Across the countryside of England there lies an ancient road, the Ridgeway, carved by the travels of the earliest Britons.  Connecting such sacred sites as Stonehenge and Silbury Mound, the Ridgeway today is hardly discernible in parts –a mere path across the fields –while elsewhere it underlies the concrete and asphalt of the motorway from London to Bristol.  Why is it that the Ridgeway, or Herapath as it is called in the West Country, has been treated so differently by history?  Why should some parts lay obscure, abandoned to the margins, whilst others have been built upon again and again, remaining vital –though of course transformed?

As with one Herapath, so with another.  John Herapath, also of the West Country, has left a similarly mixed legacy.  Some of his work was built upon, some not; and little of it was received with enthusiasm by his contemporaries.  What was at work here?  What were the laws of commerce and traffic that determined what would be built upon and what not?

Born near the turn into the 19^th century, Herapath participated in the scientific world of Dalton, Davy, Laplace, and Joule.  He also participated in the booming world of the railroad.  The railway journal he edited was successful; in time it would be named Herapath’s Journal.  As a young man Herapath threw himself into the debate over the nature of heat, and his entry effectively marked a new plateau for the notion that heat was not an ethereal substance, a material stuff, but a certain busy-ness within matter, a mode of motion.  This concept, the kinetic theory of heat, would become one of the core concepts of modern science, one that is still vital, though of course transformed.

Notable scientists before Herapath’s day had offered a notion of heat as a quality of motion, scientists such as Francis Bacon, Robert Boyle, and Daniel Bernoulli.  And in his own day there were those who leaned this way:  Humphrey Davy, president of the Royal Society, Count Rumford, the founder of the Royal Institution, Thomas Young one of the first to propose a wave theory of light, each rejected the caloric theory and sought an alternative in some quality of internal agitation of the particles of matter.

But Herapath went further than they had.  He proposed that the molecular world was a chaos, with particles of a gas, for example, moving freely, in straight lines, colliding with one another.  These collisions, he went on, should be taken to be perfectly elastic, like billiard balls in an ideal world, and he drew upon the mathematical expressions that had been worked out for such collisions.  He then proposed that the temperature of a body reflects the average value of a particular kinematic quality, momentum.  The modern theory links temperature to kinetic energy, not momentum, and there is a difference here, but Herapath was able to derive the general gas laws in a manner closely paralleling modern analyses.  With this as the core of his theory, he went on to consider a host of heat phenomena: specific heats, latent heats, heats of chemical reaction, etc.  Notably, his explanations of diffusion and of adiabatic phenomena, which followed naturally from his principles, addressed major issues then confronting the caloric theory.  His insights and the over-all form of his analysis lay at the foundations of the modern understanding.

This was a most impressive grasp of the truth with a capital “T”.  So much so that we are left with a most curious problem:  How is it that so much right-thinking, so much of what we know to be good science, the facts and perspectives we accept today, how could they have been found false?  For that is what happened.  The scientific community rejected his views.