inwood|2003|p=[https://archive.org/details/forgottengeniusb00inwo/page/62/mode/2up?view=theater 62, 63]}}

''Micrographia'' also contains Hooke's, or perhaps Boyle's and Hooke's, ideas on combustion. Hooke's experiments led him to conclude combustion involves a component of air, a statement with which modern scientists would agree but that was not understood widely, if at all, in the seventeenth century. He also concluded respiration and combustion involve a specific and limited component of air.{{sfnp|Inwood|2003|p=163}} According to Partington, if "Hooke had continued his experiments on combustion, it is probable that he would have discovered oxygen".{{sfnp|Partington|1951 | pages = 78–80 }}

[[Samuel Pepys]] wrote of the book in  [[The Diary of Samuel Pepys|his diary]] on 21 January 16{{sfrac|64|65}}{{efn|name="dual dating"}}: "Before I went to bed I sat up till two o’clock in my chamber reading of Mr. Hooke's {{notatypo|Microscopicall}} Observations, the most ingenious book that ever I read in my life".{{sfn|Pepys|1665|loc=21 January 1664/65}}

{{Gallery
| height=150
| title = Hooke's microscopy
|File:Hooke-microscope.png|Hooke's microscope, from an engraving in ''[[Micrographia]]''
|File:Hooke Microscope-03000276-FIG-4.jpg|Hooke's microscope{{sfnp|Gase|2019}}
|File:Louse diagram, Micrographia, Robert Hooke, 1667.jpg|Engraving of a louse from Hooke's ''[[Micrographia]]''
|File:HookeFlea01.jpg|Hooke's drawing of a flea
|File:RobertHookeMicrographia1665.jpg|Cell structure of [[Cork (material)|cork]] by Hooke
}}

=== Palaeontology and geology <span class="anchor" id="Palaeontology"></span><span class="anchor" id="Geology"></span> ===
One of the observations in ''Micrographia'' is of [[petrified wood|fossil wood]], the microscopic structure of which Hooke compared to that of ordinary wood. This led him to conclude that fossilised objects like petrified wood and fossil shells such as [[ammonites]] were the remains of living things that had been soaked in mineral-laden petrifying water.{{sfnp|Rudwick|1976|page=54}} He believed that such fossils provided reliable clues about the history of life on Earth and, despite the objections of contemporary naturalists like [[John Ray]]{{snd}}who found the concept of [[extinction]] theologically unacceptable{{snd}}that in some cases they might represent species that had become extinct through some geological disaster.{{sfnp|Bowler|1992|pages=118–119}} In a series of lectures in 1668, Hooke proposed the then-heretical idea the Earth's surface had been formed by volcanoes and earthquakes, and that the latter were responsible for shell fossils being found far above sea level.{{sfnp|Inwood|2003|p=112}}

In 1835, [[Charles Lyell]], the Scottish geologist and associate of [[Charles Darwin]], wrote of Hooke in ''[[Principles of Geology]]'': "His treatise&nbsp;... is the most philosophical production of that age, in regard to the causes of former changes in the organic and inorganic kingdoms of nature".{{sfnp|Lyell|1832|pages=[https://archive.org/details/in.ernet.dli.2015.168353/page/n76/mode/2up 76, 77]}}

=== Memory ===
Hooke's scientific model of human [[memory]] was one of the first of its kind. In a 1682 lecture to the Royal Society, Hooke proposed a mechanical analogue model of human memory that bore little resemblance to the mainly philosophical models of earlier writers.{{sfnp|Singer|1976|page=126}} This model addressed the components of encoding, memory capacity, repetition, retrieval, and forgetting&nbsp;– some with surprisingly modern accuracy.{{sfnp|Hintzman|2003}}  According to psychology professor Douglas Hintzman, Hooke's model's most-interesting points are that it allows for attention and other top-down influences on encoding; it uses resonance to implement parallel, cue-dependent retrieval; it explains memory for recency; it offers a single-system account of repetition and priming; and the power law of forgetting can be derived from the model's assumption in a straightforward way.{{sfnp|Hintzman|2003}}

===Other===
On 8 July 1680, Hooke observed the [[Cymatics|nodal patterns]] associated with the [[normal mode|modes of vibration]] of glass plates. He ran a [[bow (music)|bow]] along the edge of a flour-covered glass plate and saw the nodal patterns emerge.{{sfnp|McVeigh|2011}}{{sfnp|Daintith|Gjertsen|1999|page=101}} In acoustics, in 1681, Hooke showed the Royal Society that musical tones can be generated using spinning brass cogs cut with teeth in particular proportions.{{sfnp|Greated|2001}}