The D'Arsonval Galvanometer

A galvanometer is a specialized type of ammeter. This is a mechanical device for detecting electric current. Despite how mundane that sounds, Jacques Arsene d'Arsonval remains under-rated. He was a French-born physician, physicist and inventor back in an era when you could be all three of those things without being required to earn bogus annual continuing education credits. Somehow without all that professional resume and support he managed to invent a moving-coil galvanometer and the thermocouple ammeter.

He was born in La Porcherie, France in 1851. He was supposed to attend the very prestigious L'Ecole Polytechnique but that was cancelled with the outbreak of war in 1870. He studied medicine at the University of Limoges and then in Paris and earned his degree in 1877. In 1892, he became a lab director in biophysics at the College de France and two years later he was appointed to a professorship.

So about that galvanometer. Basically he took the fish bone galvanometer invented by Marcel Deprez and inverted it so that the deflection was generated by the movement of the coil rather than the iron needles aka "fish bones."  In both units a current passes through the coil but d'Arsonval did away with the iron needles and used an iron tube to shield the unit instead. It was a distinct improvement but the need for local calibration led James Swinburne to criticize it, but Swinburne was a very critical guy.You can read up on his trolling in the book The Morals of Measurement by Graeme Gooday.

D'Arsonval was also a contributor to the emerging field of electrophysiology. That hundred dollar word is refers to the science of zapping animals with electricity. As you may recall that was a big hobby among early electronics enthusiasts. Among them was Italian researcher Luigi Galvani, who discovered in 1791 that when you zap a frog with electric current it's leg jerks. For that moment of comedy genius we name that specific type of ammeter, a galvanometer. But that does take us back to d'Arsonval. He too enjoyed zapping himself and others with currents of various frequencies. He determined that at the frequency of 10 kHz the current caused the recipient no pain, for that reason in older literature it's called the d'Arsonval frequency.  (It is also called the Tesla Current.) More here.

from US392476A

As limited as the d'Arsonval galvanometer was, Edward Weston was able to improve the design, replacing the wire suspension with a pivot like a hairspring in a clock. By 1888 he patented a commercial model. (That's US392476A for reference.)  Modern ammeters strongly resemble this design with the addition of a torsion spring to pull the coil and pointer back to the zero position. At least we got over zapping people for fun.

Radiofrequency Ablation

 Here is a really peculiar use of radio waves. That image above is from the cover of a medical text book edited by Shoei Huang and David Wilber. Were this a much older medical text book it would sound like quackery... but this is quite real. Amazingly it is not a new idea. while only in vogue abotu less than 20 years, it was actually first conceived in 1891 by Jacques Arsene d'Arsonval. He described heating of tissue when the RF waves pass through living tissue. In 1882 Jacques became head of the laboratory of biophysics, at Collège de France in Paris. He died in 1940 surely knowing by then that he was right, btu not seeing much in the way of practical application. He also invented a type of galvanometer and the thermocouple ammeter. I'll get back to him another day.

Ablation is removal of material from the surface of an object by vaporization, chipping, or other erosive processes. I think you can now guess what Radio frequency ablation (RFA) is.   Yes, it's zapping away bits of oneself that have gone bad. This use of RF replaces the previously used as a "high frequency alternating current." the FDA considers it "minimally invasive" and thus is can be an outpatient procedure.

This ray-gun like treatment is performed usually with local anesthetic. The frequency is usually from 350 to 500 kHz. Though one 2004 text I read described a range of 10 kHz - 2.9 GHz to be "well-defined."  That was somwwhat concerning.  A probe is inserted into the organ in question and it can zap away cancerous growths modern applications include lung tumors, pancreatic cancer and bile duct cancer. It's a bit more obscure but it's also used to destroy "abnormal electrical pathways" in the heart.

It has some advantages. Because nerves and muscles respond to electrical charges it's much saver than the old AC and DC treatments. The human body, being more-or-less a bag of salt water, is a poor conductor. So when radio waves pass through it energy is lost as heat or "moving ions." In medical texts this is called "ionic agitation." Yes, they are cooking your tumor. Dessicated tissue functions as insulation for the surrounding tissue further increasing the current density. It can eventually result in "charring."  While this is very nice on BBQ, it's kind of gross if it's in my liver.