by Christoph
Last week I had in mind to write a short hommage to a venerable lab instrument, the flatbed chart recorder, but then the solar eclipse got in the way. More precisely, not the eclipse, but the map of the USA that went viral on social media, with the booking numbers for short-term rentals around April 8 as prominently visible markers for the large area where the total solar eclipse should be visible depending on weather conditions (Frontispiece).
Figure 1. Halley, E. & Senex, J. (1715). A description of the passage of the shadow of the moon over England as it was observed in the late total eclipse of the sun April 22, 1715. Institute of Astronomy Library (Cambridge, UK). Source (click here to download a hi-res version). Frontispiece: Share of Airbnb and Vrbo listings booked ahead of the April 8 eclipse. Data: AirDNA; Map: Erin Davis/Axios Visuals. Source
I recalled that I had seen a similar map before: "A description of the passage of the shadow of the moon over England as it was observed in the late total eclipse of the sun April 22, 1715" by Edmond Halley and cartographer John Senex (Figure 1). You may wonder about the "...as it was observed" in the title of this broadsheet publication, and assume that it is merely a record made after the event. Not so. Halley had previously calculated the date of the eclipse and the area of its totality. Because the prediction was only off by a few minutes and miles from what was observed on April 22, 1715 he was able to re‑use his earlier map. This greatly lowered costs as maps of such a high resolution were immensely difficult, time-consuming, and expensive to prepare for printing in the early 18th century (Rebekah Higgitt dives in a most entertaining way into the history of this and other "eclipse maps" in her 2015 piece in the blog 'teleskopos').
Outside of Great Britain, Edmond Halley (1656–1742) is known today above all as the namesake of the most famous periodic comet, whose return he correctly predicted for 1758, which he himself did not live to see (the naming goes back to a suggestion by the French astronomer Nicolas-Lois de Lacaille). In Great Britain, Halley is regarded as one of the luminaries of the natural sciences, which experienced their first heyday in the late 17th century. Unlike his contemporary and colleague in the Royal Society Antonie van Leeuwenhoek (1632–1723), who was more into in the Small Things, Halley was working in theory and practice on the Really Large Things, the Earth, planets, the sun and comets, and the movements of the celestial bodies, astronomy.
"In theory" here means that Halley worked out the calculations of comet orbits and the predictions of solar eclipses in collaboration with his congenial friend Isaac Newton (1643–1727), whose publication of the Principia he largely financed. "In practice" here means that – unlike his friend Newton – he always had the applicability and usefulness of his measurements and calculations in mind. It's safe to assume that Halley published his map with the detailed prediction of the solar eclipse on 22 April 1715 not only to show how good he was at math, but also to demonstrate that solar eclipses are not celestial signs of impending doom – a belief that was still widespread at the time.
Or think of the magnetic chart of the Atlantic that he published in 1700 as the result of an expedition he had led as captain to record geographical variations in compass readings, that is, the amount that the alignment of the needle differs from geographical North ("declination"). The lines in that chart, known as isogonic lines, show places where the magnetic variation is equal, which was a handy way for sailors to determine longitude in the pre-GPS days. As another example of Halley's sense of practicality, Boris Jardine recounts in his essay "State of the field: Paper tools" (2017):
...Edmund Halley set out to answer an old and seemingly intractable question: how to achieve an accurate measurement of a country’s area? Halley had been set the task by John Houghton, who was hoping to include the answer in his Collection of Letters for the Improvement of Husbandry & Trade. In 1680 a map had been produced that Halley deemed sufficiently accurate so he simply cut it up and weighed it, using a circle of known area and of the same paper as a standard. The answer Halley got, for England and Wales, was 38.7 million acres, just a shade over the modern estimate. Halley is thought to have learned the technique of 'cut‑and‑weigh' from William Petty, but in any case it was a reasonably well known trick..."
This 'cut‑and‑weigh' trick brings me straight back to the flatbed recorder, which until not so long ago was a staple in every biochemistry lab, where days and nights – and often weekends – were spent in the cold room purifying proteins/enzymes (Figure 2). Before the advent of HPLC in the 1970s, protein purification by liquid column chromatography (LC) was "an extremely time-consuming stage in any lab and can quickly become the bottleneck for any process lab" (Wikipedia).
Figure 2. GE Pharmacia Amersham Dual Channel Chart Recorder 19-8003-01 Weight 25 lbs Dimensions 23×19× 3, Voltage 120V 50Hz/60Hz. Source (Ebay)
Mechano-electrical control gave us the fraction collector, and the invention of the photodiode, a light-triggered semiconductor, and later diode arrays led to the development of the the flow-through photometer. The flatbed recorder (Figure 2) then made it possible to continuously record the signals from the photodiode, for example absorption at 280 nm for proteins. Fewer hours in the cold room, great! Determining the column resolution via the retention times for any chosen peaks became child's play (if you had noted the paper feed/minute). Molecular biologists, who according to Erwin Chargaff "essentially practice biochemistry without a license" (ref.), had more trouble determining the protein concentrations in their precious fractions. Today, in the digital age, you simply press the "conc." button on the display of your software-controlled chromatography setup. What did we do instead? During my undergraduate studies, I learned in a practical course from a very experienced, grey-haired biochemist that you don't laboriously calculate the integral of the area under a peak of the chromatogram with pen & paper. Instead, you cut out the peak and weigh it on a precision balance, accurate to ±0.1 mg (calibration with two weighed peaks for known protein conc.). Just like Halley did three hundred years earlier. It can be quite mundane to stand on the shoulders of giants, occasionally.
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