228 Historical Review of Experiments 



I was not at all surprised to find that the rays of the 

 sun excited more heat in a given time on the black and 

 unpolished iron disk than on the other two disks, which 

 were bright and polished ; I was, however, all the more 

 astonished by an entirely unexpected circumstance which 

 I noticed by chance during the cooling of the instru- 



J O D 



ments which had just been heated by the sun, a cir- 

 cumstance which arrested my attention. 



After I had placed the three boxes close together, and 

 had exposed them to the influence of the sun's rays 

 until each had reached its maximum temperature, 1 

 took them away from the window at which they had 

 been standing at the time, and put them, bottom up- 

 wards, on a cold table in a corner of the room. 



As I happened, about a quarter of an hour later, to 

 go past the table, I cast a single glance at the ther- 

 mometers, which now, in a vertical position, projected 

 from the reversed boxes. To my no slight astonish- 

 ment, I saw that the box which before contained the 

 most heat (the one which had the iron disk) was now 

 the coldest of all. 



This phenomenon surprised me so much the more, 

 as I was convinced that this rapid cooling could not be 

 due to the fact that this box did not have sufficient 

 room to take up just as much heat as the others. For, 

 as I very well knew how much in these experiments 

 depended upon the boxes being precisely alike as regards 

 their contents, I had taken the greatest pains by similar 

 distribution of the silver threads to arrange them alike 

 before I began my experiments. 



I cannot allow myself here to give in detail all the 

 conjectures and projected experiments of which this dis- 

 covery was the cause. I will, therefore, say nothing 



