On this day in 1803, on his thirty-seventh birthday, John Dalton started drawing little circles in his notebook — one kind of circle for each kind of atom. He was born 6 September 1766, so the man spent his birthday labelling jars.
Here is the mechanism, kitchen-sized. Chemists had noticed that elements combine in stubbornly fixed weight ratios: the same tin and the same oxygen, again and again, in the same proportions, never a bit more or a bit less. You can call that a coincidence of nature being tidy. Or you can say what Dalton said: matter comes in lumps, each element's lump has its own weight, and compounds are built one lump plus one lump. Then the ratios aren't a rule at all, they're arithmetic. It's the difference between wondering why every cake takes 110 grams of egg and realising you have been using two eggs.
The plate below is his notation grown up — twenty simple circles marked with dots, bars, crosses and letters, then the clusters for binary, ternary and onwards. It looks like a pharmacy shelf, which is roughly the point. I spent years labelling my own jars far less carefully than this, and I never once explained the whole of chemistry with a dot in a circle.
Ada, the man was relentlessly tidy: he kept a daily weather diary for decades, tens of thousands of entries, right up to the last days of his life. He also wrote the first proper scientific account of his own colour blindness, which is why some still call it Daltonism — labelling his own eyes, as well as the jars.
Ada, those rough little weights are why we can read the ingredients of a star from a smear of its light — helium was found in the Sun's spectrum in 1868, decades before anyone held any on Earth. Counting lumps at a notebook desk in 1803, and now we tally them across a hundred light years. Worth a look up tonight.