On Saturday, August 8, 2015 at 7:26:34 AM UTC-4, Alastair wrote:

However, if he had replaced the bulbs in the lamp posts with his bulbs, then the street would have been darker, just as if you shine cold radiation on an object it becomes colder.

Professor Darklight never carried out his experiment but Professor Pictet did. And he got the results I have described.

==============

I will jump on for one more go around. I have looked at the link you provided earlier to that experiment, and thank you for that. However, the intervening 300 years have provided ample time for Pictet's experiment to be examined. I will refer you to this link, for example:

http://www2.ups.edu/physics/faculty/evans/Pictet's%20experiment.pdf

I quote a pertinent passage here (and pay close attention to the final paragraph):

"Let us note that every object - even a cold object - con*tinually emits radiation. Each object also continually receives radiation that has been emitted by the objects sur*rounding it. The energy emitted per unit time by a given object depends both upon the object's temperature and the properties of its surface. A highly polished metal mirror is a very poor absorber of infrared radiation; it is also, consequently, a poor radiator. Thus we may safely ignore any emission or absorption of radiant heat by the mirrors them*selves. The sole function of the mirrors then consists in the reflection of the radiation that is incident upon them.

Consider first the version of the experiment involving a flask of boiling water. This flask emits radiation in all direc*tions. A negligible part of this radiation is received directly by the air thermometer, which has but a small cross-sectional area and which is placed at a considerable distance from the flask. [In Fig. 5(b)] we imagine the mirrors to be placed so that the focus of mirror A lies in the flask, and the focus of B in the bulb of the thermometer. Now we direct our attention toward that part of the radiation from the flask which happens to strike mirror A.

This radiation will, after two reflections, impinge on the bulb of the thermometer. This is radiation that the thermometer did not receive prior to the introduction of the mirrors. Of course, the thermometer also receives radiation from other objects in the room. The introduction of mirror B effectively eliminates the right third or half of the room as a source of radiation for the thermometer. The effect of the mirrors is therefore to replace a part of the ambient radiation that formerly impinged on the thermometer by the more intense radiation from the flask. The thermometer therefore grows a little warmer.

The version of the experiment involving a flask of snow may be explained in a similar way. Before the mirrors are introduced, the air thermometer receives radiation from all the objects in the room surrounding it. After the introduction of the mirrors, the radiation from the right third or half of the room is cut off from the thermometer by mirror B. This relatively high-temperature radiation is replaced by the radiation from the flask of snow. The thermometer now receives less energy per unit time than previously. The thermometer, initially at room temperature, now radiates away more energy than it absorbs, and so suffers a decrease in temperature."

From: "Pictet's experiment: The apparent radiation and reflection of cold"
James Evans, Department of Physics, University of Puget Sound, Tacoma, Washington 98416
Brian Popp, Department of Physics FM-15, University of Washington, Seattle, Washington 98195


Stephen.