For modern day people, the world seems largely straightforward. Many of the processes, natural or otherwise, that we observe around us have been understood and explained completely.
Yes, there are still holes in our knowledge, and enormous holes at that. But the questions about our day-to-day world have largely been answered for all practical purposes.
But it wasn’t always that way. Before we understood the world around us, and before our scientific probity allowed us to base our theories on useful and detailed observations, there were other theories. And these were sometimes mind-blowingly wrong.
For millennia these theories have been tied to religion. We don’t understand our world, so let’s make it something beyond our understanding, and let’s wax lyrical on what the creator of such a world would be like, until we’ve invented a whole narrative. Nobody can prove you wrong.
But the really interesting stuff comes from the later Enlightenment, as we slowly and arduously worked our way towards a true scientific understanding of the natural processes around us. The theories that sprung from these imperfect and incomplete observations were something to be seen.
Such as the idea of “caloric”, which theorized that heat was an invisible, indestructible liquid.
17th century scientists were baffled by heat, and combustion. They understood to a certain degree the chemical reactions which led to the latter, but what really stumped them was how the heat itself could be felt at a distance from the burning material.
One of the best guesses at the time was the theory of phlogiston. This theorized that something undetected in the burning material must be escaping during the blaze. Phlogiston was thought to be the very essence of heat, and as a phlogiston-containing substance was burned that heat was released.
18th century scientists built on this idea, and refined it. Finding no way to detect phlogiston and with mounting experimental evidence which seemed to contradict the theory, the French chemist Antoine Lavoisier had an idea. Rather than this undetectable substance, maybe heat was transferred by another undetectable substance, called caloric.
You can see the empirical reasoning behind these nested theories. If you slide down a rope using your hands, at the bottom your hands have become heated. It was thought that this fluid was squeezed out of the rope as you descended, remaining on your hands to heat them.
The same substance would be atomized into the air during burning, transferring the heat in much the same way as phlogiston. We may understand radiating heat and friction today, but 250 years ago this was the best idea going.
This bumped up against Isaac Newton’s theories as well. Caloric was assumed to be never destroyed, only transferred, and thus experiments were designed based around the assumption of conservation of heat. But the thing is, quite a lot of observable results support caloric theory.
A cup of hot water will get cold if left alone, as a caloric leaves the water and enters the atmosphere. Heated air expands, as it would naturally if caloric was being added to the mixture.
It would take a practical observation in an unrelated field for the cracks to finally appear in caloric theory. Count Rumford, a British physicist, published his observations regarding the manufacture of cannon in 1798.
Rumford pointed out that the cannon would need regular boring to keep the barrel free from obstruction, but also noted that the cannon got hot each time it was rebored. If the caloric fluid had left the cannon the first time, how did it return each time the cannon was rebored?
This led to more sophisticated thinking. Conservation of heat was replaced with conservation of energy. And as our understanding of energy transfer grew, there was less and less point in envisaging a fluid for this transfer.
Caloric had outlived its usefulness. But it survives today as a testament to the ingenuity and observational skills of scientists of previous centuries, trying to put the world together without all the facts.
Top Image: Antione Lavoisier with his wife. Lavoisier first theorized that heat transfer occurred through an invisibiel fluid, dubbed caloric. Source: Jacques-Louis David / Public Domain.
By Joseph Green