I found a video demonstrating Pictet's classic experiment of radiant heating and radiant cooling which inspired Rumford's work. Unfortunately the video is in Russian. but if you know what it is about it is easy to follow along.
https://www.youtube.com/watch?v=mW4T0ZaiGno There are two parabolic mirrors facing each other. Either a lit candle or what appears to be a vial of liquid nitrogen is located at the focus of the mirror on the left. At the focus of the mirror on the right is some sort of thermometer. As the horizontal line on the monitor moves up or down it indicates either an increase or decrease in temperature. Harry On Wed, Sep 16, 2020 at 1:14 AM H LV <hveeder...@gmail.com> wrote: > Sorry about the OCR errors in the last post. I cleaned them up in > this post... > > The following is from _Pictet's experiment: The apparent radiation and > reflection of cold_ by James Evans and Brian Popp (1985). (google search > for full pdf paper) > > I think Evan's and Popp's criticism of Rumford's theory in the last > paragraph below is mistaken. It is only the relative difference in > frequency that determines whether a ray will be cooling (frigorific) or > warming (calorific) rather than a relative difference in amplitude. An > increase or decrease in amplitude will only affect the rate at which > cooling or warming occurs so Rumford's theory is not plagued by internal > inconsistencies as they argued. > > Another interesting part of Rumford's theory is that a body only cools or > warms by the rays it receives rather than by the rays it emits. Evans and > Popp also insist this causes problems for Rumford's theory but they don't > say why. > > --Begin quote-- > > Rumford's own explanation of the radiation and reflection of cold was > thoroughly undulationist in nature. As suggested at the beginning of this > article, Rumford regarded radiant heat as an undulation analogous to sound, > and seems to have viewed Pictet's experiment more or less as a case of a > driven oscillator: "The cold body in one focus compels the warm body (the > thermometer) in the other focus to change its note." This was the > explanation he ventured to offer his companions at Edinburgh in 1800. > Later, in his paper of 1804, he gave a more or less complete sketch of his > view of radiant heat. > > To begin, imagine a bell, or any other body perfectly elastic, placed in a > perfectly elastic fluid medium and surrounded by other perfectly elastic > bodies. When the bell is struck and made to vibrate, its vibrations are > gradually communicated, by means of the undulations or pulsations they > occasion in the elastic fluid medium, to the other sur-rounding bodies. If > these bodies should happen already to be vibrating at the same frequency > with which the bell vibrates, the undulations occasioned in the elastic > medium by the bell would neither increase nor diminish the frequency of the > vibration of the surrounding bodies; nor would the undulations caused by > the vibrations of these bodies tend to accelerate or retard the vibrations > of the bell. But if the vibrations of the bell were more frequent than > those of the surrounding bodies, the undulations produced by the bell in > the elastic fluid would tend to accelerate the vibrations of the > surrounding bodies. On the other hand,the slower vibrations of the > surrounding bodies would retard the vibrations of the bell. The bell and > the surrounding bodies would continue to affect one another until, by the > vibrations of the latter being gradually increased and those of the former > diminished, they would be reduced to the same tone. > > Now, if heat is assumed to be nothing more than the vibrations of the > constituent particles of a body, the cooling of a hot object by radiation > will entail a series of actions and reactions similar to those just > described for the case of the bell. The rapid undulations produced in the > surrounding ethereal fluid will act as calorific rays on the neighboring > bodies, and the slower undulations produced by the vibrations of these > colder bodies will act as frigorific rays on the hot body. These reciprocal > actions will continue until the hot body and the colder bodies around it > have acquired the same temperature, i.e., until their vibrations have > become isochronous. It follows that cold and heat are relative terms. The > rays from one particular object will be either frigorific or calorific, > according as they impinge on other objects either warmer or colder than > itself. Imagine three identical bodies, A, B, and C. Let A be at the > temperature of freezing water, B at the temperature of 72 °F, and C at 112 > °F. The Rays emitted by B will be calorific with respect to the colder body > A, but frigorific with respect to C. Moreover, they will be just as > efficacious in heating the former as in cooling the latter. > > "According to this hypothesis, cold can with no more propriety be > considered as the absence of heat than a low orgrave sound can be > considered as the absence of a higheror more acute pitch; and the admission > of rays which generate cold involves no absurdity and creates no con-fusion > of ideas." 48 > > > The application of Pictet's experiment is immediate and obvious. The rapid > vibrations of the particles of the thermometer produce rapid undulations in > the surrounding elastic fluid. These undulations arrive, after two > reflections, at the cold body, where they act to raise its temperature. > Simultaneously, the slower vibrations of the cold body give rise to slower > undulations in the elastic medium which proceed, again by means of two > reflections, to the thermometer. The accumulation of these frigorific rays > in the thermometer causes its temperature to fall. And, concludes Rumford, > "...this is what actually happened in the celebrated experiment of my > ingenious friend, Professor Pictet, of Geneva.”:49 > > Rumford thus explains the experiment solely in terms of frequencies of > vibration. That is, he assumes that the "difference of temperature depends > solely on the difference of the times of the vibrations of the component > particles of bodies.” This assumption, however, was made only for the > purpose of simplifying the discussion. Rumford remarks that it is possible, > even likely, that the temperature difference depends on the velocities of > the particles. This modification of the theory was required to explain the > obvious fact that the intensity of the radiation from a hot body falls off > with distance. The pulsations produced in an elastic fluid by the > vibrations of a body immersed in it are everywhere isochronous, but the > mean speed of any individual particle of fluid diminishes with the distance > from the cen-ter of the disturbance. Thus, remarks Rumford, in the case of > sound, the frequency of the pulsations determines the note; but it is the > velocity of the particles of the air, or the amplitude of the wave, that > determines the strength or force of the sound. So too with light, it is > likely that color depends on the frequency of the pulsations that > constitute light, and that the heat produced by them is in proportion to > their force. 50 > > Thus it was clear to Rumford himself that the elegant analysis based on > frequencies alone could not stand. Yet,the introduction of amplitudes or > velocities leads to other contradictions that Rumford did not perceive. > Assume That the undulations in the elastic fluid are calorific in effect if > their amplitude, or perhaps their mean speed, is greater than that of the > particles of the body on which they im-pinge. As a hot body is moved to > greater and greater distances, the oscillations that it produces at a given > fixed point in the fluid diminish in amplitude and velocity. Thus,if the > body were removed to a great enough distance, it's undulations would > apparently change over from calorific to frigorific in effect--something > quite without foundation in experience. The essential difficulty with > Rumford's version of the undulationist theory was that he wished to > associate the change in temperature experienced by an object solely with > the radiation absorbed by it, and denied the temperature changing effect of > the emitted radiation. As a result, Rumford's system suffered from internal > inconsis-tencies that did not trouble Prevost's.51 > > -- end quote -- > > >>
