Pictets 1790 experiment shows the apparent reflection of cold from ice in the focus of a concave mirror onto an air thermometer held in the focus of a second concave mirror 12 feet away. As soon as the screen shielding the 'cold' concave mirror is moved aside the distant thermometer in the focus of the other concave mirror begins to descend under room temperature and remains there until the cold source is hidden again. http://www2.ups.edu/faculty/jcevans/Pictet's experiment.pdf I am not asking here why the thermometer reading falls. I am asking here what actual effect are these concave mirrors having upon the experimental results? Does the use of these concave mirrors force us to conclude anything particular about the observed results that in any way cause us to be concerned about what we are observing? Once again i am not asking why the thermometer becomes colder. I am just asking how we should interpret the useage of the two concave mirrors to get this result.