According to Irish writer, Flann O'Bryan's Atomic Theory of Bicycles, an atom is the smallest element of an object that contains all the parts of the whole.
So a bicycle atom looks just like the bike itself, complete with drop handlebars, saddle, bell, and lights. Cyclist atoms look just like the cyclist, down to crash helmet, funny shorts, and cleated shoes.
If a cyclist spends too much time in the saddle the atoms become mixed so that the rider becomes part bicycle, and the bike become part rider. Advanced cases of mixed atoms often lead to a bicycle somehow finding its way indoors on cold nights and resting near the fire, while the cyclist is likely to go to sleep on his feet, leaning against the wall.
I hope that helps.
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And, on another tack altogether, his original idea isn't so very different from the atomic theory proposed by Lucretius who lived in the first century, BCE.
In Lucretius's universe, there are atoms and there is void.
