During their first week, Professor Ramon Hanssen takes his students to Hofwijck – the house of Christiaan Huygens and centre of numerous scientific developments in the Golden Age.
The morning sun is beaming through the red and green tinted leaded windows. Reflections of water from the moat flicker across the low ceiling. Maybe they were what inspired Huygens to develop his wave theory. The aroma of coffee drifts out from the kitchen as administrator Jack Zuurmond puts coffee cups on the tables. “Very little has changed here since Christiaan Huygens’ time”, he explains. The same black-and-white stones are on the floor and the same white tiles bedeck the walls. Christiaan actually did not spend much of his time here. The basement with its views of the moat was really the domain of the domestic staff. Christiaan and his father Constantijn spent most of their time at their mansion in Hofwijck studying and enjoying music on the ground floor. The attic was Christiaan’s domain. Here, he ground and polished his lenses, built his pendulum clocks and discovered the rings of Saturn and its moon Titan.
Gravitation expert René Reudink and GPS specialist Dr Hans van der Marel are bringing large stands across the drawbridge into the building. The students will be working with them today, they explain. The ground-floor room has leaded windows all round it and black and white marble tiles on the floor. The beamed ceiling painted in red is 4 m high, making the room seems spacious despite its modest size. In three corners of the room, TU Delft staff are setting up experiments with a copper cone on a thin cord.
Breeding ground
There is a rumble in the hall as the students enter. They have cycled 7 km along the Vliet canal from Delft. Ninety minutes and two flat tyres later, they eventually reach the historic castle in Voorburg. They come from the United States, Germany, Greece and France, so English is the working language among these Master’s students of geoscience and remote sensing (faculty of Civil Engineering and Geosciences). For most of them, the cycle ride along the canal was their first introduction to the Netherlands. It is set to include much more than clogs, tulips and Delft blue, if Professor Ramon Hanssen has his way.
“The kitchen where we are now sitting is almost the same as it was in 1640, when Hofwijck was built as a mansion for the affluent Huygens family”, explains Hanssen. “Back then, Schiphol airport, where many of you arrived, was still a large lake. This area was an incredible breeding ground for talent, where discoveries were made that we still use today. The 17th century really was a Golden Age for science and technology too.”
As an example, Hanssen brings out a small copper object no larger than a little finger. “This is a replica of the very first microscope made by Antonie van Leeuwenhoek, who lived in Delft. The lens is no larger than a droplet of water, but it took days of grinding and polishing to create something like this.” Grinding and polishing lenses was actually all the rage at that time. Everyone with a little education tried it out.
Hanssen passes the replica around: “You have to hold the lens almost against your pupil in order to see anything. The first thing you can see is the head of the copper nail just in front. Van Leeuwenhoek discovered living creatures in a droplet of moat water hanging from that nail. This should give you some idea of how that happened.”
“The artist Johannes Vermeer also lived in Delft at that time. Here, you can see his painting ‘The Geographer’. It is a typical Vermeer, featuring a person and objects in front of a window through which light is shining. The geographer is studying an unfolded map and there is a globe on the cabinet behind him. It had just been invented and made five or ten years previously by Jodocus Hondius.” Vermeer liked to include the latest objects in his paintings: maps, Persian rugs and Chinese porcelain (from which Delft blue later originated).
“The painting is similar to ‘The Astronomer’ which depicts a man studying the night sky on a globe. If you look carefully, they both seem to be the same man. I believe that it is Van Leeuwenhoek who is portrayed here. Being the same age, both men must have known each other.”
Pendulum
Christiaan Huygens was incredibly versatile (see box) and could be described as the Netherlands’ very first engineer. He devised mathematical models about nature and built his own instruments that he could use to make new observations.
He is best known as the inventor of the pendulum clock. On the ground floor, there is a pendulum from a turret clock featuring the invention that made him famous. The problem with using a pendulum to measure time is that the oscillation period is only constant if the amplitude is small. As the amplitude increases, so does the period. Huygens attached two curved plates to the top of the pendulum shortening the pendulum, and with it the period of oscillation, when the amplitude becomes too long. This makes the oscillation period much less dependent on the amplitude. However, the pendulum was not effective for measuring time at sea or determining the East-West position that people were searching for at that time.
Another use of the pendulum is to measure gravity, explains Dr Cornelis Slobbe. He is leading the afternoon programme. If you measure the length of the pendulum and the period of oscillation, you can use it to calculate gravity. We have a tendency to consider gravity to be a constant of 9.81 m/s2. But that is only an approximation. If you measure accurately enough, gravity varies along with the height and position on Earth (greater at the poles than at the equator), with the groundwater level and even heavy rainfall.
As an exercise in modesty, the students are instructed during the afternoon to determine gravity using Huygens’s method: with a pendulum. In three groups of seven, the students gather around stands on the ground floor. They measure the length of the pendulum as accurately as possible, give it a little push and then measure the time it takes for ten oscillations. The measured oscillation period can be used to calculate the value of g (4π2L/T2). The students do this for every oscillation period measured. One group measures values between 9.2 and 9.8. In the other groups, the values vary from 9.6 to 9.9 and even between 9.7 and 12.2. With our modern-day dependency on digital devices, it is hard to imagine how tentative the first advances in science really were.
Gallery of honour
Christiaan Huygens (1629 – 1695)
Second son of the poet, diplomat and composer Constantijn Huygens. Although destined to become a diplomat, Christiaan had more interest in mathematics, physics and astronomy. Like Descartes before him, Huygens believed in the priority of his own observations over traditional teachings. He studied the theoretical and practical aspects of falling and pendulum motion and developed the pendulum clock. He formulated the laws of wave propagation and his calculation of probability laid the foundations for the insurance business. He also used the lenses he made himself to make pioneering discoveries, including the rings of Saturn and its moon Titan.
Johannes Vermeer (1632 – 1675)
This artist from Delft is renowned for his interiors illuminated by open windows, as well, of course, as his View of Delft and the Girl with the Pearl Earring. Although he produced only 34 paintings in his lifetime, he was remarkably precise in his use of perspective and light. So much so in fact, that art historians believed that Vermeer must have worked with a camera obscura or other optical equipment. No proof has ever been found for this.
Antonie van Leeuwenhoek (1632 – 1723)
He earned his living trading in cloth, involved himself in politics in Delft and became interested in reading. He was the first person to discover living creatures in moat water using a home-made microscope. He went on to discover muscle fibres, spermatozoa and blood cells. He publicised his inventions in an exchange of letters with the London-based Royal Society which Newton chaired (from 1703).
Baruch Spinoza (1632 – 1677)
Son of Portuguese Jewish parents who fled the Inquisition to the tolerant metropolis of Amsterdam. Baruch was born into the Amsterdam Jewish community, but rejected its dogmatism. As a philosopher, he was considered to be a rationalist since he believed that God and nature obeyed the same underlying rules. He earned his living grinding and polishing lenses that were highly prized by his neighbour Huygens and others.
Hugo de Groot (1583 – 1645)
A lawyer, also known as Grotius, who laid the foundations for international law and was the author of the Freedom of the Seas (Mare Liberum) based on the right of unhindered seafaring. His statue is located in the Market square in Delft. De Groot was imprisoned for his call for the separation of church and state and managed to escape from Castle Loevestein hidden in a book chest. De Groot’s father conducted a gravitational experiment in Delft with Simon Stevin.
Simon Stevin (1548 – 1620)
Hugo de Groot wrote that Stevin discovered the various movements of the Earth. The experiment that his father conducted with Stevin played a role in this. By dropping two lead balls of very different weights from a church tower (probably the Nieuwe Kerk) that landed on a wooden platform at exactly the same time, the mathematician and military engineer discovered that gravitational acceleration is independent of mass. As a result, he wrote his book ‘De Hemelloop’, which supports the Copernican theory that the Earth revolves around the sun. Stevin is also known for devising a transmission system enabling improved land reclamation and for developing a wind-propelled beach carriage, a so-called ‘land-yacht’.
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