Derby British Science Association

Science and Engineering in Derby and Derbyshire

Hooke Me Up

From Micrographia; mould.

What do horology, cellular biology, and materials engineering have in common? They all have significant contributions from one man. A man who managed not only to advance microscopy and tension theory, but also fitted in a lengthy and bitter argument with Isaac Newton.

Born in 1635 to a religious family, Robert Hooke was regarded as generally unteachable, but artistically talented. So whilst his brothers were following their curate father into the Church, Robert was following local artist John Hoskyns around the island. On his father’s death his family paid for him to be apprenticed in art, clearly not expecting fundamental engineering concepts to come out of their sickliest, most uneducated kin.

After an apprenticeship with an artist, and attending Westminster School Under infamous corporal punishment fan, Dr Busby, he attended Oxford University on a choiristor’s scholarship. He studied under the growing range of natural philosophers who were based in the town and was even inspired by John Wilkins’s book  Mathematical Magick to create a flying machine. Though he learned much, and experimented with more, he left Oxford with no degree; which wasn’t quite as horrific in those days as it might be regarded today.

He did, however, make plenty of useful contacts and got the thing most university leavers dream of: a prestigious job. Chemist Robert Boyle wanted build on the air pump experiments of Von Guericke, so contracted Hooke to build him the machine to do it. Hooke’s experiences with Boyle helped him secure a post as Curator of Experiments, at the newly formed Royal Society of London. Unfortunately for Hooke, in a scenario familiar to many people in their early career, this post was unpaid for two years until the Society could afford to pay him.

He then moved onto a post which many modern lecturers might regard as a bit of a cushy number; delivering a once a week lecture, in his role as Professor of Geometry at Gresham College. However, though he received rooms at the college, a housekeeper and money, he was obliged to deliver the lecture in both Latin and English. In 1691 he finally became a doctor, and died in 1703.

What though, did he do?

Looking through tubes…
When Van Leuwenhoek submitted his microscope findings to the Royal Society, Hooke was asked to confirm them. He built his own microscope to do this, and during the process developed the reticule (cross-hairs).

Not only did he find the same small “creatures” that Van Leuwenhoek had observed, but he took the use of the microscope even further. Looking at cork he observed components in the tissue, which he referred to as ‘cells’, the first recorded use of this word. Hooke published his microscope findings, accompanied by his careful drawings, in Micrographia. His detailed drawing of a flea still appears in biology text books the world over.

Hooke didn’t only look downwards. He built the first Gregorian reflecting telescope, which he used to observe Jupiter rotating on its axis, and designed a helioscope to observe the same on the sun. In his developments of microscopy and telescopy he also invented the iris diaphragm, essential not only to scientists but photographers. Hooke’s work on the solar system also resulted in a lengthy bitter argument by letter with Isaac Newton over the rotation of the sun. Hooke accused Newton of stealing several of his ideas, and indeed it does seem that it was Hooke who initially suggested that attraction to the sun varied depending on distance. However, unlike Newton, Hooke was unable to clearly express this relationship in mathematical terms, and so did not get the credit.

Materials and Mechanics
Take a spring and, holding it firmly at one end, pull the opposite end out. The tension that you are causing on that poor spring can be explained with Hooke’s Law. F= -kx, this catchy little equation translates as: the amount of tension on your stretched spring is proportional to the load applied to it. In other words the more force you apply to pull it out the more powerfully that twang back into shape is going to be.

The equation doesn’t only apply to springs, but to all manner of materials with some level of elasticity, which is what makes it so important in engineering. Oddly, one of the few materials it doesn’t apply to is that most elastic of substances: rubber. Unlike steel, for example, rubber’s tension is dependent not only on the pull, but also on its temperature and condition. So whilst Postman Pat’s elastic bands don’t benefit from Hooke’s work, the chassis of his van does, and so do the scales in the post office.

When he wasn’t stretching springs he was observing their oscillations, the bounce, and found that they were isochronous. In other words the same amount of time passes between each boing. Hooke suggested that this made them ideal to use in those new fangled watches. However, at about the same time so did his sometime correspondent, the Dutch watchmaker Christiaan Huygens; thus beginning another long and protracted letter based conflict.

Robert Hooke’s first published work was on a concept that contributes to both engineering and biology: capillary action. In experiments using narrow glass tubes Hooke realised that liquids were able to move along the tubes against gravity. Though his single cause explanation for the phenomenon, air pressure, was not the whole story, he clearly identified it as something worth investigating further. Using Hooke’s work as a starting point scientists have found that the interaction between the liquid and the surrounding tube, and the surface tension of the liquid, collectively result in liquids travelling up tubes, paintbrushes, and, well, capillaries.

Hooke’s mechanical contributions also include improvements to the rather unimaginatively named Universal Joint. This simple connector joins two entirely straight rods, whilst letting them retain the ability to move one another. Hooke amended the joint by adding an intermediary linkage, which connects the main rods to one another, resulting ultimately in more power being transmitted between them. More prosaically, if you are a driver who drives a front wheel drive car, and unless you have a passion for drifting or little red corvettes you probably do, Hooke’s Constant-Velocity Joint is getting the power from the engine to your wheels.

His other significant mechanical contribution was the fabulously named Anchor Escapement [AE], which despite sounding like a cunning way to leave a ship, was a method for improving clock reliability. The escapement is the part of the clock which regulates the movement of the pendulum, making the hands move around the face. Mechanical clocks had been possible since the 1300s, however, Christiaan Huygens had analysed those clocks and found they increasingly lost accuracy. Making use of Huygens’s analysis Hooke developed a more reliable model, which is unsurprisingly shaped like a ship’s anchor. However, the AE itself has been superceded by other designs, largely due to increasing inaccuracy over time, as its shape means that the cogs are turned backwards as often as they are turned forwards.

If you build it…
Though contemporary architects are most regarded for their artistic ability, their forebears of the 1600s were esteemed for their mathematical skill just as much as their abilities as draughtsmen. Hooke with his early career in art, and long interest in science was perfect in this role.

During three days in September 1666 fire destroyed over thirteen thousand houses, St Paul’s Cathedral, and most of London city’s municipal buildings. Though Christopher Wren and John Evelyn are most associated with the rebuilding of the city, Hooke was employed as a city surveyor. In this role arbitrated in 550 neighbourly disputes. He also designed a number of new buildings.

Most of Hooke’s architecture is now gone; the Royal College of Physicians was demolished in the 1800s, the Merchant Taylor’s Hall was taken out by the Luftwaffe, and Bethlam Royal Hospital moved south of the river. However, there are still two of his buildings standing: Ragley Hall in Warwickshire, and St Mary Magdelene Church in Willen.

Which just goes to show: Engineers can do Biology, Astronomers can do Horology, and science isn’t that distant from art.

Micrographia can be read online here

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About Lotte

Likes making a mess and arguing.

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This entry was posted on August 3, 2012 by in Biology, Engineering, Mathematics and tagged , , , , , , , , , .

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