A So­lar Eclipse (and the Weight of Pa­per)

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. 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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