Writing in 1797, Count Rumford (Benjamin Thompson) described the observations that led him discover convection. It was published in The Journal of Natural Philosophy, Chemistry, and the Arts, better known as Nicholson’s Journal, under the title “On the Propagation of Heat in Fluids”.
When dining, I had often observed that some particular dishes retain their heat much longer than others, and that apple pies and apples and almonds mixed ( a dish in great repute in England) remain hot a surprising length of time. Much struck with this extraordinary quality of retaining heat which apples appeared to possess, it frequently occurred to my recollection, and I never burnt my mouth with them or saw others meet with the same misfortune without endeavoring but in vain to find out some way of accounting in a satisfactory manner for this surprising phenomenon.
About four years ago, a similar accident awakened my attention and excited my curiosity still more. Being engaged in an experiment which I could not leave, in a room heated by an iron stove, my dinner which consisted of a bowl of thick rice soup was brought into the room, and as I happened to be too much engaged at the time to eat it, in order that it might not grow cold I ordered it to be set down on the top of the stove. About an hour afterwards, as near as I can remember, beginning to grow hungry and seeing my dinner standing on the stove, I went up to it and took a spoonful of the soup, which I found almost cold and quite thick. Going, by accident, deeper with the spoon the second time, this second spoonful burnt my mouth. This accident recalled very forcibly to my mind the recollection of the hot apples and almonds, with which I had so often burnt my mouth a dozen years before in England. Even this, though it surprised me very much, was not sufficient to open my eyes and to remove my prejudices respecting the conducting power of water.
He describes the movement of fluid he witnessed in a thermometer.
I saw the whole mass of the liquid in the tube in a most rapid motion running swiftly in two opposite directions, up and down at the same time. The bulb of the thermometer, which is of copper, had been made two years before I found leisure to begin my experiments, and having been left unfilled without being closed with a stopple, some fine particles of dust had found their way into it and these particles which were intimately mixed with the spirits of wine, on their being illuminated by the sun’s beam, became perfectly visible . . . and by their motions discovered the violent motions by which the spirit of wine in the tube of the thermometer was agitated. . . . On examining the motion of the spirits of wine with a lens, I found that the ascending current occupied the axis of the tube and that it descended by the sides of the tube. On inclining the tube a little, the rising current moved out of the axis and occupied the side of the tube which was uppermost, while the descending currents occupied the whole of the lower side of it. I discovered horizontal currents running in opposite directions, one above the other, or regular winds which, springing up in the different regions of this artificial atmosphere, prevailed for a long time with the utmost regularity, while small particles of the amber collecting themselves together, formed clouds of the most fascinating forms, which being carried by the winds, rendered the scene perfectly fascinating! It would be impossible to describe the avidity with which I gazed on these enchanting appearances. In the state of enthusiasm in which I then was, it really seemed to me that Nature had, for a moment, drawn back the veil with which she hides from mortal eyes, her most secret and most interesting operations, and that I now saw the machinery at work by which winds and storms are raised in the atmosphere! Nothing seemed to be wanting to complete this bewitching scene and to give it the air of perfect enchantment, but that lightning in miniature should burst from these little clouds and that they were frequently so thickened up and had so much the appearance of preparing for a storm, that had that event actually t … Having still fresh in my memory, the accidents I had so often met with in eating hot apple pies, I was very impatient when I had completed this instrument to see if apples which, as I well knew, are composed almost entirely of water, really possess a greater power of retaining heat than that liquid when it is pure or unmixed with other bodies. There is at present no single term in our language employed to denote this mode of propagation of heat; but we venture to propose for that purpose the term convection (convectio, a carrying or converging), which not only expresses the leading facts, but also accords very well with the two other terms.
The “other two terms” he refers to are radiation and conduction.
And so it was that the simple act of a man skinning his mouth on a hot pie led to an important thermodynamic discovery.
