Tag: science

May 26 2016

Book review: Lab Girl by Hope Jahren

labgirlLab Girl by Hope Jahren is an unusual book. It’s an autobiography which mixes in a fair amount of plant science. It is beautiful to read. It is strong on what being a scientist means. The closest comparison I can think of are Richard Feymann’s “Surely you are joking, Mr Feynmann” memoirs which are rather more anecdotal.

Lab Girl is chronological, starting from Jahren’s early memories of visiting the lab in her father’s school after hours but then fast forwarding to her academic career setting up laboratories in Georgia, Baltimore and finally Hawaii. It isn’t encyclopaedic in providing a detailed record of Jahren’s personal and scientific life.

A thread through the whole book is Bill, her trusty research assistant. Bill starts as a keen undergraduate who Jahren takes on when she gets her first academic position. I think in some ways Bill is something of a product of the US academic system, with support staff often funded on short term grants. In the UK such people tend to be employed on a permanent basis by the institution. My Bill was Tom when I was a PhD student, Pete and Roger when I was an assistant director of research. As a lecturer I didn’t have a Bill, and maybe that was my problem.

Several themes intertwine through the book. There is the day to day activity of a lab: labelling things, repetitive sample preparation, measuring things, fighting with equipment to get it to measure things. Wrangling undergraduates and postgraduates. There are trips out into the field. For Jahren, as a biologist, the field is very literally the field (or Irish bog, Canadian tundra etc). There is attending academic conferences. Mixed with this there is the continual struggle for tenure and funding for your research and the fight for resources with grants that don’t go quite far enough.

It’s fair to say Jahren put in an awful lot more hours than I did as a young academic but then I didn’t turn into an successful, older academic. Make of that what you will. It’s difficult to measure your success as an academic, grant applications are so hit and miss that winning them is only a measure of your luck and skill at writing grant applications, papers are relatively sparse and rarely provide much feedback. Sometimes putting in hours seems the only way of measuring your worth.

A second strand is plant biology, mingling basic background and the cutting edge research that Jahren does. I absorbed this in ambient fashion, I now think a little more like a tree. I didn’t realise that willow deliberately drop  whole branches so as to propagate themselves. This explains the success of our willow dome construction which was made by unceremoniously plonking willow sticks into the ground and weaving them together. They then gamely got on and grew. Soil is a recurring theme in the book, the teaching of the taxonomy of soil to undergraduates in particular. I had glimpses of this rich topic whilst doing a Kaggle challenge on tree cover. Finally, there is mass spectroscopy and isotope analysis.

And finally there is the personal, Jahren’s mental health, her struggles with pregnancy, marriage and a growing son. Some of this is painful and personal reading but its good to hear someone saying what we perhaps find unsayable. Lab Girl says relatively little about the difficulties she particularly faced as a woman, although Jahren has written about it elsewhere.

I observed a while back when reviewing In Defence of History that whilst historians seemed interested in literary style in technical writing, scientists rarely did. Lab Girl is an exception, which makes it well worth a read.

At the end of the book, Jahren asks us all to plant a tree. I pleased to say we’ve achieved this, although perhaps not quite the right sort of trees for American sensibilities, used to larger gardens. In the front garden we have a crab apple tree which, in the right sort of year, flowers on my birthday. There are several apple trees spread through the front garden. In both front and back gardens we have acers and now, at the bottom of the garden we have an amelanchier. I have longed for a Cedar of Lebanon in my front garden but fear I will never own a house large enough for this to be practicable.

Oct 14 2012

Book Review: Alan Turing: The Enigma by Andrew Hodges

2012editionA brief panic over running out of things to read led me to poll my twitter followers for suggestions, Andrew Hodges’ biography of Alan Turing, Alan Turing: The Enigma  was one result of that poll. Turing is most famous for his cryptanalysis work at Bletchley Park during the Second World War. He was born 23rd June 1912, so this is his 100th anniversary year. He was the child of families in the Indian Civil Service, with a baronetcy in another branch of the family.

The attitude of his public school, Sherbourne, was very much classics first, this attitude seems to have been common and perhaps persists today. Turing was something of an erratic student, outstanding in the things that interested him (although not necessarily at all tidy) and very poor in those things that did not interest him.

After Sherbourne he went to King’s College, Cambridge University on a scholarship for which he had made several attempts (one for my old college, Pembroke). The value of the scholarship, £80 per annum, is quite striking: it is double the value of unemployment benefit and half that of a skilled worker. He started study in 1931, on the mathematics Tripos. His scholarship examination performance was not outstanding. Significant at this time is the death of his close school friend, Christopher Morcom in 1930.

King’s is a notorious hotbed of radicals, and at this time Communism was somewhat in vogue, a likely stimulus for this was the Great Depression: capitalism was seen to be failing and Communism offered, at the time, an attractive alternative. Turing does not appear to have been particularly politically active though.

During his undergraduate degree, in 1933, he provided a proof of the Central Limit Theorem – it turns out a proof had already been made but this was his first significant work. He then went on to answer Hilbert’s Entscheidungsproblem (German for “Decision Problem) in mathematics with his paper, “On computable numbers”1. This is the work in which he introduced the idea of a universal machine that could read symbols from a tape, adjust its internal state on the basis of those symbols and write symbols on the tape. The revelation for me in this work was that mathematicians of Turing’s era were considering numbers and the operations on numbers to have equivalent status. It opens the floodgates for a digital computer of the modern design: data and instructions that act on data are simply bits in memory there is nothing special about either of them. In the period towards the Second World War a variety of specialised electromechanical computing devices were built, analogue hardware which attacked just one problem. Turing’s universal machine, whilst proving that it could not solve every problem, highlighted the fact that an awful lot of problems could be solved with a general computing machine – to switch to a different problem, simply change the program.

Alonzo Church, at Princeton University, produced an answer for the Entscheidungsproblem  at the same time; Turing went to Princeton to study for his doctorate with Church as his supervisor.

Turing had been involved in a minor way in codebreaking before the outbreak of World War II and he was assigned to Bletchley Park immediately war started. His work on the “Turing machine” provides a clear background for attacking German codes based on the Enigma machine. This is not the place to relate in detail the work at Bletchley: Turing’s part in it was as something of a mathematical guru but also someone interested in producing practical solutions to problems. The triumph of Bletchley was not the breaking of individual messages but the systematic breaking of German systems of communication. Frequently, it was the breaking of a system which was critical in principle the Enigma machine (or variants of it) could offer practically unbreakable codes but in practice the way it was used offered a way in. Towards the end of the war Turing was no longer needed at Bletchley and he moved to a neighbouring establishment, Hanslope Park where he built a speech encrypting system, Delilah with Don Bayley – again a very practical activity.

Following the war Turing was seconded to the National Physical Laboratory where it was intended he would help build ACE (a general purpose computer), however this was not to be – in contrast to work during the war building ACE was a slow frustrating process and ultimately he left for Manchester University who were building their own computer. Again Turing shows a high degree of practicality: he worked out that an alcohol water mixture close to the composition of gin would be almost as good as mercury for delay line memory*. Philosophically Turing’s vision for ACE was different from the American vision for electronic computing led by Von Neumann: Turing sought the simplest possible computing machinery, relying on programming to carry out complex tasks – the American vision tended towards more complex hardware. Turing was thinking about software, a frustrating process in the absence of any but the most limited working hardware and also thinking more broadly about machine intelligence.

It was after the war that Turing also became interested in morphogenesis2 – how complex forms emerge from undifferentiated blobs in the natural world, based on the kinetics of chemical reactions. He used the early Manchester computer to carry out simulations in this area. This work harks back to some practical calculations on chemical kinetics which he did before going to university.

Turing’s suicide comes rather abruptly towards the end of the book. Turing had been convicted of indecency in 1952, and had undergone hormone therapy as an alternative to prison to “correct” his homosexuality. This treatment had ended a year before his suicide in 1954. By this time the UK government had tacitly moved to a position where no homosexual could work in sensitive government areas such as GCHQ. However, there is no direct evidence that this was putting pressure on Turing personally. Reading the book there is no sick feeling of inevitability as Turing approaches the end you know he has.

Currently there are calls for Turing to be formally pardoned for his 1952 indecency conviction, personally I’m ambivalent about this – a personal pardon for Turing is irrelevant: legal sanctions against homosexual men, in particular, were widespread at the time. An individual pardon for Turing seems to say, “all those other convictions were fine, but Turing did great things so should be pardoned”. Arnold Murray, the man with whom Turing was convicted was nineteen at the time, an age at which their activities were illegal in the UK until 2000.

What struck me most about Turing from this book was his willingness to engage with practical, engineering solutions to the results his mathematical studies produced.

Hodges’ book is excellent: it’s thorough, demonstrates deep knowledge of the areas in which Turing worked and draws on personal interviews with many of the people Turing worked with.

Footnotes

1. “On computable numbers, with an application to the Entscheidungsproblem”, A.M. Turing, Proceedings of the London Mathematical Society 42:230-265 (1936).

2. “The Chemical Basis of Morphogenesis”, A.M. Turing, Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, Vol. 237, No. 641. (Aug. 14, 1952), pp. 37-72.

3. My Evernotes for the book

4. Andrew Hodges’ website to accompany the book (link)

Jun 22 2012

Book Review: Huygens–The Man Behind the Principle by C.D. Andriesse

huygens-man-behind-principle-c-d-andriesseThis post is a review of C.D. Andriesse’s biography “Huygens: The Man Behind the Principle”. Huygens Principle concerns the propagation of light but he carried out a wide range of research, including work on clocks, Saturn (discovering its moon “Titan” and hypothesizing the existence of its rings), buoyancy, circular motion, collisions, musical scales and pendulums. Huygens has made passing appearances in my blog posts on the French Académie des Sciences, on telescopes and also on clocks.

On the face of it is surprising that he is not better known, looking around for biographies of him one finds a rather short list. Andriesse puts this down to much of the personal documentation being in Dutch. The scientist in me feels there should be some quantitative way of measuring how “well known” a historical figure is now, and how “important” they were – I suspect this is an impossible programme. On completing the book I suspect a couple of factors play a part here: Huygens represents something of a transitional figure between the work of Galileo/Descartes, and Newton/Leibniz. Similarly his practical work on clocks and telescopes was impressive for its time but superseded not long thereafter. What we do now in physics owes much more to Newton than to Galileo, furthermore Newton although not prolific published more promptly than Huygens and was President of the Royal Society for 20 or so years before his death in post, whilst Huygens left L’Académie des Sciences sometime before his death in not particularly auspicious circumstances. It isn’t entirely clear whilst reading the book, but it becomes obvious that frequently Huygens’ work was done over long periods and only published quite a long time after it was started, often posthumously.

Huygens was born in the Hague in 1629 and died 1695. Christiaan Huygens’ father, Constantijn was a senior Dutch diplomat and a regular correspondent with René Descartes. Constantijn also met Francis Bacon (and was clearly impressed by him), Bacon and Descartes were important in shaping the development of science in the early 17th century. Bacon in particular set the scene for the way of doing science both in the Royal Society and  L’Académie des Sciences. Constantijn set his son off on a regime of study in the classics, with a view to him becoming a lawyer and following in his footsteps as a diplomat. Sometime around 1643, when Christiaan was 14 years old he started to show promise in mathematics.

Huygens senior provided introductions to Marin Mersenne who introduced him to those circles who became the Académie des Sciences in France. Christiaan Huygens was a paid director of science at L’Académie from its foundation in 1666 until he was excluded from it shortly after the death of Jean-Baptiste Colbert, founder of the organisation and his principle patron, in 1683. The exclusion arose from a combination of the loss of this patron, religious differences, absence due to illness, personal vendettas, opposition to membership of any foreigner and his demand for higher remuneration. Aside from this period at L’Académie, Huygens appears to have lived on the wealth and position of his father.

There’s no doubt that he made significant contributions in the area of mechanics, going beyond what Galileo and Descartes had done but his work was superseded almost immediately by that of Newton, and Leibniz, particularly in the methods of calculus which they developed. Calculus is a tool which makes much of the complex geometrical work that Huygens did obsolete. Leibniz was an informal pupil of Huygens, and they kept up a lengthy correspondence. He also had some exposure to Isaac Newton via the Royal Society.

Andriesse claims that Huygens wrote the first physics formula, relating to collisions. I think we should probably take this with a pinch of salt, but looking at the work he did do on circular motion, collisions, buoyancy, the motion of the pendulum and the shape of a catenary as well as his work on optics it is all very familiar to those that studied physics (at least to the age of 18).

Alongside his mathematical and theoretical physics work, Huygens also made contributions to the development of both clocks and telescopes. He introduced the pendulum clock, and a design of his was tested for determining the longitude by the Dutch East India Company. In practical terms this was not successful but it was a valiant first try. He also made lenses and constructed his own telescopes, here he appears to have been a competent technician and an able theoretician but not reaching the level of Newton, who constructed his own reflecting telescope – the first practical example of its type which was not exceeded for some 30 years or so.

This is a detailed biography of Huygens, drawing heavily on his personal correspondence and covering his scientific achievements in some depth, in the manner of Abraham Pais biography of Einstein. Although the book is pretty readable, the style is odd in places – Huygens is referred to frequently as “”Titan” without any real explanation as to why – it may be that in the original Dutch version, entitled “Titan kan niet slapen” (“Titan can not sleep”) this is a bit more obvious. The author also throws in the odd “Iris” when referring obliquely to sex (at least I think that’s what he’s doing!). Occasionally bits of information are scattered through the text, so we learn when Huygens is born and only 10 pages later do we learn where. There is no strong distinction of when Huygens started working on a publication and when it was actually published.

Perhaps more seriously Andriesse makes an attempt at Freudian analysis of some of Huygens illness, I’m no expert in this but I suspect this approach would be considered out-dated these days. It is also here that the translation perhaps wobbles a bit, with Huygens described as having “symptoms of the hypochondriac” which I think may be a mistranslation of melancholia hypochondriaca which I believe refers more generally to mental illness than the specific modern “hypochondria”.

This said, Andriesse’s biography of Huygens is well worth reading. Christiaan Huygens himself is an interesting subject who made important scientific discoveries across a range of areas.

Footnotes

My Evernotes for the book are here.

May 27 2012

Book Review: The History of Clocks & Watches by Eric Bruton

The-History-of-Clocks-Watches-by-Eric-BrutonEarlier, it was telescopes, now I’m on to clocks! Here I review Eric Bruton’s book “The History of Clocks & Watches”. I came to it via an edition of the Radio 4 programme “In Our Time” on the measurement of time (here). The book was originally published in 1979, the edition I read was from 2002. I mention this because there is some evidence that the text has not been fully updated.

1 Earliest clocks

The book starts with a slightly cursory look at the use of the sun to measure time, and mentions briefly the use of candles. The first mechanical clocks were based on water, and in Europe were used as timekeepers in monastic communities. No direct physical evidence appears to remain for these clocks, although there are detailed descriptions in books from the time such as Su Sung’s 1092 “New Design for a (Mechanised) Armillary (sphere) and (celestial) globe”. They appear to have been used widely in ancient times. The sandglass, superior to the water clock because of the flow properties of sand when compared to water, first appears in illustrations in 1337.

2 Advent of clockwork

“Clockwork” clocks started to appear started to towards the end of the 13th century, they were found in monasteries to call the monks to prayer. The key components of a clock are a mechanical oscillator, initially a bar with weights at the end know as a foliot, an “escapement” to allow motion coupled to the mechanical oscillator to work a display and a driving force to keep the oscillator going. In these early clocks falling weights provided the driving force. The first escapements were known as “verge escapements” and were in use until 1800, several hundred years after they were introduced. In fact it took an awfully long time for mechanical clockwork to replace solar clocks. Improvements to timepieces are in the quality of the mechanical oscillator: making it insensitive to pressure and temperature, and making sure the driving force and display train interferes minimally with the going of the oscillator.

3 Domestic Clocks

The first spring driven clocks appeared around 1430, the spring enables a rather more compact clock but the problem is the power it generates varies with how far it is unwound, this problem was addressed using a fusee which moderates the output power, apparently adapted from siege engines where it is used in reverse to enable men to wind up catapult style devices. Another trick is to use the spring only in a small part of its unwinding.

4 European mechanical clocks

It was not until 1657 that Christiaan Huygens introduced the pendulum as the oscillator for clocks, which produces a big improvement in accuracy – it actually becomes relevant for a timepiece to have a minute hand. Huygens made repeated contributions to the development of the clock, although he had a clockmaker implement his ideas in much the same manner as Robert Hooke had Thomas Tompion implement his ideas.

5 The Time at sea

As early as 1598 Philip III of Spain had offered a reward for a method to find the longitude, it was a well-recognised problem well before the Board of Longitude was created in England to provide a prize for its solution. John Harrison and his marine chronometers for determining the longitude are covered in some detail, extending beyond his life to cover the developments of other clockmakers including John Arnold, Thomas Mudge, Thomas Earnshaw and Pierre Le Roy. Harrison is famous for his dispute with Nevil Maskelyne, the Astronomer Royal, and something of an embodiment of the Board of Longitude that funded his work but it seems that clockmakers of the time were disputatious with each other and the Board.

The fields of astronomy and timekeeping are tied together, many early clocks went to great lengths to show astronomical information such as the phases of the moon. Even in the 20th century the most precise mechanical clocks were made for astronomical use, in the past Thomas Tompion was renowned for his precision timepieces supplied to the Royal Observatory. Whilst Christiaan Huygens made revolutionary advances in both clock design and telescopes. There is a relationship between dividing a quadrant, a device for measuring angles in astronomy, accurately into increments and dividing the gear wheels of a clock accurately to position the teeth.

6 The development of the watch

Personal timepieces date from the late 15th century, in fact prior to this people carried personal sundials or even used themselves as the pointer in a simple sun clock. The challenge with a watch is to produce a compact timepiece, meaning small parts, which is robust to the forces that being carried around all the time exert. I have to say here that the watches that Abraham-Louis Breuguet made at the end of the 18th century are absolutely gorgeous (see here, for example).

7 Mass production

I found it surprising the degree of precision achieved in the pre-Industrial age in the manufacture of timepieces, but then I also found pre-Industrial lens grinding semi-miraculous. This probably says more about me then anything else but perhaps the message is that bespoke precision pre-dated the Industrial Revolution whose strength was in standardising components, introducing continuous workflows and making use of less skilled labour. At points in time specific areas of England, France, Germany, Switzerland and the US were predominant centres of manufacture with the US leading the way in mass production but the Swiss picking it up in Europe.

8 The Technological Age

The 19th century saw the arrival of trains and telegraph, these bring the need to standardise time and the means to do it. Scheduling of trains means that standardising time is to some degree a safety issue, the adoption of time zones in the US in 1876 was also driven by the railways. The adoption of Greenwich Mean Time occurred in 1880, the Greenwich Observatory had been providing a time single in the form of a dropping ball since 1833. The telegraph enabled such time signals to be distributed more broadly, and used automatically. Electricity was also incorporated in the running of the clock, the 1921 Synchronome electromechanical clock providing the ultimate in accuracy until the introduction of quartz and atomic timekeepers.

9 Watches for the people

The final part of the book covers the reduction of cost to mass produce watches which all could afford, this process includes simplifying the mechanisms and sacrificing accuracy where possible. It highlights the development of digital watches in the 1970s where the prevailing mechanism for testing the quality of electronic components was to sell them and see how many were returned!

For my own amusement I present the following table which presents the accuracy of various landmark timepieces in standardised form, the first two entries are from this wikipedia article whilst the remainder are from the book:

pre-1657 15 minutes per day 328500 seconds/year
1657 Christiaan Huygens 15 second per day 5475 seconds/year
1766 Pierre Le Roy 7.5 seconds over 46 days 60 seconds/year
1921 Synchronome Fractions of a second per year 0.5 second/year
1955 Atomic clock 1s in 3000 years 0.00033 seconds/year

Coincidently the improvement in accuracy for successive entries in this table is 100-fold.

The book is heavily illustrated with pictures of timepieces, diagrams of mechanisms and engravings of workshops. I rather like this, but in places it feels like you’ve seen an image before in relation to an earlier section of the book. Although the book is logically arranged, in fact I borrowed the logic to structure this post, the presentation of how clock mechanisms work is disjoint, and scattered throughout the book.

My follow on reading from this book is on Christiaan Huygens, he isn’t a central character here but he just turns up in so many different places!

Footnotes

  • My Evernotes on the book are here.
  • The Breguet at the Lourve exhibition looks interesting (here)

Apr 17 2012

Book Review: Stargazers by Fred Watson

41W3OswkqxL._SS500_This post is a review of “Stargazers:The Life and Times of the Telescope” by Fred Watson. It traces the history, and development of the telescope from a little before its invention in 1608 to the present day.

The book begins its historical path with Tycho Brahe, a Danish astronomer who lived 1546-1601. He built an observatory, Uraniborg, on the Danish island of Hven in view of his patron, King Frederick II of Denmark. Brahe’s contribution to astronomy were the data which were to lead to Johannes Kepler’s laws of planetary motion and ultimately Isaac Newton’s laws of gravitation. On the technical side his observatory represented the best astronomy of pre-telescope days with the use of viewing sights, his Great Armillary with it axis aligned with that of the earth and graduated scales to measure angles. Watson also cites him as a first instance of a research director running a research institute – alongside the observatory he ran a print works to disseminate his results.

The telescope was first recorded in September of 1608, when Hans Lipperhey presented one to Prince Maurice of Nassau in the Netherlands. Clearly it was a device of its time since in very short order several independent inventions appeared, Galileo constructed his own version which led to his publication of “The Starry Messenger” in 1610 which reports his observations using the device. The telescope grew out of the work of spectacle makers; there are some hints of the existence of telescope-like devices in the latter half of the 16th century but these are vague and unsubstantiated. Roger Bacon and Robert Grosseteste both conceived of a telescope-like device in the 13th century, around the time the first spectacles were appearing. Although there are a few lenses from antiquity there is no good evidence that they had been used in telescopes.

The stimulus for the creation of the first telescopes seems to have been a combination of high quality glass becoming available, and skilled lens grinders. The lens making requirements for telescopes are much more taxing than for spectacles. The technology required is not that advanced, if you look around the web you’ll find a community of amateur astronomers grinding their own lenses and mirrors now using fairly simple equipment, typically a turntable with a secondary wheel which produces linear motion for the polishing head back and forward across the turning lens blank. The most technologically advanced bit is probably captured in the first step: “acquire your glass blank”.

Through the 17th century refracting telescopes were built of ever greater length in an effort to defeat chromatic aberration which arises from the differential refraction of light as a function of wavelength (colour) – long focal length lenses suffered from less chromatic aberration than the shorter focal length ones which would allow a shorter telescope. Johannes Hevelius made telescopes of 46m focal length (physically the telescope would be a little shorter than this), mounted on a 27m mast; Christiaan Huygens dispensed with the “tube” of the telescope entirely and made “aerial telescopes” with even longer focal lengths, up to 64m.

It was known through the work of Alhazen in the 10-11th century, and others, that reflecting, curved-mirrors could be used in place of lenses. A telescope constructed with such mirrors would avoid the problem of chromatic aberration. However, the polishing tolerances for a reflecting telescope are four times higher than that of a lens. Newton built the first model reflecting telescope in 1668 but no-one was to repeat the feat until John Hadley in 1721.

Theoretical understanding of telescopes developed rapidly in the 17th century both for refracting and reflecting telescopes, indeed for reflecting telescopes there were no fundamental advices in the theory between 1672 and 1905. The problem was in successfully implementing theoretical proposals. Newton claimed that chromatic aberration could not be resolved in a refracting telescope, however he was proved wrong by Chester Hall Moor in 1729, and somewhat controversially by John Dollond in 1758 who was able to obtain a patent despite this earlier work (which was defended aggressively by his son) – the trick is to build compound lenses comprised of glass of different optical properties.

Also during the 18th century the construction of reflecting telescopes became more common, William Herschel started building his own reflecting telescopes in 1773 with the aid of Robert Smith’s “Compleat system of opticks”. Ultimately he was to build a 40ft (12m) telescope with a 48 inch (1.2m) mirror in 1789, supported by a grant from George III. During his lifetime Herschel was to discover the planet Uranus (nearly called George in honour of his patron), numerous comets and nebulae. At the time “official” astronomy was more interested in the precise measurement of the positions of stars for the purpose of navigation. Herschel was to be followed by Lord Rosse with his 1.8m diameter mirror telescope built in 1845 at Birr Castle, this has been recently restored (see here). He too was interested in nebula and discovered spiral galaxies.

During the 19th century there were substantial improvements in the telescope mounts, with engineers gaining either an amateur or professional interest (men such as James Nasmyth and Thomas Grubb). Towards the end of the century photography became important, which placed more exacting standards for telescope mounts because to gain maximum benefit from photography it was necessary to accurately track stars as they moved across the sky to enable long exposure times. This is also the century in which stellar spectrography became possible with William Huggins publishing the spectra of 50 stars in 1864. Léon Foucault invented the metal coated glass mirror in 1857 which were lighter and more reflective than the metal mirrors used to that point. As the century ended the largest feasible refracting telescopes with lens diameters of 1m were just around the corner, above this size a lens distorts under its own weight reducing the image quality.

In 1930 Bernhard Schmidt designed a reflecting telescope which avoided the problem of aberrations away from the centre of the field of view making large field of view “survey” telescopes practicable. As a youth in the 1970s I learnt of the 200-inch (5 metre) Hale telescope at Mount Palomar, since then space telescopes able to see in the infra-red and ultra-violet as well as the visible have escaped the distortion the atmosphere brings; adaptive optics are used to counteract atmospheric distortion for earthbound telescopes and there are “distributed” interferometric telescopes which combine signals from several telescopes to create a virtual one of unfeasible size.

Watson mentions briefly radio telescopes and in the final chapters speculates on developments for the future and gravitational lensing – natures own telescopes built from galaxies and spread over light years.

I enjoyed “Stargazers” as a readable account of the history of the telescope which left me with a clear understanding of its principles of operation and the technological developments that enabled its use, it also provides a good jumping off point for further study.

Footnotes

My Evernotes for the book are here, featuring more detailed but slightly cryptic notes and links to related work.