73^ Letter to Pictet. 



LETTER TO PROFESSOR PICTET OF GENEVA. 



Munich, Jan. 12, 1797. 



Sir, — I ought to have acknowledged sooner the 

 receipt of your last friendly letter ; but you will excuse 

 me, I am sure, wh^n you learn that I have been exclu- 

 sively occupied in putting the last touches to my Essay 

 on the Management of Fire and the Economy of Fuel 

 which I have just sent to press. 



I thank you sincerely for your Essay on Fire. I 

 have read it with much pleasure, and it has interested 

 me peculiarly ; and all the more because the route which 

 you have followed in your researches is the same which 

 I had adopted in treating this subject. 



You know, I suppose, that Dr. Hutton has written a 

 paper to explain one of your experiments, — that in 

 which there was an apparent reflection of cold. I was 

 much struck with this result, which was not only un- 

 expected, but very extraordinary. Your explanation 

 of the phenomena is ingenious and clear; but I can- 

 not help desiring that a matter which is of so great 

 consequence, and which leads to such important con- 

 clusions with reference to the theory of heat, should be 

 examined from every point of view. 



I have a thermometer of a peculiar construction, 

 which possesses an uncommon degree of sensibility. 

 Each variation of a degree of Reaumur's scale causes an 

 index, three inches long, to make four entire revolutions 

 on a circular dial six inches in diameter. With this in- 

 strument I tried to vary your experiment by presenting 

 to the thermometer, as it hung in my room stationary 

 at about the 13th degree of Reaumur's scale, a large 

 cake, or disk, of melting ice ; but although I held it for 



