Herapath first submitted his paper to the Royal Society in 1816.  They rejected his paper.  When, in 1821, his paper did appear in The Annals of Philosophy, there is little evidence of support or acceptance.  His work lay abandoned on the margins of physical science until the 1840’s.  Why did this happen when we know that so much of his work was spot on?

Some have looked at this episode as an instance where the customary open-minded objectivity of science had been distorted.  Shadows of elitism or intellectual cowardice, they surmise, had cast a dark shroud over Herapath’s work and prevented it from being evaluated properly.  That is, Herapapth’s rejection was an instance of scientists acting under petty influences and not as good scientists.

But maybe that was not the case.  Maybe we need to open our sense for what was at stake in Herapath’s work.  Let’s look at the actual criticism contemporaries offered and try to see what made his seemingly well-formed work so objectionable.

There were four published replies to Herapath’s work, expressing concern about various aspects…he was too speculative, relied too much on mathematical deductions…but above these objections stood their concern with his portrayal of the molecular world.  He envisioned perfectly hard particles moving freely, slamming into one another and bouncing elastically…without losing momentum or energy.  This was the rub.  Herapath, it turns out, had run smack into a long standing metaphysical controversy.  Perfect hardness logically barred elasticity.

Here’s how Newton had put it in his Principia near the end of the 17^th century:

For bodies which are either absolutely hard or so soft as to be void of elasticity, will not rebound from one another. Impenetrability makes them only stop.  If two equal bodies meet directly in vacuo, they will by the Laws of Motion stop where they meet, and lose all their Motion, and remain in rest, unless they be elastic, and receive new motion from their Spring.

Since it was assumed that atoms as the fundamental particles of matter were perfectly hard…how else could they maintain themselves…they could not bounce off of one another, but would simply ‘splat’ like a snowball against a wall.  Without a source of Spring, without a repulsive force like that of Caloric, Herapath’s vision of the hidden world of atoms and molecules was rooted in contradiction.

Herapath replied to his critics, urging that such metaphysical arguments be set aside.  Grant elastic collisions, grant that somehow momentum is exchanged and no motion is lost.  The proof, he urged, should lie in the proverbial pudding –in the fruitfulness of his analysis.  His strategy works.  The result is elegant mathematically and satisfies the data.  Surely that is enough.

But the critics did not agree.

We do not need to charge Herapath’s colleagues with intellectual cowardice, elitism, or the like.  We need simply to recognize that deep metaphysical notions about the way things must be had led reasonable scientists to deny the premises of Herapath’s work.  Though the molecular world is un-observable, it is clear that Herapath’s views of molecular collisions were un-acceptable and reasonably so.  It was not a case of ‘just the facts’.