
The dour looking guy front row center is Prof Éleuthère Mascart!
This guy was a wholesale science badass, and I wrote a report on him when I was in school. He was into just about everything: electricity, meteorology, optics, chemistry, physics, math, politics, you name it. He did a heap of work on earth's magnetic field, and basically wrote the book on the subject after taking a quick field trip to Cape Horn for some measurements. He was a go-to guy for science and tech advice for several European governments for decades, sort of like a Michio Kaku to the stars. He was a research machine and churned out stuff on electricity, optics, and meteorology like crazy.
The meeting this photo was taken at was a big deal. Physicists were arguing about standardizing electrical units, and after a bunch of work (including the arguments over who to name what after) they settled on the formal definition of the Ohm, and I think the Volt as well (it was one of these meetings around this time anyway). I'd never seen this picture before! It looks like they might have stuck him in charge of moderating and photographed him after, he looks pretty ticked off.
Really good stuff!