Robert Hooke (1635–1703)
came up with a great many novel and interesting ideas and inventions; whether
one favours or opposes patents, one should therefore give at least some
consideration to the effect of the patent system on his case. He lived in an
era when useful innovation was much less widespread than it is today; when
natural philosophy was still new and the
scientific method was
still being developed; and when the patent system was a good deal less
sophisticated, being still a royal prerogative, bestowed through the favour of
the King and generally best applied for, therefore, by obtaining the services of
some one blessed with the King's favour to plead for the patent. There was also
no international propagation of patents — the King conferred the patent so
as to promote the exercise of the technology within the economy on which he got
to levy taxes. Indeed, foreigners were not even eligible to hold patents.
Hooke was one of the players in the development of half-way decent pocket watches (for truly good ones, the world had to wait another century). The pivotal invention which made this practical was the spring balance, invented in the second half of the 1600s by (at least) both Hooke and Huygens. Hooke's side of the tale reveals all the complications attached to the economic exploitation of novel ideas.
Ships at sea need to know where they are if they are to avoid disaster.
Running aground on shallows can wreck a ship in any weather; in fog, it is all
too easy to run into rock one would otherwise have seen. When sailing along a
coast, it is generally possible to keep track of progress and thus of location;
even when out of sight of land, it is possible to estimate the ship's motion and
thereby keep track of location to moderate precision, especially with the help
of a lodestone (which we now call a magnet). However, the precision of such
dead reckoning decreases with distance; the uncertainties and errors add
up from day to day, making the method singularly unreliable for long voyages.
In an age of global trade by sea, the resulting risks were of the utmost
It is possible, from astronomical observations alone, to determine latitude (how
far North or South one is), at least when the sky is clear. At the same time,
one can determine the local solar time; from which one can determine one's
longitude (East — West position) if only one also knows the time at some
place of known longitude — this difference in time is 15 degrees of
longitude for every hour of time. Thus a reliable watch mechanism promised to
the longitude problem which was one of the most commercially and
militarily important issues of the day: indeed, when Harrison finally solved it
(about a century later), it was kept secret as a matter of national security.
The (light and delicate) spring used in regulating the rate at which a watch runs should not be confused with the (stout and brutal) spring which generally powers the mechanism. The driving spring of a watch (or clock) applies a torque (twisting force) to a cog, which drives other cogs and so round to the cogs that turn the hands.
Of course, the driving spring delivers more force when it
is fully wound than when it is nearly exhausted; but that can be evened out by
the use of a
fusee. The spring is mounted on a spindle inside a
cylindrical drum which turns on the spindle due to the force of the spring. A
fine chain (one could as readily use a thread or wire) is anchored to the drum
at one end and, when the spring is fully unwound, wrapped around the drum. The
other end of the chain is attached to the base of a cone-like structure which
shares a spindle with the cog that actually drives the rest of the clockwork.
The cone has a track spiralling around it, presenting a surface parallel to the
axis at radius varying from small, at the apex, to large at the base. The peg
that one turns (generally with a key) to wind up the watch shares its spindle
with the cone. As it turns, it pulls the chain off the spring's cylinder and
onto the cone, first filling up the broad start thereof and so winding inwards
along the track on the cone's surface.
The result is that the driving spring's force pulls at variable radius upon the axle of the chain's cone, which is shared with the cog by which the main sequence of cogs is driven. When the spring is fully wound, its large force is applied to a small radius near the apex; when the spring is almost exhausted its small force is applied to a large radius near the base. If the cone's variation of radius is correctly arranged, the force of the spring times the radius at which the chain pulls on the cone can be arranged to be constant. Thus a spring, whose power is variable, may deliver constant torque to a clockwork mechanism. I do not know whether Hooke and his contemporaries had this degree of sophistication.
However, even when the spring is persuaded to deliver a constant torque to the sequence of cogs from it to the hands, one must have some way to regulate the speed at which the cogs turn. Reliance on friction alone does not provide good precision — it is too dependent on external influences and the state of wear of the watch. In any case, in the interests of making the watch durable, one wishes to minimise wear and tear on its parts, to which end one avoids friction as far as possible.
In a pendulum clock, the speed is controlled by having a cog in the sequence from spring to hands regulated by the pendulum. The pendulum can be made to cause some mechanism to rock backwards and forward at a dependable frequency, and this can be used to (for example) allow one tooth of the regulated cog to pass in each cycle, thereby regulating the speed of the cog.
For example, in 1671, William Clement invented an
escapement, known as the anchor, comprising a curved bar with two
triangular prongs on its ends that intrude into the gaps between the teeth of
the cog, preventing the cog from turning. The separation of the prongs is equal
to the gap between one tooth of the cog and the centre of the gap between two
others. The bar is so placed that there is always at least one of its prongs in
the cog's way, but it is pivoted about its middle, so that either of them can be
swung out of the way. As the bar rocks one way, its prong at one end gets out
of the way of the cog's teeth, allowing the cog to turn until a tooth strikes
the other prong; the bar then rocks the other way, bringing the first prong back
into the way of the cog's teeth and moving the second prong out of the way of
the tooth it obstructs, allowing the cog to again turn, but only as far as will
cause a tooth to strike the first prong. Each cycle of the anchor's rocking
motion thus lets the cog turn by one tooth. With a little care, the mechanism
for doing this can be so arranged as to transmit a small amount of force, from
the regulated cog (driven, indirectly, by the main spring) to the mechanism that
restricts its motion and, thus, to the pendulum, so as to ensure the pendulum
keeps swinging (care must be taken to do this without, in the process,
disrupting the regularity of the pendulum's swing).
This technology (and its less sophisticated predecessor, the verge, as modified by Huygens to use a pendulum) was well understood for pendulums, but a pendulum is very sensitive to movement of the frame from which it hangs; this makes a pendulum clock unsuitable for a pocket watch or, indeed, a ship-board clock.
The important property of a pendulum is that it swings with a period that
scarcely varies with the size of its swing (and some clever games with
catenaries can be used to eliminate such little variation as there is). This is
because it is (to a fairly good approximation) a
oscillator. Any system with a stable equilibrium position, in which the
parts move without friction and there is a restoring force, tending to move the
parts towards that equilibrium position, will be a simple harmonic oscillator if
the size of the restoring force is proportional to the size of the displacement
from equilibrium – but this was not known (or at least proved) until
after Newton and Leibniz developed the infinitesimal calculus.
More recent watch mechanisms use a fine plane spiral of wire as a spring;
its outer end is mounted on a small light cog (the
balance wheel) and its
inner end is held fixed. The wheel, when pushed off its equilibrium position,
then spins back and forth, oscillating at a regular frequency. Some lightweight
cogs and gearing then transmit the wheel's motion to a bar which rocks to and
fro, just as in a pendulum clock, to regulate the motion of the main sequence of
the watch's cogs. Such a mechanism lends itself well to the task of regulating
a watch. This is likely more sophisticated than the mechanisms Hooke and
What was needed was a mechanism that would reliably oscillate with a fixed
period, that could be used to serve in place of a pendulum in a mechanism
otherwise essentially the same as was used by clocks. Hooke discovered that the
force a spring exerts is proportional to its extension (or, indeed, compression)
ut pondus sic tensio or
sic vis. This (though he did not know it) is exactly the pre-requisite for
a spring to be a simple harmonic oscillator. Hooke noticed that a spring,
displaced from its equilibrium position and released, oscillated with a regular
frequency, so realised it could be used to regulate a watch.
In the early 1660s Hooke clearly researched the possibilities of using springs to regulate watches, leading to an attempt, in 1664, to enlist some men of influence in a scheme to get him a fourteen year royal patent for his (claimed) solution of the longitude problem. This fell through for failure to devise a contract agreeable to all parties. Hooke clearly had, and demonstrated to the others, a watch regulated by a spring: but, since he kept its details secret, we cannot know what form the spring took.
Also in 1664, Hooke gave a public lecture in which he expounded on twenty ways of using a spring to regulate a watch, and indicated that this could be done in a hundred ways. It is not clear how many, if any, of these methods he actually tried, let alone found the means to make work reliably. He described the use of counter-rotating balance wheels (on a common spindle, linked by some cogs) to ensure that shaking of the watch would not interfere with its working (because, in so far as the shaking turned one wheel with its motion, it would also turn the other against its motion) and it seems likely the watch he wanted to patent employed such a contrivance.
Huygens devised a coiled spring. He communicated to the Royal Society by a letter – which the secretary, Oldenburg, read to the assembled members on 28 January 1675 – that he had a new invention relating to watches, and included (as was common at the time — Hooke did the same for his law) an anagram which encoded the fact that he was using a coiled spring. The details of Huygens's spring are unclear, but we may surmise that it at least loosely resembled the mechanism described above that was subsequently widely used.
Hooke claimed priority over Huygens, and convinced himself that Huygens had
learned of his invention from Oldenburg (whose job, as secretary, was to
communicate the Royal Society's activities to its overseas members). However,
in 1675, Hooke clearly did not have a working watch based on a spiral spring: he
spent much of that year working with Thomas Tompion –
the father of
English watch-making – to produce such a working model. Hooke had a
widely noted habit of exaggerating his claims and of declaring everything one
might hope for from his inventions without actually going to the trouble of
overcoming the practical issues that stood between his idea and the applications
declared; so it is reasonable to treat his claims of priority with skepticism.
Oldenburg and Lord Brouncker attempted (on Huygens's behalf – as a foreigner he could not hold a patent) to persuade the King to grant them a patent; Hooke worked with Tompion on a rival bid, and Hooke endeavoured to persuade the King that Huygens's invention was a derivative of Hooke's earlier work, going back to 1658. Ultimately, the King granted no patent and the London watch industry blossomed.
If Hooke had had the modern patent system to work with, he would have taken out a patent in the 1660s covering the use of any mechanical contrivance that used the regular oscillations of a spring to control the speed of clock-work. He would not need to have made a working watch: when Huygens finally produced one, he would have had to pay Hooke for the privilege of using the idea. But the modern patent system is broken – it no longer demands a working model and (at least in fields familiar to me) the standard of examination is not such as to inspire the confidence of practitioners of the practical sciences and arts.
In reality, the prospect of getting a patent meant that Hooke had (possibly exaggerated) hopes of becoming wealthy from his invention. To do so he needed a patent, to get which he needed the backing of someone with influence in court (where someone in the modern era would need funding to properly file and pay for a patent). To obtain backing he needed partners, but he didn't dare reveal the invention to them because he didn't yet have the protection of a patent – he feared they might steal his idea. His associates were amenable to a plan to contractually organise the joint venture so as to get round that: but he and they could not agree on a contract. The sticking point, in 1664, was the prospect of incremental improvement: they held that, if someone subsequently improved on Hooke's idea, the patent (if obtained) should pass to them; Hooke objected that it is easy to enhance a good idea and he should not lose out when someone did.
Negotiations failed and the plan was scrapped. Hooke decided to keep the details of his watch secret: (at least if it worked) this delayed the introduction of a better watch mechanism by at least a decade. One may blame the uncertainties attached to the patent process (hence arguing for a more stream-lined system): or blame the hope of being granted a patent (thus arguing for the abolition of patents). None the less, he did describe the basic idea in a public lecture in 1664, but no watch maker pursued it. Perhaps the watch-making industry could, given the details of Hooke's clearly inadequately developed watch, have improved it in a short while to make better watches, had he but published the details: but equally, given what happened to some of Hooke's other ideas, he might have published and been ignored (though this might have been due to his publishing, as here, only the basic idea, not the details – a cynic might say he published only enough to establish bragging rights in the event of the idea being made to work). In any case, the tale clearly illustrates that it is one thing to have a nice idea, quite another to put it successfully into practice.
As a long time collaborator with Tompion, Hooke probably did (albeit indirectly) benefit from the flourishing of the English watch industry, though not as much as a patent would have allowed him to. A patent might well have slowed, or distorted, the industry's growth: though, unless the patent was as overly broad as modern ones all too often are, I suspect the industry's innovations in watch design would have rapidly produced watches not covered by the patent.
The case illustrates various issues relevant to consideration of the patent system (or, indeed, anything similar):
entitlementpromotes greed, avarice and pride at the expense of generosity: when disappointed, the associated expectations turn to resentments which are apt to obstruct future collaboration.